src/third-party/libpng/libpng.3 (view raw)
1.TH LIBPNG 3 "September 29, 2017"
2.SH NAME
3libpng \- Portable Network Graphics (PNG) Reference Library 1.6.34
4.SH SYNOPSIS
5\fB
6#include <png.h>\fP
7
8\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
9
10\fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
11
12\fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
13
14\fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
15
16\fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
17
18\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
19
20\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
21
22\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
23
24\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
25
26\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
27
28\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
29
30\fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
31
32\fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
33
34\fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
35
36\fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
37
38\fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask)\fP\fB);\fP
39
40\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
41
42\fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
43
44\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
45
46\fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
47
48\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
49
50\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
51
52\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
53
54\fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
55
56\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
57
58\fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
59
60\fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
61
62\fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
63
64\fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
65
66\fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
67
68\fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fP\fI*red_Z\fP\fB, double \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fP\fI*blue_X\fP\fB, double \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
69
70\fBpng_uint_32 png_get_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fI*int_red_X\fP\fB, png_fixed_point \fP\fI*int_red_Y\fP\fB, png_fixed_point \fP\fI*int_red_Z\fP\fB, png_fixed_point \fP\fI*int_green_X\fP\fB, png_fixed_point \fP\fI*int_green_Y\fP\fB, png_fixed_point \fP\fI*int_green_Z\fP\fB, png_fixed_point \fP\fI*int_blue_X\fP\fB, png_fixed_point \fP\fI*int_blue_Y\fP\fB, png_fixed_point \fI*int_blue_Z\fP\fB);\fP
71
72\fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
73
74\fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
75
76\fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
77
78\fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
79
80\fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
81
82\fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
83
84\fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
85
86\fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
87
88\fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
89
90\fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
91
92\fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
93
94\fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
95
96\fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
97
98\fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
99
100\fBpng_uint_32 png_get_eXIf (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fI*exif\fP\fB);\fP
101
102\fBpng_uint_32 png_get_eXIf_1 (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unit_32 \fP\fI*num_exif\fP\fB, png_bytep \fI*exif\fP\fB);\fP
103
104\fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
105
106\fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
107
108\fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
109
110\fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
111
112\fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
113
114\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
115
116\fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
117
118\fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
119
120\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
121
122\fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
123
124\fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
125
126\fBint png_get_palette_max(png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
127
128\fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
129
130\fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
131
132\fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
133
134\fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
135
136\fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
137
138\fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
139
140\fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
141
142\fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
143
144\fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
145
146\fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
147
148\fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
149
150\fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
151
152\fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
153
154\fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
155
156\fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
157
158\fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
159
160\fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
161
162\fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
163
164\fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
165
166\fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
167
168\fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
169
170\fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
171
172\fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
173
174\fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
175
176\fB/* This function is really an inline macro. \fI*/
177
178\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
179
180\fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
181
182\fB/* This function is really an inline macro. \fI*/
183
184\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
185
186\fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
187
188\fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
189
190\fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
191
192\fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
193
194\fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
195
196\fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
197
198\fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
199
200\fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
201
202\fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
203
204\fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
205
206\fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
207
208\fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
209
210\fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
211
212\fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
213
214\fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
215
216\fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
217
218\fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
219
220\fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
221
222\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
223
224\fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP
225
226\fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP
227
228\fBint, png_image_begin_read_from_memory (png_imagep \fP\fIimage\fP\fB, png_const_voidp \fP\fImemory\fP\fB, png_size_t \fIsize\fP\fB);\fP
229
230\fBint png_image_finish_read (png_imagep \fP\fIimage\fP\fB, png_colorp \fP\fIbackground\fP\fB, void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
231
232\fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP
233
234\fBint png_image_write_to_file (png_imagep \fP\fIimage\fP\fB, const char \fP\fI*file\fP\fB, int \fP\fIconvert_to_8bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
235
236\fBint png_image_write_to_memory (png_imagep \fP\fIimage\fP\fB, void \fP\fI*memory\fP\fB, png_alloc_size_t * PNG_RESTRICT \fP\fImemory_bytes\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, const void \fI*colormap)\fP\fB);\fP
237
238\fBint png_image_write_to_stdio (png_imagep \fP\fIimage\fP\fB, FILE \fP\fI*file\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap)\fP\fB);\fP
239
240\fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
241
242\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
243
244\fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
245
246\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
247
248\fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
249
250\fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
251
252\fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
253
254\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
255
256\fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
257
258\fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
259
260\fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
261
262\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
263
264\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
265
266\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
267
268\fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
269
270\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
271
272\fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
273
274\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
275
276\fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
277
278\fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
279
280\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
281
282\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
283
284\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
285
286\fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
287
288\fBvoid png_set_alpha_mode_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, png_fixed_point \fIoutput_gamma\fP\fB);\fP
289
290\fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
291
292\fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
293
294\fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
295
296\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
297
298\fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
299
300\fBvoid png_set_check_for_invalid_index(png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
301
302\fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
303
304\fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
305
306\fBvoid png_set_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIred_X\fP\fB, double \fP\fIred_Y\fP\fB, double \fP\fIred_Z\fP\fB, double \fP\fIgreen_X\fP\fB, double \fP\fIgreen_Y\fP\fB, double \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
307
308\fBvoid png_set_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fIint_red_X\fP\fB, png_fixed_point \fP\fIint_red_Y\fP\fB, png_fixed_point \fP\fIint_red_Z\fP\fB, png_fixed_point \fP\fIint_green_X\fP\fB, png_fixed_point \fP\fIint_green_Y\fP\fB, png_fixed_point \fP\fIint_green_Z\fP\fB, png_fixed_point \fP\fIint_blue_X\fP\fB, png_fixed_point \fP\fIint_blue_Y\fP\fB, png_fixed_point \fIint_blue_Z\fP\fB);\fP
309
310\fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
311
312\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
313
314\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
315
316\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
317
318\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
319
320\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
321
322\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
323
324\fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
325
326\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
327
328\fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
329
330\fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
331
332\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
333
334\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
335
336\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
337
338\fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
339
340\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
341
342\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
343
344\fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
345
346\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
347
348\fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
349
350\fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
351
352\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
353
354\fBvoid png_set_eXIf (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fIexif\fP\fB);\fP
355
356\fBvoid png_set_eXIf_1 (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, const png_uint_32 \fP\fInum_exif\fP\fB, png_bytep \fIexif\fP\fB);\fP
357
358\fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
359
360\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
361
362\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
363
364\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
365
366\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
367
368\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
369
370\fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
371
372\fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
373
374\fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
375
376\fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
377
378\fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
379
380\fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
381
382\fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
383
384\fBint png_set_option(png_structrp \fP\fIpng_ptr\fP\fB, int \fP\fIoption\fP\fB, int \fIonoff\fP\fB);\fP
385
386\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
387
388\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
389
390\fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
391
392\fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
393
394\fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
395
396\fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
397
398\fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
399
400\fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
401
402\fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
403
404\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
405
406\fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
407
408\fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
409
410\fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
411
412\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
413
414\fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
415
416\fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
417
418\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
419
420\fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
421
422\fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
423
424\fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
425
426\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
427
428\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
429
430\fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
431
432\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
433
434\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
435
436\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
437
438\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
439
440\fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
441
442\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
443
444\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
445
446\fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
447
448\fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
449
450\fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
451
452\fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
453
454\fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
455
456\fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
457
458\fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
459
460\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
461
462\fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
463
464\fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
465
466\fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
467
468\fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
469
470\fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
471
472\fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
473
474\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
475
476\fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
477
478\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
479
480\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
481
482\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
483
484\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
485
486\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
487
488\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
489
490\fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
491
492\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
493
494\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
495
496\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
497
498\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
499
500\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
501
502\fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
503
504\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
505
506\fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
507
508\fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
509
510.SH DESCRIPTION
511The
512.I libpng
513library supports encoding, decoding, and various manipulations of
514the Portable Network Graphics (PNG) format image files. It uses the
515.IR zlib(3)
516compression library.
517Following is a copy of the libpng-manual.txt file that accompanies libpng.
518.SH LIBPNG.TXT
519libpng-manual.txt - A description on how to use and modify libpng
520
521 libpng version 1.6.34 - September 29, 2017
522 Updated and distributed by Glenn Randers-Pehrson
523 <glennrp at users.sourceforge.net>
524 Copyright (c) 1998-2017 Glenn Randers-Pehrson
525
526 This document is released under the libpng license.
527 For conditions of distribution and use, see the disclaimer
528 and license in png.h
529
530 Based on:
531
532 libpng versions 0.97, January 1998, through 1.6.34 - September 29, 2017
533 Updated and distributed by Glenn Randers-Pehrson
534 Copyright (c) 1998-2017 Glenn Randers-Pehrson
535
536 libpng 1.0 beta 6 - version 0.96 - May 28, 1997
537 Updated and distributed by Andreas Dilger
538 Copyright (c) 1996, 1997 Andreas Dilger
539
540 libpng 1.0 beta 2 - version 0.88 - January 26, 1996
541 For conditions of distribution and use, see copyright
542 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
543 Schalnat, Group 42, Inc.
544
545 Updated/rewritten per request in the libpng FAQ
546 Copyright (c) 1995, 1996 Frank J. T. Wojcik
547 December 18, 1995 & January 20, 1996
548
549 TABLE OF CONTENTS
550
551 I. Introduction
552 II. Structures
553 III. Reading
554 IV. Writing
555 V. Simplified API
556 VI. Modifying/Customizing libpng
557 VII. MNG support
558 VIII. Changes to Libpng from version 0.88
559 IX. Changes to Libpng from version 1.0.x to 1.2.x
560 X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
561 XI. Changes to Libpng from version 1.4.x to 1.5.x
562 XII. Changes to Libpng from version 1.5.x to 1.6.x
563 XIII. Detecting libpng
564 XIV. Source code repository
565 XV. Coding style
566 XVI. Y2K Compliance in libpng
567
568.SH I. Introduction
569
570This file describes how to use and modify the PNG reference library
571(known as libpng) for your own use. In addition to this
572file, example.c is a good starting point for using the library, as
573it is heavily commented and should include everything most people
574will need. We assume that libpng is already installed; see the
575INSTALL file for instructions on how to configure and install libpng.
576
577For examples of libpng usage, see the files "example.c", "pngtest.c",
578and the files in the "contrib" directory, all of which are included in
579the libpng distribution.
580
581Libpng was written as a companion to the PNG specification, as a way
582of reducing the amount of time and effort it takes to support the PNG
583file format in application programs.
584
585The PNG specification (second edition), November 2003, is available as
586a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
587<https://www.w3.org/TR/2003/REC-PNG-20031110/
588The W3C and ISO documents have identical technical content.
589
590The PNG-1.2 specification is available at
591<https://png-mng.sourceforge.io/pub/png/spec/1.2/>.
592It is technically equivalent
593to the PNG specification (second edition) but has some additional material.
594
595The PNG-1.0 specification is available as RFC 2083
596<https://png-mng.sourceforge.io/pub/png/spec/1.0/> and as a
597W3C Recommendation <https://www.w3.org/TR/REC-png-961001>.
598
599Some additional chunks are described in the special-purpose public chunks
600documents at <http://www.libpng.org/pub/png/spec/register/>
601
602Other information
603about PNG, and the latest version of libpng, can be found at the PNG home
604page, <http://www.libpng.org/pub/png/>.
605
606Most users will not have to modify the library significantly; advanced
607users may want to modify it more. All attempts were made to make it as
608complete as possible, while keeping the code easy to understand.
609Currently, this library only supports C. Support for other languages
610is being considered.
611
612Libpng has been designed to handle multiple sessions at one time,
613to be easily modifiable, to be portable to the vast majority of
614machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
615to use. The ultimate goal of libpng is to promote the acceptance of
616the PNG file format in whatever way possible. While there is still
617work to be done (see the TODO file), libpng should cover the
618majority of the needs of its users.
619
620Libpng uses zlib for its compression and decompression of PNG files.
621Further information about zlib, and the latest version of zlib, can
622be found at the zlib home page, <https://zlib.net/>.
623The zlib compression utility is a general purpose utility that is
624useful for more than PNG files, and can be used without libpng.
625See the documentation delivered with zlib for more details.
626You can usually find the source files for the zlib utility wherever you
627find the libpng source files.
628
629Libpng is thread safe, provided the threads are using different
630instances of the structures. Each thread should have its own
631png_struct and png_info instances, and thus its own image.
632Libpng does not protect itself against two threads using the
633same instance of a structure.
634
635.SH II. Structures
636
637There are two main structures that are important to libpng, png_struct
638and png_info. Both are internal structures that are no longer exposed
639in the libpng interface (as of libpng 1.5.0).
640
641The png_info structure is designed to provide information about the
642PNG file. At one time, the fields of png_info were intended to be
643directly accessible to the user. However, this tended to cause problems
644with applications using dynamically loaded libraries, and as a result
645a set of interface functions for png_info (the png_get_*() and png_set_*()
646functions) was developed, and direct access to the png_info fields was
647deprecated..
648
649The png_struct structure is the object used by the library to decode a
650single image. As of 1.5.0 this structure is also not exposed.
651
652Almost all libpng APIs require a pointer to a png_struct as the first argument.
653Many (in particular the png_set and png_get APIs) also require a pointer
654to png_info as the second argument. Some application visible macros
655defined in png.h designed for basic data access (reading and writing
656integers in the PNG format) don't take a png_info pointer, but it's almost
657always safe to assume that a (png_struct*) has to be passed to call an API
658function.
659
660You can have more than one png_info structure associated with an image,
661as illustrated in pngtest.c, one for information valid prior to the
662IDAT chunks and another (called "end_info" below) for things after them.
663
664The png.h header file is an invaluable reference for programming with libpng.
665And while I'm on the topic, make sure you include the libpng header file:
666
667#include <png.h>
668
669and also (as of libpng-1.5.0) the zlib header file, if you need it:
670
671#include <zlib.h>
672
673.SS Types
674
675The png.h header file defines a number of integral types used by the
676APIs. Most of these are fairly obvious; for example types corresponding
677to integers of particular sizes and types for passing color values.
678
679One exception is how non-integral numbers are handled. For application
680convenience most APIs that take such numbers have C (double) arguments;
681however, internally PNG, and libpng, use 32 bit signed integers and encode
682the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
683macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
684which is simply (png_int_32).
685
686All APIs that take (double) arguments also have a matching API that
687takes the corresponding fixed point integer arguments. The fixed point
688API has the same name as the floating point one with "_fixed" appended.
689The actual range of values permitted in the APIs is frequently less than
690the full range of (png_fixed_point) (\-21474 to +21474). When APIs require
691a non-negative argument the type is recorded as png_uint_32 above. Consult
692the header file and the text below for more information.
693
694Special care must be take with sCAL chunk handling because the chunk itself
695uses non-integral values encoded as strings containing decimal floating point
696numbers. See the comments in the header file.
697
698.SS Configuration
699
700The main header file function declarations are frequently protected by C
701preprocessing directives of the form:
702
703 #ifdef PNG_feature_SUPPORTED
704 declare-function
705 #endif
706 ...
707 #ifdef PNG_feature_SUPPORTED
708 use-function
709 #endif
710
711The library can be built without support for these APIs, although a
712standard build will have all implemented APIs. Application programs
713should check the feature macros before using an API for maximum
714portability. From libpng 1.5.0 the feature macros set during the build
715of libpng are recorded in the header file "pnglibconf.h" and this file
716is always included by png.h.
717
718If you don't need to change the library configuration from the default, skip to
719the next section ("Reading").
720
721Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
722of the build project files in the 'projects' directory simply copy
723scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
724systems do not permit easy auto-configuration of the library - they only
725support the default configuration.
726
727The easiest way to make minor changes to the libpng configuration when
728auto-configuration is supported is to add definitions to the command line
729using (typically) CPPFLAGS. For example:
730
731CPPFLAGS=\-DPNG_NO_FLOATING_ARITHMETIC
732
733will change the internal libpng math implementation for gamma correction and
734other arithmetic calculations to fixed point, avoiding the need for fast
735floating point support. The result can be seen in the generated pnglibconf.h -
736make sure it contains the changed feature macro setting.
737
738If you need to make more extensive configuration changes - more than one or two
739feature macro settings - you can either add \-DPNG_USER_CONFIG to the build
740command line and put a list of feature macro settings in pngusr.h or you can set
741DFA_XTRA (a makefile variable) to a file containing the same information in the
742form of 'option' settings.
743
744A. Changing pnglibconf.h
745
746A variety of methods exist to build libpng. Not all of these support
747reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
748rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
749
750Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
751pnglibconf.h and changing the lines defining the supported features, paying
752very close attention to the 'option' information in scripts/pnglibconf.dfa
753that describes those features and their requirements. This is easy to get
754wrong.
755
756B. Configuration using DFA_XTRA
757
758Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
759variant such as 'nawk' or 'gawk', is available. The configure build will
760automatically find an appropriate awk and build pnglibconf.h.
761The scripts/pnglibconf.mak file contains a set of make rules for doing the
762same thing if configure is not used, and many of the makefiles in the scripts
763directory use this approach.
764
765When rebuilding simply write a new file containing changed options and set
766DFA_XTRA to the name of this file. This causes the build to append the new file
767to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
768of the following forms:
769
770everything = off
771
772This turns all optional features off. Include it at the start of pngusr.dfa to
773make it easier to build a minimal configuration. You will need to turn at least
774some features on afterward to enable either reading or writing code, or both.
775
776option feature on
777option feature off
778
779Enable or disable a single feature. This will automatically enable other
780features required by a feature that is turned on or disable other features that
781require a feature which is turned off. Conflicting settings will cause an error
782message to be emitted by awk.
783
784setting feature default value
785
786Changes the default value of setting 'feature' to 'value'. There are a small
787number of settings listed at the top of pnglibconf.h, they are documented in the
788source code. Most of these values have performance implications for the library
789but most of them have no visible effect on the API. Some can also be overridden
790from the API.
791
792This method of building a customized pnglibconf.h is illustrated in
793contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
794pngusr.dfa in these directories.
795
796C. Configuration using PNG_USER_CONFIG
797
798If \-DPNG_USER_CONFIG is added to the CPPFLAGS when pnglibconf.h is built,
799the file pngusr.h will automatically be included before the options in
800scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
801macro definitions turning features on or off or setting settings.
802
803Apart from the global setting "everything = off" all the options listed above
804can be set using macros in pngusr.h:
805
806#define PNG_feature_SUPPORTED
807
808is equivalent to:
809
810option feature on
811
812#define PNG_NO_feature
813
814is equivalent to:
815
816option feature off
817
818#define PNG_feature value
819
820is equivalent to:
821
822setting feature default value
823
824Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
825pngusr file you supply override the contents of scripts/pnglibconf.dfa
826
827If confusing or incomprehensible behavior results it is possible to
828examine the intermediate file pnglibconf.dfn to find the full set of
829dependency information for each setting and option. Simply locate the
830feature in the file and read the C comments that precede it.
831
832This method is also illustrated in the contrib/pngminim/* makefiles and
833pngusr.h.
834
835.SH III. Reading
836
837We'll now walk you through the possible functions to call when reading
838in a PNG file sequentially, briefly explaining the syntax and purpose
839of each one. See example.c and png.h for more detail. While
840progressive reading is covered in the next section, you will still
841need some of the functions discussed in this section to read a PNG
842file.
843
844.SS Setup
845
846You will want to do the I/O initialization(*) before you get into libpng,
847so if it doesn't work, you don't have much to undo. Of course, you
848will also want to insure that you are, in fact, dealing with a PNG
849file. Libpng provides a simple check to see if a file is a PNG file.
850To use it, pass in the first 1 to 8 bytes of the file to the function
851png_sig_cmp(), and it will return 0 (false) if the bytes match the
852corresponding bytes of the PNG signature, or nonzero (true) otherwise.
853Of course, the more bytes you pass in, the greater the accuracy of the
854prediction.
855
856If you are intending to keep the file pointer open for use in libpng,
857you must ensure you don't read more than 8 bytes from the beginning
858of the file, and you also have to make a call to png_set_sig_bytes()
859with the number of bytes you read from the beginning. Libpng will
860then only check the bytes (if any) that your program didn't read.
861
862(*): If you are not using the standard I/O functions, you will need
863to replace them with custom functions. See the discussion under
864Customizing libpng.
865
866 FILE *fp = fopen(file_name, "rb");
867 if (!fp)
868 {
869 return (ERROR);
870 }
871
872 if (fread(header, 1, number, fp) != number)
873 {
874 return (ERROR);
875 }
876
877 is_png = !png_sig_cmp(header, 0, number);
878 if (!is_png)
879 {
880 return (NOT_PNG);
881 }
882
883Next, png_struct and png_info need to be allocated and initialized. In
884order to ensure that the size of these structures is correct even with a
885dynamically linked libpng, there are functions to initialize and
886allocate the structures. We also pass the library version, optional
887pointers to error handling functions, and a pointer to a data struct for
888use by the error functions, if necessary (the pointer and functions can
889be NULL if the default error handlers are to be used). See the section
890on Changes to Libpng below regarding the old initialization functions.
891The structure allocation functions quietly return NULL if they fail to
892create the structure, so your application should check for that.
893
894 png_structp png_ptr = png_create_read_struct
895 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
896 user_error_fn, user_warning_fn);
897
898 if (!png_ptr)
899 return (ERROR);
900
901 png_infop info_ptr = png_create_info_struct(png_ptr);
902
903 if (!info_ptr)
904 {
905 png_destroy_read_struct(&png_ptr,
906 (png_infopp)NULL, (png_infopp)NULL);
907 return (ERROR);
908 }
909
910If you want to use your own memory allocation routines,
911use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
912png_create_read_struct_2() instead of png_create_read_struct():
913
914 png_structp png_ptr = png_create_read_struct_2
915 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
916 user_error_fn, user_warning_fn, (png_voidp)
917 user_mem_ptr, user_malloc_fn, user_free_fn);
918
919The error handling routines passed to png_create_read_struct()
920and the memory alloc/free routines passed to png_create_struct_2()
921are only necessary if you are not using the libpng supplied error
922handling and memory alloc/free functions.
923
924When libpng encounters an error, it expects to longjmp back
925to your routine. Therefore, you will need to call setjmp and pass
926your png_jmpbuf(png_ptr). If you read the file from different
927routines, you will need to update the longjmp buffer every time you enter
928a new routine that will call a png_*() function.
929
930See your documentation of setjmp/longjmp for your compiler for more
931information on setjmp/longjmp. See the discussion on libpng error
932handling in the Customizing Libpng section below for more information
933on the libpng error handling. If an error occurs, and libpng longjmp's
934back to your setjmp, you will want to call png_destroy_read_struct() to
935free any memory.
936
937 if (setjmp(png_jmpbuf(png_ptr)))
938 {
939 png_destroy_read_struct(&png_ptr, &info_ptr,
940 &end_info);
941 fclose(fp);
942 return (ERROR);
943 }
944
945Pass (png_infopp)NULL instead of &end_info if you didn't create
946an end_info structure.
947
948If you would rather avoid the complexity of setjmp/longjmp issues,
949you can compile libpng with PNG_NO_SETJMP, in which case
950errors will result in a call to PNG_ABORT() which defaults to abort().
951
952You can #define PNG_ABORT() to a function that does something
953more useful than abort(), as long as your function does not
954return.
955
956Now you need to set up the input code. The default for libpng is to
957use the C function fread(). If you use this, you will need to pass a
958valid FILE * in the function png_init_io(). Be sure that the file is
959opened in binary mode. If you wish to handle reading data in another
960way, you need not call the png_init_io() function, but you must then
961implement the libpng I/O methods discussed in the Customizing Libpng
962section below.
963
964 png_init_io(png_ptr, fp);
965
966If you had previously opened the file and read any of the signature from
967the beginning in order to see if this was a PNG file, you need to let
968libpng know that there are some bytes missing from the start of the file.
969
970 png_set_sig_bytes(png_ptr, number);
971
972You can change the zlib compression buffer size to be used while
973reading compressed data with
974
975 png_set_compression_buffer_size(png_ptr, buffer_size);
976
977where the default size is 8192 bytes. Note that the buffer size
978is changed immediately and the buffer is reallocated immediately,
979instead of setting a flag to be acted upon later.
980
981If you want CRC errors to be handled in a different manner than
982the default, use
983
984 png_set_crc_action(png_ptr, crit_action, ancil_action);
985
986The values for png_set_crc_action() say how libpng is to handle CRC errors in
987ancillary and critical chunks, and whether to use the data contained
988therein. Starting with libpng-1.6.26, this also governs how an ADLER32 error
989is handled while reading the IDAT chunk. Note that it is impossible to
990"discard" data in a critical chunk.
991
992Choices for (int) crit_action are
993 PNG_CRC_DEFAULT 0 error/quit
994 PNG_CRC_ERROR_QUIT 1 error/quit
995 PNG_CRC_WARN_USE 3 warn/use data
996 PNG_CRC_QUIET_USE 4 quiet/use data
997 PNG_CRC_NO_CHANGE 5 use the current value
998
999Choices for (int) ancil_action are
1000 PNG_CRC_DEFAULT 0 error/quit
1001 PNG_CRC_ERROR_QUIT 1 error/quit
1002 PNG_CRC_WARN_DISCARD 2 warn/discard data
1003 PNG_CRC_WARN_USE 3 warn/use data
1004 PNG_CRC_QUIET_USE 4 quiet/use data
1005 PNG_CRC_NO_CHANGE 5 use the current value
1006
1007When the setting for crit_action is PNG_CRC_QUIET_USE, the CRC and ADLER32
1008checksums are not only ignored, but they are not evaluated.
1009
1010.SS Setting up callback code
1011
1012You can set up a callback function to handle any unknown chunks in the
1013input stream. You must supply the function
1014
1015 read_chunk_callback(png_structp png_ptr,
1016 png_unknown_chunkp chunk);
1017 {
1018 /* The unknown chunk structure contains your
1019 chunk data, along with similar data for any other
1020 unknown chunks: */
1021
1022 png_byte name[5];
1023 png_byte *data;
1024 png_size_t size;
1025
1026 /* Note that libpng has already taken care of
1027 the CRC handling */
1028
1029 /* put your code here. Search for your chunk in the
1030 unknown chunk structure, process it, and return one
1031 of the following: */
1032
1033 return (\-n); /* chunk had an error */
1034 return (0); /* did not recognize */
1035 return (n); /* success */
1036 }
1037
1038(You can give your function another name that you like instead of
1039"read_chunk_callback")
1040
1041To inform libpng about your function, use
1042
1043 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1044 read_chunk_callback);
1045
1046This names not only the callback function, but also a user pointer that
1047you can retrieve with
1048
1049 png_get_user_chunk_ptr(png_ptr);
1050
1051If you call the png_set_read_user_chunk_fn() function, then all unknown
1052chunks which the callback does not handle will be saved when read. You can
1053cause them to be discarded by returning '1' ("handled") instead of '0'. This
1054behavior will change in libpng 1.7 and the default handling set by the
1055png_set_keep_unknown_chunks() function, described below, will be used when the
1056callback returns 0. If you want the existing behavior you should set the global
1057default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
1058versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the
1059default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
1060
1061At this point, you can set up a callback function that will be
1062called after each row has been read, which you can use to control
1063a progress meter or the like. It's demonstrated in pngtest.c.
1064You must supply a function
1065
1066 void read_row_callback(png_structp png_ptr,
1067 png_uint_32 row, int pass);
1068 {
1069 /* put your code here */
1070 }
1071
1072(You can give it another name that you like instead of "read_row_callback")
1073
1074To inform libpng about your function, use
1075
1076 png_set_read_status_fn(png_ptr, read_row_callback);
1077
1078When this function is called the row has already been completely processed and
1079the 'row' and 'pass' refer to the next row to be handled. For the
1080non-interlaced case the row that was just handled is simply one less than the
1081passed in row number, and pass will always be 0. For the interlaced case the
1082same applies unless the row value is 0, in which case the row just handled was
1083the last one from one of the preceding passes. Because interlacing may skip a
1084pass you cannot be sure that the preceding pass is just 'pass\-1'; if you really
1085need to know what the last pass is record (row,pass) from the callback and use
1086the last recorded value each time.
1087
1088As with the user transform you can find the output row using the
1089PNG_ROW_FROM_PASS_ROW macro.
1090
1091.SS Unknown-chunk handling
1092
1093Now you get to set the way the library processes unknown chunks in the
1094input PNG stream. Both known and unknown chunks will be read. Normal
1095behavior is that known chunks will be parsed into information in
1096various info_ptr members while unknown chunks will be discarded. This
1097behavior can be wasteful if your application will never use some known
1098chunk types. To change this, you can call:
1099
1100 png_set_keep_unknown_chunks(png_ptr, keep,
1101 chunk_list, num_chunks);
1102
1103 keep - 0: default unknown chunk handling
1104 1: ignore; do not keep
1105 2: keep only if safe-to-copy
1106 3: keep even if unsafe-to-copy
1107
1108 You can use these definitions:
1109 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1110 PNG_HANDLE_CHUNK_NEVER 1
1111 PNG_HANDLE_CHUNK_IF_SAFE 2
1112 PNG_HANDLE_CHUNK_ALWAYS 3
1113
1114 chunk_list - list of chunks affected (a byte string,
1115 five bytes per chunk, NULL or '\0' if
1116 num_chunks is positive; ignored if
1117 numchunks <= 0).
1118
1119 num_chunks - number of chunks affected; if 0, all
1120 unknown chunks are affected. If positive,
1121 only the chunks in the list are affected,
1122 and if negative all unknown chunks and
1123 all known chunks except for the IHDR,
1124 PLTE, tRNS, IDAT, and IEND chunks are
1125 affected.
1126
1127Unknown chunks declared in this way will be saved as raw data onto a
1128list of png_unknown_chunk structures. If a chunk that is normally
1129known to libpng is named in the list, it will be handled as unknown,
1130according to the "keep" directive. If a chunk is named in successive
1131instances of png_set_keep_unknown_chunks(), the final instance will
1132take precedence. The IHDR and IEND chunks should not be named in
1133chunk_list; if they are, libpng will process them normally anyway.
1134If you know that your application will never make use of some particular
1135chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
1136
1137Here is an example of the usage of png_set_keep_unknown_chunks(),
1138where the private "vpAg" chunk will later be processed by a user chunk
1139callback function:
1140
1141 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1142
1143 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1144 png_byte unused_chunks[]=
1145 {
1146 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1147 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1148 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1149 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1150 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1151 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1152 };
1153 #endif
1154
1155 ...
1156
1157 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1158 /* ignore all unknown chunks
1159 * (use global setting "2" for libpng16 and earlier):
1160 */
1161 png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
1162
1163 /* except for vpAg: */
1164 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1165
1166 /* also ignore unused known chunks: */
1167 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1168 (int)(sizeof unused_chunks)/5);
1169 #endif
1170
1171.SS User limits
1172
1173The PNG specification allows the width and height of an image to be as
1174large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns.
1175For safety, libpng imposes a default limit of 1 million rows and columns.
1176Larger images will be rejected immediately with a png_error() call. If
1177you wish to change these limits, you can use
1178
1179 png_set_user_limits(png_ptr, width_max, height_max);
1180
1181to set your own limits (libpng may reject some very wide images
1182anyway because of potential buffer overflow conditions).
1183
1184You should put this statement after you create the PNG structure and
1185before calling png_read_info(), png_read_png(), or png_process_data().
1186
1187When writing a PNG datastream, put this statement before calling
1188png_write_info() or png_write_png().
1189
1190If you need to retrieve the limits that are being applied, use
1191
1192 width_max = png_get_user_width_max(png_ptr);
1193 height_max = png_get_user_height_max(png_ptr);
1194
1195The PNG specification sets no limit on the number of ancillary chunks
1196allowed in a PNG datastream. By default, libpng imposes a limit of
1197a total of 1000 sPLT, tEXt, iTXt, zTXt, and unknown chunks to be stored.
1198If you have set up both info_ptr and end_info_ptr, the limit applies
1199separately to each. You can change the limit on the total number of such
1200chunks that will be stored, with
1201
1202 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1203
1204where 0x7fffffffL means unlimited. You can retrieve this limit with
1205
1206 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1207
1208Libpng imposes a limit of 8 Megabytes (8,000,000 bytes) on the amount of
1209memory that any chunk other than IDAT can occupy, originally or when
1210decompressed (prior to libpng-1.6.32 the limit was only applied to compressed
1211chunks after decompression). You can change this limit with
1212
1213 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1214
1215and you can retrieve the limit with
1216
1217 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1218
1219Any chunks that would cause either of these limits to be exceeded will
1220be ignored.
1221
1222.SS Information about your system
1223
1224If you intend to display the PNG or to incorporate it in other image data you
1225need to tell libpng information about your display or drawing surface so that
1226libpng can convert the values in the image to match the display.
1227
1228From libpng-1.5.4 this information can be set before reading the PNG file
1229header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1230called before the PNG file header had been read and png_set_alpha_mode() did not
1231exist.
1232
1233If you need to support versions prior to libpng-1.5.4 test the version number
1234as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1235described in the appropriate manual page.
1236
1237You give libpng the encoding expected by your system expressed as a 'gamma'
1238value. You can also specify a default encoding for the PNG file in
1239case the required information is missing from the file. By default libpng
1240assumes that the PNG data matches your system, to keep this default call:
1241
1242 png_set_gamma(png_ptr, screen_gamma, output_gamma);
1243
1244or you can use the fixed point equivalent:
1245
1246 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
1247 PNG_FP_1*output_gamma);
1248
1249If you don't know the gamma for your system it is probably 2.2 - a good
1250approximation to the IEC standard for display systems (sRGB). If images are
1251too contrasty or washed out you got the value wrong - check your system
1252documentation!
1253
1254Many systems permit the system gamma to be changed via a lookup table in the
1255display driver, a few systems, including older Macs, change the response by
1256default. As of 1.5.4 three special values are available to handle common
1257situations:
1258
1259 PNG_DEFAULT_sRGB: Indicates that the system conforms to the
1260 IEC 61966-2-1 standard. This matches almost
1261 all systems.
1262 PNG_GAMMA_MAC_18: Indicates that the system is an older
1263 (pre Mac OS 10.6) Apple Macintosh system with
1264 the default settings.
1265 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates
1266 that the system expects data with no gamma
1267 encoding.
1268
1269You would use the linear (unencoded) value if you need to process the pixel
1270values further because this avoids the need to decode and re-encode each
1271component value whenever arithmetic is performed. A lot of graphics software
1272uses linear values for this reason, often with higher precision component values
1273to preserve overall accuracy.
1274
1275
1276The output_gamma value expresses how to decode the output values, not how
1277they are encoded. The values used correspond to the normal numbers used to
1278describe the overall gamma of a computer display system; for example 2.2 for
1279an sRGB conformant system. The values are scaled by 100000 in the _fixed
1280version of the API (so 220000 for sRGB.)
1281
1282The inverse of the value is always used to provide a default for the PNG file
1283encoding if it has no gAMA chunk and if png_set_gamma() has not been called
1284to override the PNG gamma information.
1285
1286When the ALPHA_OPTIMIZED mode is selected the output gamma is used to encode
1287opaque pixels however pixels with lower alpha values are not encoded,
1288regardless of the output gamma setting.
1289
1290When the standard Porter Duff handling is requested with mode 1 the output
1291encoding is set to be linear and the output_gamma value is only relevant
1292as a default for input data that has no gamma information. The linear output
1293encoding will be overridden if png_set_gamma() is called - the results may be
1294highly unexpected!
1295
1296The following numbers are derived from the sRGB standard and the research
1297behind it. sRGB is defined to be approximated by a PNG gAMA chunk value of
12980.45455 (1/2.2) for PNG. The value implicitly includes any viewing
1299correction required to take account of any differences in the color
1300environment of the original scene and the intended display environment; the
1301value expresses how to *decode* the image for display, not how the original
1302data was *encoded*.
1303
1304sRGB provides a peg for the PNG standard by defining a viewing environment.
1305sRGB itself, and earlier TV standards, actually use a more complex transform
1306(a linear portion then a gamma 2.4 power law) than PNG can express. (PNG is
1307limited to simple power laws.) By saying that an image for direct display on
1308an sRGB conformant system should be stored with a gAMA chunk value of 45455
1309(11.3.3.2 and 11.3.3.5 of the ISO PNG specification) the PNG specification
1310makes it possible to derive values for other display systems and
1311environments.
1312
1313The Mac value is deduced from the sRGB based on an assumption that the actual
1314extra viewing correction used in early Mac display systems was implemented as
1315a power 1.45 lookup table.
1316
1317Any system where a programmable lookup table is used or where the behavior of
1318the final display device characteristics can be changed requires system
1319specific code to obtain the current characteristic. However this can be
1320difficult and most PNG gamma correction only requires an approximate value.
1321
1322By default, if png_set_alpha_mode() is not called, libpng assumes that all
1323values are unencoded, linear, values and that the output device also has a
1324linear characteristic. This is only very rarely correct - it is invariably
1325better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the
1326default if you don't know what the right answer is!
1327
1328The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS
132910.6) which used a correction table to implement a somewhat lower gamma on an
1330otherwise sRGB system.
1331
1332Both these values are reserved (not simple gamma values) in order to allow
1333more precise correction internally in the future.
1334
1335NOTE: the values can be passed to either the fixed or floating
1336point APIs, but the floating point API will also accept floating point
1337values.
1338
1339The second thing you may need to tell libpng about is how your system handles
1340alpha channel information. Some, but not all, PNG files contain an alpha
1341channel. To display these files correctly you need to compose the data onto a
1342suitable background, as described in the PNG specification.
1343
1344Libpng only supports composing onto a single color (using png_set_background;
1345see below). Otherwise you must do the composition yourself and, in this case,
1346you may need to call png_set_alpha_mode:
1347
1348 #if PNG_LIBPNG_VER >= 10504
1349 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1350 #else
1351 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1352 #endif
1353
1354The screen_gamma value is the same as the argument to png_set_gamma; however,
1355how it affects the output depends on the mode. png_set_alpha_mode() sets the
1356file gamma default to 1/screen_gamma, so normally you don't need to call
1357png_set_gamma. If you need different defaults call png_set_gamma() before
1358png_set_alpha_mode() - if you call it after it will override the settings made
1359by png_set_alpha_mode().
1360
1361The mode is as follows:
1362
1363 PNG_ALPHA_PNG: The data is encoded according to the PNG
1364specification. Red, green and blue, or gray, components are
1365gamma encoded color values and are not premultiplied by the
1366alpha value. The alpha value is a linear measure of the
1367contribution of the pixel to the corresponding final output pixel.
1368
1369You should normally use this format if you intend to perform
1370color correction on the color values; most, maybe all, color
1371correction software has no handling for the alpha channel and,
1372anyway, the math to handle pre-multiplied component values is
1373unnecessarily complex.
1374
1375Before you do any arithmetic on the component values you need
1376to remove the gamma encoding and multiply out the alpha
1377channel. See the PNG specification for more detail. It is
1378important to note that when an image with an alpha channel is
1379scaled, linear encoded, pre-multiplied component values must
1380be used!
1381
1382The remaining modes assume you don't need to do any further color correction or
1383that if you do, your color correction software knows all about alpha (it
1384probably doesn't!). They 'associate' the alpha with the color information by
1385storing color channel values that have been scaled by the alpha. The
1386advantage is that the color channels can be resampled (the image can be
1387scaled) in this form. The disadvantage is that normal practice is to store
1388linear, not (gamma) encoded, values and this requires 16-bit channels for
1389still images rather than the 8-bit channels that are just about sufficient if
1390gamma encoding is used. In addition all non-transparent pixel values,
1391including completely opaque ones, must be gamma encoded to produce the final
1392image. These are the 'STANDARD', 'ASSOCIATED' or 'PREMULTIPLIED' modes
1393described below (the latter being the two common names for associated alpha
1394color channels). Note that PNG files always contain non-associated color
1395channels; png_set_alpha_mode() with one of the modes causes the decoder to
1396convert the pixels to an associated form before returning them to your
1397application.
1398
1399Since it is not necessary to perform arithmetic on opaque color values so
1400long as they are not to be resampled and are in the final color space it is
1401possible to optimize the handling of alpha by storing the opaque pixels in
1402the PNG format (adjusted for the output color space) while storing partially
1403opaque pixels in the standard, linear, format. The accuracy required for
1404standard alpha composition is relatively low, because the pixels are
1405isolated, therefore typically the accuracy loss in storing 8-bit linear
1406values is acceptable. (This is not true if the alpha channel is used to
1407simulate transparency over large areas - use 16 bits or the PNG mode in
1408this case!) This is the 'OPTIMIZED' mode. For this mode a pixel is
1409treated as opaque only if the alpha value is equal to the maximum value.
1410
1411 PNG_ALPHA_STANDARD: The data libpng produces is encoded in the
1412standard way assumed by most correctly written graphics software.
1413The gamma encoding will be removed by libpng and the
1414linear component values will be pre-multiplied by the
1415alpha channel.
1416
1417With this format the final image must be re-encoded to
1418match the display gamma before the image is displayed.
1419If your system doesn't do that, yet still seems to
1420perform arithmetic on the pixels without decoding them,
1421it is broken - check out the modes below.
1422
1423With PNG_ALPHA_STANDARD libpng always produces linear
1424component values, whatever screen_gamma you supply. The
1425screen_gamma value is, however, used as a default for
1426the file gamma if the PNG file has no gamma information.
1427
1428If you call png_set_gamma() after png_set_alpha_mode() you
1429will override the linear encoding. Instead the
1430pre-multiplied pixel values will be gamma encoded but
1431the alpha channel will still be linear. This may
1432actually match the requirements of some broken software,
1433but it is unlikely.
1434
1435While linear 8-bit data is often used it has
1436insufficient precision for any image with a reasonable
1437dynamic range. To avoid problems, and if your software
1438supports it, use png_set_expand_16() to force all
1439components to 16 bits.
1440
1441 PNG_ALPHA_OPTIMIZED: This mode is the same as PNG_ALPHA_STANDARD
1442except that completely opaque pixels are gamma encoded according to
1443the screen_gamma value. Pixels with alpha less than 1.0
1444will still have linear components.
1445
1446Use this format if you have control over your
1447compositing software and so don't do other arithmetic
1448(such as scaling) on the data you get from libpng. Your
1449compositing software can simply copy opaque pixels to
1450the output but still has linear values for the
1451non-opaque pixels.
1452
1453In normal compositing, where the alpha channel encodes
1454partial pixel coverage (as opposed to broad area
1455translucency), the inaccuracies of the 8-bit
1456representation of non-opaque pixels are irrelevant.
1457
1458You can also try this format if your software is broken;
1459it might look better.
1460
1461 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; however, all component
1462values, including the alpha channel are gamma encoded. This is
1463broken because, in practice, no implementation that uses this choice
1464correctly undoes the encoding before handling alpha composition. Use this
1465choice only if other serious errors in the software or hardware you use
1466mandate it. In most cases of broken software or hardware the bug in the
1467final display manifests as a subtle halo around composited parts of the
1468image. You may not even perceive this as a halo; the composited part of
1469the image may simply appear separate from the background, as though it had
1470been cut out of paper and pasted on afterward.
1471
1472If you don't have to deal with bugs in software or hardware, or if you can fix
1473them, there are three recommended ways of using png_set_alpha_mode():
1474
1475 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1476 screen_gamma);
1477
1478You can do color correction on the result (libpng does not currently
1479support color correction internally). When you handle the alpha channel
1480you need to undo the gamma encoding and multiply out the alpha.
1481
1482 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1483 screen_gamma);
1484 png_set_expand_16(png_ptr);
1485
1486If you are using the high level interface, don't call png_set_expand_16();
1487instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1488
1489With this mode you can't do color correction, but you can do arithmetic,
1490including composition and scaling, on the data without further processing.
1491
1492 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1493 screen_gamma);
1494
1495You can avoid the expansion to 16-bit components with this mode, but you
1496lose the ability to scale the image or perform other linear arithmetic.
1497All you can do is compose the result onto a matching output. Since this
1498mode is libpng-specific you also need to write your own composition
1499software.
1500
1501The following are examples of calls to png_set_alpha_mode to achieve the
1502required overall gamma correction and, where necessary, alpha
1503premultiplication.
1504
1505 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
1506
1507Choices for the alpha_mode are
1508
1509 PNG_ALPHA_PNG 0 /* according to the PNG standard */
1510 PNG_ALPHA_STANDARD 1 /* according to Porter/Duff */
1511 PNG_ALPHA_ASSOCIATED 1 /* as above; this is the normal practice */
1512 PNG_ALPHA_PREMULTIPLIED 1 /* as above */
1513 PNG_ALPHA_OPTIMIZED 2 /* 'PNG' for opaque pixels, else 'STANDARD' */
1514 PNG_ALPHA_BROKEN 3 /* the alpha channel is gamma encoded */
1515
1516PNG_ALPHA_PNG is the default libpng handling of the alpha channel. It is not
1517pre-multiplied into the color components. In addition the call states
1518that the output is for a sRGB system and causes all PNG files without gAMA
1519chunks to be assumed to be encoded using sRGB.
1520
1521 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
1522
1523In this case the output is assumed to be something like an sRGB conformant
1524display preceeded by a power-law lookup table of power 1.45. This is how
1525early Mac systems behaved.
1526
1527 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR);
1528
1529This is the classic Jim Blinn approach and will work in academic
1530environments where everything is done by the book. It has the shortcoming
1531of assuming that input PNG data with no gamma information is linear - this
1532is unlikely to be correct unless the PNG files were generated locally.
1533Most of the time the output precision will be so low as to show
1534significant banding in dark areas of the image.
1535
1536 png_set_expand_16(pp);
1537 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_DEFAULT_sRGB);
1538
1539This is a somewhat more realistic Jim Blinn inspired approach. PNG files
1540are assumed to have the sRGB encoding if not marked with a gamma value and
1541the output is always 16 bits per component. This permits accurate scaling
1542and processing of the data. If you know that your input PNG files were
1543generated locally you might need to replace PNG_DEFAULT_sRGB with the
1544correct value for your system.
1545
1546 png_set_alpha_mode(pp, PNG_ALPHA_OPTIMIZED, PNG_DEFAULT_sRGB);
1547
1548If you just need to composite the PNG image onto an existing background
1549and if you control the code that does this you can use the optimization
1550setting. In this case you just copy completely opaque pixels to the
1551output. For pixels that are not completely transparent (you just skip
1552those) you do the composition math using png_composite or png_composite_16
1553below then encode the resultant 8-bit or 16-bit values to match the output
1554encoding.
1555
1556 Other cases
1557
1558If neither the PNG nor the standard linear encoding work for you because
1559of the software or hardware you use then you have a big problem. The PNG
1560case will probably result in halos around the image. The linear encoding
1561will probably result in a washed out, too bright, image (it's actually too
1562contrasty.) Try the ALPHA_OPTIMIZED mode above - this will probably
1563substantially reduce the halos. Alternatively try:
1564
1565 png_set_alpha_mode(pp, PNG_ALPHA_BROKEN, PNG_DEFAULT_sRGB);
1566
1567This option will also reduce the halos, but there will be slight dark
1568halos round the opaque parts of the image where the background is light.
1569In the OPTIMIZED mode the halos will be light halos where the background
1570is dark. Take your pick - the halos are unavoidable unless you can get
1571your hardware/software fixed! (The OPTIMIZED approach is slightly
1572faster.)
1573
1574When the default gamma of PNG files doesn't match the output gamma.
1575If you have PNG files with no gamma information png_set_alpha_mode allows
1576you to provide a default gamma, but it also sets the ouput gamma to the
1577matching value. If you know your PNG files have a gamma that doesn't
1578match the output you can take advantage of the fact that
1579png_set_alpha_mode always sets the output gamma but only sets the PNG
1580default if it is not already set:
1581
1582 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
1583 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
1584
1585The first call sets both the default and the output gamma values, the
1586second call overrides the output gamma without changing the default. This
1587is easier than achieving the same effect with png_set_gamma. You must use
1588PNG_ALPHA_PNG for the first call - internal checking in png_set_alpha will
1589fire if more than one call to png_set_alpha_mode and png_set_background is
1590made in the same read operation, however multiple calls with PNG_ALPHA_PNG
1591are ignored.
1592
1593If you don't need, or can't handle, the alpha channel you can call
1594png_set_background() to remove it by compositing against a fixed color. Don't
1595call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1596transparent parts of this image.
1597
1598 png_set_background(png_ptr, &background_color,
1599 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1600
1601The background_color is an RGB or grayscale value according to the data format
1602libpng will produce for you. Because you don't yet know the format of the PNG
1603file, if you call png_set_background at this point you must arrange for the
1604format produced by libpng to always have 8-bit or 16-bit components and then
1605store the color as an 8-bit or 16-bit color as appropriate. The color contains
1606separate gray and RGB component values, so you can let libpng produce gray or
1607RGB output according to the input format, but low bit depth grayscale images
1608must always be converted to at least 8-bit format. (Even though low bit depth
1609grayscale images can't have an alpha channel they can have a transparent
1610color!)
1611
1612You set the transforms you need later, either as flags to the high level
1613interface or libpng API calls for the low level interface. For reference the
1614settings and API calls required are:
1615
16168-bit values:
1617 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1618 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1619
1620 If you must get exactly the same inaccurate results
1621 produced by default in versions prior to libpng-1.5.4,
1622 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1623 instead.
1624
162516-bit values:
1626 PNG_TRANSFORM_EXPAND_16
1627 png_set_expand_16(png_ptr);
1628
1629In either case palette image data will be expanded to RGB. If you just want
1630color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1631to the list.
1632
1633Calling png_set_background before the PNG file header is read will not work
1634prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1635errors it is therefore much safer to call png_set_background after the head has
1636been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1637used with the high level interface.
1638
1639.SS The high-level read interface
1640
1641At this point there are two ways to proceed; through the high-level
1642read interface, or through a sequence of low-level read operations.
1643You can use the high-level interface if (a) you are willing to read
1644the entire image into memory, and (b) the input transformations
1645you want to do are limited to the following set:
1646
1647 PNG_TRANSFORM_IDENTITY No transformation
1648 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1649 8-bit accurately
1650 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1651 8-bit less accurately
1652 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1653 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1654 samples to bytes
1655 PNG_TRANSFORM_PACKSWAP Change order of packed
1656 pixels to LSB first
1657 PNG_TRANSFORM_EXPAND Perform set_expand()
1658 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1659 PNG_TRANSFORM_SHIFT Normalize pixels to the
1660 sBIT depth
1661 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1662 to BGRA
1663 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1664 to AG
1665 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1666 to transparency
1667 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1668 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1669 to RGB (or GA to RGBA)
1670 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
1671
1672(This excludes setting a background color, doing gamma transformation,
1673quantizing, and setting filler.) If this is the case, simply do this:
1674
1675 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1676
1677where png_transforms is an integer containing the bitwise OR of some
1678set of transformation flags. This call is equivalent to png_read_info(),
1679followed the set of transformations indicated by the transform mask,
1680then png_read_image(), and finally png_read_end().
1681
1682(The final parameter of this call is not yet used. Someday it might point
1683to transformation parameters required by some future input transform.)
1684
1685You must use png_transforms and not call any png_set_transform() functions
1686when you use png_read_png().
1687
1688After you have called png_read_png(), you can retrieve the image data
1689with
1690
1691 row_pointers = png_get_rows(png_ptr, info_ptr);
1692
1693where row_pointers is an array of pointers to the pixel data for each row:
1694
1695 png_bytep row_pointers[height];
1696
1697If you know your image size and pixel size ahead of time, you can allocate
1698row_pointers prior to calling png_read_png() with
1699
1700 if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
1701 png_error (png_ptr,
1702 "Image is too tall to process in memory");
1703
1704 if (width > PNG_UINT_32_MAX/pixel_size)
1705 png_error (png_ptr,
1706 "Image is too wide to process in memory");
1707
1708 row_pointers = png_malloc(png_ptr,
1709 height*(sizeof (png_bytep)));
1710
1711 for (int i=0; i<height, i++)
1712 row_pointers[i]=NULL; /* security precaution */
1713
1714 for (int i=0; i<height, i++)
1715 row_pointers[i]=png_malloc(png_ptr,
1716 width*pixel_size);
1717
1718 png_set_rows(png_ptr, info_ptr, &row_pointers);
1719
1720Alternatively you could allocate your image in one big block and define
1721row_pointers[i] to point into the proper places in your block, but first
1722be sure that your platform is able to allocate such a large buffer:
1723
1724 /* Guard against integer overflow */
1725 if (height > PNG_SIZE_MAX/(width*pixel_size)) {
1726 png_error(png_ptr,"image_data buffer would be too large");
1727 }
1728
1729 png_bytep buffer=png_malloc(png_ptr,height*width*pixel_size);
1730
1731 for (int i=0; i<height, i++)
1732 row_pointers[i]=buffer+i*width*pixel_size;
1733
1734 png_set_rows(png_ptr, info_ptr, &row_pointers);
1735
1736If you use png_set_rows(), the application is responsible for freeing
1737row_pointers (and row_pointers[i], if they were separately allocated).
1738
1739If you don't allocate row_pointers ahead of time, png_read_png() will
1740do it, and it'll be free'ed by libpng when you call png_destroy_*().
1741
1742.SS The low-level read interface
1743
1744If you are going the low-level route, you are now ready to read all
1745the file information up to the actual image data. You do this with a
1746call to png_read_info().
1747
1748 png_read_info(png_ptr, info_ptr);
1749
1750This will process all chunks up to but not including the image data.
1751
1752This also copies some of the data from the PNG file into the decode structure
1753for use in later transformations. Important information copied in is:
1754
17551) The PNG file gamma from the gAMA chunk. This overwrites the default value
1756provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1757
17582) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1759damages the information provided by an earlier call to png_set_background
1760resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1761
17623) The number of significant bits in each component value. Libpng uses this to
1763optimize gamma handling by reducing the internal lookup table sizes.
1764
17654) The transparent color information from a tRNS chunk. This can be modified by
1766a later call to png_set_tRNS.
1767
1768.SS Querying the info structure
1769
1770Functions are used to get the information from the info_ptr once it
1771has been read. Note that these fields may not be completely filled
1772in until png_read_end() has read the chunk data following the image.
1773
1774 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1775 &bit_depth, &color_type, &interlace_type,
1776 &compression_type, &filter_method);
1777
1778 width - holds the width of the image
1779 in pixels (up to 2^31).
1780
1781 height - holds the height of the image
1782 in pixels (up to 2^31).
1783
1784 bit_depth - holds the bit depth of one of the
1785 image channels. (valid values are
1786 1, 2, 4, 8, 16 and depend also on
1787 the color_type. See also
1788 significant bits (sBIT) below).
1789
1790 color_type - describes which color/alpha channels
1791 are present.
1792 PNG_COLOR_TYPE_GRAY
1793 (bit depths 1, 2, 4, 8, 16)
1794 PNG_COLOR_TYPE_GRAY_ALPHA
1795 (bit depths 8, 16)
1796 PNG_COLOR_TYPE_PALETTE
1797 (bit depths 1, 2, 4, 8)
1798 PNG_COLOR_TYPE_RGB
1799 (bit_depths 8, 16)
1800 PNG_COLOR_TYPE_RGB_ALPHA
1801 (bit_depths 8, 16)
1802
1803 PNG_COLOR_MASK_PALETTE
1804 PNG_COLOR_MASK_COLOR
1805 PNG_COLOR_MASK_ALPHA
1806
1807 interlace_type - (PNG_INTERLACE_NONE or
1808 PNG_INTERLACE_ADAM7)
1809
1810 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1811 for PNG 1.0)
1812
1813 filter_method - (must be PNG_FILTER_TYPE_BASE
1814 for PNG 1.0, and can also be
1815 PNG_INTRAPIXEL_DIFFERENCING if
1816 the PNG datastream is embedded in
1817 a MNG-1.0 datastream)
1818
1819 Any of width, height, color_type, bit_depth,
1820 interlace_type, compression_type, or filter_method can
1821 be NULL if you are not interested in their values.
1822
1823 Note that png_get_IHDR() returns 32-bit data into
1824 the application's width and height variables.
1825 This is an unsafe situation if these are not png_uint_32
1826 variables. In such situations, the
1827 png_get_image_width() and png_get_image_height()
1828 functions described below are safer.
1829
1830 width = png_get_image_width(png_ptr,
1831 info_ptr);
1832
1833 height = png_get_image_height(png_ptr,
1834 info_ptr);
1835
1836 bit_depth = png_get_bit_depth(png_ptr,
1837 info_ptr);
1838
1839 color_type = png_get_color_type(png_ptr,
1840 info_ptr);
1841
1842 interlace_type = png_get_interlace_type(png_ptr,
1843 info_ptr);
1844
1845 compression_type = png_get_compression_type(png_ptr,
1846 info_ptr);
1847
1848 filter_method = png_get_filter_type(png_ptr,
1849 info_ptr);
1850
1851 channels = png_get_channels(png_ptr, info_ptr);
1852
1853 channels - number of channels of info for the
1854 color type (valid values are 1 (GRAY,
1855 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1856 4 (RGB_ALPHA or RGB + filler byte))
1857
1858 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1859
1860 rowbytes - number of bytes needed to hold a row
1861 This value, the bit_depth, color_type,
1862 and the number of channels can change
1863 if you use transforms such as
1864 png_set_expand(). See
1865 png_read_update_info(), below.
1866
1867 signature = png_get_signature(png_ptr, info_ptr);
1868
1869 signature - holds the signature read from the
1870 file (if any). The data is kept in
1871 the same offset it would be if the
1872 whole signature were read (i.e. if an
1873 application had already read in 4
1874 bytes of signature before starting
1875 libpng, the remaining 4 bytes would
1876 be in signature[4] through signature[7]
1877 (see png_set_sig_bytes())).
1878
1879These are also important, but their validity depends on whether the chunk
1880has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1881png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1882data has been read, or zero if it is missing. The parameters to the
1883png_get_<chunk> are set directly if they are simple data types, or a
1884pointer into the info_ptr is returned for any complex types.
1885
1886The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
1887is simply returned to give the application information about how the
1888image was encoded. Libpng itself only does transformations using the file
1889gamma when combining semitransparent pixels with the background color, and,
1890since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels
1891within the simplified API. Libpng also uses the file gamma when converting
1892RGB to gray, beginning with libpng-1.0.5, if the application calls
1893png_set_rgb_to_gray()).
1894
1895 png_get_PLTE(png_ptr, info_ptr, &palette,
1896 &num_palette);
1897
1898 palette - the palette for the file
1899 (array of png_color)
1900
1901 num_palette - number of entries in the palette
1902
1903 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
1904 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
1905
1906 file_gamma - the gamma at which the file is
1907 written (PNG_INFO_gAMA)
1908
1909 int_file_gamma - 100,000 times the gamma at which the
1910 file is written
1911
1912 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
1913 &red_y, &green_x, &green_y, &blue_x, &blue_y)
1914 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z,
1915 &green_X, &green_Y, &green_Z, &blue_X, &blue_Y,
1916 &blue_Z)
1917 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x,
1918 &int_white_y, &int_red_x, &int_red_y,
1919 &int_green_x, &int_green_y, &int_blue_x,
1920 &int_blue_y)
1921 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
1922 &int_red_Z, &int_green_X, &int_green_Y,
1923 &int_green_Z, &int_blue_X, &int_blue_Y,
1924 &int_blue_Z)
1925
1926 {white,red,green,blue}_{x,y}
1927 A color space encoding specified using the
1928 chromaticities of the end points and the
1929 white point. (PNG_INFO_cHRM)
1930
1931 {red,green,blue}_{X,Y,Z}
1932 A color space encoding specified using the
1933 encoding end points - the CIE tristimulus
1934 specification of the intended color of the red,
1935 green and blue channels in the PNG RGB data.
1936 The white point is simply the sum of the three
1937 end points. (PNG_INFO_cHRM)
1938
1939 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1940
1941 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1942 The presence of the sRGB chunk
1943 means that the pixel data is in the
1944 sRGB color space. This chunk also
1945 implies specific values of gAMA and
1946 cHRM.
1947
1948 png_get_iCCP(png_ptr, info_ptr, &name,
1949 &compression_type, &profile, &proflen);
1950
1951 name - The profile name.
1952
1953 compression_type - The compression type; always
1954 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1955 You may give NULL to this argument to
1956 ignore it.
1957
1958 profile - International Color Consortium color
1959 profile data. May contain NULs.
1960
1961 proflen - length of profile data in bytes.
1962
1963 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1964
1965 sig_bit - the number of significant bits for
1966 (PNG_INFO_sBIT) each of the gray,
1967 red, green, and blue channels,
1968 whichever are appropriate for the
1969 given color type (png_color_16)
1970
1971 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1972 &num_trans, &trans_color);
1973
1974 trans_alpha - array of alpha (transparency)
1975 entries for palette (PNG_INFO_tRNS)
1976
1977 num_trans - number of transparent entries
1978 (PNG_INFO_tRNS)
1979
1980 trans_color - graylevel or color sample values of
1981 the single transparent color for
1982 non-paletted images (PNG_INFO_tRNS)
1983
1984 png_get_eXIf_1(png_ptr, info_ptr, &num_exif, &exif);
1985 (PNG_INFO_eXIf)
1986
1987 exif - Exif profile (array of png_byte)
1988
1989 png_get_hIST(png_ptr, info_ptr, &hist);
1990 (PNG_INFO_hIST)
1991
1992 hist - histogram of palette (array of
1993 png_uint_16)
1994
1995 png_get_tIME(png_ptr, info_ptr, &mod_time);
1996
1997 mod_time - time image was last modified
1998 (PNG_VALID_tIME)
1999
2000 png_get_bKGD(png_ptr, info_ptr, &background);
2001
2002 background - background color (of type
2003 png_color_16p) (PNG_VALID_bKGD)
2004 valid 16-bit red, green and blue
2005 values, regardless of color_type
2006
2007 num_comments = png_get_text(png_ptr, info_ptr,
2008 &text_ptr, &num_text);
2009
2010 num_comments - number of comments
2011
2012 text_ptr - array of png_text holding image
2013 comments
2014
2015 text_ptr[i].compression - type of compression used
2016 on "text" PNG_TEXT_COMPRESSION_NONE
2017 PNG_TEXT_COMPRESSION_zTXt
2018 PNG_ITXT_COMPRESSION_NONE
2019 PNG_ITXT_COMPRESSION_zTXt
2020
2021 text_ptr[i].key - keyword for comment. Must contain
2022 1-79 characters.
2023
2024 text_ptr[i].text - text comments for current
2025 keyword. Can be empty.
2026
2027 text_ptr[i].text_length - length of text string,
2028 after decompression, 0 for iTXt
2029
2030 text_ptr[i].itxt_length - length of itxt string,
2031 after decompression, 0 for tEXt/zTXt
2032
2033 text_ptr[i].lang - language of comment (empty
2034 string for unknown).
2035
2036 text_ptr[i].lang_key - keyword in UTF-8
2037 (empty string for unknown).
2038
2039 Note that the itxt_length, lang, and lang_key
2040 members of the text_ptr structure only exist when the
2041 library is built with iTXt chunk support. Prior to
2042 libpng-1.4.0 the library was built by default without
2043 iTXt support. Also note that when iTXt is supported,
2044 they contain NULL pointers when the "compression"
2045 field contains PNG_TEXT_COMPRESSION_NONE or
2046 PNG_TEXT_COMPRESSION_zTXt.
2047
2048 num_text - number of comments (same as
2049 num_comments; you can put NULL here
2050 to avoid the duplication)
2051
2052 Note while png_set_text() will accept text, language,
2053 and translated keywords that can be NULL pointers, the
2054 structure returned by png_get_text will always contain
2055 regular zero-terminated C strings. They might be
2056 empty strings but they will never be NULL pointers.
2057
2058 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
2059 &palette_ptr);
2060
2061 num_spalettes - number of sPLT chunks read.
2062
2063 palette_ptr - array of palette structures holding
2064 contents of one or more sPLT chunks
2065 read.
2066
2067 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
2068 &unit_type);
2069
2070 offset_x - positive offset from the left edge
2071 of the screen (can be negative)
2072
2073 offset_y - positive offset from the top edge
2074 of the screen (can be negative)
2075
2076 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2077
2078 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
2079 &unit_type);
2080
2081 res_x - pixels/unit physical resolution in
2082 x direction
2083
2084 res_y - pixels/unit physical resolution in
2085 x direction
2086
2087 unit_type - PNG_RESOLUTION_UNKNOWN,
2088 PNG_RESOLUTION_METER
2089
2090 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
2091 &height)
2092
2093 unit - physical scale units (an integer)
2094
2095 width - width of a pixel in physical scale units
2096
2097 height - height of a pixel in physical scale units
2098 (width and height are doubles)
2099
2100 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
2101 &height)
2102
2103 unit - physical scale units (an integer)
2104
2105 width - width of a pixel in physical scale units
2106 (expressed as a string)
2107
2108 height - height of a pixel in physical scale units
2109 (width and height are strings like "2.54")
2110
2111 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
2112 info_ptr, &unknowns)
2113
2114 unknowns - array of png_unknown_chunk
2115 structures holding unknown chunks
2116
2117 unknowns[i].name - name of unknown chunk
2118
2119 unknowns[i].data - data of unknown chunk
2120
2121 unknowns[i].size - size of unknown chunk's data
2122
2123 unknowns[i].location - position of chunk in file
2124
2125 The value of "i" corresponds to the order in which the
2126 chunks were read from the PNG file or inserted with the
2127 png_set_unknown_chunks() function.
2128
2129 The value of "location" is a bitwise "or" of
2130
2131 PNG_HAVE_IHDR (0x01)
2132 PNG_HAVE_PLTE (0x02)
2133 PNG_AFTER_IDAT (0x08)
2134
2135The data from the pHYs chunk can be retrieved in several convenient
2136forms:
2137
2138 res_x = png_get_x_pixels_per_meter(png_ptr,
2139 info_ptr)
2140
2141 res_y = png_get_y_pixels_per_meter(png_ptr,
2142 info_ptr)
2143
2144 res_x_and_y = png_get_pixels_per_meter(png_ptr,
2145 info_ptr)
2146
2147 res_x = png_get_x_pixels_per_inch(png_ptr,
2148 info_ptr)
2149
2150 res_y = png_get_y_pixels_per_inch(png_ptr,
2151 info_ptr)
2152
2153 res_x_and_y = png_get_pixels_per_inch(png_ptr,
2154 info_ptr)
2155
2156 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
2157 info_ptr)
2158
2159 Each of these returns 0 [signifying "unknown"] if
2160 the data is not present or if res_x is 0;
2161 res_x_and_y is 0 if res_x != res_y
2162
2163 Note that because of the way the resolutions are
2164 stored internally, the inch conversions won't
2165 come out to exactly even number. For example,
2166 72 dpi is stored as 0.28346 pixels/meter, and
2167 when this is retrieved it is 71.9988 dpi, so
2168 be sure to round the returned value appropriately
2169 if you want to display a reasonable-looking result.
2170
2171The data from the oFFs chunk can be retrieved in several convenient
2172forms:
2173
2174 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
2175
2176 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
2177
2178 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
2179
2180 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
2181
2182 Each of these returns 0 [signifying "unknown" if both
2183 x and y are 0] if the data is not present or if the
2184 chunk is present but the unit is the pixel. The
2185 remark about inexact inch conversions applies here
2186 as well, because a value in inches can't always be
2187 converted to microns and back without some loss
2188 of precision.
2189
2190For more information, see the
2191PNG specification for chunk contents. Be careful with trusting
2192rowbytes, as some of the transformations could increase the space
2193needed to hold a row (expand, filler, gray_to_rgb, etc.).
2194See png_read_update_info(), below.
2195
2196A quick word about text_ptr and num_text. PNG stores comments in
2197keyword/text pairs, one pair per chunk, with no limit on the number
2198of text chunks, and a 2^31 byte limit on their size. While there are
2199suggested keywords, there is no requirement to restrict the use to these
2200strings. It is strongly suggested that keywords and text be sensible
2201to humans (that's the point), so don't use abbreviations. Non-printing
2202symbols are not allowed. See the PNG specification for more details.
2203There is also no requirement to have text after the keyword.
2204
2205Keywords should be limited to 79 Latin-1 characters without leading or
2206trailing spaces, but non-consecutive spaces are allowed within the
2207keyword. It is possible to have the same keyword any number of times.
2208The text_ptr is an array of png_text structures, each holding a
2209pointer to a language string, a pointer to a keyword and a pointer to
2210a text string. The text string, language code, and translated
2211keyword may be empty or NULL pointers. The keyword/text
2212pairs are put into the array in the order that they are received.
2213However, some or all of the text chunks may be after the image, so, to
2214make sure you have read all the text chunks, don't mess with these
2215until after you read the stuff after the image. This will be
2216mentioned again below in the discussion that goes with png_read_end().
2217
2218.SS Input transformations
2219
2220After you've read the header information, you can set up the library
2221to handle any special transformations of the image data. The various
2222ways to transform the data will be described in the order that they
2223should occur. This is important, as some of these change the color
2224type and/or bit depth of the data, and some others only work on
2225certain color types and bit depths.
2226
2227Transformations you request are ignored if they don't have any meaning for a
2228particular input data format. However some transformations can have an effect
2229as a result of a previous transformation. If you specify a contradictory set of
2230transformations, for example both adding and removing the alpha channel, you
2231cannot predict the final result.
2232
2233The color used for the transparency values should be supplied in the same
2234format/depth as the current image data. It is stored in the same format/depth
2235as the image data in a tRNS chunk, so this is what libpng expects for this data.
2236
2237The color used for the background value depends on the need_expand argument as
2238described below.
2239
2240Data will be decoded into the supplied row buffers packed into bytes
2241unless the library has been told to transform it into another format.
2242For example, 4 bit/pixel paletted or grayscale data will be returned
22432 pixels/byte with the leftmost pixel in the high-order bits of the byte,
2244unless png_set_packing() is called. 8-bit RGB data will be stored
2245in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2246is called to insert filler bytes, either before or after each RGB triplet.
2247
224816-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
2249byte of the color value first, unless png_set_scale_16() is called to
2250transform it to regular RGB RGB triplets, or png_set_filler() or
2251png_set_add alpha() is called to insert two filler bytes, either before
2252or after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
2253be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
2254or png_set_scale_16().
2255
2256The following code transforms grayscale images of less than 8 to 8 bits,
2257changes paletted images to RGB, and adds a full alpha channel if there is
2258transparency information in a tRNS chunk. This is most useful on
2259grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2260viewing application that wishes to treat all images in the same way.
2261
2262 if (color_type == PNG_COLOR_TYPE_PALETTE)
2263 png_set_palette_to_rgb(png_ptr);
2264
2265 if (png_get_valid(png_ptr, info_ptr,
2266 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2267
2268 if (color_type == PNG_COLOR_TYPE_GRAY &&
2269 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2270
2271The first two functions are actually aliases for png_set_expand(), added
2272in libpng version 1.0.4, with the function names expanded to improve code
2273readability. In some future version they may actually do different
2274things.
2275
2276As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2277added. It expands the sample depth without changing tRNS to alpha.
2278
2279As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2280png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2281Use this when the output color or gray channels are made linear to avoid fairly
2282severe accuracy loss.
2283
2284 if (bit_depth < 16)
2285 png_set_expand_16(png_ptr);
2286
2287PNG can have files with 16 bits per channel. If you only can handle
22888 bits per channel, this will strip the pixels down to 8-bit.
2289
2290 if (bit_depth == 16)
2291#if PNG_LIBPNG_VER >= 10504
2292 png_set_scale_16(png_ptr);
2293#else
2294 png_set_strip_16(png_ptr);
2295#endif
2296
2297(The more accurate "png_set_scale_16()" API became available in libpng version
22981.5.4).
2299
2300If you need to process the alpha channel on the image separately from the image
2301data (for example if you convert it to a bitmap mask) it is possible to have
2302libpng strip the channel leaving just RGB or gray data:
2303
2304 if (color_type & PNG_COLOR_MASK_ALPHA)
2305 png_set_strip_alpha(png_ptr);
2306
2307If you strip the alpha channel you need to find some other way of dealing with
2308the information. If, instead, you want to convert the image to an opaque
2309version with no alpha channel use png_set_background; see below.
2310
2311As of libpng version 1.5.2, almost all useful expansions are supported, the
2312major ommissions are conversion of grayscale to indexed images (which can be
2313done trivially in the application) and conversion of indexed to grayscale (which
2314can be done by a trivial manipulation of the palette.)
2315
2316In the following table, the 01 means grayscale with depth<8, 31 means
2317indexed with depth<8, other numerals represent the color type, "T" means
2318the tRNS chunk is present, A means an alpha channel is present, and O
2319means tRNS or alpha is present but all pixels in the image are opaque.
2320
2321 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2322 TO
2323 01 - [G] - - - - - - - - - - - - -
2324 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2325 0 1 G + . . G G G G G G B B GB GB
2326 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2327 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2328 2 C P C C C + . . C - - CB CB B B
2329 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2330 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2331 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2332 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2333 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2334 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2335 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2336 6A CA PA CA C C A T tT PA P P C CBA + BA
2337 6O CA PBA CA C C A tT T PA P P CBA C BA +
2338
2339Within the matrix,
2340 "+" identifies entries where 'from' and 'to' are the same.
2341 "-" means the transformation is not supported.
2342 "." means nothing is necessary (a tRNS chunk can just be ignored).
2343 "t" means the transformation is obtained by png_set_tRNS.
2344 "A" means the transformation is obtained by png_set_add_alpha().
2345 "X" means the transformation is obtained by png_set_expand().
2346 "1" means the transformation is obtained by
2347 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
2348 if there is no transparency in the original or the final
2349 format).
2350 "C" means the transformation is obtained by png_set_gray_to_rgb().
2351 "G" means the transformation is obtained by png_set_rgb_to_gray().
2352 "P" means the transformation is obtained by
2353 png_set_expand_palette_to_rgb().
2354 "p" means the transformation is obtained by png_set_packing().
2355 "Q" means the transformation is obtained by png_set_quantize().
2356 "T" means the transformation is obtained by
2357 png_set_tRNS_to_alpha().
2358 "B" means the transformation is obtained by
2359 png_set_background(), or png_strip_alpha().
2360
2361When an entry has multiple transforms listed all are required to cause the
2362right overall transformation. When two transforms are separated by a comma
2363either will do the job. When transforms are enclosed in [] the transform should
2364do the job but this is currently unimplemented - a different format will result
2365if the suggested transformations are used.
2366
2367In PNG files, the alpha channel in an image
2368is the level of opacity. If you need the alpha channel in an image to
2369be the level of transparency instead of opacity, you can invert the
2370alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2371fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2372images) is fully transparent, with
2373
2374 png_set_invert_alpha(png_ptr);
2375
2376PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2377they can, resulting in, for example, 8 pixels per byte for 1 bit
2378files. This code expands to 1 pixel per byte without changing the
2379values of the pixels:
2380
2381 if (bit_depth < 8)
2382 png_set_packing(png_ptr);
2383
2384PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2385stored in a PNG image have been "scaled" or "shifted" up to the next
2386higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2387to 8 bits/sample in the range [0, 255]). However, it is also possible
2388to convert the PNG pixel data back to the original bit depth of the
2389image. This call reduces the pixels back down to the original bit depth:
2390
2391 png_color_8p sig_bit;
2392
2393 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2394 png_set_shift(png_ptr, sig_bit);
2395
2396PNG files store 3-color pixels in red, green, blue order. This code
2397changes the storage of the pixels to blue, green, red:
2398
2399 if (color_type == PNG_COLOR_TYPE_RGB ||
2400 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2401 png_set_bgr(png_ptr);
2402
2403PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2404into 4 or 8 bytes for windowing systems that need them in this format:
2405
2406 if (color_type == PNG_COLOR_TYPE_RGB)
2407 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2408
2409where "filler" is the 8-bit or 16-bit number to fill with, and the location
2410is either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2411you want the filler before the RGB or after. When filling an 8-bit pixel,
2412the least significant 8 bits of the number are used, if a 16-bit number is
2413supplied. This transformation does not affect images that already have full
2414alpha channels. To add an opaque alpha channel, use filler=0xffff and
2415PNG_FILLER_AFTER which will generate RGBA pixels.
2416
2417Note that png_set_filler() does not change the color type. If you want
2418to do that, you can add a true alpha channel with
2419
2420 if (color_type == PNG_COLOR_TYPE_RGB ||
2421 color_type == PNG_COLOR_TYPE_GRAY)
2422 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2423
2424where "filler" contains the alpha value to assign to each pixel.
2425The png_set_add_alpha() function was added in libpng-1.2.7.
2426
2427If you are reading an image with an alpha channel, and you need the
2428data as ARGB instead of the normal PNG format RGBA:
2429
2430 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2431 png_set_swap_alpha(png_ptr);
2432
2433For some uses, you may want a grayscale image to be represented as
2434RGB. This code will do that conversion:
2435
2436 if (color_type == PNG_COLOR_TYPE_GRAY ||
2437 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2438 png_set_gray_to_rgb(png_ptr);
2439
2440Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2441with alpha.
2442
2443 if (color_type == PNG_COLOR_TYPE_RGB ||
2444 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2445 png_set_rgb_to_gray(png_ptr, error_action,
2446 double red_weight, double green_weight);
2447
2448 error_action = 1: silently do the conversion
2449
2450 error_action = 2: issue a warning if the original
2451 image has any pixel where
2452 red != green or red != blue
2453
2454 error_action = 3: issue an error and abort the
2455 conversion if the original
2456 image has any pixel where
2457 red != green or red != blue
2458
2459 red_weight: weight of red component
2460
2461 green_weight: weight of green component
2462 If either weight is negative, default
2463 weights are used.
2464
2465In the corresponding fixed point API the red_weight and green_weight values are
2466simply scaled by 100,000:
2467
2468 png_set_rgb_to_gray(png_ptr, error_action,
2469 png_fixed_point red_weight,
2470 png_fixed_point green_weight);
2471
2472If you have set error_action = 1 or 2, you can
2473later check whether the image really was gray, after processing
2474the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2475It will return a png_byte that is zero if the image was gray or
24761 if there were any non-gray pixels. Background and sBIT data
2477will be silently converted to grayscale, using the green channel
2478data for sBIT, regardless of the error_action setting.
2479
2480The default values come from the PNG file cHRM chunk if present; otherwise, the
2481defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2482space, as recommended in the Charles Poynton's Colour FAQ,
2483Copyright (c) 2006-11-28 Charles Poynton, in section 9:
2484
2485<http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
2486
2487 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2488
2489Previous versions of this document, 1998 through 2002, recommended a slightly
2490different formula:
2491
2492 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2493
2494Libpng uses an integer approximation:
2495
2496 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2497
2498The calculation is done in a linear colorspace, if the image gamma
2499can be determined.
2500
2501The png_set_background() function has been described already; it tells libpng to
2502composite images with alpha or simple transparency against the supplied
2503background color. For compatibility with versions of libpng earlier than
2504libpng-1.5.4 it is recommended that you call the function after reading the file
2505header, even if you don't want to use the color in a bKGD chunk, if one exists.
2506
2507If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2508you may use this color, or supply another color more suitable for
2509the current display (e.g., the background color from a web page). You
2510need to tell libpng how the color is represented, both the format of the
2511component values in the color (the number of bits) and the gamma encoding of the
2512color. The function takes two arguments, background_gamma_mode and need_expand
2513to convey this information; however, only two combinations are likely to be
2514useful:
2515
2516 png_color_16 my_background;
2517 png_color_16p image_background;
2518
2519 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2520 png_set_background(png_ptr, image_background,
2521 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
2522 else
2523 png_set_background(png_ptr, &my_background,
2524 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
2525
2526The second call was described above - my_background is in the format of the
2527final, display, output produced by libpng. Because you now know the format of
2528the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2529output and to retain palette images (the palette colors will be modified
2530appropriately and the tRNS chunk removed.) However, if you are doing this,
2531take great care not to ask for transformations without checking first that
2532they apply!
2533
2534In the first call the background color has the original bit depth and color type
2535of the PNG file. So, for palette images the color is supplied as a palette
2536index and for low bit greyscale images the color is a reduced bit value in
2537image_background->gray.
2538
2539If you didn't call png_set_gamma() before reading the file header, for example
2540if you need your code to remain compatible with older versions of libpng prior
2541to libpng-1.5.4, this is the place to call it.
2542
2543Do not call it if you called png_set_alpha_mode(); doing so will damage the
2544settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2545supported then you can certainly do png_set_gamma() before reading the PNG
2546header.)
2547
2548This API unconditionally sets the screen and file gamma values, so it will
2549override the value in the PNG file unless it is called before the PNG file
2550reading starts. For this reason you must always call it with the PNG file
2551value when you call it in this position:
2552
2553 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2554 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2555
2556 else
2557 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2558
2559If you need to reduce an RGB file to a paletted file, or if a paletted
2560file has more entries than will fit on your screen, png_set_quantize()
2561will do that. Note that this is a simple match quantization that merely
2562finds the closest color available. This should work fairly well with
2563optimized palettes, but fairly badly with linear color cubes. If you
2564pass a palette that is larger than maximum_colors, the file will
2565reduce the number of colors in the palette so it will fit into
2566maximum_colors. If there is a histogram, libpng will use it to make
2567more intelligent choices when reducing the palette. If there is no
2568histogram, it may not do as good a job.
2569
2570 if (color_type & PNG_COLOR_MASK_COLOR)
2571 {
2572 if (png_get_valid(png_ptr, info_ptr,
2573 PNG_INFO_PLTE))
2574 {
2575 png_uint_16p histogram = NULL;
2576
2577 png_get_hIST(png_ptr, info_ptr,
2578 &histogram);
2579 png_set_quantize(png_ptr, palette, num_palette,
2580 max_screen_colors, histogram, 1);
2581 }
2582
2583 else
2584 {
2585 png_color std_color_cube[MAX_SCREEN_COLORS] =
2586 { ... colors ... };
2587
2588 png_set_quantize(png_ptr, std_color_cube,
2589 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2590 NULL,0);
2591 }
2592 }
2593
2594PNG files describe monochrome as black being zero and white being one.
2595The following code will reverse this (make black be one and white be
2596zero):
2597
2598 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2599 png_set_invert_mono(png_ptr);
2600
2601This function can also be used to invert grayscale and gray-alpha images:
2602
2603 if (color_type == PNG_COLOR_TYPE_GRAY ||
2604 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2605 png_set_invert_mono(png_ptr);
2606
2607PNG files store 16-bit pixels in network byte order (big-endian,
2608ie. most significant bits first). This code changes the storage to the
2609other way (little-endian, i.e. least significant bits first, the
2610way PCs store them):
2611
2612 if (bit_depth == 16)
2613 png_set_swap(png_ptr);
2614
2615If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2616need to change the order the pixels are packed into bytes, you can use:
2617
2618 if (bit_depth < 8)
2619 png_set_packswap(png_ptr);
2620
2621Finally, you can write your own transformation function if none of
2622the existing ones meets your needs. This is done by setting a callback
2623with
2624
2625 png_set_read_user_transform_fn(png_ptr,
2626 read_transform_fn);
2627
2628You must supply the function
2629
2630 void read_transform_fn(png_structp png_ptr, png_row_infop
2631 row_info, png_bytep data)
2632
2633See pngtest.c for a working example. Your function will be called
2634after all of the other transformations have been processed. Take care with
2635interlaced images if you do the interlace yourself - the width of the row is the
2636width in 'row_info', not the overall image width.
2637
2638If supported, libpng provides two information routines that you can use to find
2639where you are in processing the image:
2640
2641 png_get_current_pass_number(png_structp png_ptr);
2642 png_get_current_row_number(png_structp png_ptr);
2643
2644Don't try using these outside a transform callback - firstly they are only
2645supported if user transforms are supported, secondly they may well return
2646unexpected results unless the row is actually being processed at the moment they
2647are called.
2648
2649With interlaced
2650images the value returned is the row in the input sub-image image. Use
2651PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2652find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2653
2654The discussion of interlace handling above contains more information on how to
2655use these values.
2656
2657You can also set up a pointer to a user structure for use by your
2658callback function, and you can inform libpng that your transform
2659function will change the number of channels or bit depth with the
2660function
2661
2662 png_set_user_transform_info(png_ptr, user_ptr,
2663 user_depth, user_channels);
2664
2665The user's application, not libpng, is responsible for allocating and
2666freeing any memory required for the user structure.
2667
2668You can retrieve the pointer via the function
2669png_get_user_transform_ptr(). For example:
2670
2671 voidp read_user_transform_ptr =
2672 png_get_user_transform_ptr(png_ptr);
2673
2674The last thing to handle is interlacing; this is covered in detail below,
2675but you must call the function here if you want libpng to handle expansion
2676of the interlaced image.
2677
2678 number_of_passes = png_set_interlace_handling(png_ptr);
2679
2680After setting the transformations, libpng can update your png_info
2681structure to reflect any transformations you've requested with this
2682call.
2683
2684 png_read_update_info(png_ptr, info_ptr);
2685
2686This is most useful to update the info structure's rowbytes
2687field so you can use it to allocate your image memory. This function
2688will also update your palette with the correct screen_gamma and
2689background if these have been given with the calls above. You may
2690only call png_read_update_info() once with a particular info_ptr.
2691
2692After you call png_read_update_info(), you can allocate any
2693memory you need to hold the image. The row data is simply
2694raw byte data for all forms of images. As the actual allocation
2695varies among applications, no example will be given. If you
2696are allocating one large chunk, you will need to build an
2697array of pointers to each row, as it will be needed for some
2698of the functions below.
2699
2700Be sure that your platform can allocate the buffer that you'll need.
2701libpng internally checks for oversize width, but you'll need to
2702do your own check for number_of_rows*width*pixel_size if you are using
2703a multiple-row buffer:
2704
2705 /* Guard against integer overflow */
2706 if (number_of_rows > PNG_SIZE_MAX/(width*pixel_size)) {
2707 png_error(png_ptr,"image_data buffer would be too large");
2708 }
2709
2710Remember: Before you call png_read_update_info(), the png_get_*()
2711functions return the values corresponding to the original PNG image.
2712After you call png_read_update_info the values refer to the image
2713that libpng will output. Consequently you must call all the png_set_
2714functions before you call png_read_update_info(). This is particularly
2715important for png_set_interlace_handling() - if you are going to call
2716png_read_update_info() you must call png_set_interlace_handling() before
2717it unless you want to receive interlaced output.
2718
2719.SS Reading image data
2720
2721After you've allocated memory, you can read the image data.
2722The simplest way to do this is in one function call. If you are
2723allocating enough memory to hold the whole image, you can just
2724call png_read_image() and libpng will read in all the image data
2725and put it in the memory area supplied. You will need to pass in
2726an array of pointers to each row.
2727
2728This function automatically handles interlacing, so you don't
2729need to call png_set_interlace_handling() (unless you call
2730png_read_update_info()) or call this function multiple times, or any
2731of that other stuff necessary with png_read_rows().
2732
2733 png_read_image(png_ptr, row_pointers);
2734
2735where row_pointers is:
2736
2737 png_bytep row_pointers[height];
2738
2739You can point to void or char or whatever you use for pixels.
2740
2741If you don't want to read in the whole image at once, you can
2742use png_read_rows() instead. If there is no interlacing (check
2743interlace_type == PNG_INTERLACE_NONE), this is simple:
2744
2745 png_read_rows(png_ptr, row_pointers, NULL,
2746 number_of_rows);
2747
2748where row_pointers is the same as in the png_read_image() call.
2749
2750If you are doing this just one row at a time, you can do this with
2751a single row_pointer instead of an array of row_pointers:
2752
2753 png_bytep row_pointer = row;
2754 png_read_row(png_ptr, row_pointer, NULL);
2755
2756If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2757get somewhat harder. The only current (PNG Specification version 1.2)
2758interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2759a somewhat complicated 2D interlace scheme, known as Adam7, that
2760breaks down an image into seven smaller images of varying size, based
2761on an 8x8 grid. This number is defined (from libpng 1.5) as
2762PNG_INTERLACE_ADAM7_PASSES in png.h
2763
2764libpng can fill out those images or it can give them to you "as is".
2765It is almost always better to have libpng handle the interlacing for you.
2766If you want the images filled out, there are two ways to do that. The one
2767mentioned in the PNG specification is to expand each pixel to cover
2768those pixels that have not been read yet (the "rectangle" method).
2769This results in a blocky image for the first pass, which gradually
2770smooths out as more pixels are read. The other method is the "sparkle"
2771method, where pixels are drawn only in their final locations, with the
2772rest of the image remaining whatever colors they were initialized to
2773before the start of the read. The first method usually looks better,
2774but tends to be slower, as there are more pixels to put in the rows.
2775
2776If, as is likely, you want libpng to expand the images, call this before
2777calling png_start_read_image() or png_read_update_info():
2778
2779 if (interlace_type == PNG_INTERLACE_ADAM7)
2780 number_of_passes
2781 = png_set_interlace_handling(png_ptr);
2782
2783This will return the number of passes needed. Currently, this is seven,
2784but may change if another interlace type is added. This function can be
2785called even if the file is not interlaced, where it will return one pass.
2786You then need to read the whole image 'number_of_passes' times. Each time
2787will distribute the pixels from the current pass to the correct place in
2788the output image, so you need to supply the same rows to png_read_rows in
2789each pass.
2790
2791If you are not going to display the image after each pass, but are
2792going to wait until the entire image is read in, use the sparkle
2793effect. This effect is faster and the end result of either method
2794is exactly the same. If you are planning on displaying the image
2795after each pass, the "rectangle" effect is generally considered the
2796better looking one.
2797
2798If you only want the "sparkle" effect, just call png_read_row() or
2799png_read_rows() as
2800normal, with the third parameter NULL. Make sure you make pass over
2801the image number_of_passes times, and you don't change the data in the
2802rows between calls. You can change the locations of the data, just
2803not the data. Each pass only writes the pixels appropriate for that
2804pass, and assumes the data from previous passes is still valid.
2805
2806 png_read_rows(png_ptr, row_pointers, NULL,
2807 number_of_rows);
2808 or
2809 png_read_row(png_ptr, row_pointers, NULL);
2810
2811If you only want the first effect (the rectangles), do the same as
2812before except pass the row buffer in the third parameter, and leave
2813the second parameter NULL.
2814
2815 png_read_rows(png_ptr, NULL, row_pointers,
2816 number_of_rows);
2817 or
2818 png_read_row(png_ptr, NULL, row_pointers);
2819
2820If you don't want libpng to handle the interlacing details, just call
2821png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
2822Each of the images is a valid image by itself; however, you will almost
2823certainly need to distribute the pixels from each sub-image to the
2824correct place. This is where everything gets very tricky.
2825
2826If you want to retrieve the separate images you must pass the correct
2827number of rows to each successive call of png_read_rows(). The calculation
2828gets pretty complicated for small images, where some sub-images may
2829not even exist because either their width or height ends up zero.
2830libpng provides two macros to help you in 1.5 and later versions:
2831
2832 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
2833 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
2834
2835Respectively these tell you the width and height of the sub-image
2836corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
2837this can be confusing because the specification refers to the same passes
2838as 1 to 7! Be careful, you must check both the width and height before
2839calling png_read_rows() and not call it for that pass if either is zero.
2840
2841You can, of course, read each sub-image row by row. If you want to
2842produce optimal code to make a pixel-by-pixel transformation of an
2843interlaced image this is the best approach; read each row of each pass,
2844transform it, and write it out to a new interlaced image.
2845
2846If you want to de-interlace the image yourself libpng provides further
2847macros to help that tell you where to place the pixels in the output image.
2848Because the interlacing scheme is rectangular - sub-image pixels are always
2849arranged on a rectangular grid - all you need to know for each pass is the
2850starting column and row in the output image of the first pixel plus the
2851spacing between each pixel. As of libpng 1.5 there are four macros to
2852retrieve this information:
2853
2854 png_uint_32 x = PNG_PASS_START_COL(pass);
2855 png_uint_32 y = PNG_PASS_START_ROW(pass);
2856 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
2857 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
2858
2859These allow you to write the obvious loop:
2860
2861 png_uint_32 input_y = 0;
2862 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
2863
2864 while (output_y < output_image_height)
2865 {
2866 png_uint_32 input_x = 0;
2867 png_uint_32 output_x = PNG_PASS_START_COL(pass);
2868
2869 while (output_x < output_image_width)
2870 {
2871 image[output_y][output_x] =
2872 subimage[pass][input_y][input_x++];
2873
2874 output_x += xStep;
2875 }
2876
2877 ++input_y;
2878 output_y += yStep;
2879 }
2880
2881Notice that the steps between successive output rows and columns are
2882returned as shifts. This is possible because the pixels in the subimages
2883are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
2884image. In practice you may need to directly calculate the output coordinate
2885given an input coordinate. libpng provides two further macros for this
2886purpose:
2887
2888 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
2889 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
2890
2891Finally a pair of macros are provided to tell you if a particular image
2892row or column appears in a given pass:
2893
2894 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
2895 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
2896
2897Bear in mind that you will probably also need to check the width and height
2898of the pass in addition to the above to be sure the pass even exists!
2899
2900With any luck you are convinced by now that you don't want to do your own
2901interlace handling. In reality normally the only good reason for doing this
2902is if you are processing PNG files on a pixel-by-pixel basis and don't want
2903to load the whole file into memory when it is interlaced.
2904
2905libpng includes a test program, pngvalid, that illustrates reading and
2906writing of interlaced images. If you can't get interlacing to work in your
2907code and don't want to leave it to libpng (the recommended approach), see
2908how pngvalid.c does it.
2909
2910.SS Finishing a sequential read
2911
2912After you are finished reading the image through the
2913low-level interface, you can finish reading the file.
2914
2915If you want to use a different crc action for handling CRC errors in
2916chunks after the image data, you can call png_set_crc_action()
2917again at this point.
2918
2919If you are interested in comments or time, which may be stored either
2920before or after the image data, you should pass the separate png_info
2921struct if you want to keep the comments from before and after the image
2922separate.
2923
2924 png_infop end_info = png_create_info_struct(png_ptr);
2925
2926 if (!end_info)
2927 {
2928 png_destroy_read_struct(&png_ptr, &info_ptr,
2929 (png_infopp)NULL);
2930 return (ERROR);
2931 }
2932
2933 png_read_end(png_ptr, end_info);
2934
2935If you are not interested, you should still call png_read_end()
2936but you can pass NULL, avoiding the need to create an end_info structure.
2937If you do this, libpng will not process any chunks after IDAT other than
2938skipping over them and perhaps (depending on whether you have called
2939png_set_crc_action) checking their CRCs while looking for the IEND chunk.
2940
2941 png_read_end(png_ptr, (png_infop)NULL);
2942
2943If you don't call png_read_end(), then your file pointer will be
2944left pointing to the first chunk after the last IDAT, which is probably
2945not what you want if you expect to read something beyond the end of
2946the PNG datastream.
2947
2948When you are done, you can free all memory allocated by libpng like this:
2949
2950 png_destroy_read_struct(&png_ptr, &info_ptr,
2951 &end_info);
2952
2953or, if you didn't create an end_info structure,
2954
2955 png_destroy_read_struct(&png_ptr, &info_ptr,
2956 (png_infopp)NULL);
2957
2958It is also possible to individually free the info_ptr members that
2959point to libpng-allocated storage with the following function:
2960
2961 png_free_data(png_ptr, info_ptr, mask, seq)
2962
2963 mask - identifies data to be freed, a mask
2964 containing the bitwise OR of one or
2965 more of
2966 PNG_FREE_PLTE, PNG_FREE_TRNS,
2967 PNG_FREE_HIST, PNG_FREE_ICCP,
2968 PNG_FREE_PCAL, PNG_FREE_ROWS,
2969 PNG_FREE_SCAL, PNG_FREE_SPLT,
2970 PNG_FREE_TEXT, PNG_FREE_UNKN,
2971 or simply PNG_FREE_ALL
2972
2973 seq - sequence number of item to be freed
2974 (\-1 for all items)
2975
2976This function may be safely called when the relevant storage has
2977already been freed, or has not yet been allocated, or was allocated
2978by the user and not by libpng, and will in those cases do nothing.
2979The "seq" parameter is ignored if only one item of the selected data
2980type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
2981are allowed for the data type identified in the mask, such as text or
2982sPLT, only the n'th item in the structure is freed, where n is "seq".
2983
2984The default behavior is only to free data that was allocated internally
2985by libpng. This can be changed, so that libpng will not free the data,
2986or so that it will free data that was allocated by the user with png_malloc()
2987or png_calloc() and passed in via a png_set_*() function, with
2988
2989 png_data_freer(png_ptr, info_ptr, freer, mask)
2990
2991 freer - one of
2992 PNG_DESTROY_WILL_FREE_DATA
2993 PNG_SET_WILL_FREE_DATA
2994 PNG_USER_WILL_FREE_DATA
2995
2996 mask - which data elements are affected
2997 same choices as in png_free_data()
2998
2999This function only affects data that has already been allocated.
3000You can call this function after reading the PNG data but before calling
3001any png_set_*() functions, to control whether the user or the png_set_*()
3002function is responsible for freeing any existing data that might be present,
3003and again after the png_set_*() functions to control whether the user
3004or png_destroy_*() is supposed to free the data. When the user assumes
3005responsibility for libpng-allocated data, the application must use
3006png_free() to free it, and when the user transfers responsibility to libpng
3007for data that the user has allocated, the user must have used png_malloc()
3008or png_calloc() to allocate it.
3009
3010If you allocated your row_pointers in a single block, as suggested above in
3011the description of the high level read interface, you must not transfer
3012responsibility for freeing it to the png_set_rows or png_read_destroy function,
3013because they would also try to free the individual row_pointers[i].
3014
3015If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3016separately, do not transfer responsibility for freeing text_ptr to libpng,
3017because when libpng fills a png_text structure it combines these members with
3018the key member, and png_free_data() will free only text_ptr.key. Similarly,
3019if you transfer responsibility for free'ing text_ptr from libpng to your
3020application, your application must not separately free those members.
3021
3022The png_free_data() function will turn off the "valid" flag for anything
3023it frees. If you need to turn the flag off for a chunk that was freed by
3024your application instead of by libpng, you can use
3025
3026 png_set_invalid(png_ptr, info_ptr, mask);
3027
3028 mask - identifies the chunks to be made invalid,
3029 containing the bitwise OR of one or
3030 more of
3031 PNG_INFO_gAMA, PNG_INFO_sBIT,
3032 PNG_INFO_cHRM, PNG_INFO_PLTE,
3033 PNG_INFO_tRNS, PNG_INFO_bKGD,
3034 PNG_INFO_eXIf,
3035 PNG_INFO_hIST, PNG_INFO_pHYs,
3036 PNG_INFO_oFFs, PNG_INFO_tIME,
3037 PNG_INFO_pCAL, PNG_INFO_sRGB,
3038 PNG_INFO_iCCP, PNG_INFO_sPLT,
3039 PNG_INFO_sCAL, PNG_INFO_IDAT
3040
3041For a more compact example of reading a PNG image, see the file example.c.
3042
3043.SS Reading PNG files progressively
3044
3045The progressive reader is slightly different from the non-progressive
3046reader. Instead of calling png_read_info(), png_read_rows(), and
3047png_read_end(), you make one call to png_process_data(), which calls
3048callbacks when it has the info, a row, or the end of the image. You
3049set up these callbacks with png_set_progressive_read_fn(). You don't
3050have to worry about the input/output functions of libpng, as you are
3051giving the library the data directly in png_process_data(). I will
3052assume that you have read the section on reading PNG files above,
3053so I will only highlight the differences (although I will show
3054all of the code).
3055
3056png_structp png_ptr;
3057png_infop info_ptr;
3058
3059 /* An example code fragment of how you would
3060 initialize the progressive reader in your
3061 application. */
3062 int
3063 initialize_png_reader()
3064 {
3065 png_ptr = png_create_read_struct
3066 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3067 user_error_fn, user_warning_fn);
3068
3069 if (!png_ptr)
3070 return (ERROR);
3071
3072 info_ptr = png_create_info_struct(png_ptr);
3073
3074 if (!info_ptr)
3075 {
3076 png_destroy_read_struct(&png_ptr,
3077 (png_infopp)NULL, (png_infopp)NULL);
3078 return (ERROR);
3079 }
3080
3081 if (setjmp(png_jmpbuf(png_ptr)))
3082 {
3083 png_destroy_read_struct(&png_ptr, &info_ptr,
3084 (png_infopp)NULL);
3085 return (ERROR);
3086 }
3087
3088 /* This one's new. You can provide functions
3089 to be called when the header info is valid,
3090 when each row is completed, and when the image
3091 is finished. If you aren't using all functions,
3092 you can specify NULL parameters. Even when all
3093 three functions are NULL, you need to call
3094 png_set_progressive_read_fn(). You can use
3095 any struct as the user_ptr (cast to a void pointer
3096 for the function call), and retrieve the pointer
3097 from inside the callbacks using the function
3098
3099 png_get_progressive_ptr(png_ptr);
3100
3101 which will return a void pointer, which you have
3102 to cast appropriately.
3103 */
3104 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
3105 info_callback, row_callback, end_callback);
3106
3107 return 0;
3108 }
3109
3110 /* A code fragment that you call as you receive blocks
3111 of data */
3112 int
3113 process_data(png_bytep buffer, png_uint_32 length)
3114 {
3115 if (setjmp(png_jmpbuf(png_ptr)))
3116 {
3117 png_destroy_read_struct(&png_ptr, &info_ptr,
3118 (png_infopp)NULL);
3119 return (ERROR);
3120 }
3121
3122 /* This one's new also. Simply give it a chunk
3123 of data from the file stream (in order, of
3124 course). On machines with segmented memory
3125 models machines, don't give it any more than
3126 64K. The library seems to run fine with sizes
3127 of 4K. Although you can give it much less if
3128 necessary (I assume you can give it chunks of
3129 1 byte, I haven't tried less than 256 bytes
3130 yet). When this function returns, you may
3131 want to display any rows that were generated
3132 in the row callback if you don't already do
3133 so there.
3134 */
3135 png_process_data(png_ptr, info_ptr, buffer, length);
3136
3137 /* At this point you can call png_process_data_skip if
3138 you want to handle data the library will skip yourself;
3139 it simply returns the number of bytes to skip (and stops
3140 libpng skipping that number of bytes on the next
3141 png_process_data call).
3142 return 0;
3143 }
3144
3145 /* This function is called (as set by
3146 png_set_progressive_read_fn() above) when enough data
3147 has been supplied so all of the header has been
3148 read.
3149 */
3150 void
3151 info_callback(png_structp png_ptr, png_infop info)
3152 {
3153 /* Do any setup here, including setting any of
3154 the transformations mentioned in the Reading
3155 PNG files section. For now, you _must_ call
3156 either png_start_read_image() or
3157 png_read_update_info() after all the
3158 transformations are set (even if you don't set
3159 any). You may start getting rows before
3160 png_process_data() returns, so this is your
3161 last chance to prepare for that.
3162
3163 This is where you turn on interlace handling,
3164 assuming you don't want to do it yourself.
3165
3166 If you need to you can stop the processing of
3167 your original input data at this point by calling
3168 png_process_data_pause. This returns the number
3169 of unprocessed bytes from the last png_process_data
3170 call - it is up to you to ensure that the next call
3171 sees these bytes again. If you don't want to bother
3172 with this you can get libpng to cache the unread
3173 bytes by setting the 'save' parameter (see png.h) but
3174 then libpng will have to copy the data internally.
3175 */
3176 }
3177
3178 /* This function is called when each row of image
3179 data is complete */
3180 void
3181 row_callback(png_structp png_ptr, png_bytep new_row,
3182 png_uint_32 row_num, int pass)
3183 {
3184 /* If the image is interlaced, and you turned
3185 on the interlace handler, this function will
3186 be called for every row in every pass. Some
3187 of these rows will not be changed from the
3188 previous pass. When the row is not changed,
3189 the new_row variable will be NULL. The rows
3190 and passes are called in order, so you don't
3191 really need the row_num and pass, but I'm
3192 supplying them because it may make your life
3193 easier.
3194
3195 If you did not turn on interlace handling then
3196 the callback is called for each row of each
3197 sub-image when the image is interlaced. In this
3198 case 'row_num' is the row in the sub-image, not
3199 the row in the output image as it is in all other
3200 cases.
3201
3202 For the non-NULL rows of interlaced images when
3203 you have switched on libpng interlace handling,
3204 you must call png_progressive_combine_row()
3205 passing in the row and the old row. You can
3206 call this function for NULL rows (it will just
3207 return) and for non-interlaced images (it just
3208 does the memcpy for you) if it will make the
3209 code easier. Thus, you can just do this for
3210 all cases if you switch on interlace handling;
3211 */
3212
3213 png_progressive_combine_row(png_ptr, old_row,
3214 new_row);
3215
3216 /* where old_row is what was displayed
3217 previously for the row. Note that the first
3218 pass (pass == 0, really) will completely cover
3219 the old row, so the rows do not have to be
3220 initialized. After the first pass (and only
3221 for interlaced images), you will have to pass
3222 the current row, and the function will combine
3223 the old row and the new row.
3224
3225 You can also call png_process_data_pause in this
3226 callback - see above.
3227 */
3228 }
3229
3230 void
3231 end_callback(png_structp png_ptr, png_infop info)
3232 {
3233 /* This function is called after the whole image
3234 has been read, including any chunks after the
3235 image (up to and including the IEND). You
3236 will usually have the same info chunk as you
3237 had in the header, although some data may have
3238 been added to the comments and time fields.
3239
3240 Most people won't do much here, perhaps setting
3241 a flag that marks the image as finished.
3242 */
3243 }
3244
3245
3246
3247.SH IV. Writing
3248
3249Much of this is very similar to reading. However, everything of
3250importance is repeated here, so you won't have to constantly look
3251back up in the reading section to understand writing.
3252
3253.SS Setup
3254
3255You will want to do the I/O initialization before you get into libpng,
3256so if it doesn't work, you don't have anything to undo. If you are not
3257using the standard I/O functions, you will need to replace them with
3258custom writing functions. See the discussion under Customizing libpng.
3259
3260 FILE *fp = fopen(file_name, "wb");
3261
3262 if (!fp)
3263 return (ERROR);
3264
3265Next, png_struct and png_info need to be allocated and initialized.
3266As these can be both relatively large, you may not want to store these
3267on the stack, unless you have stack space to spare. Of course, you
3268will want to check if they return NULL. If you are also reading,
3269you won't want to name your read structure and your write structure
3270both "png_ptr"; you can call them anything you like, such as
3271"read_ptr" and "write_ptr". Look at pngtest.c, for example.
3272
3273 png_structp png_ptr = png_create_write_struct
3274 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3275 user_error_fn, user_warning_fn);
3276
3277 if (!png_ptr)
3278 return (ERROR);
3279
3280 png_infop info_ptr = png_create_info_struct(png_ptr);
3281 if (!info_ptr)
3282 {
3283 png_destroy_write_struct(&png_ptr,
3284 (png_infopp)NULL);
3285 return (ERROR);
3286 }
3287
3288If you want to use your own memory allocation routines,
3289define PNG_USER_MEM_SUPPORTED and use
3290png_create_write_struct_2() instead of png_create_write_struct():
3291
3292 png_structp png_ptr = png_create_write_struct_2
3293 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3294 user_error_fn, user_warning_fn, (png_voidp)
3295 user_mem_ptr, user_malloc_fn, user_free_fn);
3296
3297After you have these structures, you will need to set up the
3298error handling. When libpng encounters an error, it expects to
3299longjmp() back to your routine. Therefore, you will need to call
3300setjmp() and pass the png_jmpbuf(png_ptr). If you
3301write the file from different routines, you will need to update
3302the png_jmpbuf(png_ptr) every time you enter a new routine that will
3303call a png_*() function. See your documentation of setjmp/longjmp
3304for your compiler for more information on setjmp/longjmp. See
3305the discussion on libpng error handling in the Customizing Libpng
3306section below for more information on the libpng error handling.
3307
3308 if (setjmp(png_jmpbuf(png_ptr)))
3309 {
3310 png_destroy_write_struct(&png_ptr, &info_ptr);
3311 fclose(fp);
3312 return (ERROR);
3313 }
3314 ...
3315 return;
3316
3317If you would rather avoid the complexity of setjmp/longjmp issues,
3318you can compile libpng with PNG_NO_SETJMP, in which case
3319errors will result in a call to PNG_ABORT() which defaults to abort().
3320
3321You can #define PNG_ABORT() to a function that does something
3322more useful than abort(), as long as your function does not
3323return.
3324
3325Checking for invalid palette index on write was added at libpng
33261.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
3327a benign error. This is enabled by default because this condition is an
3328error according to the PNG specification, Clause 11.3.2, but the error can
3329be ignored in each png_ptr with
3330
3331 png_set_check_for_invalid_index(png_ptr, 0);
3332
3333If the error is ignored, or if png_benign_error() treats it as a warning,
3334any invalid pixels are written as-is by the encoder, resulting in an
3335invalid PNG datastream as output. In this case the application is
3336responsible for ensuring that the pixel indexes are in range when it writes
3337a PLTE chunk with fewer entries than the bit depth would allow.
3338
3339Now you need to set up the output code. The default for libpng is to
3340use the C function fwrite(). If you use this, you will need to pass a
3341valid FILE * in the function png_init_io(). Be sure that the file is
3342opened in binary mode. Again, if you wish to handle writing data in
3343another way, see the discussion on libpng I/O handling in the Customizing
3344Libpng section below.
3345
3346 png_init_io(png_ptr, fp);
3347
3348If you are embedding your PNG into a datastream such as MNG, and don't
3349want libpng to write the 8-byte signature, or if you have already
3350written the signature in your application, use
3351
3352 png_set_sig_bytes(png_ptr, 8);
3353
3354to inform libpng that it should not write a signature.
3355
3356.SS Write callbacks
3357
3358At this point, you can set up a callback function that will be
3359called after each row has been written, which you can use to control
3360a progress meter or the like. It's demonstrated in pngtest.c.
3361You must supply a function
3362
3363 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3364 int pass);
3365 {
3366 /* put your code here */
3367 }
3368
3369(You can give it another name that you like instead of "write_row_callback")
3370
3371To inform libpng about your function, use
3372
3373 png_set_write_status_fn(png_ptr, write_row_callback);
3374
3375When this function is called the row has already been completely processed and
3376it has also been written out. The 'row' and 'pass' refer to the next row to be
3377handled. For the
3378non-interlaced case the row that was just handled is simply one less than the
3379passed in row number, and pass will always be 0. For the interlaced case the
3380same applies unless the row value is 0, in which case the row just handled was
3381the last one from one of the preceding passes. Because interlacing may skip a
3382pass you cannot be sure that the preceding pass is just 'pass\-1', if you really
3383need to know what the last pass is record (row,pass) from the callback and use
3384the last recorded value each time.
3385
3386As with the user transform you can find the output row using the
3387PNG_ROW_FROM_PASS_ROW macro.
3388
3389You now have the option of modifying how the compression library will
3390run. The following functions are mainly for testing, but may be useful
3391in some cases, like if you need to write PNG files extremely fast and
3392are willing to give up some compression, or if you want to get the
3393maximum possible compression at the expense of slower writing. If you
3394have no special needs in this area, let the library do what it wants by
3395not calling this function at all, as it has been tuned to deliver a good
3396speed/compression ratio. The second parameter to png_set_filter() is
3397the filter method, for which the only valid values are 0 (as of the
3398July 1999 PNG specification, version 1.2) or 64 (if you are writing
3399a PNG datastream that is to be embedded in a MNG datastream). The third
3400parameter is a flag that indicates which filter type(s) are to be tested
3401for each scanline. See the PNG specification for details on the specific
3402filter types.
3403
3404
3405 /* turn on or off filtering, and/or choose
3406 specific filters. You can use either a single
3407 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3408 or more PNG_FILTER_NAME masks.
3409 */
3410 png_set_filter(png_ptr, 0,
3411 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3412 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3413 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3414 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3415 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3416 PNG_ALL_FILTERS | PNG_FAST_FILTERS);
3417
3418If an application wants to start and stop using particular filters during
3419compression, it should start out with all of the filters (to ensure that
3420the previous row of pixels will be stored in case it's needed later),
3421and then add and remove them after the start of compression.
3422
3423If you are writing a PNG datastream that is to be embedded in a MNG
3424datastream, the second parameter can be either 0 or 64.
3425
3426The png_set_compression_*() functions interface to the zlib compression
3427library, and should mostly be ignored unless you really know what you are
3428doing. The only generally useful call is png_set_compression_level()
3429which changes how much time zlib spends on trying to compress the image
3430data. See the Compression Library (zlib.h and algorithm.txt, distributed
3431with zlib) for details on the compression levels.
3432
3433 #include zlib.h
3434
3435 /* Set the zlib compression level */
3436 png_set_compression_level(png_ptr,
3437 Z_BEST_COMPRESSION);
3438
3439 /* Set other zlib parameters for compressing IDAT */
3440 png_set_compression_mem_level(png_ptr, 8);
3441 png_set_compression_strategy(png_ptr,
3442 Z_DEFAULT_STRATEGY);
3443 png_set_compression_window_bits(png_ptr, 15);
3444 png_set_compression_method(png_ptr, 8);
3445 png_set_compression_buffer_size(png_ptr, 8192)
3446
3447 /* Set zlib parameters for text compression
3448 * If you don't call these, the parameters
3449 * fall back on those defined for IDAT chunks
3450 */
3451 png_set_text_compression_mem_level(png_ptr, 8);
3452 png_set_text_compression_strategy(png_ptr,
3453 Z_DEFAULT_STRATEGY);
3454 png_set_text_compression_window_bits(png_ptr, 15);
3455 png_set_text_compression_method(png_ptr, 8);
3456
3457.SS Setting the contents of info for output
3458
3459You now need to fill in the png_info structure with all the data you
3460wish to write before the actual image. Note that the only thing you
3461are allowed to write after the image is the text chunks and the time
3462chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3463the latest PNG specification for more information on that. If you
3464wish to write them before the image, fill them in now, and flag that
3465data as being valid. If you want to wait until after the data, don't
3466fill them until png_write_end(). For all the fields in png_info and
3467their data types, see png.h. For explanations of what the fields
3468contain, see the PNG specification.
3469
3470Some of the more important parts of the png_info are:
3471
3472 png_set_IHDR(png_ptr, info_ptr, width, height,
3473 bit_depth, color_type, interlace_type,
3474 compression_type, filter_method)
3475
3476 width - holds the width of the image
3477 in pixels (up to 2^31).
3478
3479 height - holds the height of the image
3480 in pixels (up to 2^31).
3481
3482 bit_depth - holds the bit depth of one of the
3483 image channels.
3484 (valid values are 1, 2, 4, 8, 16
3485 and depend also on the
3486 color_type. See also significant
3487 bits (sBIT) below).
3488
3489 color_type - describes which color/alpha
3490 channels are present.
3491 PNG_COLOR_TYPE_GRAY
3492 (bit depths 1, 2, 4, 8, 16)
3493 PNG_COLOR_TYPE_GRAY_ALPHA
3494 (bit depths 8, 16)
3495 PNG_COLOR_TYPE_PALETTE
3496 (bit depths 1, 2, 4, 8)
3497 PNG_COLOR_TYPE_RGB
3498 (bit_depths 8, 16)
3499 PNG_COLOR_TYPE_RGB_ALPHA
3500 (bit_depths 8, 16)
3501
3502 PNG_COLOR_MASK_PALETTE
3503 PNG_COLOR_MASK_COLOR
3504 PNG_COLOR_MASK_ALPHA
3505
3506 interlace_type - PNG_INTERLACE_NONE or
3507 PNG_INTERLACE_ADAM7
3508
3509 compression_type - (must be
3510 PNG_COMPRESSION_TYPE_DEFAULT)
3511
3512 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3513 or, if you are writing a PNG to
3514 be embedded in a MNG datastream,
3515 can also be
3516 PNG_INTRAPIXEL_DIFFERENCING)
3517
3518If you call png_set_IHDR(), the call must appear before any of the
3519other png_set_*() functions, because they might require access to some of
3520the IHDR settings. The remaining png_set_*() functions can be called
3521in any order.
3522
3523If you wish, you can reset the compression_type, interlace_type, or
3524filter_method later by calling png_set_IHDR() again; if you do this, the
3525width, height, bit_depth, and color_type must be the same in each call.
3526
3527 png_set_PLTE(png_ptr, info_ptr, palette,
3528 num_palette);
3529
3530 palette - the palette for the file
3531 (array of png_color)
3532 num_palette - number of entries in the palette
3533
3534
3535 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3536 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3537
3538 file_gamma - the gamma at which the image was
3539 created (PNG_INFO_gAMA)
3540
3541 int_file_gamma - 100,000 times the gamma at which
3542 the image was created
3543
3544 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3545 green_x, green_y, blue_x, blue_y)
3546 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3547 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3548 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3549 int_red_x, int_red_y, int_green_x, int_green_y,
3550 int_blue_x, int_blue_y)
3551 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3552 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3553 int_blue_X, int_blue_Y, int_blue_Z)
3554
3555 {white,red,green,blue}_{x,y}
3556 A color space encoding specified using the chromaticities
3557 of the end points and the white point.
3558
3559 {red,green,blue}_{X,Y,Z}
3560 A color space encoding specified using the encoding end
3561 points - the CIE tristimulus specification of the intended
3562 color of the red, green and blue channels in the PNG RGB
3563 data. The white point is simply the sum of the three end
3564 points.
3565
3566 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3567
3568 srgb_intent - the rendering intent
3569 (PNG_INFO_sRGB) The presence of
3570 the sRGB chunk means that the pixel
3571 data is in the sRGB color space.
3572 This chunk also implies specific
3573 values of gAMA and cHRM. Rendering
3574 intent is the CSS-1 property that
3575 has been defined by the International
3576 Color Consortium
3577 (http://www.color.org).
3578 It can be one of
3579 PNG_sRGB_INTENT_SATURATION,
3580 PNG_sRGB_INTENT_PERCEPTUAL,
3581 PNG_sRGB_INTENT_ABSOLUTE, or
3582 PNG_sRGB_INTENT_RELATIVE.
3583
3584
3585 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3586 srgb_intent);
3587
3588 srgb_intent - the rendering intent
3589 (PNG_INFO_sRGB) The presence of the
3590 sRGB chunk means that the pixel
3591 data is in the sRGB color space.
3592 This function also causes gAMA and
3593 cHRM chunks with the specific values
3594 that are consistent with sRGB to be
3595 written.
3596
3597 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3598 profile, proflen);
3599
3600 name - The profile name.
3601
3602 compression_type - The compression type; always
3603 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3604 You may give NULL to this argument to
3605 ignore it.
3606
3607 profile - International Color Consortium color
3608 profile data. May contain NULs.
3609
3610 proflen - length of profile data in bytes.
3611
3612 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3613
3614 sig_bit - the number of significant bits for
3615 (PNG_INFO_sBIT) each of the gray, red,
3616 green, and blue channels, whichever are
3617 appropriate for the given color type
3618 (png_color_16)
3619
3620 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3621 num_trans, trans_color);
3622
3623 trans_alpha - array of alpha (transparency)
3624 entries for palette (PNG_INFO_tRNS)
3625
3626 num_trans - number of transparent entries
3627 (PNG_INFO_tRNS)
3628
3629 trans_color - graylevel or color sample values
3630 (in order red, green, blue) of the
3631 single transparent color for
3632 non-paletted images (PNG_INFO_tRNS)
3633
3634 png_set_eXIf_1(png_ptr, info_ptr, num_exif, exif);
3635
3636 exif - Exif profile (array of
3637 png_byte) (PNG_INFO_eXIf)
3638
3639 png_set_hIST(png_ptr, info_ptr, hist);
3640
3641 hist - histogram of palette (array of
3642 png_uint_16) (PNG_INFO_hIST)
3643
3644 png_set_tIME(png_ptr, info_ptr, mod_time);
3645
3646 mod_time - time image was last modified
3647 (PNG_VALID_tIME)
3648
3649 png_set_bKGD(png_ptr, info_ptr, background);
3650
3651 background - background color (of type
3652 png_color_16p) (PNG_VALID_bKGD)
3653
3654 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3655
3656 text_ptr - array of png_text holding image
3657 comments
3658
3659 text_ptr[i].compression - type of compression used
3660 on "text" PNG_TEXT_COMPRESSION_NONE
3661 PNG_TEXT_COMPRESSION_zTXt
3662 PNG_ITXT_COMPRESSION_NONE
3663 PNG_ITXT_COMPRESSION_zTXt
3664 text_ptr[i].key - keyword for comment. Must contain
3665 1-79 characters.
3666 text_ptr[i].text - text comments for current
3667 keyword. Can be NULL or empty.
3668 text_ptr[i].text_length - length of text string,
3669 after decompression, 0 for iTXt
3670 text_ptr[i].itxt_length - length of itxt string,
3671 after decompression, 0 for tEXt/zTXt
3672 text_ptr[i].lang - language of comment (NULL or
3673 empty for unknown).
3674 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3675 or empty for unknown).
3676
3677 Note that the itxt_length, lang, and lang_key
3678 members of the text_ptr structure only exist when the
3679 library is built with iTXt chunk support. Prior to
3680 libpng-1.4.0 the library was built by default without
3681 iTXt support. Also note that when iTXt is supported,
3682 they contain NULL pointers when the "compression"
3683 field contains PNG_TEXT_COMPRESSION_NONE or
3684 PNG_TEXT_COMPRESSION_zTXt.
3685
3686 num_text - number of comments
3687
3688 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3689 num_spalettes);
3690
3691 palette_ptr - array of png_sPLT_struct structures
3692 to be added to the list of palettes
3693 in the info structure.
3694 num_spalettes - number of palette structures to be
3695 added.
3696
3697 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3698 unit_type);
3699
3700 offset_x - positive offset from the left
3701 edge of the screen
3702
3703 offset_y - positive offset from the top
3704 edge of the screen
3705
3706 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3707
3708 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3709 unit_type);
3710
3711 res_x - pixels/unit physical resolution
3712 in x direction
3713
3714 res_y - pixels/unit physical resolution
3715 in y direction
3716
3717 unit_type - PNG_RESOLUTION_UNKNOWN,
3718 PNG_RESOLUTION_METER
3719
3720 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3721
3722 unit - physical scale units (an integer)
3723
3724 width - width of a pixel in physical scale units
3725
3726 height - height of a pixel in physical scale units
3727 (width and height are doubles)
3728
3729 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3730
3731 unit - physical scale units (an integer)
3732
3733 width - width of a pixel in physical scale units
3734 expressed as a string
3735
3736 height - height of a pixel in physical scale units
3737 (width and height are strings like "2.54")
3738
3739 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3740 num_unknowns)
3741
3742 unknowns - array of png_unknown_chunk
3743 structures holding unknown chunks
3744 unknowns[i].name - name of unknown chunk
3745 unknowns[i].data - data of unknown chunk
3746 unknowns[i].size - size of unknown chunk's data
3747 unknowns[i].location - position to write chunk in file
3748 0: do not write chunk
3749 PNG_HAVE_IHDR: before PLTE
3750 PNG_HAVE_PLTE: before IDAT
3751 PNG_AFTER_IDAT: after IDAT
3752
3753The "location" member is set automatically according to
3754what part of the output file has already been written.
3755You can change its value after calling png_set_unknown_chunks()
3756as demonstrated in pngtest.c. Within each of the "locations",
3757the chunks are sequenced according to their position in the
3758structure (that is, the value of "i", which is the order in which
3759the chunk was either read from the input file or defined with
3760png_set_unknown_chunks).
3761
3762A quick word about text and num_text. text is an array of png_text
3763structures. num_text is the number of valid structures in the array.
3764Each png_text structure holds a language code, a keyword, a text value,
3765and a compression type.
3766
3767The compression types have the same valid numbers as the compression
3768types of the image data. Currently, the only valid number is zero.
3769However, you can store text either compressed or uncompressed, unlike
3770images, which always have to be compressed. So if you don't want the
3771text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3772Because tEXt and zTXt chunks don't have a language field, if you
3773specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3774any language code or translated keyword will not be written out.
3775
3776Until text gets around a few hundred bytes, it is not worth compressing it.
3777After the text has been written out to the file, the compression type
3778is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3779so that it isn't written out again at the end (in case you are calling
3780png_write_end() with the same struct).
3781
3782The keywords that are given in the PNG Specification are:
3783
3784 Title Short (one line) title or
3785 caption for image
3786
3787 Author Name of image's creator
3788
3789 Description Description of image (possibly long)
3790
3791 Copyright Copyright notice
3792
3793 Creation Time Time of original image creation
3794 (usually RFC 1123 format, see below)
3795
3796 Software Software used to create the image
3797
3798 Disclaimer Legal disclaimer
3799
3800 Warning Warning of nature of content
3801
3802 Source Device used to create the image
3803
3804 Comment Miscellaneous comment; conversion
3805 from other image format
3806
3807The keyword-text pairs work like this. Keywords should be short
3808simple descriptions of what the comment is about. Some typical
3809keywords are found in the PNG specification, as is some recommendations
3810on keywords. You can repeat keywords in a file. You can even write
3811some text before the image and some after. For example, you may want
3812to put a description of the image before the image, but leave the
3813disclaimer until after, so viewers working over modem connections
3814don't have to wait for the disclaimer to go over the modem before
3815they start seeing the image. Finally, keywords should be full
3816words, not abbreviations. Keywords and text are in the ISO 8859-1
3817(Latin-1) character set (a superset of regular ASCII) and can not
3818contain NUL characters, and should not contain control or other
3819unprintable characters. To make the comments widely readable, stick
3820with basic ASCII, and avoid machine specific character set extensions
3821like the IBM-PC character set. The keyword must be present, but
3822you can leave off the text string on non-compressed pairs.
3823Compressed pairs must have a text string, as only the text string
3824is compressed anyway, so the compression would be meaningless.
3825
3826PNG supports modification time via the png_time structure. Two
3827conversion routines are provided, png_convert_from_time_t() for
3828time_t and png_convert_from_struct_tm() for struct tm. The
3829time_t routine uses gmtime(). You don't have to use either of
3830these, but if you wish to fill in the png_time structure directly,
3831you should provide the time in universal time (GMT) if possible
3832instead of your local time. Note that the year number is the full
3833year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3834that months start with 1.
3835
3836If you want to store the time of the original image creation, you should
3837use a plain tEXt chunk with the "Creation Time" keyword. This is
3838necessary because the "creation time" of a PNG image is somewhat vague,
3839depending on whether you mean the PNG file, the time the image was
3840created in a non-PNG format, a still photo from which the image was
3841scanned, or possibly the subject matter itself. In order to facilitate
3842machine-readable dates, it is recommended that the "Creation Time"
3843tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
3844although this isn't a requirement. Unlike the tIME chunk, the
3845"Creation Time" tEXt chunk is not expected to be automatically changed
3846by the software. To facilitate the use of RFC 1123 dates, a function
3847png_convert_to_rfc1123_buffer(buffer, png_timep) is provided to
3848convert from PNG time to an RFC 1123 format string. The caller must provide
3849a writeable buffer of at least 29 bytes.
3850
3851.SS Writing unknown chunks
3852
3853You can use the png_set_unknown_chunks function to queue up private chunks
3854for writing. You give it a chunk name, location, raw data, and a size. You
3855also must use png_set_keep_unknown_chunks() to ensure that libpng will
3856handle them. That's all there is to it. The chunks will be written by the
3857next following png_write_info_before_PLTE, png_write_info, or png_write_end
3858function, depending upon the specified location. Any chunks previously
3859read into the info structure's unknown-chunk list will also be written out
3860in a sequence that satisfies the PNG specification's ordering rules.
3861
3862Here is an example of writing two private chunks, prVt and miNE:
3863
3864 #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
3865 /* Set unknown chunk data */
3866 png_unknown_chunk unk_chunk[2];
3867 strcpy((char *) unk_chunk[0].name, "prVt";
3868 unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
3869 unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
3870 unk_chunk[0].location = PNG_HAVE_IHDR;
3871 strcpy((char *) unk_chunk[1].name, "miNE";
3872 unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
3873 unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
3874 unk_chunk[1].location = PNG_AFTER_IDAT;
3875 png_set_unknown_chunks(write_ptr, write_info_ptr,
3876 unk_chunk, 2);
3877 /* Needed because miNE is not safe-to-copy */
3878 png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
3879 (png_bytep) "miNE", 1);
3880 # if PNG_LIBPNG_VER < 10600
3881 /* Deal with unknown chunk location bug in 1.5.x and earlier */
3882 png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
3883 png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
3884 # endif
3885 # if PNG_LIBPNG_VER < 10500
3886 /* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
3887 * one before IDAT and another after IDAT, so don't use it; only use
3888 * PNG_HAVE_IHDR location. This call resets the location previously
3889 * set by assignment and png_set_unknown_chunk_location() for chunk 1.
3890 */
3891 png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
3892 # endif
3893 #endif
3894
3895.SS The high-level write interface
3896
3897At this point there are two ways to proceed; through the high-level
3898write interface, or through a sequence of low-level write operations.
3899You can use the high-level interface if your image data is present
3900in the info structure. All defined output
3901transformations are permitted, enabled by the following masks.
3902
3903 PNG_TRANSFORM_IDENTITY No transformation
3904 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
3905 PNG_TRANSFORM_PACKSWAP Change order of packed
3906 pixels to LSB first
3907 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
3908 PNG_TRANSFORM_SHIFT Normalize pixels to the
3909 sBIT depth
3910 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
3911 to BGRA
3912 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
3913 to AG
3914 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
3915 to transparency
3916 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
3917 PNG_TRANSFORM_STRIP_FILLER Strip out filler
3918 bytes (deprecated).
3919 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
3920 filler bytes
3921 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
3922 filler bytes
3923
3924If you have valid image data in the info structure (you can use
3925png_set_rows() to put image data in the info structure), simply do this:
3926
3927 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
3928
3929where png_transforms is an integer containing the bitwise OR of some set of
3930transformation flags. This call is equivalent to png_write_info(),
3931followed the set of transformations indicated by the transform mask,
3932then png_write_image(), and finally png_write_end().
3933
3934(The final parameter of this call is not yet used. Someday it might point
3935to transformation parameters required by some future output transform.)
3936
3937You must use png_transforms and not call any png_set_transform() functions
3938when you use png_write_png().
3939
3940.SS The low-level write interface
3941
3942If you are going the low-level route instead, you are now ready to
3943write all the file information up to the actual image data. You do
3944this with a call to png_write_info().
3945
3946 png_write_info(png_ptr, info_ptr);
3947
3948Note that there is one transformation you may need to do before
3949png_write_info(). In PNG files, the alpha channel in an image is the
3950level of opacity. If your data is supplied as a level of transparency,
3951you can invert the alpha channel before you write it, so that 0 is
3952fully transparent and 255 (in 8-bit or paletted images) or 65535
3953(in 16-bit images) is fully opaque, with
3954
3955 png_set_invert_alpha(png_ptr);
3956
3957This must appear before png_write_info() instead of later with the
3958other transformations because in the case of paletted images the tRNS
3959chunk data has to be inverted before the tRNS chunk is written. If
3960your image is not a paletted image, the tRNS data (which in such cases
3961represents a single color to be rendered as transparent) won't need to
3962be changed, and you can safely do this transformation after your
3963png_write_info() call.
3964
3965If you need to write a private chunk that you want to appear before
3966the PLTE chunk when PLTE is present, you can write the PNG info in
3967two steps, and insert code to write your own chunk between them:
3968
3969 png_write_info_before_PLTE(png_ptr, info_ptr);
3970 png_set_unknown_chunks(png_ptr, info_ptr, ...);
3971 png_write_info(png_ptr, info_ptr);
3972
3973After you've written the file information, you can set up the library
3974to handle any special transformations of the image data. The various
3975ways to transform the data will be described in the order that they
3976should occur. This is important, as some of these change the color
3977type and/or bit depth of the data, and some others only work on
3978certain color types and bit depths. Even though each transformation
3979checks to see if it has data that it can do something with, you should
3980make sure to only enable a transformation if it will be valid for the
3981data. For example, don't swap red and blue on grayscale data.
3982
3983PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
3984the library to strip input data that has 4 or 8 bytes per pixel down
3985to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
3986bytes per pixel).
3987
3988 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
3989
3990where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
3991PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
3992is stored XRGB or RGBX.
3993
3994PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
3995they can, resulting in, for example, 8 pixels per byte for 1 bit files.
3996If the data is supplied at 1 pixel per byte, use this code, which will
3997correctly pack the pixels into a single byte:
3998
3999 png_set_packing(png_ptr);
4000
4001PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
4002data is of another bit depth, you can write an sBIT chunk into the
4003file so that decoders can recover the original data if desired.
4004
4005 /* Set the true bit depth of the image data */
4006 if (color_type & PNG_COLOR_MASK_COLOR)
4007 {
4008 sig_bit.red = true_bit_depth;
4009 sig_bit.green = true_bit_depth;
4010 sig_bit.blue = true_bit_depth;
4011 }
4012
4013 else
4014 {
4015 sig_bit.gray = true_bit_depth;
4016 }
4017
4018 if (color_type & PNG_COLOR_MASK_ALPHA)
4019 {
4020 sig_bit.alpha = true_bit_depth;
4021 }
4022
4023 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
4024
4025If the data is stored in the row buffer in a bit depth other than
4026one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
4027this will scale the values to appear to be the correct bit depth as
4028is required by PNG.
4029
4030 png_set_shift(png_ptr, &sig_bit);
4031
4032PNG files store 16-bit pixels in network byte order (big-endian,
4033ie. most significant bits first). This code would be used if they are
4034supplied the other way (little-endian, i.e. least significant bits
4035first, the way PCs store them):
4036
4037 if (bit_depth > 8)
4038 png_set_swap(png_ptr);
4039
4040If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
4041need to change the order the pixels are packed into bytes, you can use:
4042
4043 if (bit_depth < 8)
4044 png_set_packswap(png_ptr);
4045
4046PNG files store 3 color pixels in red, green, blue order. This code
4047would be used if they are supplied as blue, green, red:
4048
4049 png_set_bgr(png_ptr);
4050
4051PNG files describe monochrome as black being zero and white being
4052one. This code would be used if the pixels are supplied with this reversed
4053(black being one and white being zero):
4054
4055 png_set_invert_mono(png_ptr);
4056
4057Finally, you can write your own transformation function if none of
4058the existing ones meets your needs. This is done by setting a callback
4059with
4060
4061 png_set_write_user_transform_fn(png_ptr,
4062 write_transform_fn);
4063
4064You must supply the function
4065
4066 void write_transform_fn(png_structp png_ptr, png_row_infop
4067 row_info, png_bytep data)
4068
4069See pngtest.c for a working example. Your function will be called
4070before any of the other transformations are processed. If supported
4071libpng also supplies an information routine that may be called from
4072your callback:
4073
4074 png_get_current_row_number(png_ptr);
4075 png_get_current_pass_number(png_ptr);
4076
4077This returns the current row passed to the transform. With interlaced
4078images the value returned is the row in the input sub-image image. Use
4079PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
4080find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
4081
4082The discussion of interlace handling above contains more information on how to
4083use these values.
4084
4085You can also set up a pointer to a user structure for use by your
4086callback function.
4087
4088 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
4089
4090The user_channels and user_depth parameters of this function are ignored
4091when writing; you can set them to zero as shown.
4092
4093You can retrieve the pointer via the function png_get_user_transform_ptr().
4094For example:
4095
4096 voidp write_user_transform_ptr =
4097 png_get_user_transform_ptr(png_ptr);
4098
4099It is possible to have libpng flush any pending output, either manually,
4100or automatically after a certain number of lines have been written. To
4101flush the output stream a single time call:
4102
4103 png_write_flush(png_ptr);
4104
4105and to have libpng flush the output stream periodically after a certain
4106number of scanlines have been written, call:
4107
4108 png_set_flush(png_ptr, nrows);
4109
4110Note that the distance between rows is from the last time png_write_flush()
4111was called, or the first row of the image if it has never been called.
4112So if you write 50 lines, and then png_set_flush 25, it will flush the
4113output on the next scanline, and every 25 lines thereafter, unless
4114png_write_flush() is called before 25 more lines have been written.
4115If nrows is too small (less than about 10 lines for a 640 pixel wide
4116RGB image) the image compression may decrease noticeably (although this
4117may be acceptable for real-time applications). Infrequent flushing will
4118only degrade the compression performance by a few percent over images
4119that do not use flushing.
4120
4121.SS Writing the image data
4122
4123That's it for the transformations. Now you can write the image data.
4124The simplest way to do this is in one function call. If you have the
4125whole image in memory, you can just call png_write_image() and libpng
4126will write the image. You will need to pass in an array of pointers to
4127each row. This function automatically handles interlacing, so you don't
4128need to call png_set_interlace_handling() or call this function multiple
4129times, or any of that other stuff necessary with png_write_rows().
4130
4131 png_write_image(png_ptr, row_pointers);
4132
4133where row_pointers is:
4134
4135 png_byte *row_pointers[height];
4136
4137You can point to void or char or whatever you use for pixels.
4138
4139If you don't want to write the whole image at once, you can
4140use png_write_rows() instead. If the file is not interlaced,
4141this is simple:
4142
4143 png_write_rows(png_ptr, row_pointers,
4144 number_of_rows);
4145
4146row_pointers is the same as in the png_write_image() call.
4147
4148If you are just writing one row at a time, you can do this with
4149a single row_pointer instead of an array of row_pointers:
4150
4151 png_bytep row_pointer = row;
4152
4153 png_write_row(png_ptr, row_pointer);
4154
4155When the file is interlaced, things can get a good deal more complicated.
4156The only currently (as of the PNG Specification version 1.2, dated July
41571999) defined interlacing scheme for PNG files is the "Adam7" interlace
4158scheme, that breaks down an image into seven smaller images of varying
4159size. libpng will build these images for you, or you can do them
4160yourself. If you want to build them yourself, see the PNG specification
4161for details of which pixels to write when.
4162
4163If you don't want libpng to handle the interlacing details, just
4164use png_set_interlace_handling() and call png_write_rows() the
4165correct number of times to write all the sub-images
4166(png_set_interlace_handling() returns the number of sub-images.)
4167
4168If you want libpng to build the sub-images, call this before you start
4169writing any rows:
4170
4171 number_of_passes = png_set_interlace_handling(png_ptr);
4172
4173This will return the number of passes needed. Currently, this is seven,
4174but may change if another interlace type is added.
4175
4176Then write the complete image number_of_passes times.
4177
4178 png_write_rows(png_ptr, row_pointers, number_of_rows);
4179
4180Think carefully before you write an interlaced image. Typically code that
4181reads such images reads all the image data into memory, uncompressed, before
4182doing any processing. Only code that can display an image on the fly can
4183take advantage of the interlacing and even then the image has to be exactly
4184the correct size for the output device, because scaling an image requires
4185adjacent pixels and these are not available until all the passes have been
4186read.
4187
4188If you do write an interlaced image you will hardly ever need to handle
4189the interlacing yourself. Call png_set_interlace_handling() and use the
4190approach described above.
4191
4192The only time it is conceivable that you will really need to write an
4193interlaced image pass-by-pass is when you have read one pass by pass and
4194made some pixel-by-pixel transformation to it, as described in the read
4195code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
4196to determine the size of each sub-image in turn and simply write the rows
4197you obtained from the read code.
4198
4199.SS Finishing a sequential write
4200
4201After you are finished writing the image, you should finish writing
4202the file. If you are interested in writing comments or time, you should
4203pass an appropriately filled png_info pointer. If you are not interested,
4204you can pass NULL.
4205
4206 png_write_end(png_ptr, info_ptr);
4207
4208When you are done, you can free all memory used by libpng like this:
4209
4210 png_destroy_write_struct(&png_ptr, &info_ptr);
4211
4212It is also possible to individually free the info_ptr members that
4213point to libpng-allocated storage with the following function:
4214
4215 png_free_data(png_ptr, info_ptr, mask, seq)
4216
4217 mask - identifies data to be freed, a mask
4218 containing the bitwise OR of one or
4219 more of
4220 PNG_FREE_PLTE, PNG_FREE_TRNS,
4221 PNG_FREE_HIST, PNG_FREE_ICCP,
4222 PNG_FREE_PCAL, PNG_FREE_ROWS,
4223 PNG_FREE_SCAL, PNG_FREE_SPLT,
4224 PNG_FREE_TEXT, PNG_FREE_UNKN,
4225 or simply PNG_FREE_ALL
4226
4227 seq - sequence number of item to be freed
4228 (\-1 for all items)
4229
4230This function may be safely called when the relevant storage has
4231already been freed, or has not yet been allocated, or was allocated
4232by the user and not by libpng, and will in those cases do nothing.
4233The "seq" parameter is ignored if only one item of the selected data
4234type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
4235are allowed for the data type identified in the mask, such as text or
4236sPLT, only the n'th item in the structure is freed, where n is "seq".
4237
4238If you allocated data such as a palette that you passed in to libpng
4239with png_set_*, you must not free it until just before the call to
4240png_destroy_write_struct().
4241
4242The default behavior is only to free data that was allocated internally
4243by libpng. This can be changed, so that libpng will not free the data,
4244or so that it will free data that was allocated by the user with png_malloc()
4245or png_calloc() and passed in via a png_set_*() function, with
4246
4247 png_data_freer(png_ptr, info_ptr, freer, mask)
4248
4249 freer - one of
4250 PNG_DESTROY_WILL_FREE_DATA
4251 PNG_SET_WILL_FREE_DATA
4252 PNG_USER_WILL_FREE_DATA
4253
4254 mask - which data elements are affected
4255 same choices as in png_free_data()
4256
4257For example, to transfer responsibility for some data from a read structure
4258to a write structure, you could use
4259
4260 png_data_freer(read_ptr, read_info_ptr,
4261 PNG_USER_WILL_FREE_DATA,
4262 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4263
4264 png_data_freer(write_ptr, write_info_ptr,
4265 PNG_DESTROY_WILL_FREE_DATA,
4266 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4267
4268thereby briefly reassigning responsibility for freeing to the user but
4269immediately afterwards reassigning it once more to the write_destroy
4270function. Having done this, it would then be safe to destroy the read
4271structure and continue to use the PLTE, tRNS, and hIST data in the write
4272structure.
4273
4274This function only affects data that has already been allocated.
4275You can call this function before calling after the png_set_*() functions
4276to control whether the user or png_destroy_*() is supposed to free the data.
4277When the user assumes responsibility for libpng-allocated data, the
4278application must use
4279png_free() to free it, and when the user transfers responsibility to libpng
4280for data that the user has allocated, the user must have used png_malloc()
4281or png_calloc() to allocate it.
4282
4283If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
4284separately, do not transfer responsibility for freeing text_ptr to libpng,
4285because when libpng fills a png_text structure it combines these members with
4286the key member, and png_free_data() will free only text_ptr.key. Similarly,
4287if you transfer responsibility for free'ing text_ptr from libpng to your
4288application, your application must not separately free those members.
4289For a more compact example of writing a PNG image, see the file example.c.
4290
4291.SH V. Simplified API
4292
4293The simplified API, which became available in libpng-1.6.0, hides the details
4294of both libpng and the PNG file format itself.
4295It allows PNG files to be read into a very limited number of
4296in-memory bitmap formats or to be written from the same formats. If these
4297formats do not accommodate your needs then you can, and should, use the more
4298sophisticated APIs above - these support a wide variety of in-memory formats
4299and a wide variety of sophisticated transformations to those formats as well
4300as a wide variety of APIs to manipulate ancilliary information.
4301
4302To read a PNG file using the simplified API:
4303
4304 1) Declare a 'png_image' structure (see below) on the stack, set the
4305 version field to PNG_IMAGE_VERSION and the 'opaque' pointer to NULL
4306 (this is REQUIRED, your program may crash if you don't do it.)
4307
4308 2) Call the appropriate png_image_begin_read... function.
4309
4310 3) Set the png_image 'format' member to the required sample format.
4311
4312 4) Allocate a buffer for the image and, if required, the color-map.
4313
4314 5) Call png_image_finish_read to read the image and, if required, the
4315 color-map into your buffers.
4316
4317There are no restrictions on the format of the PNG input itself; all valid
4318color types, bit depths, and interlace methods are acceptable, and the
4319input image is transformed as necessary to the requested in-memory format
4320during the png_image_finish_read() step. The only caveat is that if you
4321request a color-mapped image from a PNG that is full-color or makes
4322complex use of an alpha channel the transformation is extremely lossy and the
4323result may look terrible.
4324
4325To write a PNG file using the simplified API:
4326
4327 1) Declare a 'png_image' structure on the stack and memset()
4328 it to all zero.
4329
4330 2) Initialize the members of the structure that describe the
4331 image, setting the 'format' member to the format of the
4332 image samples.
4333
4334 3) Call the appropriate png_image_write... function with a
4335 pointer to the image and, if necessary, the color-map to write
4336 the PNG data.
4337
4338png_image is a structure that describes the in-memory format of an image
4339when it is being read or defines the in-memory format of an image that you
4340need to write. The "png_image" structure contains the following members:
4341
4342 png_controlp opaque Initialize to NULL, free with png_image_free
4343 png_uint_32 version Set to PNG_IMAGE_VERSION
4344 png_uint_32 width Image width in pixels (columns)
4345 png_uint_32 height Image height in pixels (rows)
4346 png_uint_32 format Image format as defined below
4347 png_uint_32 flags A bit mask containing informational flags
4348 png_uint_32 colormap_entries; Number of entries in the color-map
4349 png_uint_32 warning_or_error;
4350 char message[64];
4351
4352In the event of an error or warning the "warning_or_error"
4353field will be set to a non-zero value and the 'message' field will contain
4354a '\0' terminated string with the libpng error or warning message. If both
4355warnings and an error were encountered, only the error is recorded. If there
4356are multiple warnings, only the first one is recorded.
4357
4358The upper 30 bits of the "warning_or_error" value are reserved; the low two
4359bits contain a two bit code such that a value more than 1 indicates a failure
4360in the API just called:
4361
4362 0 - no warning or error
4363 1 - warning
4364 2 - error
4365 3 - error preceded by warning
4366
4367The pixels (samples) of the image have one to four channels whose components
4368have original values in the range 0 to 1.0:
4369
4370 1: A single gray or luminance channel (G).
4371 2: A gray/luminance channel and an alpha channel (GA).
4372 3: Three red, green, blue color channels (RGB).
4373 4: Three color channels and an alpha channel (RGBA).
4374
4375The channels are encoded in one of two ways:
4376
4377 a) As a small integer, value 0..255, contained in a single byte. For the
4378alpha channel the original value is simply value/255. For the color or
4379luminance channels the value is encoded according to the sRGB specification
4380and matches the 8-bit format expected by typical display devices.
4381
4382The color/gray channels are not scaled (pre-multiplied) by the alpha
4383channel and are suitable for passing to color management software.
4384
4385 b) As a value in the range 0..65535, contained in a 2-byte integer, in
4386the native byte order of the platform on which the application is running.
4387All channels can be converted to the original value by dividing by 65535; all
4388channels are linear. Color channels use the RGB encoding (RGB end-points) of
4389the sRGB specification. This encoding is identified by the
4390PNG_FORMAT_FLAG_LINEAR flag below.
4391
4392When the simplified API needs to convert between sRGB and linear colorspaces,
4393the actual sRGB transfer curve defined in the sRGB specification (see the
4394article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
4395approximation used elsewhere in libpng.
4396
4397When an alpha channel is present it is expected to denote pixel coverage
4398of the color or luminance channels and is returned as an associated alpha
4399channel: the color/gray channels are scaled (pre-multiplied) by the alpha
4400value.
4401
4402The samples are either contained directly in the image data, between 1 and 8
4403bytes per pixel according to the encoding, or are held in a color-map indexed
4404by bytes in the image data. In the case of a color-map the color-map entries
4405are individual samples, encoded as above, and the image data has one byte per
4406pixel to select the relevant sample from the color-map.
4407
4408PNG_FORMAT_*
4409
4410The #defines to be used in png_image::format. Each #define identifies a
4411particular layout of channel data and, if present, alpha values. There are
4412separate defines for each of the two component encodings.
4413
4414A format is built up using single bit flag values. All combinations are
4415valid. Formats can be built up from the flag values or you can use one of
4416the predefined values below. When testing formats always use the FORMAT_FLAG
4417macros to test for individual features - future versions of the library may
4418add new flags.
4419
4420When reading or writing color-mapped images the format should be set to the
4421format of the entries in the color-map then png_image_{read,write}_colormap
4422called to read or write the color-map and set the format correctly for the
4423image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly!
4424
4425NOTE: libpng can be built with particular features disabled. If you see
4426compiler errors because the definition of one of the following flags has been
4427compiled out it is because libpng does not have the required support. It is
4428possible, however, for the libpng configuration to enable the format on just
4429read or just write; in that case you may see an error at run time.
4430You can guard against this by checking for the definition of the
4431appropriate "_SUPPORTED" macro, one of:
4432
4433 PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED
4434
4435 PNG_FORMAT_FLAG_ALPHA format with an alpha channel
4436 PNG_FORMAT_FLAG_COLOR color format: otherwise grayscale
4437 PNG_FORMAT_FLAG_LINEAR 2-byte channels else 1-byte
4438 PNG_FORMAT_FLAG_COLORMAP image data is color-mapped
4439 PNG_FORMAT_FLAG_BGR BGR colors, else order is RGB
4440 PNG_FORMAT_FLAG_AFIRST alpha channel comes first
4441
4442Supported formats are as follows. Future versions of libpng may support more
4443formats; for compatibility with older versions simply check if the format
4444macro is defined using #ifdef. These defines describe the in-memory layout
4445of the components of the pixels of the image.
4446
4447First the single byte (sRGB) formats:
4448
4449 PNG_FORMAT_GRAY
4450 PNG_FORMAT_GA
4451 PNG_FORMAT_AG
4452 PNG_FORMAT_RGB
4453 PNG_FORMAT_BGR
4454 PNG_FORMAT_RGBA
4455 PNG_FORMAT_ARGB
4456 PNG_FORMAT_BGRA
4457 PNG_FORMAT_ABGR
4458
4459Then the linear 2-byte formats. When naming these "Y" is used to
4460indicate a luminance (gray) channel. The component order within the pixel
4461is always the same - there is no provision for swapping the order of the
4462components in the linear format. The components are 16-bit integers in
4463the native byte order for your platform, and there is no provision for
4464swapping the bytes to a different endian condition.
4465
4466 PNG_FORMAT_LINEAR_Y
4467 PNG_FORMAT_LINEAR_Y_ALPHA
4468 PNG_FORMAT_LINEAR_RGB
4469 PNG_FORMAT_LINEAR_RGB_ALPHA
4470
4471With color-mapped formats the image data is one byte for each pixel. The byte
4472is an index into the color-map which is formatted as above. To obtain a
4473color-mapped format it is sufficient just to add the PNG_FOMAT_FLAG_COLORMAP
4474to one of the above definitions, or you can use one of the definitions below.
4475
4476 PNG_FORMAT_RGB_COLORMAP
4477 PNG_FORMAT_BGR_COLORMAP
4478 PNG_FORMAT_RGBA_COLORMAP
4479 PNG_FORMAT_ARGB_COLORMAP
4480 PNG_FORMAT_BGRA_COLORMAP
4481 PNG_FORMAT_ABGR_COLORMAP
4482
4483PNG_IMAGE macros
4484
4485These are convenience macros to derive information from a png_image
4486structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the
4487actual image sample values - either the entries in the color-map or the
4488pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values
4489for the pixels and will always return 1 for color-mapped formats. The
4490remaining macros return information about the rows in the image and the
4491complete image.
4492
4493NOTE: All the macros that take a png_image::format parameter are compile time
4494constants if the format parameter is, itself, a constant. Therefore these
4495macros can be used in array declarations and case labels where required.
4496Similarly the macros are also pre-processor constants (sizeof is not used) so
4497they can be used in #if tests.
4498
4499 PNG_IMAGE_SAMPLE_CHANNELS(fmt)
4500 Returns the total number of channels in a given format: 1..4
4501
4502 PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt)
4503 Returns the size in bytes of a single component of a pixel or color-map
4504 entry (as appropriate) in the image: 1 or 2.
4505
4506 PNG_IMAGE_SAMPLE_SIZE(fmt)
4507 This is the size of the sample data for one sample. If the image is
4508 color-mapped it is the size of one color-map entry (and image pixels are
4509 one byte in size), otherwise it is the size of one image pixel.
4510
4511 PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt)
4512 The maximum size of the color-map required by the format expressed in a
4513 count of components. This can be used to compile-time allocate a
4514 color-map:
4515
4516 png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)];
4517
4518 png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
4519
4520 Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
4521 information from one of the png_image_begin_read_ APIs and dynamically
4522 allocate the required memory.
4523
4524 PNG_IMAGE_COLORMAP_SIZE(fmt)
4525 The size of the color-map required by the format; this is the size of the
4526 color-map buffer passed to the png_image_{read,write}_colormap APIs. It is
4527 a fixed number determined by the format so can easily be allocated on the
4528 stack if necessary.
4529
4530Corresponding information about the pixels
4531
4532 PNG_IMAGE_PIXEL_CHANNELS(fmt)
4533 The number of separate channels (components) in a pixel; 1 for a
4534 color-mapped image.
4535
4536 PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\
4537 The size, in bytes, of each component in a pixel; 1 for a color-mapped
4538 image.
4539
4540 PNG_IMAGE_PIXEL_SIZE(fmt)
4541 The size, in bytes, of a complete pixel; 1 for a color-mapped image.
4542
4543Information about the whole row, or whole image
4544
4545 PNG_IMAGE_ROW_STRIDE(image)
4546 Returns the total number of components in a single row of the image; this
4547 is the minimum 'row stride', the minimum count of components between each
4548 row. For a color-mapped image this is the minimum number of bytes in a
4549 row.
4550
4551 If you need the stride measured in bytes, row_stride_bytes is
4552 PNG_IMAGE_ROW_STRIDE(image) * PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)
4553 plus any padding bytes that your application might need, for example
4554 to start the next row on a 4-byte boundary.
4555
4556 PNG_IMAGE_BUFFER_SIZE(image, row_stride)
4557 Return the size, in bytes, of an image buffer given a png_image and a row
4558 stride - the number of components to leave space for in each row.
4559
4560 PNG_IMAGE_SIZE(image)
4561 Return the size, in bytes, of the image in memory given just a png_image;
4562 the row stride is the minimum stride required for the image.
4563
4564 PNG_IMAGE_COLORMAP_SIZE(image)
4565 Return the size, in bytes, of the color-map of this image. If the image
4566 format is not a color-map format this will return a size sufficient for
4567 256 entries in the given format; check PNG_FORMAT_FLAG_COLORMAP if
4568 you don't want to allocate a color-map in this case.
4569
4570PNG_IMAGE_FLAG_*
4571
4572Flags containing additional information about the image are held in
4573the 'flags' field of png_image.
4574
4575 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
4576 This indicates the the RGB values of the in-memory bitmap do not
4577 correspond to the red, green and blue end-points defined by sRGB.
4578
4579 PNG_IMAGE_FLAG_FAST == 0x02
4580 On write emphasise speed over compression; the resultant PNG file will be
4581 larger but will be produced significantly faster, particular for large
4582 images. Do not use this option for images which will be distributed, only
4583 used it when producing intermediate files that will be read back in
4584 repeatedly. For a typical 24-bit image the option will double the read
4585 speed at the cost of increasing the image size by 25%, however for many
4586 more compressible images the PNG file can be 10 times larger with only a
4587 slight speed gain.
4588
4589 PNG_IMAGE_FLAG_16BIT_sRGB == 0x04
4590 On read if the image is a 16-bit per component image and there is no gAMA
4591 or sRGB chunk assume that the components are sRGB encoded. Notice that
4592 images output by the simplified API always have gamma information; setting
4593 this flag only affects the interpretation of 16-bit images from an
4594 external source. It is recommended that the application expose this flag
4595 to the user; the user can normally easily recognize the difference between
4596 linear and sRGB encoding. This flag has no effect on write - the data
4597 passed to the write APIs must have the correct encoding (as defined
4598 above.)
4599
4600 If the flag is not set (the default) input 16-bit per component data is
4601 assumed to be linear.
4602
4603 NOTE: the flag can only be set after the png_image_begin_read_ call,
4604 because that call initializes the 'flags' field.
4605
4606READ APIs
4607
4608 The png_image passed to the read APIs must have been initialized by setting
4609 the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.)
4610
4611 int png_image_begin_read_from_file( png_imagep image,
4612 const char *file_name)
4613
4614 The named file is opened for read and the image header
4615 is filled in from the PNG header in the file.
4616
4617 int png_image_begin_read_from_stdio (png_imagep image,
4618 FILE* file)
4619
4620 The PNG header is read from the stdio FILE object.
4621
4622 int png_image_begin_read_from_memory(png_imagep image,
4623 png_const_voidp memory, png_size_t size)
4624
4625 The PNG header is read from the given memory buffer.
4626
4627 int png_image_finish_read(png_imagep image,
4628 png_colorp background, void *buffer,
4629 png_int_32 row_stride, void *colormap));
4630
4631 Finish reading the image into the supplied buffer and
4632 clean up the png_image structure.
4633
4634 row_stride is the step, in png_byte or png_uint_16 units
4635 as appropriate, between adjacent rows. A positive stride
4636 indicates that the top-most row is first in the buffer -
4637 the normal top-down arrangement. A negative stride
4638 indicates that the bottom-most row is first in the buffer.
4639
4640 background need only be supplied if an alpha channel must
4641 be removed from a png_byte format and the removal is to be
4642 done by compositing on a solid color; otherwise it may be
4643 NULL and any composition will be done directly onto the
4644 buffer. The value is an sRGB color to use for the
4645 background, for grayscale output the green channel is used.
4646
4647 For linear output removing the alpha channel is always done
4648 by compositing on black.
4649
4650 void png_image_free(png_imagep image)
4651
4652 Free any data allocated by libpng in image->opaque,
4653 setting the pointer to NULL. May be called at any time
4654 after the structure is initialized.
4655
4656When the simplified API needs to convert between sRGB and linear colorspaces,
4657the actual sRGB transfer curve defined in the sRGB specification (see the
4658article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
4659approximation used elsewhere in libpng.
4660
4661WRITE APIS
4662
4663For write you must initialize a png_image structure to describe the image to
4664be written:
4665
4666 version: must be set to PNG_IMAGE_VERSION
4667 opaque: must be initialized to NULL
4668 width: image width in pixels
4669 height: image height in rows
4670 format: the format of the data you wish to write
4671 flags: set to 0 unless one of the defined flags applies; set
4672 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images
4673 where the RGB values do not correspond to the colors in sRGB.
4674 colormap_entries: set to the number of entries in the color-map (0 to 256)
4675
4676 int png_image_write_to_file, (png_imagep image,
4677 const char *file, int convert_to_8bit, const void *buffer,
4678 png_int_32 row_stride, const void *colormap));
4679
4680 Write the image to the named file.
4681
4682 int png_image_write_to_memory (png_imagep image, void *memory,
4683 png_alloc_size_t * PNG_RESTRICT memory_bytes,
4684 int convert_to_8_bit, const void *buffer, ptrdiff_t row_stride,
4685 const void *colormap));
4686
4687 Write the image to memory.
4688
4689 int png_image_write_to_stdio(png_imagep image, FILE *file,
4690 int convert_to_8_bit, const void *buffer,
4691 png_int_32 row_stride, const void *colormap)
4692
4693 Write the image to the given (FILE*).
4694
4695With all write APIs if image is in one of the linear formats with
4696(png_uint_16) data then setting convert_to_8_bit will cause the output to be
4697a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise
4698a 16-bit linear encoded PNG file is written.
4699
4700With all APIs row_stride is handled as in the read APIs - it is the spacing
4701from one row to the next in component sized units (float) and if negative
4702indicates a bottom-up row layout in the buffer. If you pass zero, libpng will
4703calculate the row_stride for you from the width and number of channels.
4704
4705Note that the write API does not support interlacing, sub-8-bit pixels,
4706indexed (paletted) images, or most ancillary chunks.
4707
4708.SH VI. Modifying/Customizing libpng
4709
4710There are two issues here. The first is changing how libpng does
4711standard things like memory allocation, input/output, and error handling.
4712The second deals with more complicated things like adding new chunks,
4713adding new transformations, and generally changing how libpng works.
4714Both of those are compile-time issues; that is, they are generally
4715determined at the time the code is written, and there is rarely a need
4716to provide the user with a means of changing them.
4717
4718Memory allocation, input/output, and error handling
4719
4720All of the memory allocation, input/output, and error handling in libpng
4721goes through callbacks that are user-settable. The default routines are
4722in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4723these functions, call the appropriate png_set_*_fn() function.
4724
4725Memory allocation is done through the functions png_malloc(), png_calloc(),
4726and png_free(). The png_malloc() and png_free() functions currently just
4727call the standard C functions and png_calloc() calls png_malloc() and then
4728clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
4729is not the same as the calloc(number, size) function provided by stdlib.h.
4730There is limited support for certain systems with segmented memory
4731architectures and the types of pointers declared by png.h match this; you
4732will have to use appropriate pointers in your application. If you prefer
4733to use a different method of allocating and freeing data, you can use
4734png_create_read_struct_2() or png_create_write_struct_2() to register your
4735own functions as described above. These functions also provide a void
4736pointer that can be retrieved via
4737
4738 mem_ptr=png_get_mem_ptr(png_ptr);
4739
4740Your replacement memory functions must have prototypes as follows:
4741
4742 png_voidp malloc_fn(png_structp png_ptr,
4743 png_alloc_size_t size);
4744
4745 void free_fn(png_structp png_ptr, png_voidp ptr);
4746
4747Your malloc_fn() must return NULL in case of failure. The png_malloc()
4748function will normally call png_error() if it receives a NULL from the
4749system memory allocator or from your replacement malloc_fn().
4750
4751Your free_fn() will never be called with a NULL ptr, since libpng's
4752png_free() checks for NULL before calling free_fn().
4753
4754Input/Output in libpng is done through png_read() and png_write(),
4755which currently just call fread() and fwrite(). The FILE * is stored in
4756png_struct and is initialized via png_init_io(). If you wish to change
4757the method of I/O, the library supplies callbacks that you can set
4758through the function png_set_read_fn() and png_set_write_fn() at run
4759time, instead of calling the png_init_io() function. These functions
4760also provide a void pointer that can be retrieved via the function
4761png_get_io_ptr(). For example:
4762
4763 png_set_read_fn(png_structp read_ptr,
4764 voidp read_io_ptr, png_rw_ptr read_data_fn)
4765
4766 png_set_write_fn(png_structp write_ptr,
4767 voidp write_io_ptr, png_rw_ptr write_data_fn,
4768 png_flush_ptr output_flush_fn);
4769
4770 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4771 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4772
4773The replacement I/O functions must have prototypes as follows:
4774
4775 void user_read_data(png_structp png_ptr,
4776 png_bytep data, png_size_t length);
4777
4778 void user_write_data(png_structp png_ptr,
4779 png_bytep data, png_size_t length);
4780
4781 void user_flush_data(png_structp png_ptr);
4782
4783The user_read_data() function is responsible for detecting and
4784handling end-of-data errors.
4785
4786Supplying NULL for the read, write, or flush functions sets them back
4787to using the default C stream functions, which expect the io_ptr to
4788point to a standard *FILE structure. It is probably a mistake
4789to use NULL for one of write_data_fn and output_flush_fn but not both
4790of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4791It is an error to read from a write stream, and vice versa.
4792
4793Error handling in libpng is done through png_error() and png_warning().
4794Errors handled through png_error() are fatal, meaning that png_error()
4795should never return to its caller. Currently, this is handled via
4796setjmp() and longjmp() (unless you have compiled libpng with
4797PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4798but you could change this to do things like exit() if you should wish,
4799as long as your function does not return.
4800
4801On non-fatal errors, png_warning() is called
4802to print a warning message, and then control returns to the calling code.
4803By default png_error() and png_warning() print a message on stderr via
4804fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4805(because you don't want the messages) or PNG_NO_STDIO defined (because
4806fprintf() isn't available). If you wish to change the behavior of the error
4807functions, you will need to set up your own message callbacks. These
4808functions are normally supplied at the time that the png_struct is created.
4809It is also possible to redirect errors and warnings to your own replacement
4810functions after png_create_*_struct() has been called by calling:
4811
4812 png_set_error_fn(png_structp png_ptr,
4813 png_voidp error_ptr, png_error_ptr error_fn,
4814 png_error_ptr warning_fn);
4815
4816If NULL is supplied for either error_fn or warning_fn, then the libpng
4817default function will be used, calling fprintf() and/or longjmp() if a
4818problem is encountered. The replacement error functions should have
4819parameters as follows:
4820
4821 void user_error_fn(png_structp png_ptr,
4822 png_const_charp error_msg);
4823
4824 void user_warning_fn(png_structp png_ptr,
4825 png_const_charp warning_msg);
4826
4827Then, within your user_error_fn or user_warning_fn, you can retrieve
4828the error_ptr if you need it, by calling
4829
4830 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4831
4832The motivation behind using setjmp() and longjmp() is the C++ throw and
4833catch exception handling methods. This makes the code much easier to write,
4834as there is no need to check every return code of every function call.
4835However, there are some uncertainties about the status of local variables
4836after a longjmp, so the user may want to be careful about doing anything
4837after setjmp returns non-zero besides returning itself. Consult your
4838compiler documentation for more details. For an alternative approach, you
4839may wish to use the "cexcept" facility (see https://cexcept.sourceforge.io/),
4840which is illustrated in pngvalid.c and in contrib/visupng.
4841
4842Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
4843You can use this to handle certain errors (normally handled as errors)
4844as warnings.
4845
4846 png_set_benign_errors (png_ptr, int allowed);
4847
4848 allowed: 0: treat png_benign_error() as an error.
4849 1: treat png_benign_error() as a warning.
4850
4851As of libpng-1.6.0, the default condition is to treat benign errors as
4852warnings while reading and as errors while writing.
4853
4854.SS Custom chunks
4855
4856If you need to read or write custom chunks, you may need to get deeper
4857into the libpng code. The library now has mechanisms for storing
4858and writing chunks of unknown type; you can even declare callbacks
4859for custom chunks. However, this may not be good enough if the
4860library code itself needs to know about interactions between your
4861chunk and existing `intrinsic' chunks.
4862
4863If you need to write a new intrinsic chunk, first read the PNG
4864specification. Acquire a first level of understanding of how it works.
4865Pay particular attention to the sections that describe chunk names,
4866and look at how other chunks were designed, so you can do things
4867similarly. Second, check out the sections of libpng that read and
4868write chunks. Try to find a chunk that is similar to yours and use
4869it as a template. More details can be found in the comments inside
4870the code. It is best to handle private or unknown chunks in a generic method,
4871via callback functions, instead of by modifying libpng functions. This
4872is illustrated in pngtest.c, which uses a callback function to handle a
4873private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4874libpng.
4875
4876If you wish to write your own transformation for the data, look through
4877the part of the code that does the transformations, and check out some of
4878the simpler ones to get an idea of how they work. Try to find a similar
4879transformation to the one you want to add and copy off of it. More details
4880can be found in the comments inside the code itself.
4881
4882.SS Configuring for gui/windowing platforms:
4883
4884You will need to write new error and warning functions that use the GUI
4885interface, as described previously, and set them to be the error and
4886warning functions at the time that png_create_*_struct() is called,
4887in order to have them available during the structure initialization.
4888They can be changed later via png_set_error_fn(). On some compilers,
4889you may also have to change the memory allocators (png_malloc, etc.).
4890
4891.SS Configuring zlib:
4892
4893There are special functions to configure the compression. Perhaps the
4894most useful one changes the compression level, which currently uses
4895input compression values in the range 0 - 9. The library normally
4896uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4897have shown that for a large majority of images, compression values in
4898the range 3-6 compress nearly as well as higher levels, and do so much
4899faster. For online applications it may be desirable to have maximum speed
4900(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4901specify no compression (Z_NO_COMPRESSION = 0), but this would create
4902files larger than just storing the raw bitmap. You can specify the
4903compression level by calling:
4904
4905 #include zlib.h
4906 png_set_compression_level(png_ptr, level);
4907
4908Another useful one is to reduce the memory level used by the library.
4909The memory level defaults to 8, but it can be lowered if you are
4910short on memory (running DOS, for example, where you only have 640K).
4911Note that the memory level does have an effect on compression; among
4912other things, lower levels will result in sections of incompressible
4913data being emitted in smaller stored blocks, with a correspondingly
4914larger relative overhead of up to 15% in the worst case.
4915
4916 #include zlib.h
4917 png_set_compression_mem_level(png_ptr, level);
4918
4919The other functions are for configuring zlib. They are not recommended
4920for normal use and may result in writing an invalid PNG file. See
4921zlib.h for more information on what these mean.
4922
4923 #include zlib.h
4924 png_set_compression_strategy(png_ptr,
4925 strategy);
4926
4927 png_set_compression_window_bits(png_ptr,
4928 window_bits);
4929
4930 png_set_compression_method(png_ptr, method);
4931
4932This controls the size of the IDAT chunks (default 8192):
4933
4934 png_set_compression_buffer_size(png_ptr, size);
4935
4936As of libpng version 1.5.4, additional APIs became
4937available to set these separately for non-IDAT
4938compressed chunks such as zTXt, iTXt, and iCCP:
4939
4940 #include zlib.h
4941 #if PNG_LIBPNG_VER >= 10504
4942 png_set_text_compression_level(png_ptr, level);
4943
4944 png_set_text_compression_mem_level(png_ptr, level);
4945
4946 png_set_text_compression_strategy(png_ptr,
4947 strategy);
4948
4949 png_set_text_compression_window_bits(png_ptr,
4950 window_bits);
4951
4952 png_set_text_compression_method(png_ptr, method);
4953 #endif
4954
4955.SS Controlling row filtering
4956
4957If you want to control whether libpng uses filtering or not, which
4958filters are used, and how it goes about picking row filters, you
4959can call one of these functions. The selection and configuration
4960of row filters can have a significant impact on the size and
4961encoding speed and a somewhat lesser impact on the decoding speed
4962of an image. Filtering is enabled by default for RGB and grayscale
4963images (with and without alpha), but not for paletted images nor
4964for any images with bit depths less than 8 bits/pixel.
4965
4966The 'method' parameter sets the main filtering method, which is
4967currently only '0' in the PNG 1.2 specification. The 'filters'
4968parameter sets which filter(s), if any, should be used for each
4969scanline. Possible values are PNG_ALL_FILTERS, PNG_NO_FILTERS,
4970or PNG_FAST_FILTERS to turn filtering on and off, or to turn on
4971just the fast-decoding subset of filters, respectively.
4972
4973Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4974PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4975ORed together with '|' to specify one or more filters to use.
4976These filters are described in more detail in the PNG specification.
4977If you intend to change the filter type during the course of writing
4978the image, you should start with flags set for all of the filters
4979you intend to use so that libpng can initialize its internal
4980structures appropriately for all of the filter types. (Note that this
4981means the first row must always be adaptively filtered, because libpng
4982currently does not allocate the filter buffers until png_write_row()
4983is called for the first time.)
4984
4985 filters = PNG_NO_FILTERS;
4986 filters = PNG_ALL_FILTERS;
4987 filters = PNG_FAST_FILTERS;
4988
4989 or
4990
4991 filters = PNG_FILTER_NONE | PNG_FILTER_SUB |
4992 PNG_FILTER_UP | PNG_FILTER_AVG |
4993 PNG_FILTER_PAETH;
4994
4995 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4996 filters);
4997
4998 The second parameter can also be
4999 PNG_INTRAPIXEL_DIFFERENCING if you are
5000 writing a PNG to be embedded in a MNG
5001 datastream. This parameter must be the
5002 same as the value of filter_method used
5003 in png_set_IHDR().
5004
5005.SS Requesting debug printout
5006
5007The macro definition PNG_DEBUG can be used to request debugging
5008printout. Set it to an integer value in the range 0 to 3. Higher
5009numbers result in increasing amounts of debugging information. The
5010information is printed to the "stderr" file, unless another file
5011name is specified in the PNG_DEBUG_FILE macro definition.
5012
5013When PNG_DEBUG > 0, the following functions (macros) become available:
5014
5015 png_debug(level, message)
5016 png_debug1(level, message, p1)
5017 png_debug2(level, message, p1, p2)
5018
5019in which "level" is compared to PNG_DEBUG to decide whether to print
5020the message, "message" is the formatted string to be printed,
5021and p1 and p2 are parameters that are to be embedded in the string
5022according to printf-style formatting directives. For example,
5023
5024 png_debug1(2, "foo=%d", foo);
5025
5026is expanded to
5027
5028 if (PNG_DEBUG > 2)
5029 fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo);
5030
5031When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
5032can still use PNG_DEBUG to control your own debugging:
5033
5034 #ifdef PNG_DEBUG
5035 fprintf(stderr, ...
5036 #endif
5037
5038When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
5039having level = 0 will be printed. There aren't any such statements in
5040this version of libpng, but if you insert some they will be printed.
5041
5042.SH VII. MNG support
5043
5044The MNG specification (available at http://www.libpng.org/pub/mng) allows
5045certain extensions to PNG for PNG images that are embedded in MNG datastreams.
5046Libpng can support some of these extensions. To enable them, use the
5047png_permit_mng_features() function:
5048
5049 feature_set = png_permit_mng_features(png_ptr, mask)
5050
5051 mask is a png_uint_32 containing the bitwise OR of the
5052 features you want to enable. These include
5053 PNG_FLAG_MNG_EMPTY_PLTE
5054 PNG_FLAG_MNG_FILTER_64
5055 PNG_ALL_MNG_FEATURES
5056
5057 feature_set is a png_uint_32 that is the bitwise AND of
5058 your mask with the set of MNG features that is
5059 supported by the version of libpng that you are using.
5060
5061It is an error to use this function when reading or writing a standalone
5062PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
5063in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
5064and the MHDR and MEND chunks. Libpng does not provide support for these
5065or any other MNG chunks; your application must provide its own support for
5066them. You may wish to consider using libmng (available at
5067https://www.libmng.com/) instead.
5068
5069.SH VIII. Changes to Libpng from version 0.88
5070
5071It should be noted that versions of libpng later than 0.96 are not
5072distributed by the original libpng author, Guy Schalnat, nor by
5073Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
5074distributed versions 0.89 through 0.96, but rather by another member
5075of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
5076still alive and well, but they have moved on to other things.
5077
5078The old libpng functions png_read_init(), png_write_init(),
5079png_info_init(), png_read_destroy(), and png_write_destroy() have been
5080moved to PNG_INTERNAL in version 0.95 to discourage their use. These
5081functions will be removed from libpng version 1.4.0.
5082
5083The preferred method of creating and initializing the libpng structures is
5084via the png_create_read_struct(), png_create_write_struct(), and
5085png_create_info_struct() because they isolate the size of the structures
5086from the application, allow version error checking, and also allow the
5087use of custom error handling routines during the initialization, which
5088the old functions do not. The functions png_read_destroy() and
5089png_write_destroy() do not actually free the memory that libpng
5090allocated for these structs, but just reset the data structures, so they
5091can be used instead of png_destroy_read_struct() and
5092png_destroy_write_struct() if you feel there is too much system overhead
5093allocating and freeing the png_struct for each image read.
5094
5095Setting the error callbacks via png_set_message_fn() before
5096png_read_init() as was suggested in libpng-0.88 is no longer supported
5097because this caused applications that do not use custom error functions
5098to fail if the png_ptr was not initialized to zero. It is still possible
5099to set the error callbacks AFTER png_read_init(), or to change them with
5100png_set_error_fn(), which is essentially the same function, but with a new
5101name to force compilation errors with applications that try to use the old
5102method.
5103
5104Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
5105however, iTXt support was not enabled by default.
5106
5107Starting with version 1.0.7, you can find out which version of the library
5108you are using at run-time:
5109
5110 png_uint_32 libpng_vn = png_access_version_number();
5111
5112The number libpng_vn is constructed from the major version, minor
5113version with leading zero, and release number with leading zero,
5114(e.g., libpng_vn for version 1.0.7 is 10007).
5115
5116Note that this function does not take a png_ptr, so you can call it
5117before you've created one.
5118
5119You can also check which version of png.h you used when compiling your
5120application:
5121
5122 png_uint_32 application_vn = PNG_LIBPNG_VER;
5123
5124.SH IX. Changes to Libpng from version 1.0.x to 1.2.x
5125
5126Support for user memory management was enabled by default. To
5127accomplish this, the functions png_create_read_struct_2(),
5128png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
5129png_malloc_default(), and png_free_default() were added.
5130
5131Support for the iTXt chunk has been enabled by default as of
5132version 1.2.41.
5133
5134Support for certain MNG features was enabled.
5135
5136Support for numbered error messages was added. However, we never got
5137around to actually numbering the error messages. The function
5138png_set_strip_error_numbers() was added (Note: the prototype for this
5139function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
5140builds of libpng-1.2.15. It was restored in libpng-1.2.36).
5141
5142The png_malloc_warn() function was added at libpng-1.2.3. This issues
5143a png_warning and returns NULL instead of aborting when it fails to
5144acquire the requested memory allocation.
5145
5146Support for setting user limits on image width and height was enabled
5147by default. The functions png_set_user_limits(), png_get_user_width_max(),
5148and png_get_user_height_max() were added at libpng-1.2.6.
5149
5150The png_set_add_alpha() function was added at libpng-1.2.7.
5151
5152The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
5153Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
5154tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
5155deprecated.
5156
5157A number of macro definitions in support of runtime selection of
5158assembler code features (especially Intel MMX code support) were
5159added at libpng-1.2.0:
5160
5161 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
5162 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
5163 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
5164 PNG_ASM_FLAG_MMX_READ_INTERLACE
5165 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
5166 PNG_ASM_FLAG_MMX_READ_FILTER_UP
5167 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
5168 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
5169 PNG_ASM_FLAGS_INITIALIZED
5170 PNG_MMX_READ_FLAGS
5171 PNG_MMX_FLAGS
5172 PNG_MMX_WRITE_FLAGS
5173 PNG_MMX_FLAGS
5174
5175We added the following functions in support of runtime
5176selection of assembler code features:
5177
5178 png_get_mmx_flagmask()
5179 png_set_mmx_thresholds()
5180 png_get_asm_flags()
5181 png_get_mmx_bitdepth_threshold()
5182 png_get_mmx_rowbytes_threshold()
5183 png_set_asm_flags()
5184
5185We replaced all of these functions with simple stubs in libpng-1.2.20,
5186when the Intel assembler code was removed due to a licensing issue.
5187
5188These macros are deprecated:
5189
5190 PNG_READ_TRANSFORMS_NOT_SUPPORTED
5191 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
5192 PNG_NO_SEQUENTIAL_READ_SUPPORTED
5193 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
5194 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
5195 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
5196
5197They have been replaced, respectively, by:
5198
5199 PNG_NO_READ_TRANSFORMS
5200 PNG_NO_PROGRESSIVE_READ
5201 PNG_NO_SEQUENTIAL_READ
5202 PNG_NO_WRITE_TRANSFORMS
5203 PNG_NO_READ_ANCILLARY_CHUNKS
5204 PNG_NO_WRITE_ANCILLARY_CHUNKS
5205
5206PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
5207deprecated since libpng-1.0.16 and libpng-1.2.6.
5208
5209The function
5210 png_check_sig(sig, num)
5211was replaced with
5212 !png_sig_cmp(sig, 0, num)
5213It has been deprecated since libpng-0.90.
5214
5215The function
5216 png_set_gray_1_2_4_to_8()
5217which also expands tRNS to alpha was replaced with
5218 png_set_expand_gray_1_2_4_to_8()
5219which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
5220
5221.SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
5222
5223Private libpng prototypes and macro definitions were moved from
5224png.h and pngconf.h into a new pngpriv.h header file.
5225
5226Functions png_set_benign_errors(), png_benign_error(), and
5227png_chunk_benign_error() were added.
5228
5229Support for setting the maximum amount of memory that the application
5230will allocate for reading chunks was added, as a security measure.
5231The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
5232were added to the library.
5233
5234We implemented support for I/O states by adding png_ptr member io_state
5235and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
5236
5237We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
5238input transforms.
5239
5240Checking for and reporting of errors in the IHDR chunk is more thorough.
5241
5242Support for global arrays was removed, to improve thread safety.
5243
5244Some obsolete/deprecated macros and functions have been removed.
5245
5246Typecasted NULL definitions such as
5247 #define png_voidp_NULL (png_voidp)NULL
5248were eliminated. If you used these in your application, just use
5249NULL instead.
5250
5251The png_struct and info_struct members "trans" and "trans_values" were
5252changed to "trans_alpha" and "trans_color", respectively.
5253
5254The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
5255were removed.
5256
5257The PNG_1_0_X and PNG_1_2_X macros were eliminated.
5258
5259The PNG_LEGACY_SUPPORTED macro was eliminated.
5260
5261Many WIN32_WCE #ifdefs were removed.
5262
5263The functions png_read_init(info_ptr), png_write_init(info_ptr),
5264png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
5265have been removed. They have been deprecated since libpng-0.95.
5266
5267The png_permit_empty_plte() was removed. It has been deprecated
5268since libpng-1.0.9. Use png_permit_mng_features() instead.
5269
5270We removed the obsolete stub functions png_get_mmx_flagmask(),
5271png_set_mmx_thresholds(), png_get_asm_flags(),
5272png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
5273png_set_asm_flags(), and png_mmx_supported()
5274
5275We removed the obsolete png_check_sig(), png_memcpy_check(), and
5276png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
5277and memset(), respectively.
5278
5279The function png_set_gray_1_2_4_to_8() was removed. It has been
5280deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
5281png_set_expand_gray_1_2_4_to_8() because the former function also
5282expanded any tRNS chunk to an alpha channel.
5283
5284Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
5285were added and are used by default instead of the corresponding
5286functions. Unfortunately,
5287from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5288function) incorrectly returned a value of type png_uint_32.
5289
5290We changed the prototype for png_malloc() from
5291 png_malloc(png_structp png_ptr, png_uint_32 size)
5292to
5293 png_malloc(png_structp png_ptr, png_alloc_size_t size)
5294
5295This also applies to the prototype for the user replacement malloc_fn().
5296
5297The png_calloc() function was added and is used in place of
5298of "png_malloc(); memset();" except in the case in png_read_png()
5299where the array consists of pointers; in this case a "for" loop is used
5300after the png_malloc() to set the pointers to NULL, to give robust.
5301behavior in case the application runs out of memory part-way through
5302the process.
5303
5304We changed the prototypes of png_get_compression_buffer_size() and
5305png_set_compression_buffer_size() to work with png_size_t instead of
5306png_uint_32.
5307
5308Support for numbered error messages was removed by default, since we
5309never got around to actually numbering the error messages. The function
5310png_set_strip_error_numbers() was removed from the library by default.
5311
5312The png_zalloc() and png_zfree() functions are no longer exported.
5313The png_zalloc() function no longer zeroes out the memory that it
5314allocates. Applications that called png_zalloc(png_ptr, number, size)
5315can call png_calloc(png_ptr, number*size) instead, and can call
5316png_free() instead of png_zfree().
5317
5318Support for dithering was disabled by default in libpng-1.4.0, because
5319it has not been well tested and doesn't actually "dither".
5320The code was not
5321removed, however, and could be enabled by building libpng with
5322PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
5323was re-enabled, but the function was renamed png_set_quantize() to
5324reflect more accurately what it actually does. At the same time,
5325the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
5326PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
5327was renamed to PNG_READ_QUANTIZE_SUPPORTED.
5328
5329We removed the trailing '.' from the warning and error messages.
5330
5331.SH XI. Changes to Libpng from version 1.4.x to 1.5.x
5332
5333From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5334function) incorrectly returned a value of type png_uint_32.
5335The incorrect macro was removed from libpng-1.4.5.
5336
5337Checking for invalid palette index on write was added at libpng
53381.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
5339a benign error. This is enabled by default because this condition is an
5340error according to the PNG specification, Clause 11.3.2, but the error can
5341be ignored in each png_ptr with
5342
5343 png_set_check_for_invalid_index(png_ptr, allowed);
5344
5345 allowed - one of
5346 0: disable benign error (accept the
5347 invalid data without warning).
5348 1: enable benign error (treat the
5349 invalid data as an error or a
5350 warning).
5351
5352If the error is ignored, or if png_benign_error() treats it as a warning,
5353any invalid pixels are decoded as opaque black by the decoder and written
5354as-is by the encoder.
5355
5356Retrieving the maximum palette index found was added at libpng-1.5.15.
5357This statement must appear after png_read_png() or png_read_image() while
5358reading, and after png_write_png() or png_write_image() while writing.
5359
5360 int max_palette = png_get_palette_max(png_ptr, info_ptr);
5361
5362This will return the maximum palette index found in the image, or "\-1" if
5363the palette was not checked, or "0" if no palette was found. Note that this
5364does not account for any palette index used by ancillary chunks such as the
5365bKGD chunk; you must check those separately to determine the maximum
5366palette index actually used.
5367
5368There are no substantial API changes between the non-deprecated parts of
5369the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
5370members of the main libpng control structures, png_struct and png_info,
5371deprecated in earlier versions of libpng, has been completely removed from
5372libpng 1.5, and new private "pngstruct.h", "pnginfo.h", and "pngdebug.h"
5373header files were created.
5374
5375We no longer include zlib.h in png.h. The include statement has been moved
5376to pngstruct.h, where it is not accessible by applications. Applications that
5377need access to information in zlib.h will need to add the '#include "zlib.h"'
5378directive. It does not matter whether this is placed prior to or after
5379the '"#include png.h"' directive.
5380
5381The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
5382and were removed.
5383
5384We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
5385macros into a private header file (pngpriv.h) that is not accessible to
5386applications.
5387
5388In png_get_iCCP, the type of "profile" was changed from png_charpp
5389to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
5390
5391There are changes of form in png.h, including new and changed macros to
5392declare parts of the API. Some API functions with arguments that are
5393pointers to data not modified within the function have been corrected to
5394declare these arguments with PNG_CONST.
5395
5396Much of the internal use of C macros to control the library build has also
5397changed and some of this is visible in the exported header files, in
5398particular the use of macros to control data and API elements visible
5399during application compilation may require significant revision to
5400application code. (It is extremely rare for an application to do this.)
5401
5402Any program that compiled against libpng 1.4 and did not use deprecated
5403features or access internal library structures should compile and work
5404against libpng 1.5, except for the change in the prototype for
5405png_get_iCCP() and png_set_iCCP() API functions mentioned above.
5406
5407libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
5408interlaced images. The macros return the number of rows and columns in
5409each pass and information that can be used to de-interlace and (if
5410absolutely necessary) interlace an image.
5411
5412libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
5413the application-provided png_longjmp_ptr on the internal, but application
5414initialized, longjmp buffer. It is provided as a convenience to avoid
5415the need to use the png_jmpbuf macro, which had the unnecessary side
5416effect of resetting the internal png_longjmp_ptr value.
5417
5418libpng 1.5.0 includes a complete fixed point API. By default this is
5419present along with the corresponding floating point API. In general the
5420fixed point API is faster and smaller than the floating point one because
5421the PNG file format used fixed point, not floating point. This applies
5422even if the library uses floating point in internal calculations. A new
5423macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
5424uses floating point arithmetic (the default) or fixed point arithmetic
5425internally for performance critical calculations such as gamma correction.
5426In some cases, the gamma calculations may produce slightly different
5427results. This has changed the results in png_rgb_to_gray and in alpha
5428composition (png_set_background for example). This applies even if the
5429original image was already linear (gamma == 1.0) and, therefore, it is
5430not necessary to linearize the image. This is because libpng has *not*
5431been changed to optimize that case correctly, yet.
5432
5433Fixed point support for the sCAL chunk comes with an important caveat;
5434the sCAL specification uses a decimal encoding of floating point values
5435and the accuracy of PNG fixed point values is insufficient for
5436representation of these values. Consequently a "string" API
5437(png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
5438arbitrary sCAL chunks in the absence of either the floating point API or
5439internal floating point calculations. Starting with libpng-1.5.0, both
5440of these functions are present when PNG_sCAL_SUPPORTED is defined. Prior
5441to libpng-1.5.0, their presence also depended upon PNG_FIXED_POINT_SUPPORTED
5442being defined and PNG_FLOATING_POINT_SUPPORTED not being defined.
5443
5444Applications no longer need to include the optional distribution header
5445file pngusr.h or define the corresponding macros during application
5446build in order to see the correct variant of the libpng API. From 1.5.0
5447application code can check for the corresponding _SUPPORTED macro:
5448
5449#ifdef PNG_INCH_CONVERSIONS_SUPPORTED
5450 /* code that uses the inch conversion APIs. */
5451#endif
5452
5453This macro will only be defined if the inch conversion functions have been
5454compiled into libpng. The full set of macros, and whether or not support
5455has been compiled in, are available in the header file pnglibconf.h.
5456This header file is specific to the libpng build. Notice that prior to
54571.5.0 the _SUPPORTED macros would always have the default definition unless
5458reset by pngusr.h or by explicit settings on the compiler command line.
5459These settings may produce compiler warnings or errors in 1.5.0 because
5460of macro redefinition.
5461
5462Applications can now choose whether to use these macros or to call the
5463corresponding function by defining PNG_USE_READ_MACROS or
5464PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
5465only supported from 1.5.0; defining PNG_NO_USE_READ_MACROS prior to 1.5.0
5466will lead to a link failure.
5467
5468Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
5469when compressing the IDAT data and textual data such as zTXt and iCCP.
5470In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
5471We added five png_set_text_*() functions for setting the parameters to
5472use with textual data.
5473
5474Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5475option was off by default, and slightly inaccurate scaling occurred.
5476This option can no longer be turned off, and the choice of accurate
5477or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
5478API for accurate scaling or the old png_set_strip_16_to_8() API for simple
5479chopping. In libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5480macro became PNG_READ_SCALE_16_TO_8_SUPPORTED, and the PNG_READ_16_TO_8
5481macro became PNG_READ_STRIP_16_TO_8_SUPPORTED, to enable the two
5482png_set_*_16_to_8() functions separately.
5483
5484Prior to libpng-1.5.4, the png_set_user_limits() function could only be
5485used to reduce the width and height limits from the value of
5486PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
5487that it could be used to override them. Now this function will reduce or
5488increase the limits.
5489
5490Starting in libpng-1.5.22, default user limits were established. These
5491can be overridden by application calls to png_set_user_limits(),
5492png_set_user_chunk_cache_max(), and/or png_set_user_malloc_max().
5493The limits are now
5494 max possible default
5495 png_user_width_max 0x7fffffff 1,000,000
5496 png_user_height_max 0x7fffffff 1,000,000
5497 png_user_chunk_cache_max 0 (unlimited) 1000
5498 png_user_chunk_malloc_max 0 (unlimited) 8,000,000
5499
5500The png_set_option() function (and the "options" member of the png struct) was
5501added to libpng-1.5.15, with option PNG_ARM_NEON.
5502
5503The library now supports a complete fixed point implementation and can
5504thus be used on systems that have no floating point support or very
5505limited or slow support. Previously gamma correction, an essential part
5506of complete PNG support, required reasonably fast floating point.
5507
5508As part of this the choice of internal implementation has been made
5509independent of the choice of fixed versus floating point APIs and all the
5510missing fixed point APIs have been implemented.
5511
5512The exact mechanism used to control attributes of API functions has
5513changed, as described in the INSTALL file.
5514
5515A new test program, pngvalid, is provided in addition to pngtest.
5516pngvalid validates the arithmetic accuracy of the gamma correction
5517calculations and includes a number of validations of the file format.
5518A subset of the full range of tests is run when "make check" is done
5519(in the 'configure' build.) pngvalid also allows total allocated memory
5520usage to be evaluated and performs additional memory overwrite validation.
5521
5522Many changes to individual feature macros have been made. The following
5523are the changes most likely to be noticed by library builders who
5524configure libpng:
5525
55261) All feature macros now have consistent naming:
5527
5528#define PNG_NO_feature turns the feature off
5529#define PNG_feature_SUPPORTED turns the feature on
5530
5531pnglibconf.h contains one line for each feature macro which is either:
5532
5533#define PNG_feature_SUPPORTED
5534
5535if the feature is supported or:
5536
5537/*#undef PNG_feature_SUPPORTED*/
5538
5539if it is not. Library code consistently checks for the 'SUPPORTED' macro.
5540It does not, and libpng applications should not, check for the 'NO' macro
5541which will not normally be defined even if the feature is not supported.
5542The 'NO' macros are only used internally for setting or not setting the
5543corresponding 'SUPPORTED' macros.
5544
5545Compatibility with the old names is provided as follows:
5546
5547PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
5548
5549And the following definitions disable the corresponding feature:
5550
5551PNG_SETJMP_NOT_SUPPORTED disables SETJMP
5552PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
5553PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
5554PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
5555PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
5556PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
5557
5558Library builders should remove use of the above, inconsistent, names.
5559
55602) Warning and error message formatting was previously conditional on
5561the STDIO feature. The library has been changed to use the
5562CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
5563the library no longer uses the printf(3) functions, even though the
5564default read/write implementations use (FILE) style stdio.h functions.
5565
55663) Three feature macros now control the fixed/floating point decisions:
5567
5568PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
5569
5570PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
5571practice these are normally required internally anyway (because the PNG
5572file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
5573merely stops the function from being exported.
5574
5575PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
5576point implementation or the fixed point one. Typically the fixed point
5577implementation is larger and slower than the floating point implementation
5578on a system that supports floating point; however, it may be faster on a
5579system which lacks floating point hardware and therefore uses a software
5580emulation.
5581
55824) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
5583functions to read and write ints to be disabled independently of
5584PNG_USE_READ_MACROS, which allows libpng to be built with the functions
5585even though the default is to use the macros - this allows applications
5586to choose at app buildtime whether or not to use macros (previously
5587impossible because the functions weren't in the default build.)
5588
5589.SH XII. Changes to Libpng from version 1.5.x to 1.6.x
5590
5591A "simplified API" has been added (see documentation in png.h and a simple
5592example in contrib/examples/pngtopng.c). The new publicly visible API
5593includes the following:
5594
5595 macros:
5596 PNG_FORMAT_*
5597 PNG_IMAGE_*
5598 structures:
5599 png_control
5600 png_image
5601 read functions
5602 png_image_begin_read_from_file()
5603 png_image_begin_read_from_stdio()
5604 png_image_begin_read_from_memory()
5605 png_image_finish_read()
5606 png_image_free()
5607 write functions
5608 png_image_write_to_file()
5609 png_image_write_to_memory()
5610 png_image_write_to_stdio()
5611
5612Starting with libpng-1.6.0, you can configure libpng to prefix all exported
5613symbols, using the PNG_PREFIX macro.
5614
5615We no longer include string.h in png.h. The include statement has been moved
5616to pngpriv.h, where it is not accessible by applications. Applications that
5617need access to information in string.h must add an '#include <string.h>'
5618directive. It does not matter whether this is placed prior to or after
5619the '#include "png.h"' directive.
5620
5621The following API are now DEPRECATED:
5622 png_info_init_3()
5623 png_convert_to_rfc1123() which has been replaced
5624 with png_convert_to_rfc1123_buffer()
5625 png_malloc_default()
5626 png_free_default()
5627 png_reset_zstream()
5628
5629The following have been removed:
5630 png_get_io_chunk_name(), which has been replaced
5631 with png_get_io_chunk_type(). The new
5632 function returns a 32-bit integer instead of
5633 a string.
5634 The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
5635 png_memset() macros are no longer used in the libpng sources and
5636 have been removed. These had already been made invisible to applications
5637 (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
5638
5639The signatures of many exported functions were changed, such that
5640 png_structp became png_structrp or png_const_structrp
5641 png_infop became png_inforp or png_const_inforp
5642where "rp" indicates a "restricted pointer".
5643
5644Dropped support for 16-bit platforms. The support for FAR/far types has
5645been eliminated and the definition of png_alloc_size_t is now controlled
5646by a flag so that 'small size_t' systems can select it if necessary.
5647
5648Error detection in some chunks has improved; in particular the iCCP chunk
5649reader now does pretty complete validation of the basic format. Some bad
5650profiles that were previously accepted are now accepted with a warning or
5651rejected, depending upon the png_set_benign_errors() setting, in particular
5652the very old broken Microsoft/HP 3144-byte sRGB profile. Starting with
5653libpng-1.6.11, recognizing and checking sRGB profiles can be avoided by
5654means of
5655
5656 #if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && \
5657 defined(PNG_SET_OPTION_SUPPORTED)
5658 png_set_option(png_ptr, PNG_SKIP_sRGB_CHECK_PROFILE,
5659 PNG_OPTION_ON);
5660 #endif
5661
5662It's not a good idea to do this if you are using the "simplified API",
5663which needs to be able to recognize sRGB profiles conveyed via the iCCP
5664chunk.
5665
5666The PNG spec requirement that only grayscale profiles may appear in images
5667with color type 0 or 4 and that even if the image only contains gray pixels,
5668only RGB profiles may appear in images with color type 2, 3, or 6, is now
5669enforced. The sRGB chunk is allowed to appear in images with any color type
5670and is interpreted by libpng to convey a one-tracer-curve gray profile or a
5671three-tracer-curve RGB profile as appropriate.
5672
5673Libpng 1.5.x erroneously used /MD for Debug DLL builds; if you used the debug
5674builds in your app and you changed your app to use /MD you will need to
5675change it back to /MDd for libpng 1.6.x.
5676
5677Prior to libpng-1.6.0 a warning would be issued if the iTXt chunk contained
5678an empty language field or an empty translated keyword. Both of these
5679are allowed by the PNG specification, so these warnings are no longer issued.
5680
5681The library now issues an error if the application attempts to set a
5682transform after it calls png_read_update_info() or if it attempts to call
5683both png_read_update_info() and png_start_read_image() or to call either
5684of them more than once.
5685
5686The default condition for benign_errors is now to treat benign errors as
5687warnings while reading and as errors while writing.
5688
5689The library now issues a warning if both background processing and RGB to
5690gray are used when gamma correction happens. As with previous versions of
5691the library the results are numerically very incorrect in this case.
5692
5693There are some minor arithmetic changes in some transforms such as
5694png_set_background(), that might be detected by certain regression tests.
5695
5696Unknown chunk handling has been improved internally, without any API change.
5697This adds more correct option control of the unknown handling, corrects
5698a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
5699it possible to skip IDAT chunks in the sequential reader.
5700
5701The machine-generated configure files are no longer included in branches
5702libpng16 and later of the GIT repository. They continue to be included
5703in the tarball releases, however.
5704
5705Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
5706stream to set the size of the sliding window for reading instead of using the
5707default 32-kbyte sliding window size. It was discovered that there are
5708hundreds of PNG files in the wild that have incorrect CMF bytes that caused
5709zlib to issue the "invalid distance too far back" error and reject the file.
5710Libpng-1.6.3 and later calculate their own safe CMF from the image dimensions,
5711provide a way to revert to the libpng-1.5.x behavior (ignoring the CMF bytes
5712and using a 32-kbyte sliding window), by using
5713
5714 png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
5715 PNG_OPTION_ON);
5716
5717and provide a tool (contrib/tools/pngfix) for rewriting a PNG file while
5718optimizing the CMF bytes in its IDAT chunk correctly.
5719
5720Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong
5721length, which resulted in PNG files that cannot be read beyond the bad iTXt
5722chunk. This error was fixed in libpng-1.6.3, and a tool (called
5723contrib/tools/png-fix-itxt) has been added to the libpng distribution.
5724
5725Starting with libpng-1.6.17, the PNG_SAFE_LIMITS macro was eliminated
5726and safe limits are used by default (users who need larger limits
5727can still override them at compile time or run time, as described above).
5728
5729The new limits are
5730 default spec limit
5731 png_user_width_max 1,000,000 2,147,483,647
5732 png_user_height_max 1,000,000 2,147,483,647
5733 png_user_chunk_cache_max 128 unlimited
5734 png_user_chunk_malloc_max 8,000,000 unlimited
5735
5736Starting with libpng-1.6.18, a PNG_RELEASE_BUILD macro was added, which allows
5737library builders to control compilation for an installed system (a release build).
5738It can be set for testing debug or beta builds to ensure that they will compile
5739when the build type is switched to RC or STABLE. In essence this overrides the
5740PNG_LIBPNG_BUILD_BASE_TYPE definition which is not directly user controllable.
5741
5742Starting with libpng-1.6.19, attempting to set an over-length PLTE chunk
5743is an error. Previously this requirement of the PNG specification was not
5744enforced, and the palette was always limited to 256 entries. An over-length
5745PLTE chunk found in an input PNG is silently truncated.
5746
5747Starting with libpng-1.6.31, the eXIf chunk is supported. Libpng does not
5748attempt to decode the Exif profile; it simply returns a byte array
5749containing the profile to the calling application which must do its own
5750decoding.
5751
5752.SH XIII. Detecting libpng
5753
5754The png_get_io_ptr() function has been present since libpng-0.88, has never
5755changed, and is unaffected by conditional compilation macros. It is the
5756best choice for use in configure scripts for detecting the presence of any
5757libpng version since 0.88. In an autoconf "configure.in" you could use
5758
5759 AC_CHECK_LIB(png, png_get_io_ptr, ...
5760
5761.SH XV. Source code repository
5762
5763Since about February 2009, version 1.2.34, libpng has been under "git" source
5764control. The git repository was built from old libpng-x.y.z.tar.gz files
5765going back to version 0.70. You can access the git repository (read only)
5766at
5767
5768 https://github.com/glennrp/libpng or
5769 https://git.code.sf.net/p/libpng/code.git
5770
5771or you can browse it with a web browser at
5772
5773 https://github.com/glennrp/libpng or
5774 https://sourceforge.net/p/libpng/code/ci/libpng16/tree/
5775
5776Patches can be sent to glennrp at users.sourceforge.net or to
5777png-mng-implement at lists.sourceforge.net or you can upload them to
5778the libpng bug tracker at
5779
5780 https://libpng.sourceforge.io/
5781
5782or as a "pull request" to
5783
5784 https://github.com/glennrp/libpng/pulls
5785
5786We also accept patches built from the tar or zip distributions, and
5787simple verbal discriptions of bug fixes, reported either to the
5788SourceForge bug tracker, to the png-mng-implement at lists.sf.net
5789mailing list, as github issues, or directly to glennrp.
5790
5791.SH XV. Coding style
5792
5793Our coding style is similar to the "Allman" style
5794(See https://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
5795braces on separate lines:
5796
5797 if (condition)
5798 {
5799 action;
5800 }
5801
5802 else if (another condition)
5803 {
5804 another action;
5805 }
5806
5807The braces can be omitted from simple one-line actions:
5808
5809 if (condition)
5810 return (0);
5811
5812We use 3-space indentation, except for continued statements which
5813are usually indented the same as the first line of the statement
5814plus four more spaces.
5815
5816For macro definitions we use 2-space indentation, always leaving the "#"
5817in the first column.
5818
5819 #ifndef PNG_NO_FEATURE
5820 # ifndef PNG_FEATURE_SUPPORTED
5821 # define PNG_FEATURE_SUPPORTED
5822 # endif
5823 #endif
5824
5825Comments appear with the leading "/*" at the same indentation as
5826the statement that follows the comment:
5827
5828 /* Single-line comment */
5829 statement;
5830
5831 /* This is a multiple-line
5832 * comment.
5833 */
5834 statement;
5835
5836Very short comments can be placed after the end of the statement
5837to which they pertain:
5838
5839 statement; /* comment */
5840
5841We don't use C++ style ("//") comments. We have, however,
5842used them in the past in some now-abandoned MMX assembler
5843code.
5844
5845Functions and their curly braces are not indented, and
5846exported functions are marked with PNGAPI:
5847
5848 /* This is a public function that is visible to
5849 * application programmers. It does thus-and-so.
5850 */
5851 void PNGAPI
5852 png_exported_function(png_ptr, png_info, foo)
5853 {
5854 body;
5855 }
5856
5857The return type and decorations are placed on a separate line
5858ahead of the function name, as illustrated above.
5859
5860The prototypes for all exported functions appear in png.h,
5861above the comment that says
5862
5863 /* Maintainer: Put new public prototypes here ... */
5864
5865We mark all non-exported functions with "/* PRIVATE */"":
5866
5867 void /* PRIVATE */
5868 png_non_exported_function(png_ptr, png_info, foo)
5869 {
5870 body;
5871 }
5872
5873The prototypes for non-exported functions (except for those in
5874pngtest) appear in pngpriv.h above the comment that says
5875
5876 /* Maintainer: Put new private prototypes here ^ */
5877
5878To avoid polluting the global namespace, the names of all exported
5879functions and variables begin with "png_", and all publicly visible C
5880preprocessor macros begin with "PNG". We request that applications that
5881use libpng *not* begin any of their own symbols with either of these strings.
5882
5883We put a space after the "sizeof" operator and we omit the
5884optional parentheses around its argument when the argument
5885is an expression, not a type name, and we always enclose the
5886sizeof operator, with its argument, in parentheses:
5887
5888 (sizeof (png_uint_32))
5889 (sizeof array)
5890
5891Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
5892though it were a function.
5893
5894Control keywords if, for, while, and switch are always followed by a space
5895to distinguish them from function calls, which have no trailing space.
5896
5897We put a space after each comma and after each semicolon
5898in "for" statements, and we put spaces before and after each
5899C binary operator and after "for" or "while", and before
5900"?". We don't put a space between a typecast and the expression
5901being cast, nor do we put one between a function name and the
5902left parenthesis that follows it:
5903
5904 for (i = 2; i > 0; \-\-i)
5905 y[i] = a(x) + (int)b;
5906
5907We prefer #ifdef and #ifndef to #if defined() and #if !defined()
5908when there is only one macro being tested. We always use parentheses
5909with "defined".
5910
5911We express integer constants that are used as bit masks in hex format,
5912with an even number of lower-case hex digits, and to make them unsigned
5913(e.g., 0x00U, 0xffU, 0x0100U) and long if they are greater than 0x7fff
5914(e.g., 0xffffUL).
5915
5916We prefer to use underscores rather than camelCase in names, except
5917for a few type names that we inherit from zlib.h.
5918
5919We prefer "if (something != 0)" and "if (something == 0)" over
5920"if (something)" and if "(!something)", respectively, and for pointers
5921we prefer "if (some_pointer != NULL)" or "if (some_pointer == NULL)".
5922
5923We do not use the TAB character for indentation in the C sources.
5924
5925Lines do not exceed 80 characters.
5926
5927Other rules can be inferred by inspecting the libpng source.
5928
5929.SH XVI. Y2K Compliance in libpng
5930
5931Since the PNG Development group is an ad-hoc body, we can't make
5932an official declaration.
5933
5934This is your unofficial assurance that libpng from version 0.71 and
5935upward through 1.6.34 are Y2K compliant. It is my belief that earlier
5936versions were also Y2K compliant.
5937
5938Libpng only has two year fields. One is a 2-byte unsigned integer
5939that will hold years up to 65535. The other, which is deprecated,
5940holds the date in text format, and will hold years up to 9999.
5941
5942The integer is
5943 "png_uint_16 year" in png_time_struct.
5944
5945The string is
5946 "char time_buffer[29]" in png_struct. This is no longer used
5947in libpng-1.6.x and will be removed from libpng-1.7.0.
5948
5949There are seven time-related functions:
5950
5951 png_convert_to_rfc_1123_buffer() in png.c
5952 (formerly png_convert_to_rfc_1152() in error, and
5953 also formerly png_convert_to_rfc_1123())
5954 png_convert_from_struct_tm() in pngwrite.c, called
5955 in pngwrite.c
5956 png_convert_from_time_t() in pngwrite.c
5957 png_get_tIME() in pngget.c
5958 png_handle_tIME() in pngrutil.c, called in pngread.c
5959 png_set_tIME() in pngset.c
5960 png_write_tIME() in pngwutil.c, called in pngwrite.c
5961
5962All appear to handle dates properly in a Y2K environment. The
5963png_convert_from_time_t() function calls gmtime() to convert from system
5964clock time, which returns (year - 1900), which we properly convert to
5965the full 4-digit year. There is a possibility that applications using
5966libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5967function, or that they are incorrectly passing only a 2-digit year
5968instead of "year - 1900" into the png_convert_from_struct_tm() function,
5969but this is not under our control. The libpng documentation has always
5970stated that it works with 4-digit years, and the APIs have been
5971documented as such.
5972
5973The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5974integer to hold the year, and can hold years as large as 65535.
5975
5976zlib, upon which libpng depends, is also Y2K compliant. It contains
5977no date-related code.
5978
5979
5980 Glenn Randers-Pehrson
5981 libpng maintainer
5982 PNG Development Group
5983
5984.SH NOTE
5985
5986Note about libpng version numbers:
5987
5988Due to various miscommunications, unforeseen code incompatibilities
5989and occasional factors outside the authors' control, version numbering
5990on the library has not always been consistent and straightforward.
5991The following table summarizes matters since version 0.89c, which was
5992the first widely used release:
5993
5994 source png.h png.h shared-lib
5995 version string int version
5996 ------- ------ ----- ----------
5997 0.89c "1.0 beta 3" 0.89 89 1.0.89
5998 0.90 "1.0 beta 4" 0.90 90 0.90 [should have been 2.0.90]
5999 0.95 "1.0 beta 5" 0.95 95 0.95 [should have been 2.0.95]
6000 0.96 "1.0 beta 6" 0.96 96 0.96 [should have been 2.0.96]
6001 0.97b "1.00.97 beta 7" 1.00.97 97 1.0.1 [should have been 2.0.97]
6002 0.97c 0.97 97 2.0.97
6003 0.98 0.98 98 2.0.98
6004 0.99 0.99 98 2.0.99
6005 0.99a-m 0.99 99 2.0.99
6006 1.00 1.00 100 2.1.0 [100 should be 10000]
6007 1.0.0 (from here on, the 100 2.1.0 [100 should be 10000]
6008 1.0.1 png.h string is 10001 2.1.0
6009 1.0.1a-e identical to the 10002 from here on, the shared library
6010 1.0.2 source version) 10002 is 2.V where V is the source code
6011 1.0.2a-b 10003 version, except as noted.
6012 1.0.3 10003
6013 1.0.3a-d 10004
6014 1.0.4 10004
6015 1.0.4a-f 10005
6016 1.0.5 (+ 2 patches) 10005
6017 1.0.5a-d 10006
6018 1.0.5e-r 10100 (not source compatible)
6019 1.0.5s-v 10006 (not binary compatible)
6020 1.0.6 (+ 3 patches) 10006 (still binary incompatible)
6021 1.0.6d-f 10007 (still binary incompatible)
6022 1.0.6g 10007
6023 1.0.6h 10007 10.6h (testing xy.z so-numbering)
6024 1.0.6i 10007 10.6i
6025 1.0.6j 10007 2.1.0.6j (incompatible with 1.0.0)
6026 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 (binary compatible)
6027 1.0.7beta15-18 1 10007 2.1.0.7beta15-18 (binary compatible)
6028 1.0.7rc1-2 1 10007 2.1.0.7rc1-2 (binary compatible)
6029 1.0.7 1 10007 (still compatible)
6030 ...
6031 1.0.19 10 10019 10.so.0.19[.0]
6032 ...
6033 1.2.59 13 10259 12.so.0.59[.0]
6034 ...
6035 1.5.30 15 10530 15.so.15.30[.0]
6036 ...
6037 1.6.34 16 10634 16.so.16.34[.0]
6038
6039Henceforth the source version will match the shared-library minor
6040and patch numbers; the shared-library major version number will be
6041used for changes in backward compatibility, as it is intended. The
6042PNG_PNGLIB_VER macro, which is not used within libpng but is available
6043for applications, is an unsigned integer of the form xyyzz corresponding
6044to the source version x.y.z (leading zeros in y and z). Beta versions
6045were given the previous public release number plus a letter, until
6046version 1.0.6j; from then on they were given the upcoming public
6047release number plus "betaNN" or "rcNN".
6048
6049.SH "SEE ALSO"
6050.IR libpngpf(3) ", " png(5)
6051.LP
6052.IR libpng :
6053.IP
6054https://libpng.sourceforge.io/ (follow the [DOWNLOAD] link)
6055http://www.libpng.org/pub/png
6056
6057.LP
6058.IR zlib :
6059.IP
6060(generally) at the same location as
6061.I libpng
6062or at
6063.br
6064https://zlib.net/
6065
6066.LP
6067.IR PNG specification: RFC 2083
6068.IP
6069(generally) at the same location as
6070.I libpng
6071or at
6072.br
6073https://www.ietf.org/rfc/rfc2083.txt
6074.br
6075or (as a W3C Recommendation) at
6076.br
6077https://www.w3.org/TR/REC-png.html
6078
6079.LP
6080In the case of any inconsistency between the PNG specification
6081and this library, the specification takes precedence.
6082
6083.SH AUTHORS
6084This man page: Glenn Randers-Pehrson
6085<glennrp at users.sourceforge.net>
6086
6087The contributing authors would like to thank all those who helped
6088with testing, bug fixes, and patience. This wouldn't have been
6089possible without all of you.
6090
6091Thanks to Frank J. T. Wojcik for helping with the documentation.
6092
6093Libpng version 1.6.34 - September 29, 2017:
6094Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
6095Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
6096
6097Supported by the PNG development group
6098.br
6099png-mng-implement at lists.sf.net
6100(subscription required; visit
6101png-mng-implement at lists.sourceforge.net (subscription required; visit
6102https://lists.sourceforge.net/lists/listinfo/png-mng-implement
6103to subscribe).
6104
6105.SH NOTICES:
6106
6107This copy of the libpng notices is provided for your convenience. In case of
6108any discrepancy between this copy and the notices in the file png.h that is
6109included in the libpng distribution, the latter shall prevail.
6110
6111COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
6112
6113If you modify libpng you may insert additional notices immediately following
6114this sentence.
6115
6116This code is released under the libpng license.
6117
6118libpng versions 1.0.7, July 1, 2000 through 1.6.34, September 29, 2017 are
6119Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
6120derived from libpng-1.0.6, and are distributed according to the same
6121disclaimer and license as libpng-1.0.6 with the following individuals
6122added to the list of Contributing Authors:
6123
6124 Simon-Pierre Cadieux
6125 Eric S. Raymond
6126 Mans Rullgard
6127 Cosmin Truta
6128 Gilles Vollant
6129 James Yu
6130 Mandar Sahastrabuddhe
6131 Google Inc.
6132 Vadim Barkov
6133
6134and with the following additions to the disclaimer:
6135
6136 There is no warranty against interference with your enjoyment of the
6137 library or against infringement. There is no warranty that our
6138 efforts or the library will fulfill any of your particular purposes
6139 or needs. This library is provided with all faults, and the entire
6140 risk of satisfactory quality, performance, accuracy, and effort is with
6141 the user.
6142
6143Some files in the "contrib" directory and some configure-generated
6144files that are distributed with libpng have other copyright owners and
6145are released under other open source licenses.
6146
6147libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
6148Copyright (c) 1998-2000 Glenn Randers-Pehrson, are derived from
6149libpng-0.96, and are distributed according to the same disclaimer and
6150license as libpng-0.96, with the following individuals added to the list
6151of Contributing Authors:
6152
6153 Tom Lane
6154 Glenn Randers-Pehrson
6155 Willem van Schaik
6156
6157libpng versions 0.89, June 1996, through 0.96, May 1997, are
6158Copyright (c) 1996-1997 Andreas Dilger, are derived from libpng-0.88,
6159and are distributed according to the same disclaimer and license as
6160libpng-0.88, with the following individuals added to the list of
6161Contributing Authors:
6162
6163 John Bowler
6164 Kevin Bracey
6165 Sam Bushell
6166 Magnus Holmgren
6167 Greg Roelofs
6168 Tom Tanner
6169
6170Some files in the "scripts" directory have other copyright owners
6171but are released under this license.
6172
6173libpng versions 0.5, May 1995, through 0.88, January 1996, are
6174Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
6175
6176For the purposes of this copyright and license, "Contributing Authors"
6177is defined as the following set of individuals:
6178
6179 Andreas Dilger
6180 Dave Martindale
6181 Guy Eric Schalnat
6182 Paul Schmidt
6183 Tim Wegner
6184
6185The PNG Reference Library is supplied "AS IS". The Contributing Authors
6186and Group 42, Inc. disclaim all warranties, expressed or implied,
6187including, without limitation, the warranties of merchantability and of
6188fitness for any purpose. The Contributing Authors and Group 42, Inc.
6189assume no liability for direct, indirect, incidental, special, exemplary,
6190or consequential damages, which may result from the use of the PNG
6191Reference Library, even if advised of the possibility of such damage.
6192
6193Permission is hereby granted to use, copy, modify, and distribute this
6194source code, or portions hereof, for any purpose, without fee, subject
6195to the following restrictions:
6196
6197 1. The origin of this source code must not be misrepresented.
6198
6199 2. Altered versions must be plainly marked as such and must not
6200 be misrepresented as being the original source.
6201
6202 3. This Copyright notice may not be removed or altered from any
6203 source or altered source distribution.
6204
6205The Contributing Authors and Group 42, Inc. specifically permit, without
6206fee, and encourage the use of this source code as a component to
6207supporting the PNG file format in commercial products. If you use this
6208source code in a product, acknowledgment is not required but would be
6209appreciated.
6210
6211END OF COPYRIGHT NOTICE, DISCLAIMER, and LICENSE.
6212
6213TRADEMARK:
6214
6215The name "libpng" has not been registered by the Copyright owner
6216as a trademark in any jurisdiction. However, because libpng has
6217been distributed and maintained world-wide, continually since 1995,
6218the Copyright owner claims "common-law trademark protection" in any
6219jurisdiction where common-law trademark is recognized.
6220
6221OSI CERTIFICATION:
6222
6223Libpng is OSI Certified Open Source Software. OSI Certified Open Source is
6224a certification mark of the Open Source Initiative. OSI has not addressed
6225the additional disclaimers inserted at version 1.0.7.
6226
6227EXPORT CONTROL:
6228
6229The Copyright owner believes that the Export Control Classification
6230Number (ECCN) for libpng is EAR99, which means not subject to export
6231controls or International Traffic in Arms Regulations (ITAR) because
6232it is open source, publicly available software, that does not contain
6233any encryption software. See the EAR, paragraphs 734.3(b)(3) and
6234734.7(b).
6235
6236A "png_get_copyright" function is available, for convenient use in "about"
6237boxes and the like:
6238
6239 printf("%s", png_get_copyright(NULL));
6240
6241Also, the PNG logo (in PNG format, of course) is supplied in the
6242files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
6243
6244Glenn Randers-Pehrson
6245glennrp at users.sourceforge.net
6246September 29, 2017
6247
6248.\" end of man page
6249