src/third-party/libpng/libpng.3 (view raw)
1.TH LIBPNG 3 "March 26, 2015"
2.SH NAME
3libpng \- Portable Network Graphics (PNG) Reference Library 1.6.17
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_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
101
102\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
103
104\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
105
106\fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
107
108\fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
109
110\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
111
112\fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
113
114\fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
115
116\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
117
118\fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
119
120\fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
121
122\fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
123
124\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
125
126\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
127
128\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
129
130\fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
131
132\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
133
134\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
135
136\fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
137
138\fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
139
140\fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
141
142\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
143
144\fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
145
146\fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
147
148\fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
149
150\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
151
152\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
153
154\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
155
156\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
157
158\fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
159
160\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
161
162\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
163
164\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
165
166\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
167
168\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
169
170\fB/* This function is really an inline macro. \fI*/
171
172\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
173
174\fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
175
176\fB/* This function is really an inline macro. \fI*/
177
178\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
179
180\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
181
182\fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
183
184\fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
185
186\fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
187
188\fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
189
190\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
191
192\fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
193
194\fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
195
196\fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
197
198\fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
199
200\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
201
202\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
203
204\fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
205
206\fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
207
208\fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
209
210\fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
211
212\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
213
214\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
215
216\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
217
218\fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP
219
220\fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP
221
222\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
223
224\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
225
226\fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP
227
228\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
229
230\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
231
232\fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
233
234\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
235
236\fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
237
238\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
239
240\fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
241
242\fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
243
244\fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
245
246\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
247
248\fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
249
250\fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
251
252\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
253
254\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
255
256\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
257
258\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
259
260\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
261
262\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
263
264\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
265
266\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
267
268\fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
269
270\fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
271
272\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
273
274\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
275
276\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
277
278\fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
279
280\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
281
282\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
283
284\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
285
286\fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
287
288\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
289
290\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
291
292\fBvoid png_set_check_for_invalid_index(png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
293
294\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
295
296\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
297
298\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
299
300\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
301
302\fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
303
304\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
305
306\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
307
308\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
309
310\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
311
312\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
313
314\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
315
316\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
317
318\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
319
320\fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
321
322\fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
323
324\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
325
326\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
327
328\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
329
330\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
331
332\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
333
334\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
335
336\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
337
338\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
339
340\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
341
342\fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
343
344\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
345
346\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
347
348\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
349
350\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
351
352\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
353
354\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
355
356\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
357
358\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
359
360\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
361
362\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
363
364\fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
365
366\fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
367
368\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
369
370\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
371
372\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
373
374\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
375
376\fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
377
378\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
379
380\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
381
382\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
383
384\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
385
386\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
387
388\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
389
390\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
391
392\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
393
394\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
395
396\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
397
398\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
399
400\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
401
402\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
403
404\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
405
406\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
407
408\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
409
410\fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
411
412\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
413
414\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
415
416\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
417
418\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
419
420\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
421
422\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
423
424\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
425
426\fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
427
428\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
429
430\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
431
432\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
433
434\fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
435
436\fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
437
438\fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
439
440\fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
441
442\fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
443
444\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
445
446\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
447
448\fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
449
450\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
451
452\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
453
454\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
455
456\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
457
458\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
459
460\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
461
462\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
463
464\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
465
466\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
467
468\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
469
470\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
471
472\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
473
474\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
475
476\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
477
478\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
479
480\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
481
482\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
483
484\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
485
486\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
487
488\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
489
490\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
491
492\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
493
494\fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
495
496.SH DESCRIPTION
497The
498.I libpng
499library supports encoding, decoding, and various manipulations of
500the Portable Network Graphics (PNG) format image files. It uses the
501.IR zlib(3)
502compression library.
503Following is a copy of the libpng-manual.txt file that accompanies libpng.
504.SH LIBPNG.TXT
505libpng-manual.txt - A description on how to use and modify libpng
506
507 libpng version 1.6.17 - March 26, 2015
508 Updated and distributed by Glenn Randers-Pehrson
509 <glennrp at users.sourceforge.net>
510 Copyright (c) 1998-2015 Glenn Randers-Pehrson
511
512 This document is released under the libpng license.
513 For conditions of distribution and use, see the disclaimer
514 and license in png.h
515
516 Based on:
517
518 libpng versions 0.97, January 1998, through 1.6.17 - March 26, 2015
519 Updated and distributed by Glenn Randers-Pehrson
520 Copyright (c) 1998-2015 Glenn Randers-Pehrson
521
522 libpng 1.0 beta 6 - version 0.96 - May 28, 1997
523 Updated and distributed by Andreas Dilger
524 Copyright (c) 1996, 1997 Andreas Dilger
525
526 libpng 1.0 beta 2 - version 0.88 - January 26, 1996
527 For conditions of distribution and use, see copyright
528 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
529 Schalnat, Group 42, Inc.
530
531 Updated/rewritten per request in the libpng FAQ
532 Copyright (c) 1995, 1996 Frank J. T. Wojcik
533 December 18, 1995 & January 20, 1996
534
535 TABLE OF CONTENTS
536
537 I. Introduction
538 II. Structures
539 III. Reading
540 IV. Writing
541 V. Simplified API
542 VI. Modifying/Customizing libpng
543 VII. MNG support
544 VIII. Changes to Libpng from version 0.88
545 IX. Changes to Libpng from version 1.0.x to 1.2.x
546 X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
547 XI. Changes to Libpng from version 1.4.x to 1.5.x
548 XII. Changes to Libpng from version 1.5.x to 1.6.x
549 XIII. Detecting libpng
550 XIV. Source code repository
551 XV. Coding style
552 XVI. Y2K Compliance in libpng
553
554.SH I. Introduction
555
556This file describes how to use and modify the PNG reference library
557(known as libpng) for your own use. In addition to this
558file, example.c is a good starting point for using the library, as
559it is heavily commented and should include everything most people
560will need. We assume that libpng is already installed; see the
561INSTALL file for instructions on how to configure and install libpng.
562
563For examples of libpng usage, see the files "example.c", "pngtest.c",
564and the files in the "contrib" directory, all of which are included in
565the libpng distribution.
566
567Libpng was written as a companion to the PNG specification, as a way
568of reducing the amount of time and effort it takes to support the PNG
569file format in application programs.
570
571The PNG specification (second edition), November 2003, is available as
572a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
573<http://www.w3.org/TR/2003/REC-PNG-20031110/
574The W3C and ISO documents have identical technical content.
575
576The PNG-1.2 specification is available at
577<http://www.libpng.org/pub/png/documents/>. It is technically equivalent
578to the PNG specification (second edition) but has some additional material.
579
580The PNG-1.0 specification is available
581as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
582W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
583
584Some additional chunks are described in the special-purpose public chunks
585documents at <http://www.libpng.org/pub/png/documents/>.
586
587Other information
588about PNG, and the latest version of libpng, can be found at the PNG home
589page, <http://www.libpng.org/pub/png/>.
590
591Most users will not have to modify the library significantly; advanced
592users may want to modify it more. All attempts were made to make it as
593complete as possible, while keeping the code easy to understand.
594Currently, this library only supports C. Support for other languages
595is being considered.
596
597Libpng has been designed to handle multiple sessions at one time,
598to be easily modifiable, to be portable to the vast majority of
599machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
600to use. The ultimate goal of libpng is to promote the acceptance of
601the PNG file format in whatever way possible. While there is still
602work to be done (see the TODO file), libpng should cover the
603majority of the needs of its users.
604
605Libpng uses zlib for its compression and decompression of PNG files.
606Further information about zlib, and the latest version of zlib, can
607be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
608The zlib compression utility is a general purpose utility that is
609useful for more than PNG files, and can be used without libpng.
610See the documentation delivered with zlib for more details.
611You can usually find the source files for the zlib utility wherever you
612find the libpng source files.
613
614Libpng is thread safe, provided the threads are using different
615instances of the structures. Each thread should have its own
616png_struct and png_info instances, and thus its own image.
617Libpng does not protect itself against two threads using the
618same instance of a structure.
619
620.SH II. Structures
621
622There are two main structures that are important to libpng, png_struct
623and png_info. Both are internal structures that are no longer exposed
624in the libpng interface (as of libpng 1.5.0).
625
626The png_info structure is designed to provide information about the
627PNG file. At one time, the fields of png_info were intended to be
628directly accessible to the user. However, this tended to cause problems
629with applications using dynamically loaded libraries, and as a result
630a set of interface functions for png_info (the png_get_*() and png_set_*()
631functions) was developed, and direct access to the png_info fields was
632deprecated..
633
634The png_struct structure is the object used by the library to decode a
635single image. As of 1.5.0 this structure is also not exposed.
636
637Almost all libpng APIs require a pointer to a png_struct as the first argument.
638Many (in particular the png_set and png_get APIs) also require a pointer
639to png_info as the second argument. Some application visible macros
640defined in png.h designed for basic data access (reading and writing
641integers in the PNG format) don't take a png_info pointer, but it's almost
642always safe to assume that a (png_struct*) has to be passed to call an API
643function.
644
645You can have more than one png_info structure associated with an image,
646as illustrated in pngtest.c, one for information valid prior to the
647IDAT chunks and another (called "end_info" below) for things after them.
648
649The png.h header file is an invaluable reference for programming with libpng.
650And while I'm on the topic, make sure you include the libpng header file:
651
652#include <png.h>
653
654and also (as of libpng-1.5.0) the zlib header file, if you need it:
655
656#include <zlib.h>
657
658.SS Types
659
660The png.h header file defines a number of integral types used by the
661APIs. Most of these are fairly obvious; for example types corresponding
662to integers of particular sizes and types for passing color values.
663
664One exception is how non-integral numbers are handled. For application
665convenience most APIs that take such numbers have C (double) arguments;
666however, internally PNG, and libpng, use 32 bit signed integers and encode
667the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
668macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
669which is simply (png_int_32).
670
671All APIs that take (double) arguments also have a matching API that
672takes the corresponding fixed point integer arguments. The fixed point
673API has the same name as the floating point one with "_fixed" appended.
674The actual range of values permitted in the APIs is frequently less than
675the full range of (png_fixed_point) (\-21474 to +21474). When APIs require
676a non-negative argument the type is recorded as png_uint_32 above. Consult
677the header file and the text below for more information.
678
679Special care must be take with sCAL chunk handling because the chunk itself
680uses non-integral values encoded as strings containing decimal floating point
681numbers. See the comments in the header file.
682
683.SS Configuration
684
685The main header file function declarations are frequently protected by C
686preprocessing directives of the form:
687
688 #ifdef PNG_feature_SUPPORTED
689 declare-function
690 #endif
691 ...
692 #ifdef PNG_feature_SUPPORTED
693 use-function
694 #endif
695
696The library can be built without support for these APIs, although a
697standard build will have all implemented APIs. Application programs
698should check the feature macros before using an API for maximum
699portability. From libpng 1.5.0 the feature macros set during the build
700of libpng are recorded in the header file "pnglibconf.h" and this file
701is always included by png.h.
702
703If you don't need to change the library configuration from the default, skip to
704the next section ("Reading").
705
706Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
707of the build project files in the 'projects' directory simply copy
708scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
709systems do not permit easy auto-configuration of the library - they only
710support the default configuration.
711
712The easiest way to make minor changes to the libpng configuration when
713auto-configuration is supported is to add definitions to the command line
714using (typically) CPPFLAGS. For example:
715
716CPPFLAGS=\-DPNG_NO_FLOATING_ARITHMETIC
717
718will change the internal libpng math implementation for gamma correction and
719other arithmetic calculations to fixed point, avoiding the need for fast
720floating point support. The result can be seen in the generated pnglibconf.h -
721make sure it contains the changed feature macro setting.
722
723If you need to make more extensive configuration changes - more than one or two
724feature macro settings - you can either add \-DPNG_USER_CONFIG to the build
725command line and put a list of feature macro settings in pngusr.h or you can set
726DFA_XTRA (a makefile variable) to a file containing the same information in the
727form of 'option' settings.
728
729A. Changing pnglibconf.h
730
731A variety of methods exist to build libpng. Not all of these support
732reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
733rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
734
735Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
736pnglibconf.h and changing the lines defining the supported features, paying
737very close attention to the 'option' information in scripts/pnglibconf.dfa
738that describes those features and their requirements. This is easy to get
739wrong.
740
741B. Configuration using DFA_XTRA
742
743Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
744variant such as 'nawk' or 'gawk', is available. The configure build will
745automatically find an appropriate awk and build pnglibconf.h.
746The scripts/pnglibconf.mak file contains a set of make rules for doing the
747same thing if configure is not used, and many of the makefiles in the scripts
748directory use this approach.
749
750When rebuilding simply write a new file containing changed options and set
751DFA_XTRA to the name of this file. This causes the build to append the new file
752to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
753of the following forms:
754
755everything = off
756
757This turns all optional features off. Include it at the start of pngusr.dfa to
758make it easier to build a minimal configuration. You will need to turn at least
759some features on afterward to enable either reading or writing code, or both.
760
761option feature on
762option feature off
763
764Enable or disable a single feature. This will automatically enable other
765features required by a feature that is turned on or disable other features that
766require a feature which is turned off. Conflicting settings will cause an error
767message to be emitted by awk.
768
769setting feature default value
770
771Changes the default value of setting 'feature' to 'value'. There are a small
772number of settings listed at the top of pnglibconf.h, they are documented in the
773source code. Most of these values have performance implications for the library
774but most of them have no visible effect on the API. Some can also be overridden
775from the API.
776
777This method of building a customized pnglibconf.h is illustrated in
778contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
779pngusr.dfa in these directories.
780
781C. Configuration using PNG_USER_CONFIG
782
783If \-DPNG_USER_CONFIG is added to the CPPFLAGS when pnglibconf.h is built,
784the file pngusr.h will automatically be included before the options in
785scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
786macro definitions turning features on or off or setting settings.
787
788Apart from the global setting "everything = off" all the options listed above
789can be set using macros in pngusr.h:
790
791#define PNG_feature_SUPPORTED
792
793is equivalent to:
794
795option feature on
796
797#define PNG_NO_feature
798
799is equivalent to:
800
801option feature off
802
803#define PNG_feature value
804
805is equivalent to:
806
807setting feature default value
808
809Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
810pngusr file you supply override the contents of scripts/pnglibconf.dfa
811
812If confusing or incomprehensible behavior results it is possible to
813examine the intermediate file pnglibconf.dfn to find the full set of
814dependency information for each setting and option. Simply locate the
815feature in the file and read the C comments that precede it.
816
817This method is also illustrated in the contrib/pngminim/* makefiles and
818pngusr.h.
819
820.SH III. Reading
821
822We'll now walk you through the possible functions to call when reading
823in a PNG file sequentially, briefly explaining the syntax and purpose
824of each one. See example.c and png.h for more detail. While
825progressive reading is covered in the next section, you will still
826need some of the functions discussed in this section to read a PNG
827file.
828
829.SS Setup
830
831You will want to do the I/O initialization(*) before you get into libpng,
832so if it doesn't work, you don't have much to undo. Of course, you
833will also want to insure that you are, in fact, dealing with a PNG
834file. Libpng provides a simple check to see if a file is a PNG file.
835To use it, pass in the first 1 to 8 bytes of the file to the function
836png_sig_cmp(), and it will return 0 (false) if the bytes match the
837corresponding bytes of the PNG signature, or nonzero (true) otherwise.
838Of course, the more bytes you pass in, the greater the accuracy of the
839prediction.
840
841If you are intending to keep the file pointer open for use in libpng,
842you must ensure you don't read more than 8 bytes from the beginning
843of the file, and you also have to make a call to png_set_sig_bytes()
844with the number of bytes you read from the beginning. Libpng will
845then only check the bytes (if any) that your program didn't read.
846
847(*): If you are not using the standard I/O functions, you will need
848to replace them with custom functions. See the discussion under
849Customizing libpng.
850
851 FILE *fp = fopen(file_name, "rb");
852 if (!fp)
853 {
854 return (ERROR);
855 }
856
857 if (fread(header, 1, number, fp) != number)
858 {
859 return (ERROR);
860 }
861
862 is_png = !png_sig_cmp(header, 0, number);
863 if (!is_png)
864 {
865 return (NOT_PNG);
866 }
867
868Next, png_struct and png_info need to be allocated and initialized. In
869order to ensure that the size of these structures is correct even with a
870dynamically linked libpng, there are functions to initialize and
871allocate the structures. We also pass the library version, optional
872pointers to error handling functions, and a pointer to a data struct for
873use by the error functions, if necessary (the pointer and functions can
874be NULL if the default error handlers are to be used). See the section
875on Changes to Libpng below regarding the old initialization functions.
876The structure allocation functions quietly return NULL if they fail to
877create the structure, so your application should check for that.
878
879 png_structp png_ptr = png_create_read_struct
880 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
881 user_error_fn, user_warning_fn);
882
883 if (!png_ptr)
884 return (ERROR);
885
886 png_infop info_ptr = png_create_info_struct(png_ptr);
887
888 if (!info_ptr)
889 {
890 png_destroy_read_struct(&png_ptr,
891 (png_infopp)NULL, (png_infopp)NULL);
892 return (ERROR);
893 }
894
895If you want to use your own memory allocation routines,
896use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
897png_create_read_struct_2() instead of png_create_read_struct():
898
899 png_structp png_ptr = png_create_read_struct_2
900 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
901 user_error_fn, user_warning_fn, (png_voidp)
902 user_mem_ptr, user_malloc_fn, user_free_fn);
903
904The error handling routines passed to png_create_read_struct()
905and the memory alloc/free routines passed to png_create_struct_2()
906are only necessary if you are not using the libpng supplied error
907handling and memory alloc/free functions.
908
909When libpng encounters an error, it expects to longjmp back
910to your routine. Therefore, you will need to call setjmp and pass
911your png_jmpbuf(png_ptr). If you read the file from different
912routines, you will need to update the longjmp buffer every time you enter
913a new routine that will call a png_*() function.
914
915See your documentation of setjmp/longjmp for your compiler for more
916information on setjmp/longjmp. See the discussion on libpng error
917handling in the Customizing Libpng section below for more information
918on the libpng error handling. If an error occurs, and libpng longjmp's
919back to your setjmp, you will want to call png_destroy_read_struct() to
920free any memory.
921
922 if (setjmp(png_jmpbuf(png_ptr)))
923 {
924 png_destroy_read_struct(&png_ptr, &info_ptr,
925 &end_info);
926 fclose(fp);
927 return (ERROR);
928 }
929
930Pass (png_infopp)NULL instead of &end_info if you didn't create
931an end_info structure.
932
933If you would rather avoid the complexity of setjmp/longjmp issues,
934you can compile libpng with PNG_NO_SETJMP, in which case
935errors will result in a call to PNG_ABORT() which defaults to abort().
936
937You can #define PNG_ABORT() to a function that does something
938more useful than abort(), as long as your function does not
939return.
940
941Now you need to set up the input code. The default for libpng is to
942use the C function fread(). If you use this, you will need to pass a
943valid FILE * in the function png_init_io(). Be sure that the file is
944opened in binary mode. If you wish to handle reading data in another
945way, you need not call the png_init_io() function, but you must then
946implement the libpng I/O methods discussed in the Customizing Libpng
947section below.
948
949 png_init_io(png_ptr, fp);
950
951If you had previously opened the file and read any of the signature from
952the beginning in order to see if this was a PNG file, you need to let
953libpng know that there are some bytes missing from the start of the file.
954
955 png_set_sig_bytes(png_ptr, number);
956
957You can change the zlib compression buffer size to be used while
958reading compressed data with
959
960 png_set_compression_buffer_size(png_ptr, buffer_size);
961
962where the default size is 8192 bytes. Note that the buffer size
963is changed immediately and the buffer is reallocated immediately,
964instead of setting a flag to be acted upon later.
965
966If you want CRC errors to be handled in a different manner than
967the default, use
968
969 png_set_crc_action(png_ptr, crit_action, ancil_action);
970
971The values for png_set_crc_action() say how libpng is to handle CRC errors in
972ancillary and critical chunks, and whether to use the data contained
973therein. Note that it is impossible to "discard" data in a critical
974chunk.
975
976Choices for (int) crit_action are
977 PNG_CRC_DEFAULT 0 error/quit
978 PNG_CRC_ERROR_QUIT 1 error/quit
979 PNG_CRC_WARN_USE 3 warn/use data
980 PNG_CRC_QUIET_USE 4 quiet/use data
981 PNG_CRC_NO_CHANGE 5 use the current value
982
983Choices for (int) ancil_action are
984 PNG_CRC_DEFAULT 0 error/quit
985 PNG_CRC_ERROR_QUIT 1 error/quit
986 PNG_CRC_WARN_DISCARD 2 warn/discard data
987 PNG_CRC_WARN_USE 3 warn/use data
988 PNG_CRC_QUIET_USE 4 quiet/use data
989 PNG_CRC_NO_CHANGE 5 use the current value
990
991.SS Setting up callback code
992
993You can set up a callback function to handle any unknown chunks in the
994input stream. You must supply the function
995
996 read_chunk_callback(png_structp png_ptr,
997 png_unknown_chunkp chunk);
998 {
999 /* The unknown chunk structure contains your
1000 chunk data, along with similar data for any other
1001 unknown chunks: */
1002
1003 png_byte name[5];
1004 png_byte *data;
1005 png_size_t size;
1006
1007 /* Note that libpng has already taken care of
1008 the CRC handling */
1009
1010 /* put your code here. Search for your chunk in the
1011 unknown chunk structure, process it, and return one
1012 of the following: */
1013
1014 return (\-n); /* chunk had an error */
1015 return (0); /* did not recognize */
1016 return (n); /* success */
1017 }
1018
1019(You can give your function another name that you like instead of
1020"read_chunk_callback")
1021
1022To inform libpng about your function, use
1023
1024 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1025 read_chunk_callback);
1026
1027This names not only the callback function, but also a user pointer that
1028you can retrieve with
1029
1030 png_get_user_chunk_ptr(png_ptr);
1031
1032If you call the png_set_read_user_chunk_fn() function, then all unknown
1033chunks which the callback does not handle will be saved when read. You can
1034cause them to be discarded by returning '1' ("handled") instead of '0'. This
1035behavior will change in libpng 1.7 and the default handling set by the
1036png_set_keep_unknown_chunks() function, described below, will be used when the
1037callback returns 0. If you want the existing behavior you should set the global
1038default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
1039versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the
1040default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
1041
1042At this point, you can set up a callback function that will be
1043called after each row has been read, which you can use to control
1044a progress meter or the like. It's demonstrated in pngtest.c.
1045You must supply a function
1046
1047 void read_row_callback(png_structp png_ptr,
1048 png_uint_32 row, int pass);
1049 {
1050 /* put your code here */
1051 }
1052
1053(You can give it another name that you like instead of "read_row_callback")
1054
1055To inform libpng about your function, use
1056
1057 png_set_read_status_fn(png_ptr, read_row_callback);
1058
1059When this function is called the row has already been completely processed and
1060the 'row' and 'pass' refer to the next row to be handled. For the
1061non-interlaced case the row that was just handled is simply one less than the
1062passed in row number, and pass will always be 0. For the interlaced case the
1063same applies unless the row value is 0, in which case the row just handled was
1064the last one from one of the preceding passes. Because interlacing may skip a
1065pass you cannot be sure that the preceding pass is just 'pass\-1', if you really
1066need to know what the last pass is record (row,pass) from the callback and use
1067the last recorded value each time.
1068
1069As with the user transform you can find the output row using the
1070PNG_ROW_FROM_PASS_ROW macro.
1071
1072.SS Unknown-chunk handling
1073
1074Now you get to set the way the library processes unknown chunks in the
1075input PNG stream. Both known and unknown chunks will be read. Normal
1076behavior is that known chunks will be parsed into information in
1077various info_ptr members while unknown chunks will be discarded. This
1078behavior can be wasteful if your application will never use some known
1079chunk types. To change this, you can call:
1080
1081 png_set_keep_unknown_chunks(png_ptr, keep,
1082 chunk_list, num_chunks);
1083
1084 keep - 0: default unknown chunk handling
1085 1: ignore; do not keep
1086 2: keep only if safe-to-copy
1087 3: keep even if unsafe-to-copy
1088
1089 You can use these definitions:
1090 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1091 PNG_HANDLE_CHUNK_NEVER 1
1092 PNG_HANDLE_CHUNK_IF_SAFE 2
1093 PNG_HANDLE_CHUNK_ALWAYS 3
1094
1095 chunk_list - list of chunks affected (a byte string,
1096 five bytes per chunk, NULL or '\0' if
1097 num_chunks is positive; ignored if
1098 numchunks <= 0).
1099
1100 num_chunks - number of chunks affected; if 0, all
1101 unknown chunks are affected. If positive,
1102 only the chunks in the list are affected,
1103 and if negative all unknown chunks and
1104 all known chunks except for the IHDR,
1105 PLTE, tRNS, IDAT, and IEND chunks are
1106 affected.
1107
1108Unknown chunks declared in this way will be saved as raw data onto a
1109list of png_unknown_chunk structures. If a chunk that is normally
1110known to libpng is named in the list, it will be handled as unknown,
1111according to the "keep" directive. If a chunk is named in successive
1112instances of png_set_keep_unknown_chunks(), the final instance will
1113take precedence. The IHDR and IEND chunks should not be named in
1114chunk_list; if they are, libpng will process them normally anyway.
1115If you know that your application will never make use of some particular
1116chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
1117
1118Here is an example of the usage of png_set_keep_unknown_chunks(),
1119where the private "vpAg" chunk will later be processed by a user chunk
1120callback function:
1121
1122 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1123
1124 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1125 png_byte unused_chunks[]=
1126 {
1127 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1128 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1129 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1130 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1131 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1132 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1133 };
1134 #endif
1135
1136 ...
1137
1138 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1139 /* ignore all unknown chunks
1140 * (use global setting "2" for libpng16 and earlier):
1141 */
1142 png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
1143
1144 /* except for vpAg: */
1145 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1146
1147 /* also ignore unused known chunks: */
1148 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1149 (int)(sizeof unused_chunks)/5);
1150 #endif
1151
1152.SS User limits
1153
1154The PNG specification allows the width and height of an image to be as
1155large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns.
1156Larger images will be rejected immediately with a png_error() call. If
1157you wish to change these limits, you can use
1158
1159 png_set_user_limits(png_ptr, width_max, height_max);
1160
1161to set your own limits (libpng may reject some very wide images
1162anyway because of potential buffer overflow conditions).
1163
1164You should put this statement after you create the PNG structure and
1165before calling png_read_info(), png_read_png(), or png_process_data().
1166
1167When writing a PNG datastream, put this statement before calling
1168png_write_info() or png_write_png().
1169
1170If you need to retrieve the limits that are being applied, use
1171
1172 width_max = png_get_user_width_max(png_ptr);
1173 height_max = png_get_user_height_max(png_ptr);
1174
1175The PNG specification sets no limit on the number of ancillary chunks
1176allowed in a PNG datastream. You can impose a limit on the total number
1177of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1178
1179 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1180
1181where 0x7fffffffL means unlimited. You can retrieve this limit with
1182
1183 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1184
1185You can also set a limit on the amount of memory that a compressed chunk
1186other than IDAT can occupy, with
1187
1188 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1189
1190and you can retrieve the limit with
1191
1192 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1193
1194Any chunks that would cause either of these limits to be exceeded will
1195be ignored.
1196
1197.SS Information about your system
1198
1199If you intend to display the PNG or to incorporate it in other image data you
1200need to tell libpng information about your display or drawing surface so that
1201libpng can convert the values in the image to match the display.
1202
1203From libpng-1.5.4 this information can be set before reading the PNG file
1204header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1205called before the PNG file header had been read and png_set_alpha_mode() did not
1206exist.
1207
1208If you need to support versions prior to libpng-1.5.4 test the version number
1209as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1210described in the appropriate manual page.
1211
1212You give libpng the encoding expected by your system expressed as a 'gamma'
1213value. You can also specify a default encoding for the PNG file in
1214case the required information is missing from the file. By default libpng
1215assumes that the PNG data matches your system, to keep this default call:
1216
1217 png_set_gamma(png_ptr, screen_gamma, output_gamma);
1218
1219or you can use the fixed point equivalent:
1220
1221 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
1222 PNG_FP_1*output_gamma);
1223
1224If you don't know the gamma for your system it is probably 2.2 - a good
1225approximation to the IEC standard for display systems (sRGB). If images are
1226too contrasty or washed out you got the value wrong - check your system
1227documentation!
1228
1229Many systems permit the system gamma to be changed via a lookup table in the
1230display driver, a few systems, including older Macs, change the response by
1231default. As of 1.5.4 three special values are available to handle common
1232situations:
1233
1234 PNG_DEFAULT_sRGB: Indicates that the system conforms to the
1235 IEC 61966-2-1 standard. This matches almost
1236 all systems.
1237 PNG_GAMMA_MAC_18: Indicates that the system is an older
1238 (pre Mac OS 10.6) Apple Macintosh system with
1239 the default settings.
1240 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates
1241 that the system expects data with no gamma
1242 encoding.
1243
1244You would use the linear (unencoded) value if you need to process the pixel
1245values further because this avoids the need to decode and re-encode each
1246component value whenever arithmetic is performed. A lot of graphics software
1247uses linear values for this reason, often with higher precision component values
1248to preserve overall accuracy.
1249
1250
1251The output_gamma value expresses how to decode the output values, not how
1252they are encoded. The values used correspond to the normal numbers used to
1253describe the overall gamma of a computer display system; for example 2.2 for
1254an sRGB conformant system. The values are scaled by 100000 in the _fixed
1255version of the API (so 220000 for sRGB.)
1256
1257The inverse of the value is always used to provide a default for the PNG file
1258encoding if it has no gAMA chunk and if png_set_gamma() has not been called
1259to override the PNG gamma information.
1260
1261When the ALPHA_OPTIMIZED mode is selected the output gamma is used to encode
1262opaque pixels however pixels with lower alpha values are not encoded,
1263regardless of the output gamma setting.
1264
1265When the standard Porter Duff handling is requested with mode 1 the output
1266encoding is set to be linear and the output_gamma value is only relevant
1267as a default for input data that has no gamma information. The linear output
1268encoding will be overridden if png_set_gamma() is called - the results may be
1269highly unexpected!
1270
1271The following numbers are derived from the sRGB standard and the research
1272behind it. sRGB is defined to be approximated by a PNG gAMA chunk value of
12730.45455 (1/2.2) for PNG. The value implicitly includes any viewing
1274correction required to take account of any differences in the color
1275environment of the original scene and the intended display environment; the
1276value expresses how to *decode* the image for display, not how the original
1277data was *encoded*.
1278
1279sRGB provides a peg for the PNG standard by defining a viewing environment.
1280sRGB itself, and earlier TV standards, actually use a more complex transform
1281(a linear portion then a gamma 2.4 power law) than PNG can express. (PNG is
1282limited to simple power laws.) By saying that an image for direct display on
1283an sRGB conformant system should be stored with a gAMA chunk value of 45455
1284(11.3.3.2 and 11.3.3.5 of the ISO PNG specification) the PNG specification
1285makes it possible to derive values for other display systems and
1286environments.
1287
1288The Mac value is deduced from the sRGB based on an assumption that the actual
1289extra viewing correction used in early Mac display systems was implemented as
1290a power 1.45 lookup table.
1291
1292Any system where a programmable lookup table is used or where the behavior of
1293the final display device characteristics can be changed requires system
1294specific code to obtain the current characteristic. However this can be
1295difficult and most PNG gamma correction only requires an approximate value.
1296
1297By default, if png_set_alpha_mode() is not called, libpng assumes that all
1298values are unencoded, linear, values and that the output device also has a
1299linear characteristic. This is only very rarely correct - it is invariably
1300better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the
1301default if you don't know what the right answer is!
1302
1303The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS
130410.6) which used a correction table to implement a somewhat lower gamma on an
1305otherwise sRGB system.
1306
1307Both these values are reserved (not simple gamma values) in order to allow
1308more precise correction internally in the future.
1309
1310NOTE: the values can be passed to either the fixed or floating
1311point APIs, but the floating point API will also accept floating point
1312values.
1313
1314The second thing you may need to tell libpng about is how your system handles
1315alpha channel information. Some, but not all, PNG files contain an alpha
1316channel. To display these files correctly you need to compose the data onto a
1317suitable background, as described in the PNG specification.
1318
1319Libpng only supports composing onto a single color (using png_set_background;
1320see below). Otherwise you must do the composition yourself and, in this case,
1321you may need to call png_set_alpha_mode:
1322
1323 #if PNG_LIBPNG_VER >= 10504
1324 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1325 #else
1326 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1327 #endif
1328
1329The screen_gamma value is the same as the argument to png_set_gamma; however,
1330how it affects the output depends on the mode. png_set_alpha_mode() sets the
1331file gamma default to 1/screen_gamma, so normally you don't need to call
1332png_set_gamma. If you need different defaults call png_set_gamma() before
1333png_set_alpha_mode() - if you call it after it will override the settings made
1334by png_set_alpha_mode().
1335
1336The mode is as follows:
1337
1338 PNG_ALPHA_PNG: The data is encoded according to the PNG
1339specification. Red, green and blue, or gray, components are
1340gamma encoded color values and are not premultiplied by the
1341alpha value. The alpha value is a linear measure of the
1342contribution of the pixel to the corresponding final output pixel.
1343
1344You should normally use this format if you intend to perform
1345color correction on the color values; most, maybe all, color
1346correction software has no handling for the alpha channel and,
1347anyway, the math to handle pre-multiplied component values is
1348unnecessarily complex.
1349
1350Before you do any arithmetic on the component values you need
1351to remove the gamma encoding and multiply out the alpha
1352channel. See the PNG specification for more detail. It is
1353important to note that when an image with an alpha channel is
1354scaled, linear encoded, pre-multiplied component values must
1355be used!
1356
1357The remaining modes assume you don't need to do any further color correction or
1358that if you do, your color correction software knows all about alpha (it
1359probably doesn't!). They 'associate' the alpha with the color information by
1360storing color channel values that have been scaled by the alpha. The
1361advantage is that the color channels can be resampled (the image can be
1362scaled) in this form. The disadvantage is that normal practice is to store
1363linear, not (gamma) encoded, values and this requires 16-bit channels for
1364still images rather than the 8-bit channels that are just about sufficient if
1365gamma encoding is used. In addition all non-transparent pixel values,
1366including completely opaque ones, must be gamma encoded to produce the final
1367image. These are the 'STANDARD', 'ASSOCIATED' or 'PREMULTIPLIED' modes
1368described below (the latter being the two common names for associated alpha
1369color channels). Note that PNG files always contain non-associated color
1370channels; png_set_alpha_mode() with one of the modes causes the decoder to
1371convert the pixels to an associated form before returning them to your
1372application.
1373
1374Since it is not necessary to perform arithmetic on opaque color values so
1375long as they are not to be resampled and are in the final color space it is
1376possible to optimize the handling of alpha by storing the opaque pixels in
1377the PNG format (adjusted for the output color space) while storing partially
1378opaque pixels in the standard, linear, format. The accuracy required for
1379standard alpha composition is relatively low, because the pixels are
1380isolated, therefore typically the accuracy loss in storing 8-bit linear
1381values is acceptable. (This is not true if the alpha channel is used to
1382simulate transparency over large areas - use 16 bits or the PNG mode in
1383this case!) This is the 'OPTIMIZED' mode. For this mode a pixel is
1384treated as opaque only if the alpha value is equal to the maximum value.
1385
1386 PNG_ALPHA_STANDARD: The data libpng produces is encoded in the
1387standard way assumed by most correctly written graphics software.
1388The gamma encoding will be removed by libpng and the
1389linear component values will be pre-multiplied by the
1390alpha channel.
1391
1392With this format the final image must be re-encoded to
1393match the display gamma before the image is displayed.
1394If your system doesn't do that, yet still seems to
1395perform arithmetic on the pixels without decoding them,
1396it is broken - check out the modes below.
1397
1398With PNG_ALPHA_STANDARD libpng always produces linear
1399component values, whatever screen_gamma you supply. The
1400screen_gamma value is, however, used as a default for
1401the file gamma if the PNG file has no gamma information.
1402
1403If you call png_set_gamma() after png_set_alpha_mode() you
1404will override the linear encoding. Instead the
1405pre-multiplied pixel values will be gamma encoded but
1406the alpha channel will still be linear. This may
1407actually match the requirements of some broken software,
1408but it is unlikely.
1409
1410While linear 8-bit data is often used it has
1411insufficient precision for any image with a reasonable
1412dynamic range. To avoid problems, and if your software
1413supports it, use png_set_expand_16() to force all
1414components to 16 bits.
1415
1416 PNG_ALPHA_OPTIMIZED: This mode is the same as PNG_ALPHA_STANDARD
1417except that completely opaque pixels are gamma encoded according to
1418the screen_gamma value. Pixels with alpha less than 1.0
1419will still have linear components.
1420
1421Use this format if you have control over your
1422compositing software and so don't do other arithmetic
1423(such as scaling) on the data you get from libpng. Your
1424compositing software can simply copy opaque pixels to
1425the output but still has linear values for the
1426non-opaque pixels.
1427
1428In normal compositing, where the alpha channel encodes
1429partial pixel coverage (as opposed to broad area
1430translucency), the inaccuracies of the 8-bit
1431representation of non-opaque pixels are irrelevant.
1432
1433You can also try this format if your software is broken;
1434it might look better.
1435
1436 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; however, all component
1437values, including the alpha channel are gamma encoded. This is
1438broken because, in practice, no implementation that uses this choice
1439correctly undoes the encoding before handling alpha composition. Use this
1440choice only if other serious errors in the software or hardware you use
1441mandate it. In most cases of broken software or hardware the bug in the
1442final display manifests as a subtle halo around composited parts of the
1443image. You may not even perceive this as a halo; the composited part of
1444the image may simply appear separate from the background, as though it had
1445been cut out of paper and pasted on afterward.
1446
1447If you don't have to deal with bugs in software or hardware, or if you can fix
1448them, there are three recommended ways of using png_set_alpha_mode():
1449
1450 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1451 screen_gamma);
1452
1453You can do color correction on the result (libpng does not currently
1454support color correction internally). When you handle the alpha channel
1455you need to undo the gamma encoding and multiply out the alpha.
1456
1457 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1458 screen_gamma);
1459 png_set_expand_16(png_ptr);
1460
1461If you are using the high level interface, don't call png_set_expand_16();
1462instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1463
1464With this mode you can't do color correction, but you can do arithmetic,
1465including composition and scaling, on the data without further processing.
1466
1467 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1468 screen_gamma);
1469
1470You can avoid the expansion to 16-bit components with this mode, but you
1471lose the ability to scale the image or perform other linear arithmetic.
1472All you can do is compose the result onto a matching output. Since this
1473mode is libpng-specific you also need to write your own composition
1474software.
1475
1476The following are examples of calls to png_set_alpha_mode to achieve the
1477required overall gamma correction and, where necessary, alpha
1478premultiplication.
1479
1480 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
1481
1482This is the default libpng handling of the alpha channel - it is not
1483pre-multiplied into the color components. In addition the call states
1484that the output is for a sRGB system and causes all PNG files without gAMA
1485chunks to be assumed to be encoded using sRGB.
1486
1487 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
1488
1489In this case the output is assumed to be something like an sRGB conformant
1490display preceeded by a power-law lookup table of power 1.45. This is how
1491early Mac systems behaved.
1492
1493 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR);
1494
1495This is the classic Jim Blinn approach and will work in academic
1496environments where everything is done by the book. It has the shortcoming
1497of assuming that input PNG data with no gamma information is linear - this
1498is unlikely to be correct unless the PNG files where generated locally.
1499Most of the time the output precision will be so low as to show
1500significant banding in dark areas of the image.
1501
1502 png_set_expand_16(pp);
1503 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_DEFAULT_sRGB);
1504
1505This is a somewhat more realistic Jim Blinn inspired approach. PNG files
1506are assumed to have the sRGB encoding if not marked with a gamma value and
1507the output is always 16 bits per component. This permits accurate scaling
1508and processing of the data. If you know that your input PNG files were
1509generated locally you might need to replace PNG_DEFAULT_sRGB with the
1510correct value for your system.
1511
1512 png_set_alpha_mode(pp, PNG_ALPHA_OPTIMIZED, PNG_DEFAULT_sRGB);
1513
1514If you just need to composite the PNG image onto an existing background
1515and if you control the code that does this you can use the optimization
1516setting. In this case you just copy completely opaque pixels to the
1517output. For pixels that are not completely transparent (you just skip
1518those) you do the composition math using png_composite or png_composite_16
1519below then encode the resultant 8-bit or 16-bit values to match the output
1520encoding.
1521
1522 Other cases
1523
1524If neither the PNG nor the standard linear encoding work for you because
1525of the software or hardware you use then you have a big problem. The PNG
1526case will probably result in halos around the image. The linear encoding
1527will probably result in a washed out, too bright, image (it's actually too
1528contrasty.) Try the ALPHA_OPTIMIZED mode above - this will probably
1529substantially reduce the halos. Alternatively try:
1530
1531 png_set_alpha_mode(pp, PNG_ALPHA_BROKEN, PNG_DEFAULT_sRGB);
1532
1533This option will also reduce the halos, but there will be slight dark
1534halos round the opaque parts of the image where the background is light.
1535In the OPTIMIZED mode the halos will be light halos where the background
1536is dark. Take your pick - the halos are unavoidable unless you can get
1537your hardware/software fixed! (The OPTIMIZED approach is slightly
1538faster.)
1539
1540When the default gamma of PNG files doesn't match the output gamma.
1541If you have PNG files with no gamma information png_set_alpha_mode allows
1542you to provide a default gamma, but it also sets the ouput gamma to the
1543matching value. If you know your PNG files have a gamma that doesn't
1544match the output you can take advantage of the fact that
1545png_set_alpha_mode always sets the output gamma but only sets the PNG
1546default if it is not already set:
1547
1548 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
1549 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
1550
1551The first call sets both the default and the output gamma values, the
1552second call overrides the output gamma without changing the default. This
1553is easier than achieving the same effect with png_set_gamma. You must use
1554PNG_ALPHA_PNG for the first call - internal checking in png_set_alpha will
1555fire if more than one call to png_set_alpha_mode and png_set_background is
1556made in the same read operation, however multiple calls with PNG_ALPHA_PNG
1557are ignored.
1558
1559If you don't need, or can't handle, the alpha channel you can call
1560png_set_background() to remove it by compositing against a fixed color. Don't
1561call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1562transparent parts of this image.
1563
1564 png_set_background(png_ptr, &background_color,
1565 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1566
1567The background_color is an RGB or grayscale value according to the data format
1568libpng will produce for you. Because you don't yet know the format of the PNG
1569file, if you call png_set_background at this point you must arrange for the
1570format produced by libpng to always have 8-bit or 16-bit components and then
1571store the color as an 8-bit or 16-bit color as appropriate. The color contains
1572separate gray and RGB component values, so you can let libpng produce gray or
1573RGB output according to the input format, but low bit depth grayscale images
1574must always be converted to at least 8-bit format. (Even though low bit depth
1575grayscale images can't have an alpha channel they can have a transparent
1576color!)
1577
1578You set the transforms you need later, either as flags to the high level
1579interface or libpng API calls for the low level interface. For reference the
1580settings and API calls required are:
1581
15828-bit values:
1583 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1584 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1585
1586 If you must get exactly the same inaccurate results
1587 produced by default in versions prior to libpng-1.5.4,
1588 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1589 instead.
1590
159116-bit values:
1592 PNG_TRANSFORM_EXPAND_16
1593 png_set_expand_16(png_ptr);
1594
1595In either case palette image data will be expanded to RGB. If you just want
1596color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1597to the list.
1598
1599Calling png_set_background before the PNG file header is read will not work
1600prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1601errors it is therefore much safer to call png_set_background after the head has
1602been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1603used with the high level interface.
1604
1605.SS The high-level read interface
1606
1607At this point there are two ways to proceed; through the high-level
1608read interface, or through a sequence of low-level read operations.
1609You can use the high-level interface if (a) you are willing to read
1610the entire image into memory, and (b) the input transformations
1611you want to do are limited to the following set:
1612
1613 PNG_TRANSFORM_IDENTITY No transformation
1614 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1615 8-bit accurately
1616 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1617 8-bit less accurately
1618 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1619 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1620 samples to bytes
1621 PNG_TRANSFORM_PACKSWAP Change order of packed
1622 pixels to LSB first
1623 PNG_TRANSFORM_EXPAND Perform set_expand()
1624 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1625 PNG_TRANSFORM_SHIFT Normalize pixels to the
1626 sBIT depth
1627 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1628 to BGRA
1629 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1630 to AG
1631 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1632 to transparency
1633 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1634 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1635 to RGB (or GA to RGBA)
1636 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
1637
1638(This excludes setting a background color, doing gamma transformation,
1639quantizing, and setting filler.) If this is the case, simply do this:
1640
1641 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1642
1643where png_transforms is an integer containing the bitwise OR of some
1644set of transformation flags. This call is equivalent to png_read_info(),
1645followed the set of transformations indicated by the transform mask,
1646then png_read_image(), and finally png_read_end().
1647
1648(The final parameter of this call is not yet used. Someday it might point
1649to transformation parameters required by some future input transform.)
1650
1651You must use png_transforms and not call any png_set_transform() functions
1652when you use png_read_png().
1653
1654After you have called png_read_png(), you can retrieve the image data
1655with
1656
1657 row_pointers = png_get_rows(png_ptr, info_ptr);
1658
1659where row_pointers is an array of pointers to the pixel data for each row:
1660
1661 png_bytep row_pointers[height];
1662
1663If you know your image size and pixel size ahead of time, you can allocate
1664row_pointers prior to calling png_read_png() with
1665
1666 if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
1667 png_error (png_ptr,
1668 "Image is too tall to process in memory");
1669
1670 if (width > PNG_UINT_32_MAX/pixel_size)
1671 png_error (png_ptr,
1672 "Image is too wide to process in memory");
1673
1674 row_pointers = png_malloc(png_ptr,
1675 height*(sizeof (png_bytep)));
1676
1677 for (int i=0; i<height, i++)
1678 row_pointers[i]=NULL; /* security precaution */
1679
1680 for (int i=0; i<height, i++)
1681 row_pointers[i]=png_malloc(png_ptr,
1682 width*pixel_size);
1683
1684 png_set_rows(png_ptr, info_ptr, &row_pointers);
1685
1686Alternatively you could allocate your image in one big block and define
1687row_pointers[i] to point into the proper places in your block.
1688
1689If you use png_set_rows(), the application is responsible for freeing
1690row_pointers (and row_pointers[i], if they were separately allocated).
1691
1692If you don't allocate row_pointers ahead of time, png_read_png() will
1693do it, and it'll be free'ed by libpng when you call png_destroy_*().
1694
1695.SS The low-level read interface
1696
1697If you are going the low-level route, you are now ready to read all
1698the file information up to the actual image data. You do this with a
1699call to png_read_info().
1700
1701 png_read_info(png_ptr, info_ptr);
1702
1703This will process all chunks up to but not including the image data.
1704
1705This also copies some of the data from the PNG file into the decode structure
1706for use in later transformations. Important information copied in is:
1707
17081) The PNG file gamma from the gAMA chunk. This overwrites the default value
1709provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1710
17112) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1712damages the information provided by an earlier call to png_set_background
1713resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1714
17153) The number of significant bits in each component value. Libpng uses this to
1716optimize gamma handling by reducing the internal lookup table sizes.
1717
17184) The transparent color information from a tRNS chunk. This can be modified by
1719a later call to png_set_tRNS.
1720
1721.SS Querying the info structure
1722
1723Functions are used to get the information from the info_ptr once it
1724has been read. Note that these fields may not be completely filled
1725in until png_read_end() has read the chunk data following the image.
1726
1727 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1728 &bit_depth, &color_type, &interlace_type,
1729 &compression_type, &filter_method);
1730
1731 width - holds the width of the image
1732 in pixels (up to 2^31).
1733
1734 height - holds the height of the image
1735 in pixels (up to 2^31).
1736
1737 bit_depth - holds the bit depth of one of the
1738 image channels. (valid values are
1739 1, 2, 4, 8, 16 and depend also on
1740 the color_type. See also
1741 significant bits (sBIT) below).
1742
1743 color_type - describes which color/alpha channels
1744 are present.
1745 PNG_COLOR_TYPE_GRAY
1746 (bit depths 1, 2, 4, 8, 16)
1747 PNG_COLOR_TYPE_GRAY_ALPHA
1748 (bit depths 8, 16)
1749 PNG_COLOR_TYPE_PALETTE
1750 (bit depths 1, 2, 4, 8)
1751 PNG_COLOR_TYPE_RGB
1752 (bit_depths 8, 16)
1753 PNG_COLOR_TYPE_RGB_ALPHA
1754 (bit_depths 8, 16)
1755
1756 PNG_COLOR_MASK_PALETTE
1757 PNG_COLOR_MASK_COLOR
1758 PNG_COLOR_MASK_ALPHA
1759
1760 interlace_type - (PNG_INTERLACE_NONE or
1761 PNG_INTERLACE_ADAM7)
1762
1763 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1764 for PNG 1.0)
1765
1766 filter_method - (must be PNG_FILTER_TYPE_BASE
1767 for PNG 1.0, and can also be
1768 PNG_INTRAPIXEL_DIFFERENCING if
1769 the PNG datastream is embedded in
1770 a MNG-1.0 datastream)
1771
1772 Any of width, height, color_type, bit_depth,
1773 interlace_type, compression_type, or filter_method can
1774 be NULL if you are not interested in their values.
1775
1776 Note that png_get_IHDR() returns 32-bit data into
1777 the application's width and height variables.
1778 This is an unsafe situation if these are not png_uint_32
1779 variables. In such situations, the
1780 png_get_image_width() and png_get_image_height()
1781 functions described below are safer.
1782
1783 width = png_get_image_width(png_ptr,
1784 info_ptr);
1785
1786 height = png_get_image_height(png_ptr,
1787 info_ptr);
1788
1789 bit_depth = png_get_bit_depth(png_ptr,
1790 info_ptr);
1791
1792 color_type = png_get_color_type(png_ptr,
1793 info_ptr);
1794
1795 interlace_type = png_get_interlace_type(png_ptr,
1796 info_ptr);
1797
1798 compression_type = png_get_compression_type(png_ptr,
1799 info_ptr);
1800
1801 filter_method = png_get_filter_type(png_ptr,
1802 info_ptr);
1803
1804 channels = png_get_channels(png_ptr, info_ptr);
1805
1806 channels - number of channels of info for the
1807 color type (valid values are 1 (GRAY,
1808 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1809 4 (RGB_ALPHA or RGB + filler byte))
1810
1811 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1812
1813 rowbytes - number of bytes needed to hold a row
1814
1815 signature = png_get_signature(png_ptr, info_ptr);
1816
1817 signature - holds the signature read from the
1818 file (if any). The data is kept in
1819 the same offset it would be if the
1820 whole signature were read (i.e. if an
1821 application had already read in 4
1822 bytes of signature before starting
1823 libpng, the remaining 4 bytes would
1824 be in signature[4] through signature[7]
1825 (see png_set_sig_bytes())).
1826
1827These are also important, but their validity depends on whether the chunk
1828has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1829png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1830data has been read, or zero if it is missing. The parameters to the
1831png_get_<chunk> are set directly if they are simple data types, or a
1832pointer into the info_ptr is returned for any complex types.
1833
1834The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
1835is simply returned to give the application information about how the
1836image was encoded. Libpng itself only does transformations using the file
1837gamma when combining semitransparent pixels with the background color, and,
1838since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels
1839within the simplified API. Libpng also uses the file gamma when converting
1840RGB to gray, beginning with libpng-1.0.5, if the application calls
1841png_set_rgb_to_gray()).
1842
1843 png_get_PLTE(png_ptr, info_ptr, &palette,
1844 &num_palette);
1845
1846 palette - the palette for the file
1847 (array of png_color)
1848
1849 num_palette - number of entries in the palette
1850
1851 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
1852 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
1853
1854 file_gamma - the gamma at which the file is
1855 written (PNG_INFO_gAMA)
1856
1857 int_file_gamma - 100,000 times the gamma at which the
1858 file is written
1859
1860 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
1861 &red_y, &green_x, &green_y, &blue_x, &blue_y)
1862 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z,
1863 &green_X, &green_Y, &green_Z, &blue_X, &blue_Y,
1864 &blue_Z)
1865 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x,
1866 &int_white_y, &int_red_x, &int_red_y,
1867 &int_green_x, &int_green_y, &int_blue_x,
1868 &int_blue_y)
1869 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
1870 &int_red_Z, &int_green_X, &int_green_Y,
1871 &int_green_Z, &int_blue_X, &int_blue_Y,
1872 &int_blue_Z)
1873
1874 {white,red,green,blue}_{x,y}
1875 A color space encoding specified using the
1876 chromaticities of the end points and the
1877 white point. (PNG_INFO_cHRM)
1878
1879 {red,green,blue}_{X,Y,Z}
1880 A color space encoding specified using the
1881 encoding end points - the CIE tristimulus
1882 specification of the intended color of the red,
1883 green and blue channels in the PNG RGB data.
1884 The white point is simply the sum of the three
1885 end points. (PNG_INFO_cHRM)
1886
1887 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1888
1889 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1890 The presence of the sRGB chunk
1891 means that the pixel data is in the
1892 sRGB color space. This chunk also
1893 implies specific values of gAMA and
1894 cHRM.
1895
1896 png_get_iCCP(png_ptr, info_ptr, &name,
1897 &compression_type, &profile, &proflen);
1898
1899 name - The profile name.
1900
1901 compression_type - The compression type; always
1902 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1903 You may give NULL to this argument to
1904 ignore it.
1905
1906 profile - International Color Consortium color
1907 profile data. May contain NULs.
1908
1909 proflen - length of profile data in bytes.
1910
1911 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1912
1913 sig_bit - the number of significant bits for
1914 (PNG_INFO_sBIT) each of the gray,
1915 red, green, and blue channels,
1916 whichever are appropriate for the
1917 given color type (png_color_16)
1918
1919 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1920 &num_trans, &trans_color);
1921
1922 trans_alpha - array of alpha (transparency)
1923 entries for palette (PNG_INFO_tRNS)
1924
1925 num_trans - number of transparent entries
1926 (PNG_INFO_tRNS)
1927
1928 trans_color - graylevel or color sample values of
1929 the single transparent color for
1930 non-paletted images (PNG_INFO_tRNS)
1931
1932 png_get_hIST(png_ptr, info_ptr, &hist);
1933 (PNG_INFO_hIST)
1934
1935 hist - histogram of palette (array of
1936 png_uint_16)
1937
1938 png_get_tIME(png_ptr, info_ptr, &mod_time);
1939
1940 mod_time - time image was last modified
1941 (PNG_VALID_tIME)
1942
1943 png_get_bKGD(png_ptr, info_ptr, &background);
1944
1945 background - background color (of type
1946 png_color_16p) (PNG_VALID_bKGD)
1947 valid 16-bit red, green and blue
1948 values, regardless of color_type
1949
1950 num_comments = png_get_text(png_ptr, info_ptr,
1951 &text_ptr, &num_text);
1952
1953 num_comments - number of comments
1954
1955 text_ptr - array of png_text holding image
1956 comments
1957
1958 text_ptr[i].compression - type of compression used
1959 on "text" PNG_TEXT_COMPRESSION_NONE
1960 PNG_TEXT_COMPRESSION_zTXt
1961 PNG_ITXT_COMPRESSION_NONE
1962 PNG_ITXT_COMPRESSION_zTXt
1963
1964 text_ptr[i].key - keyword for comment. Must contain
1965 1-79 characters.
1966
1967 text_ptr[i].text - text comments for current
1968 keyword. Can be empty.
1969
1970 text_ptr[i].text_length - length of text string,
1971 after decompression, 0 for iTXt
1972
1973 text_ptr[i].itxt_length - length of itxt string,
1974 after decompression, 0 for tEXt/zTXt
1975
1976 text_ptr[i].lang - language of comment (empty
1977 string for unknown).
1978
1979 text_ptr[i].lang_key - keyword in UTF-8
1980 (empty string for unknown).
1981
1982 Note that the itxt_length, lang, and lang_key
1983 members of the text_ptr structure only exist when the
1984 library is built with iTXt chunk support. Prior to
1985 libpng-1.4.0 the library was built by default without
1986 iTXt support. Also note that when iTXt is supported,
1987 they contain NULL pointers when the "compression"
1988 field contains PNG_TEXT_COMPRESSION_NONE or
1989 PNG_TEXT_COMPRESSION_zTXt.
1990
1991 num_text - number of comments (same as
1992 num_comments; you can put NULL here
1993 to avoid the duplication)
1994
1995 Note while png_set_text() will accept text, language,
1996 and translated keywords that can be NULL pointers, the
1997 structure returned by png_get_text will always contain
1998 regular zero-terminated C strings. They might be
1999 empty strings but they will never be NULL pointers.
2000
2001 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
2002 &palette_ptr);
2003
2004 num_spalettes - number of sPLT chunks read.
2005
2006 palette_ptr - array of palette structures holding
2007 contents of one or more sPLT chunks
2008 read.
2009
2010 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
2011 &unit_type);
2012
2013 offset_x - positive offset from the left edge
2014 of the screen (can be negative)
2015
2016 offset_y - positive offset from the top edge
2017 of the screen (can be negative)
2018
2019 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2020
2021 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
2022 &unit_type);
2023
2024 res_x - pixels/unit physical resolution in
2025 x direction
2026
2027 res_y - pixels/unit physical resolution in
2028 x direction
2029
2030 unit_type - PNG_RESOLUTION_UNKNOWN,
2031 PNG_RESOLUTION_METER
2032
2033 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
2034 &height)
2035
2036 unit - physical scale units (an integer)
2037
2038 width - width of a pixel in physical scale units
2039
2040 height - height of a pixel in physical scale units
2041 (width and height are doubles)
2042
2043 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
2044 &height)
2045
2046 unit - physical scale units (an integer)
2047
2048 width - width of a pixel in physical scale units
2049 (expressed as a string)
2050
2051 height - height of a pixel in physical scale units
2052 (width and height are strings like "2.54")
2053
2054 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
2055 info_ptr, &unknowns)
2056
2057 unknowns - array of png_unknown_chunk
2058 structures holding unknown chunks
2059
2060 unknowns[i].name - name of unknown chunk
2061
2062 unknowns[i].data - data of unknown chunk
2063
2064 unknowns[i].size - size of unknown chunk's data
2065
2066 unknowns[i].location - position of chunk in file
2067
2068 The value of "i" corresponds to the order in which the
2069 chunks were read from the PNG file or inserted with the
2070 png_set_unknown_chunks() function.
2071
2072 The value of "location" is a bitwise "or" of
2073
2074 PNG_HAVE_IHDR (0x01)
2075 PNG_HAVE_PLTE (0x02)
2076 PNG_AFTER_IDAT (0x08)
2077
2078The data from the pHYs chunk can be retrieved in several convenient
2079forms:
2080
2081 res_x = png_get_x_pixels_per_meter(png_ptr,
2082 info_ptr)
2083
2084 res_y = png_get_y_pixels_per_meter(png_ptr,
2085 info_ptr)
2086
2087 res_x_and_y = png_get_pixels_per_meter(png_ptr,
2088 info_ptr)
2089
2090 res_x = png_get_x_pixels_per_inch(png_ptr,
2091 info_ptr)
2092
2093 res_y = png_get_y_pixels_per_inch(png_ptr,
2094 info_ptr)
2095
2096 res_x_and_y = png_get_pixels_per_inch(png_ptr,
2097 info_ptr)
2098
2099 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
2100 info_ptr)
2101
2102 Each of these returns 0 [signifying "unknown"] if
2103 the data is not present or if res_x is 0;
2104 res_x_and_y is 0 if res_x != res_y
2105
2106 Note that because of the way the resolutions are
2107 stored internally, the inch conversions won't
2108 come out to exactly even number. For example,
2109 72 dpi is stored as 0.28346 pixels/meter, and
2110 when this is retrieved it is 71.9988 dpi, so
2111 be sure to round the returned value appropriately
2112 if you want to display a reasonable-looking result.
2113
2114The data from the oFFs chunk can be retrieved in several convenient
2115forms:
2116
2117 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
2118
2119 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
2120
2121 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
2122
2123 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
2124
2125 Each of these returns 0 [signifying "unknown" if both
2126 x and y are 0] if the data is not present or if the
2127 chunk is present but the unit is the pixel. The
2128 remark about inexact inch conversions applies here
2129 as well, because a value in inches can't always be
2130 converted to microns and back without some loss
2131 of precision.
2132
2133For more information, see the
2134PNG specification for chunk contents. Be careful with trusting
2135rowbytes, as some of the transformations could increase the space
2136needed to hold a row (expand, filler, gray_to_rgb, etc.).
2137See png_read_update_info(), below.
2138
2139A quick word about text_ptr and num_text. PNG stores comments in
2140keyword/text pairs, one pair per chunk, with no limit on the number
2141of text chunks, and a 2^31 byte limit on their size. While there are
2142suggested keywords, there is no requirement to restrict the use to these
2143strings. It is strongly suggested that keywords and text be sensible
2144to humans (that's the point), so don't use abbreviations. Non-printing
2145symbols are not allowed. See the PNG specification for more details.
2146There is also no requirement to have text after the keyword.
2147
2148Keywords should be limited to 79 Latin-1 characters without leading or
2149trailing spaces, but non-consecutive spaces are allowed within the
2150keyword. It is possible to have the same keyword any number of times.
2151The text_ptr is an array of png_text structures, each holding a
2152pointer to a language string, a pointer to a keyword and a pointer to
2153a text string. The text string, language code, and translated
2154keyword may be empty or NULL pointers. The keyword/text
2155pairs are put into the array in the order that they are received.
2156However, some or all of the text chunks may be after the image, so, to
2157make sure you have read all the text chunks, don't mess with these
2158until after you read the stuff after the image. This will be
2159mentioned again below in the discussion that goes with png_read_end().
2160
2161.SS Input transformations
2162
2163After you've read the header information, you can set up the library
2164to handle any special transformations of the image data. The various
2165ways to transform the data will be described in the order that they
2166should occur. This is important, as some of these change the color
2167type and/or bit depth of the data, and some others only work on
2168certain color types and bit depths.
2169
2170Transformations you request are ignored if they don't have any meaning for a
2171particular input data format. However some transformations can have an effect
2172as a result of a previous transformation. If you specify a contradictory set of
2173transformations, for example both adding and removing the alpha channel, you
2174cannot predict the final result.
2175
2176The color used for the transparency values should be supplied in the same
2177format/depth as the current image data. It is stored in the same format/depth
2178as the image data in a tRNS chunk, so this is what libpng expects for this data.
2179
2180The color used for the background value depends on the need_expand argument as
2181described below.
2182
2183Data will be decoded into the supplied row buffers packed into bytes
2184unless the library has been told to transform it into another format.
2185For example, 4 bit/pixel paletted or grayscale data will be returned
21862 pixels/byte with the leftmost pixel in the high-order bits of the
2187byte, unless png_set_packing() is called. 8-bit RGB data will be stored
2188in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2189is called to insert filler bytes, either before or after each RGB triplet.
219016-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
2191byte of the color value first, unless png_set_scale_16() is called to
2192transform it to regular RGB RGB triplets, or png_set_filler() or
2193png_set_add alpha() is called to insert filler bytes, either before or
2194after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
2195be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
2196or png_set_scale_16().
2197
2198The following code transforms grayscale images of less than 8 to 8 bits,
2199changes paletted images to RGB, and adds a full alpha channel if there is
2200transparency information in a tRNS chunk. This is most useful on
2201grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2202viewing application that wishes to treat all images in the same way.
2203
2204 if (color_type == PNG_COLOR_TYPE_PALETTE)
2205 png_set_palette_to_rgb(png_ptr);
2206
2207 if (png_get_valid(png_ptr, info_ptr,
2208 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2209
2210 if (color_type == PNG_COLOR_TYPE_GRAY &&
2211 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2212
2213The first two functions are actually aliases for png_set_expand(), added
2214in libpng version 1.0.4, with the function names expanded to improve code
2215readability. In some future version they may actually do different
2216things.
2217
2218As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2219added. It expands the sample depth without changing tRNS to alpha.
2220
2221As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2222png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2223Use this when the output color or gray channels are made linear to avoid fairly
2224severe accuracy loss.
2225
2226 if (bit_depth < 16)
2227 png_set_expand_16(png_ptr);
2228
2229PNG can have files with 16 bits per channel. If you only can handle
22308 bits per channel, this will strip the pixels down to 8-bit.
2231
2232 if (bit_depth == 16)
2233#if PNG_LIBPNG_VER >= 10504
2234 png_set_scale_16(png_ptr);
2235#else
2236 png_set_strip_16(png_ptr);
2237#endif
2238
2239(The more accurate "png_set_scale_16()" API became available in libpng version
22401.5.4).
2241
2242If you need to process the alpha channel on the image separately from the image
2243data (for example if you convert it to a bitmap mask) it is possible to have
2244libpng strip the channel leaving just RGB or gray data:
2245
2246 if (color_type & PNG_COLOR_MASK_ALPHA)
2247 png_set_strip_alpha(png_ptr);
2248
2249If you strip the alpha channel you need to find some other way of dealing with
2250the information. If, instead, you want to convert the image to an opaque
2251version with no alpha channel use png_set_background; see below.
2252
2253As of libpng version 1.5.2, almost all useful expansions are supported, the
2254major ommissions are conversion of grayscale to indexed images (which can be
2255done trivially in the application) and conversion of indexed to grayscale (which
2256can be done by a trivial manipulation of the palette.)
2257
2258In the following table, the 01 means grayscale with depth<8, 31 means
2259indexed with depth<8, other numerals represent the color type, "T" means
2260the tRNS chunk is present, A means an alpha channel is present, and O
2261means tRNS or alpha is present but all pixels in the image are opaque.
2262
2263 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2264 TO
2265 01 - [G] - - - - - - - - - - - - -
2266 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2267 0 1 G + . . G G G G G G B B GB GB
2268 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2269 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2270 2 C P C C C + . . C - - CB CB B B
2271 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2272 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2273 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2274 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2275 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2276 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2277 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2278 6A CA PA CA C C A T tT PA P P C CBA + BA
2279 6O CA PBA CA C C A tT T PA P P CBA C BA +
2280
2281Within the matrix,
2282 "+" identifies entries where 'from' and 'to' are the same.
2283 "-" means the transformation is not supported.
2284 "." means nothing is necessary (a tRNS chunk can just be ignored).
2285 "t" means the transformation is obtained by png_set_tRNS.
2286 "A" means the transformation is obtained by png_set_add_alpha().
2287 "X" means the transformation is obtained by png_set_expand().
2288 "1" means the transformation is obtained by
2289 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
2290 if there is no transparency in the original or the final
2291 format).
2292 "C" means the transformation is obtained by png_set_gray_to_rgb().
2293 "G" means the transformation is obtained by png_set_rgb_to_gray().
2294 "P" means the transformation is obtained by
2295 png_set_expand_palette_to_rgb().
2296 "p" means the transformation is obtained by png_set_packing().
2297 "Q" means the transformation is obtained by png_set_quantize().
2298 "T" means the transformation is obtained by
2299 png_set_tRNS_to_alpha().
2300 "B" means the transformation is obtained by
2301 png_set_background(), or png_strip_alpha().
2302
2303When an entry has multiple transforms listed all are required to cause the
2304right overall transformation. When two transforms are separated by a comma
2305either will do the job. When transforms are enclosed in [] the transform should
2306do the job but this is currently unimplemented - a different format will result
2307if the suggested transformations are used.
2308
2309In PNG files, the alpha channel in an image
2310is the level of opacity. If you need the alpha channel in an image to
2311be the level of transparency instead of opacity, you can invert the
2312alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2313fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2314images) is fully transparent, with
2315
2316 png_set_invert_alpha(png_ptr);
2317
2318PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2319they can, resulting in, for example, 8 pixels per byte for 1 bit
2320files. This code expands to 1 pixel per byte without changing the
2321values of the pixels:
2322
2323 if (bit_depth < 8)
2324 png_set_packing(png_ptr);
2325
2326PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2327stored in a PNG image have been "scaled" or "shifted" up to the next
2328higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2329to 8 bits/sample in the range [0, 255]). However, it is also possible
2330to convert the PNG pixel data back to the original bit depth of the
2331image. This call reduces the pixels back down to the original bit depth:
2332
2333 png_color_8p sig_bit;
2334
2335 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2336 png_set_shift(png_ptr, sig_bit);
2337
2338PNG files store 3-color pixels in red, green, blue order. This code
2339changes the storage of the pixels to blue, green, red:
2340
2341 if (color_type == PNG_COLOR_TYPE_RGB ||
2342 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2343 png_set_bgr(png_ptr);
2344
2345PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2346into 4 or 8 bytes for windowing systems that need them in this format:
2347
2348 if (color_type == PNG_COLOR_TYPE_RGB)
2349 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2350
2351where "filler" is the 8 or 16-bit number to fill with, and the location is
2352either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2353you want the filler before the RGB or after. This transformation
2354does not affect images that already have full alpha channels. To add an
2355opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2356will generate RGBA pixels.
2357
2358Note that png_set_filler() does not change the color type. If you want
2359to do that, you can add a true alpha channel with
2360
2361 if (color_type == PNG_COLOR_TYPE_RGB ||
2362 color_type == PNG_COLOR_TYPE_GRAY)
2363 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2364
2365where "filler" contains the alpha value to assign to each pixel.
2366This function was added in libpng-1.2.7.
2367
2368If you are reading an image with an alpha channel, and you need the
2369data as ARGB instead of the normal PNG format RGBA:
2370
2371 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2372 png_set_swap_alpha(png_ptr);
2373
2374For some uses, you may want a grayscale image to be represented as
2375RGB. This code will do that conversion:
2376
2377 if (color_type == PNG_COLOR_TYPE_GRAY ||
2378 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2379 png_set_gray_to_rgb(png_ptr);
2380
2381Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2382with alpha.
2383
2384 if (color_type == PNG_COLOR_TYPE_RGB ||
2385 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2386 png_set_rgb_to_gray(png_ptr, error_action,
2387 double red_weight, double green_weight);
2388
2389 error_action = 1: silently do the conversion
2390
2391 error_action = 2: issue a warning if the original
2392 image has any pixel where
2393 red != green or red != blue
2394
2395 error_action = 3: issue an error and abort the
2396 conversion if the original
2397 image has any pixel where
2398 red != green or red != blue
2399
2400 red_weight: weight of red component
2401
2402 green_weight: weight of green component
2403 If either weight is negative, default
2404 weights are used.
2405
2406In the corresponding fixed point API the red_weight and green_weight values are
2407simply scaled by 100,000:
2408
2409 png_set_rgb_to_gray(png_ptr, error_action,
2410 png_fixed_point red_weight,
2411 png_fixed_point green_weight);
2412
2413If you have set error_action = 1 or 2, you can
2414later check whether the image really was gray, after processing
2415the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2416It will return a png_byte that is zero if the image was gray or
24171 if there were any non-gray pixels. Background and sBIT data
2418will be silently converted to grayscale, using the green channel
2419data for sBIT, regardless of the error_action setting.
2420
2421The default values come from the PNG file cHRM chunk if present; otherwise, the
2422defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2423space, as recommended in the Charles Poynton's Colour FAQ,
2424<http://www.poynton.com/>, in section 9:
2425
2426 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
2427
2428 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2429
2430Previous versions of this document, 1998 through 2002, recommended a slightly
2431different formula:
2432
2433 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2434
2435Libpng uses an integer approximation:
2436
2437 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2438
2439The calculation is done in a linear colorspace, if the image gamma
2440can be determined.
2441
2442The png_set_background() function has been described already; it tells libpng to
2443composite images with alpha or simple transparency against the supplied
2444background color. For compatibility with versions of libpng earlier than
2445libpng-1.5.4 it is recommended that you call the function after reading the file
2446header, even if you don't want to use the color in a bKGD chunk, if one exists.
2447
2448If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2449you may use this color, or supply another color more suitable for
2450the current display (e.g., the background color from a web page). You
2451need to tell libpng how the color is represented, both the format of the
2452component values in the color (the number of bits) and the gamma encoding of the
2453color. The function takes two arguments, background_gamma_mode and need_expand
2454to convey this information; however, only two combinations are likely to be
2455useful:
2456
2457 png_color_16 my_background;
2458 png_color_16p image_background;
2459
2460 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2461 png_set_background(png_ptr, image_background,
2462 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
2463 else
2464 png_set_background(png_ptr, &my_background,
2465 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
2466
2467The second call was described above - my_background is in the format of the
2468final, display, output produced by libpng. Because you now know the format of
2469the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2470output and to retain palette images (the palette colors will be modified
2471appropriately and the tRNS chunk removed.) However, if you are doing this,
2472take great care not to ask for transformations without checking first that
2473they apply!
2474
2475In the first call the background color has the original bit depth and color type
2476of the PNG file. So, for palette images the color is supplied as a palette
2477index and for low bit greyscale images the color is a reduced bit value in
2478image_background->gray.
2479
2480If you didn't call png_set_gamma() before reading the file header, for example
2481if you need your code to remain compatible with older versions of libpng prior
2482to libpng-1.5.4, this is the place to call it.
2483
2484Do not call it if you called png_set_alpha_mode(); doing so will damage the
2485settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2486supported then you can certainly do png_set_gamma() before reading the PNG
2487header.)
2488
2489This API unconditionally sets the screen and file gamma values, so it will
2490override the value in the PNG file unless it is called before the PNG file
2491reading starts. For this reason you must always call it with the PNG file
2492value when you call it in this position:
2493
2494 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2495 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2496
2497 else
2498 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2499
2500If you need to reduce an RGB file to a paletted file, or if a paletted
2501file has more entries than will fit on your screen, png_set_quantize()
2502will do that. Note that this is a simple match quantization that merely
2503finds the closest color available. This should work fairly well with
2504optimized palettes, but fairly badly with linear color cubes. If you
2505pass a palette that is larger than maximum_colors, the file will
2506reduce the number of colors in the palette so it will fit into
2507maximum_colors. If there is a histogram, libpng will use it to make
2508more intelligent choices when reducing the palette. If there is no
2509histogram, it may not do as good a job.
2510
2511 if (color_type & PNG_COLOR_MASK_COLOR)
2512 {
2513 if (png_get_valid(png_ptr, info_ptr,
2514 PNG_INFO_PLTE))
2515 {
2516 png_uint_16p histogram = NULL;
2517
2518 png_get_hIST(png_ptr, info_ptr,
2519 &histogram);
2520 png_set_quantize(png_ptr, palette, num_palette,
2521 max_screen_colors, histogram, 1);
2522 }
2523
2524 else
2525 {
2526 png_color std_color_cube[MAX_SCREEN_COLORS] =
2527 { ... colors ... };
2528
2529 png_set_quantize(png_ptr, std_color_cube,
2530 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2531 NULL,0);
2532 }
2533 }
2534
2535PNG files describe monochrome as black being zero and white being one.
2536The following code will reverse this (make black be one and white be
2537zero):
2538
2539 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2540 png_set_invert_mono(png_ptr);
2541
2542This function can also be used to invert grayscale and gray-alpha images:
2543
2544 if (color_type == PNG_COLOR_TYPE_GRAY ||
2545 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2546 png_set_invert_mono(png_ptr);
2547
2548PNG files store 16-bit pixels in network byte order (big-endian,
2549ie. most significant bits first). This code changes the storage to the
2550other way (little-endian, i.e. least significant bits first, the
2551way PCs store them):
2552
2553 if (bit_depth == 16)
2554 png_set_swap(png_ptr);
2555
2556If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2557need to change the order the pixels are packed into bytes, you can use:
2558
2559 if (bit_depth < 8)
2560 png_set_packswap(png_ptr);
2561
2562Finally, you can write your own transformation function if none of
2563the existing ones meets your needs. This is done by setting a callback
2564with
2565
2566 png_set_read_user_transform_fn(png_ptr,
2567 read_transform_fn);
2568
2569You must supply the function
2570
2571 void read_transform_fn(png_structp png_ptr, png_row_infop
2572 row_info, png_bytep data)
2573
2574See pngtest.c for a working example. Your function will be called
2575after all of the other transformations have been processed. Take care with
2576interlaced images if you do the interlace yourself - the width of the row is the
2577width in 'row_info', not the overall image width.
2578
2579If supported, libpng provides two information routines that you can use to find
2580where you are in processing the image:
2581
2582 png_get_current_pass_number(png_structp png_ptr);
2583 png_get_current_row_number(png_structp png_ptr);
2584
2585Don't try using these outside a transform callback - firstly they are only
2586supported if user transforms are supported, secondly they may well return
2587unexpected results unless the row is actually being processed at the moment they
2588are called.
2589
2590With interlaced
2591images the value returned is the row in the input sub-image image. Use
2592PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2593find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2594
2595The discussion of interlace handling above contains more information on how to
2596use these values.
2597
2598You can also set up a pointer to a user structure for use by your
2599callback function, and you can inform libpng that your transform
2600function will change the number of channels or bit depth with the
2601function
2602
2603 png_set_user_transform_info(png_ptr, user_ptr,
2604 user_depth, user_channels);
2605
2606The user's application, not libpng, is responsible for allocating and
2607freeing any memory required for the user structure.
2608
2609You can retrieve the pointer via the function
2610png_get_user_transform_ptr(). For example:
2611
2612 voidp read_user_transform_ptr =
2613 png_get_user_transform_ptr(png_ptr);
2614
2615The last thing to handle is interlacing; this is covered in detail below,
2616but you must call the function here if you want libpng to handle expansion
2617of the interlaced image.
2618
2619 number_of_passes = png_set_interlace_handling(png_ptr);
2620
2621After setting the transformations, libpng can update your png_info
2622structure to reflect any transformations you've requested with this
2623call.
2624
2625 png_read_update_info(png_ptr, info_ptr);
2626
2627This is most useful to update the info structure's rowbytes
2628field so you can use it to allocate your image memory. This function
2629will also update your palette with the correct screen_gamma and
2630background if these have been given with the calls above. You may
2631only call png_read_update_info() once with a particular info_ptr.
2632
2633After you call png_read_update_info(), you can allocate any
2634memory you need to hold the image. The row data is simply
2635raw byte data for all forms of images. As the actual allocation
2636varies among applications, no example will be given. If you
2637are allocating one large chunk, you will need to build an
2638array of pointers to each row, as it will be needed for some
2639of the functions below.
2640
2641Remember: Before you call png_read_update_info(), the png_get_*()
2642functions return the values corresponding to the original PNG image.
2643After you call png_read_update_info the values refer to the image
2644that libpng will output. Consequently you must call all the png_set_
2645functions before you call png_read_update_info(). This is particularly
2646important for png_set_interlace_handling() - if you are going to call
2647png_read_update_info() you must call png_set_interlace_handling() before
2648it unless you want to receive interlaced output.
2649
2650.SS Reading image data
2651
2652After you've allocated memory, you can read the image data.
2653The simplest way to do this is in one function call. If you are
2654allocating enough memory to hold the whole image, you can just
2655call png_read_image() and libpng will read in all the image data
2656and put it in the memory area supplied. You will need to pass in
2657an array of pointers to each row.
2658
2659This function automatically handles interlacing, so you don't
2660need to call png_set_interlace_handling() (unless you call
2661png_read_update_info()) or call this function multiple times, or any
2662of that other stuff necessary with png_read_rows().
2663
2664 png_read_image(png_ptr, row_pointers);
2665
2666where row_pointers is:
2667
2668 png_bytep row_pointers[height];
2669
2670You can point to void or char or whatever you use for pixels.
2671
2672If you don't want to read in the whole image at once, you can
2673use png_read_rows() instead. If there is no interlacing (check
2674interlace_type == PNG_INTERLACE_NONE), this is simple:
2675
2676 png_read_rows(png_ptr, row_pointers, NULL,
2677 number_of_rows);
2678
2679where row_pointers is the same as in the png_read_image() call.
2680
2681If you are doing this just one row at a time, you can do this with
2682a single row_pointer instead of an array of row_pointers:
2683
2684 png_bytep row_pointer = row;
2685 png_read_row(png_ptr, row_pointer, NULL);
2686
2687If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2688get somewhat harder. The only current (PNG Specification version 1.2)
2689interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2690a somewhat complicated 2D interlace scheme, known as Adam7, that
2691breaks down an image into seven smaller images of varying size, based
2692on an 8x8 grid. This number is defined (from libpng 1.5) as
2693PNG_INTERLACE_ADAM7_PASSES in png.h
2694
2695libpng can fill out those images or it can give them to you "as is".
2696It is almost always better to have libpng handle the interlacing for you.
2697If you want the images filled out, there are two ways to do that. The one
2698mentioned in the PNG specification is to expand each pixel to cover
2699those pixels that have not been read yet (the "rectangle" method).
2700This results in a blocky image for the first pass, which gradually
2701smooths out as more pixels are read. The other method is the "sparkle"
2702method, where pixels are drawn only in their final locations, with the
2703rest of the image remaining whatever colors they were initialized to
2704before the start of the read. The first method usually looks better,
2705but tends to be slower, as there are more pixels to put in the rows.
2706
2707If, as is likely, you want libpng to expand the images, call this before
2708calling png_start_read_image() or png_read_update_info():
2709
2710 if (interlace_type == PNG_INTERLACE_ADAM7)
2711 number_of_passes
2712 = png_set_interlace_handling(png_ptr);
2713
2714This will return the number of passes needed. Currently, this is seven,
2715but may change if another interlace type is added. This function can be
2716called even if the file is not interlaced, where it will return one pass.
2717You then need to read the whole image 'number_of_passes' times. Each time
2718will distribute the pixels from the current pass to the correct place in
2719the output image, so you need to supply the same rows to png_read_rows in
2720each pass.
2721
2722If you are not going to display the image after each pass, but are
2723going to wait until the entire image is read in, use the sparkle
2724effect. This effect is faster and the end result of either method
2725is exactly the same. If you are planning on displaying the image
2726after each pass, the "rectangle" effect is generally considered the
2727better looking one.
2728
2729If you only want the "sparkle" effect, just call png_read_rows() as
2730normal, with the third parameter NULL. Make sure you make pass over
2731the image number_of_passes times, and you don't change the data in the
2732rows between calls. You can change the locations of the data, just
2733not the data. Each pass only writes the pixels appropriate for that
2734pass, and assumes the data from previous passes is still valid.
2735
2736 png_read_rows(png_ptr, row_pointers, NULL,
2737 number_of_rows);
2738
2739If you only want the first effect (the rectangles), do the same as
2740before except pass the row buffer in the third parameter, and leave
2741the second parameter NULL.
2742
2743 png_read_rows(png_ptr, NULL, row_pointers,
2744 number_of_rows);
2745
2746If you don't want libpng to handle the interlacing details, just call
2747png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
2748Each of the images is a valid image by itself; however, you will almost
2749certainly need to distribute the pixels from each sub-image to the
2750correct place. This is where everything gets very tricky.
2751
2752If you want to retrieve the separate images you must pass the correct
2753number of rows to each successive call of png_read_rows(). The calculation
2754gets pretty complicated for small images, where some sub-images may
2755not even exist because either their width or height ends up zero.
2756libpng provides two macros to help you in 1.5 and later versions:
2757
2758 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
2759 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
2760
2761Respectively these tell you the width and height of the sub-image
2762corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
2763this can be confusing because the specification refers to the same passes
2764as 1 to 7! Be careful, you must check both the width and height before
2765calling png_read_rows() and not call it for that pass if either is zero.
2766
2767You can, of course, read each sub-image row by row. If you want to
2768produce optimal code to make a pixel-by-pixel transformation of an
2769interlaced image this is the best approach; read each row of each pass,
2770transform it, and write it out to a new interlaced image.
2771
2772If you want to de-interlace the image yourself libpng provides further
2773macros to help that tell you where to place the pixels in the output image.
2774Because the interlacing scheme is rectangular - sub-image pixels are always
2775arranged on a rectangular grid - all you need to know for each pass is the
2776starting column and row in the output image of the first pixel plus the
2777spacing between each pixel. As of libpng 1.5 there are four macros to
2778retrieve this information:
2779
2780 png_uint_32 x = PNG_PASS_START_COL(pass);
2781 png_uint_32 y = PNG_PASS_START_ROW(pass);
2782 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
2783 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
2784
2785These allow you to write the obvious loop:
2786
2787 png_uint_32 input_y = 0;
2788 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
2789
2790 while (output_y < output_image_height)
2791 {
2792 png_uint_32 input_x = 0;
2793 png_uint_32 output_x = PNG_PASS_START_COL(pass);
2794
2795 while (output_x < output_image_width)
2796 {
2797 image[output_y][output_x] =
2798 subimage[pass][input_y][input_x++];
2799
2800 output_x += xStep;
2801 }
2802
2803 ++input_y;
2804 output_y += yStep;
2805 }
2806
2807Notice that the steps between successive output rows and columns are
2808returned as shifts. This is possible because the pixels in the subimages
2809are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
2810image. In practice you may need to directly calculate the output coordinate
2811given an input coordinate. libpng provides two further macros for this
2812purpose:
2813
2814 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
2815 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
2816
2817Finally a pair of macros are provided to tell you if a particular image
2818row or column appears in a given pass:
2819
2820 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
2821 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
2822
2823Bear in mind that you will probably also need to check the width and height
2824of the pass in addition to the above to be sure the pass even exists!
2825
2826With any luck you are convinced by now that you don't want to do your own
2827interlace handling. In reality normally the only good reason for doing this
2828is if you are processing PNG files on a pixel-by-pixel basis and don't want
2829to load the whole file into memory when it is interlaced.
2830
2831libpng includes a test program, pngvalid, that illustrates reading and
2832writing of interlaced images. If you can't get interlacing to work in your
2833code and don't want to leave it to libpng (the recommended approach), see
2834how pngvalid.c does it.
2835
2836.SS Finishing a sequential read
2837
2838After you are finished reading the image through the
2839low-level interface, you can finish reading the file.
2840
2841If you want to use a different crc action for handling CRC errors in
2842chunks after the image data, you can call png_set_crc_action()
2843again at this point.
2844
2845If you are interested in comments or time, which may be stored either
2846before or after the image data, you should pass the separate png_info
2847struct if you want to keep the comments from before and after the image
2848separate.
2849
2850 png_infop end_info = png_create_info_struct(png_ptr);
2851
2852 if (!end_info)
2853 {
2854 png_destroy_read_struct(&png_ptr, &info_ptr,
2855 (png_infopp)NULL);
2856 return (ERROR);
2857 }
2858
2859 png_read_end(png_ptr, end_info);
2860
2861If you are not interested, you should still call png_read_end()
2862but you can pass NULL, avoiding the need to create an end_info structure.
2863If you do this, libpng will not process any chunks after IDAT other than
2864skipping over them and perhaps (depending on whether you have called
2865png_set_crc_action) checking their CRCs while looking for the IEND chunk.
2866
2867 png_read_end(png_ptr, (png_infop)NULL);
2868
2869If you don't call png_read_end(), then your file pointer will be
2870left pointing to the first chunk after the last IDAT, which is probably
2871not what you want if you expect to read something beyond the end of
2872the PNG datastream.
2873
2874When you are done, you can free all memory allocated by libpng like this:
2875
2876 png_destroy_read_struct(&png_ptr, &info_ptr,
2877 &end_info);
2878
2879or, if you didn't create an end_info structure,
2880
2881 png_destroy_read_struct(&png_ptr, &info_ptr,
2882 (png_infopp)NULL);
2883
2884It is also possible to individually free the info_ptr members that
2885point to libpng-allocated storage with the following function:
2886
2887 png_free_data(png_ptr, info_ptr, mask, seq)
2888
2889 mask - identifies data to be freed, a mask
2890 containing the bitwise OR of one or
2891 more of
2892 PNG_FREE_PLTE, PNG_FREE_TRNS,
2893 PNG_FREE_HIST, PNG_FREE_ICCP,
2894 PNG_FREE_PCAL, PNG_FREE_ROWS,
2895 PNG_FREE_SCAL, PNG_FREE_SPLT,
2896 PNG_FREE_TEXT, PNG_FREE_UNKN,
2897 or simply PNG_FREE_ALL
2898
2899 seq - sequence number of item to be freed
2900 (\-1 for all items)
2901
2902This function may be safely called when the relevant storage has
2903already been freed, or has not yet been allocated, or was allocated
2904by the user and not by libpng, and will in those cases do nothing.
2905The "seq" parameter is ignored if only one item of the selected data
2906type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
2907are allowed for the data type identified in the mask, such as text or
2908sPLT, only the n'th item in the structure is freed, where n is "seq".
2909
2910The default behavior is only to free data that was allocated internally
2911by libpng. This can be changed, so that libpng will not free the data,
2912or so that it will free data that was allocated by the user with png_malloc()
2913or png_calloc() and passed in via a png_set_*() function, with
2914
2915 png_data_freer(png_ptr, info_ptr, freer, mask)
2916
2917 freer - one of
2918 PNG_DESTROY_WILL_FREE_DATA
2919 PNG_SET_WILL_FREE_DATA
2920 PNG_USER_WILL_FREE_DATA
2921
2922 mask - which data elements are affected
2923 same choices as in png_free_data()
2924
2925This function only affects data that has already been allocated.
2926You can call this function after reading the PNG data but before calling
2927any png_set_*() functions, to control whether the user or the png_set_*()
2928function is responsible for freeing any existing data that might be present,
2929and again after the png_set_*() functions to control whether the user
2930or png_destroy_*() is supposed to free the data. When the user assumes
2931responsibility for libpng-allocated data, the application must use
2932png_free() to free it, and when the user transfers responsibility to libpng
2933for data that the user has allocated, the user must have used png_malloc()
2934or png_calloc() to allocate it.
2935
2936If you allocated your row_pointers in a single block, as suggested above in
2937the description of the high level read interface, you must not transfer
2938responsibility for freeing it to the png_set_rows or png_read_destroy function,
2939because they would also try to free the individual row_pointers[i].
2940
2941If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2942separately, do not transfer responsibility for freeing text_ptr to libpng,
2943because when libpng fills a png_text structure it combines these members with
2944the key member, and png_free_data() will free only text_ptr.key. Similarly,
2945if you transfer responsibility for free'ing text_ptr from libpng to your
2946application, your application must not separately free those members.
2947
2948The png_free_data() function will turn off the "valid" flag for anything
2949it frees. If you need to turn the flag off for a chunk that was freed by
2950your application instead of by libpng, you can use
2951
2952 png_set_invalid(png_ptr, info_ptr, mask);
2953
2954 mask - identifies the chunks to be made invalid,
2955 containing the bitwise OR of one or
2956 more of
2957 PNG_INFO_gAMA, PNG_INFO_sBIT,
2958 PNG_INFO_cHRM, PNG_INFO_PLTE,
2959 PNG_INFO_tRNS, PNG_INFO_bKGD,
2960 PNG_INFO_hIST, PNG_INFO_pHYs,
2961 PNG_INFO_oFFs, PNG_INFO_tIME,
2962 PNG_INFO_pCAL, PNG_INFO_sRGB,
2963 PNG_INFO_iCCP, PNG_INFO_sPLT,
2964 PNG_INFO_sCAL, PNG_INFO_IDAT
2965
2966For a more compact example of reading a PNG image, see the file example.c.
2967
2968.SS Reading PNG files progressively
2969
2970The progressive reader is slightly different from the non-progressive
2971reader. Instead of calling png_read_info(), png_read_rows(), and
2972png_read_end(), you make one call to png_process_data(), which calls
2973callbacks when it has the info, a row, or the end of the image. You
2974set up these callbacks with png_set_progressive_read_fn(). You don't
2975have to worry about the input/output functions of libpng, as you are
2976giving the library the data directly in png_process_data(). I will
2977assume that you have read the section on reading PNG files above,
2978so I will only highlight the differences (although I will show
2979all of the code).
2980
2981png_structp png_ptr;
2982png_infop info_ptr;
2983
2984 /* An example code fragment of how you would
2985 initialize the progressive reader in your
2986 application. */
2987 int
2988 initialize_png_reader()
2989 {
2990 png_ptr = png_create_read_struct
2991 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2992 user_error_fn, user_warning_fn);
2993
2994 if (!png_ptr)
2995 return (ERROR);
2996
2997 info_ptr = png_create_info_struct(png_ptr);
2998
2999 if (!info_ptr)
3000 {
3001 png_destroy_read_struct(&png_ptr,
3002 (png_infopp)NULL, (png_infopp)NULL);
3003 return (ERROR);
3004 }
3005
3006 if (setjmp(png_jmpbuf(png_ptr)))
3007 {
3008 png_destroy_read_struct(&png_ptr, &info_ptr,
3009 (png_infopp)NULL);
3010 return (ERROR);
3011 }
3012
3013 /* This one's new. You can provide functions
3014 to be called when the header info is valid,
3015 when each row is completed, and when the image
3016 is finished. If you aren't using all functions,
3017 you can specify NULL parameters. Even when all
3018 three functions are NULL, you need to call
3019 png_set_progressive_read_fn(). You can use
3020 any struct as the user_ptr (cast to a void pointer
3021 for the function call), and retrieve the pointer
3022 from inside the callbacks using the function
3023
3024 png_get_progressive_ptr(png_ptr);
3025
3026 which will return a void pointer, which you have
3027 to cast appropriately.
3028 */
3029 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
3030 info_callback, row_callback, end_callback);
3031
3032 return 0;
3033 }
3034
3035 /* A code fragment that you call as you receive blocks
3036 of data */
3037 int
3038 process_data(png_bytep buffer, png_uint_32 length)
3039 {
3040 if (setjmp(png_jmpbuf(png_ptr)))
3041 {
3042 png_destroy_read_struct(&png_ptr, &info_ptr,
3043 (png_infopp)NULL);
3044 return (ERROR);
3045 }
3046
3047 /* This one's new also. Simply give it a chunk
3048 of data from the file stream (in order, of
3049 course). On machines with segmented memory
3050 models machines, don't give it any more than
3051 64K. The library seems to run fine with sizes
3052 of 4K. Although you can give it much less if
3053 necessary (I assume you can give it chunks of
3054 1 byte, I haven't tried less than 256 bytes
3055 yet). When this function returns, you may
3056 want to display any rows that were generated
3057 in the row callback if you don't already do
3058 so there.
3059 */
3060 png_process_data(png_ptr, info_ptr, buffer, length);
3061
3062 /* At this point you can call png_process_data_skip if
3063 you want to handle data the library will skip yourself;
3064 it simply returns the number of bytes to skip (and stops
3065 libpng skipping that number of bytes on the next
3066 png_process_data call).
3067 return 0;
3068 }
3069
3070 /* This function is called (as set by
3071 png_set_progressive_read_fn() above) when enough data
3072 has been supplied so all of the header has been
3073 read.
3074 */
3075 void
3076 info_callback(png_structp png_ptr, png_infop info)
3077 {
3078 /* Do any setup here, including setting any of
3079 the transformations mentioned in the Reading
3080 PNG files section. For now, you _must_ call
3081 either png_start_read_image() or
3082 png_read_update_info() after all the
3083 transformations are set (even if you don't set
3084 any). You may start getting rows before
3085 png_process_data() returns, so this is your
3086 last chance to prepare for that.
3087
3088 This is where you turn on interlace handling,
3089 assuming you don't want to do it yourself.
3090
3091 If you need to you can stop the processing of
3092 your original input data at this point by calling
3093 png_process_data_pause. This returns the number
3094 of unprocessed bytes from the last png_process_data
3095 call - it is up to you to ensure that the next call
3096 sees these bytes again. If you don't want to bother
3097 with this you can get libpng to cache the unread
3098 bytes by setting the 'save' parameter (see png.h) but
3099 then libpng will have to copy the data internally.
3100 */
3101 }
3102
3103 /* This function is called when each row of image
3104 data is complete */
3105 void
3106 row_callback(png_structp png_ptr, png_bytep new_row,
3107 png_uint_32 row_num, int pass)
3108 {
3109 /* If the image is interlaced, and you turned
3110 on the interlace handler, this function will
3111 be called for every row in every pass. Some
3112 of these rows will not be changed from the
3113 previous pass. When the row is not changed,
3114 the new_row variable will be NULL. The rows
3115 and passes are called in order, so you don't
3116 really need the row_num and pass, but I'm
3117 supplying them because it may make your life
3118 easier.
3119
3120 If you did not turn on interlace handling then
3121 the callback is called for each row of each
3122 sub-image when the image is interlaced. In this
3123 case 'row_num' is the row in the sub-image, not
3124 the row in the output image as it is in all other
3125 cases.
3126
3127 For the non-NULL rows of interlaced images when
3128 you have switched on libpng interlace handling,
3129 you must call png_progressive_combine_row()
3130 passing in the row and the old row. You can
3131 call this function for NULL rows (it will just
3132 return) and for non-interlaced images (it just
3133 does the memcpy for you) if it will make the
3134 code easier. Thus, you can just do this for
3135 all cases if you switch on interlace handling;
3136 */
3137
3138 png_progressive_combine_row(png_ptr, old_row,
3139 new_row);
3140
3141 /* where old_row is what was displayed
3142 previously for the row. Note that the first
3143 pass (pass == 0, really) will completely cover
3144 the old row, so the rows do not have to be
3145 initialized. After the first pass (and only
3146 for interlaced images), you will have to pass
3147 the current row, and the function will combine
3148 the old row and the new row.
3149
3150 You can also call png_process_data_pause in this
3151 callback - see above.
3152 */
3153 }
3154
3155 void
3156 end_callback(png_structp png_ptr, png_infop info)
3157 {
3158 /* This function is called after the whole image
3159 has been read, including any chunks after the
3160 image (up to and including the IEND). You
3161 will usually have the same info chunk as you
3162 had in the header, although some data may have
3163 been added to the comments and time fields.
3164
3165 Most people won't do much here, perhaps setting
3166 a flag that marks the image as finished.
3167 */
3168 }
3169
3170
3171
3172.SH IV. Writing
3173
3174Much of this is very similar to reading. However, everything of
3175importance is repeated here, so you won't have to constantly look
3176back up in the reading section to understand writing.
3177
3178.SS Setup
3179
3180You will want to do the I/O initialization before you get into libpng,
3181so if it doesn't work, you don't have anything to undo. If you are not
3182using the standard I/O functions, you will need to replace them with
3183custom writing functions. See the discussion under Customizing libpng.
3184
3185 FILE *fp = fopen(file_name, "wb");
3186
3187 if (!fp)
3188 return (ERROR);
3189
3190Next, png_struct and png_info need to be allocated and initialized.
3191As these can be both relatively large, you may not want to store these
3192on the stack, unless you have stack space to spare. Of course, you
3193will want to check if they return NULL. If you are also reading,
3194you won't want to name your read structure and your write structure
3195both "png_ptr"; you can call them anything you like, such as
3196"read_ptr" and "write_ptr". Look at pngtest.c, for example.
3197
3198 png_structp png_ptr = png_create_write_struct
3199 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3200 user_error_fn, user_warning_fn);
3201
3202 if (!png_ptr)
3203 return (ERROR);
3204
3205 png_infop info_ptr = png_create_info_struct(png_ptr);
3206 if (!info_ptr)
3207 {
3208 png_destroy_write_struct(&png_ptr,
3209 (png_infopp)NULL);
3210 return (ERROR);
3211 }
3212
3213If you want to use your own memory allocation routines,
3214define PNG_USER_MEM_SUPPORTED and use
3215png_create_write_struct_2() instead of png_create_write_struct():
3216
3217 png_structp png_ptr = png_create_write_struct_2
3218 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3219 user_error_fn, user_warning_fn, (png_voidp)
3220 user_mem_ptr, user_malloc_fn, user_free_fn);
3221
3222After you have these structures, you will need to set up the
3223error handling. When libpng encounters an error, it expects to
3224longjmp() back to your routine. Therefore, you will need to call
3225setjmp() and pass the png_jmpbuf(png_ptr). If you
3226write the file from different routines, you will need to update
3227the png_jmpbuf(png_ptr) every time you enter a new routine that will
3228call a png_*() function. See your documentation of setjmp/longjmp
3229for your compiler for more information on setjmp/longjmp. See
3230the discussion on libpng error handling in the Customizing Libpng
3231section below for more information on the libpng error handling.
3232
3233 if (setjmp(png_jmpbuf(png_ptr)))
3234 {
3235 png_destroy_write_struct(&png_ptr, &info_ptr);
3236 fclose(fp);
3237 return (ERROR);
3238 }
3239 ...
3240 return;
3241
3242If you would rather avoid the complexity of setjmp/longjmp issues,
3243you can compile libpng with PNG_NO_SETJMP, in which case
3244errors will result in a call to PNG_ABORT() which defaults to abort().
3245
3246You can #define PNG_ABORT() to a function that does something
3247more useful than abort(), as long as your function does not
3248return.
3249
3250Checking for invalid palette index on write was added at libpng
32511.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
3252a benign error. This is enabled by default because this condition is an
3253error according to the PNG specification, Clause 11.3.2, but the error can
3254be ignored in each png_ptr with
3255
3256 png_set_check_for_invalid_index(png_ptr, 0);
3257
3258If the error is ignored, or if png_benign_error() treats it as a warning,
3259any invalid pixels are written as-is by the encoder, resulting in an
3260invalid PNG datastream as output. In this case the application is
3261responsible for ensuring that the pixel indexes are in range when it writes
3262a PLTE chunk with fewer entries than the bit depth would allow.
3263
3264Now you need to set up the output code. The default for libpng is to
3265use the C function fwrite(). If you use this, you will need to pass a
3266valid FILE * in the function png_init_io(). Be sure that the file is
3267opened in binary mode. Again, if you wish to handle writing data in
3268another way, see the discussion on libpng I/O handling in the Customizing
3269Libpng section below.
3270
3271 png_init_io(png_ptr, fp);
3272
3273If you are embedding your PNG into a datastream such as MNG, and don't
3274want libpng to write the 8-byte signature, or if you have already
3275written the signature in your application, use
3276
3277 png_set_sig_bytes(png_ptr, 8);
3278
3279to inform libpng that it should not write a signature.
3280
3281.SS Write callbacks
3282
3283At this point, you can set up a callback function that will be
3284called after each row has been written, which you can use to control
3285a progress meter or the like. It's demonstrated in pngtest.c.
3286You must supply a function
3287
3288 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3289 int pass);
3290 {
3291 /* put your code here */
3292 }
3293
3294(You can give it another name that you like instead of "write_row_callback")
3295
3296To inform libpng about your function, use
3297
3298 png_set_write_status_fn(png_ptr, write_row_callback);
3299
3300When this function is called the row has already been completely processed and
3301it has also been written out. The 'row' and 'pass' refer to the next row to be
3302handled. For the
3303non-interlaced case the row that was just handled is simply one less than the
3304passed in row number, and pass will always be 0. For the interlaced case the
3305same applies unless the row value is 0, in which case the row just handled was
3306the last one from one of the preceding passes. Because interlacing may skip a
3307pass you cannot be sure that the preceding pass is just 'pass\-1', if you really
3308need to know what the last pass is record (row,pass) from the callback and use
3309the last recorded value each time.
3310
3311As with the user transform you can find the output row using the
3312PNG_ROW_FROM_PASS_ROW macro.
3313
3314You now have the option of modifying how the compression library will
3315run. The following functions are mainly for testing, but may be useful
3316in some cases, like if you need to write PNG files extremely fast and
3317are willing to give up some compression, or if you want to get the
3318maximum possible compression at the expense of slower writing. If you
3319have no special needs in this area, let the library do what it wants by
3320not calling this function at all, as it has been tuned to deliver a good
3321speed/compression ratio. The second parameter to png_set_filter() is
3322the filter method, for which the only valid values are 0 (as of the
3323July 1999 PNG specification, version 1.2) or 64 (if you are writing
3324a PNG datastream that is to be embedded in a MNG datastream). The third
3325parameter is a flag that indicates which filter type(s) are to be tested
3326for each scanline. See the PNG specification for details on the specific
3327filter types.
3328
3329
3330 /* turn on or off filtering, and/or choose
3331 specific filters. You can use either a single
3332 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3333 or more PNG_FILTER_NAME masks.
3334 */
3335 png_set_filter(png_ptr, 0,
3336 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3337 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3338 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3339 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3340 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3341 PNG_ALL_FILTERS);
3342
3343If an application wants to start and stop using particular filters during
3344compression, it should start out with all of the filters (to ensure that
3345the previous row of pixels will be stored in case it's needed later),
3346and then add and remove them after the start of compression.
3347
3348If you are writing a PNG datastream that is to be embedded in a MNG
3349datastream, the second parameter can be either 0 or 64.
3350
3351The png_set_compression_*() functions interface to the zlib compression
3352library, and should mostly be ignored unless you really know what you are
3353doing. The only generally useful call is png_set_compression_level()
3354which changes how much time zlib spends on trying to compress the image
3355data. See the Compression Library (zlib.h and algorithm.txt, distributed
3356with zlib) for details on the compression levels.
3357
3358 #include zlib.h
3359
3360 /* Set the zlib compression level */
3361 png_set_compression_level(png_ptr,
3362 Z_BEST_COMPRESSION);
3363
3364 /* Set other zlib parameters for compressing IDAT */
3365 png_set_compression_mem_level(png_ptr, 8);
3366 png_set_compression_strategy(png_ptr,
3367 Z_DEFAULT_STRATEGY);
3368 png_set_compression_window_bits(png_ptr, 15);
3369 png_set_compression_method(png_ptr, 8);
3370 png_set_compression_buffer_size(png_ptr, 8192)
3371
3372 /* Set zlib parameters for text compression
3373 * If you don't call these, the parameters
3374 * fall back on those defined for IDAT chunks
3375 */
3376 png_set_text_compression_mem_level(png_ptr, 8);
3377 png_set_text_compression_strategy(png_ptr,
3378 Z_DEFAULT_STRATEGY);
3379 png_set_text_compression_window_bits(png_ptr, 15);
3380 png_set_text_compression_method(png_ptr, 8);
3381
3382.SS Setting the contents of info for output
3383
3384You now need to fill in the png_info structure with all the data you
3385wish to write before the actual image. Note that the only thing you
3386are allowed to write after the image is the text chunks and the time
3387chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3388the latest PNG specification for more information on that. If you
3389wish to write them before the image, fill them in now, and flag that
3390data as being valid. If you want to wait until after the data, don't
3391fill them until png_write_end(). For all the fields in png_info and
3392their data types, see png.h. For explanations of what the fields
3393contain, see the PNG specification.
3394
3395Some of the more important parts of the png_info are:
3396
3397 png_set_IHDR(png_ptr, info_ptr, width, height,
3398 bit_depth, color_type, interlace_type,
3399 compression_type, filter_method)
3400
3401 width - holds the width of the image
3402 in pixels (up to 2^31).
3403
3404 height - holds the height of the image
3405 in pixels (up to 2^31).
3406
3407 bit_depth - holds the bit depth of one of the
3408 image channels.
3409 (valid values are 1, 2, 4, 8, 16
3410 and depend also on the
3411 color_type. See also significant
3412 bits (sBIT) below).
3413
3414 color_type - describes which color/alpha
3415 channels are present.
3416 PNG_COLOR_TYPE_GRAY
3417 (bit depths 1, 2, 4, 8, 16)
3418 PNG_COLOR_TYPE_GRAY_ALPHA
3419 (bit depths 8, 16)
3420 PNG_COLOR_TYPE_PALETTE
3421 (bit depths 1, 2, 4, 8)
3422 PNG_COLOR_TYPE_RGB
3423 (bit_depths 8, 16)
3424 PNG_COLOR_TYPE_RGB_ALPHA
3425 (bit_depths 8, 16)
3426
3427 PNG_COLOR_MASK_PALETTE
3428 PNG_COLOR_MASK_COLOR
3429 PNG_COLOR_MASK_ALPHA
3430
3431 interlace_type - PNG_INTERLACE_NONE or
3432 PNG_INTERLACE_ADAM7
3433
3434 compression_type - (must be
3435 PNG_COMPRESSION_TYPE_DEFAULT)
3436
3437 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3438 or, if you are writing a PNG to
3439 be embedded in a MNG datastream,
3440 can also be
3441 PNG_INTRAPIXEL_DIFFERENCING)
3442
3443If you call png_set_IHDR(), the call must appear before any of the
3444other png_set_*() functions, because they might require access to some of
3445the IHDR settings. The remaining png_set_*() functions can be called
3446in any order.
3447
3448If you wish, you can reset the compression_type, interlace_type, or
3449filter_method later by calling png_set_IHDR() again; if you do this, the
3450width, height, bit_depth, and color_type must be the same in each call.
3451
3452 png_set_PLTE(png_ptr, info_ptr, palette,
3453 num_palette);
3454
3455 palette - the palette for the file
3456 (array of png_color)
3457 num_palette - number of entries in the palette
3458
3459 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3460 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3461
3462 file_gamma - the gamma at which the image was
3463 created (PNG_INFO_gAMA)
3464
3465 int_file_gamma - 100,000 times the gamma at which
3466 the image was created
3467
3468 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3469 green_x, green_y, blue_x, blue_y)
3470 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3471 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3472 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3473 int_red_x, int_red_y, int_green_x, int_green_y,
3474 int_blue_x, int_blue_y)
3475 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3476 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3477 int_blue_X, int_blue_Y, int_blue_Z)
3478
3479 {white,red,green,blue}_{x,y}
3480 A color space encoding specified using the chromaticities
3481 of the end points and the white point.
3482
3483 {red,green,blue}_{X,Y,Z}
3484 A color space encoding specified using the encoding end
3485 points - the CIE tristimulus specification of the intended
3486 color of the red, green and blue channels in the PNG RGB
3487 data. The white point is simply the sum of the three end
3488 points.
3489
3490 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3491
3492 srgb_intent - the rendering intent
3493 (PNG_INFO_sRGB) The presence of
3494 the sRGB chunk means that the pixel
3495 data is in the sRGB color space.
3496 This chunk also implies specific
3497 values of gAMA and cHRM. Rendering
3498 intent is the CSS-1 property that
3499 has been defined by the International
3500 Color Consortium
3501 (http://www.color.org).
3502 It can be one of
3503 PNG_sRGB_INTENT_SATURATION,
3504 PNG_sRGB_INTENT_PERCEPTUAL,
3505 PNG_sRGB_INTENT_ABSOLUTE, or
3506 PNG_sRGB_INTENT_RELATIVE.
3507
3508
3509 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3510 srgb_intent);
3511
3512 srgb_intent - the rendering intent
3513 (PNG_INFO_sRGB) The presence of the
3514 sRGB chunk means that the pixel
3515 data is in the sRGB color space.
3516 This function also causes gAMA and
3517 cHRM chunks with the specific values
3518 that are consistent with sRGB to be
3519 written.
3520
3521 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3522 profile, proflen);
3523
3524 name - The profile name.
3525
3526 compression_type - The compression type; always
3527 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3528 You may give NULL to this argument to
3529 ignore it.
3530
3531 profile - International Color Consortium color
3532 profile data. May contain NULs.
3533
3534 proflen - length of profile data in bytes.
3535
3536 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3537
3538 sig_bit - the number of significant bits for
3539 (PNG_INFO_sBIT) each of the gray, red,
3540 green, and blue channels, whichever are
3541 appropriate for the given color type
3542 (png_color_16)
3543
3544 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3545 num_trans, trans_color);
3546
3547 trans_alpha - array of alpha (transparency)
3548 entries for palette (PNG_INFO_tRNS)
3549
3550 num_trans - number of transparent entries
3551 (PNG_INFO_tRNS)
3552
3553 trans_color - graylevel or color sample values
3554 (in order red, green, blue) of the
3555 single transparent color for
3556 non-paletted images (PNG_INFO_tRNS)
3557
3558 png_set_hIST(png_ptr, info_ptr, hist);
3559
3560 hist - histogram of palette (array of
3561 png_uint_16) (PNG_INFO_hIST)
3562
3563 png_set_tIME(png_ptr, info_ptr, mod_time);
3564
3565 mod_time - time image was last modified
3566 (PNG_VALID_tIME)
3567
3568 png_set_bKGD(png_ptr, info_ptr, background);
3569
3570 background - background color (of type
3571 png_color_16p) (PNG_VALID_bKGD)
3572
3573 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3574
3575 text_ptr - array of png_text holding image
3576 comments
3577
3578 text_ptr[i].compression - type of compression used
3579 on "text" PNG_TEXT_COMPRESSION_NONE
3580 PNG_TEXT_COMPRESSION_zTXt
3581 PNG_ITXT_COMPRESSION_NONE
3582 PNG_ITXT_COMPRESSION_zTXt
3583 text_ptr[i].key - keyword for comment. Must contain
3584 1-79 characters.
3585 text_ptr[i].text - text comments for current
3586 keyword. Can be NULL or empty.
3587 text_ptr[i].text_length - length of text string,
3588 after decompression, 0 for iTXt
3589 text_ptr[i].itxt_length - length of itxt string,
3590 after decompression, 0 for tEXt/zTXt
3591 text_ptr[i].lang - language of comment (NULL or
3592 empty for unknown).
3593 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3594 or empty for unknown).
3595
3596 Note that the itxt_length, lang, and lang_key
3597 members of the text_ptr structure only exist when the
3598 library is built with iTXt chunk support. Prior to
3599 libpng-1.4.0 the library was built by default without
3600 iTXt support. Also note that when iTXt is supported,
3601 they contain NULL pointers when the "compression"
3602 field contains PNG_TEXT_COMPRESSION_NONE or
3603 PNG_TEXT_COMPRESSION_zTXt.
3604
3605 num_text - number of comments
3606
3607 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3608 num_spalettes);
3609
3610 palette_ptr - array of png_sPLT_struct structures
3611 to be added to the list of palettes
3612 in the info structure.
3613 num_spalettes - number of palette structures to be
3614 added.
3615
3616 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3617 unit_type);
3618
3619 offset_x - positive offset from the left
3620 edge of the screen
3621
3622 offset_y - positive offset from the top
3623 edge of the screen
3624
3625 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3626
3627 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3628 unit_type);
3629
3630 res_x - pixels/unit physical resolution
3631 in x direction
3632
3633 res_y - pixels/unit physical resolution
3634 in y direction
3635
3636 unit_type - PNG_RESOLUTION_UNKNOWN,
3637 PNG_RESOLUTION_METER
3638
3639 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3640
3641 unit - physical scale units (an integer)
3642
3643 width - width of a pixel in physical scale units
3644
3645 height - height of a pixel in physical scale units
3646 (width and height are doubles)
3647
3648 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3649
3650 unit - physical scale units (an integer)
3651
3652 width - width of a pixel in physical scale units
3653 expressed as a string
3654
3655 height - height of a pixel in physical scale units
3656 (width and height are strings like "2.54")
3657
3658 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3659 num_unknowns)
3660
3661 unknowns - array of png_unknown_chunk
3662 structures holding unknown chunks
3663 unknowns[i].name - name of unknown chunk
3664 unknowns[i].data - data of unknown chunk
3665 unknowns[i].size - size of unknown chunk's data
3666 unknowns[i].location - position to write chunk in file
3667 0: do not write chunk
3668 PNG_HAVE_IHDR: before PLTE
3669 PNG_HAVE_PLTE: before IDAT
3670 PNG_AFTER_IDAT: after IDAT
3671
3672The "location" member is set automatically according to
3673what part of the output file has already been written.
3674You can change its value after calling png_set_unknown_chunks()
3675as demonstrated in pngtest.c. Within each of the "locations",
3676the chunks are sequenced according to their position in the
3677structure (that is, the value of "i", which is the order in which
3678the chunk was either read from the input file or defined with
3679png_set_unknown_chunks).
3680
3681A quick word about text and num_text. text is an array of png_text
3682structures. num_text is the number of valid structures in the array.
3683Each png_text structure holds a language code, a keyword, a text value,
3684and a compression type.
3685
3686The compression types have the same valid numbers as the compression
3687types of the image data. Currently, the only valid number is zero.
3688However, you can store text either compressed or uncompressed, unlike
3689images, which always have to be compressed. So if you don't want the
3690text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3691Because tEXt and zTXt chunks don't have a language field, if you
3692specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3693any language code or translated keyword will not be written out.
3694
3695Until text gets around a few hundred bytes, it is not worth compressing it.
3696After the text has been written out to the file, the compression type
3697is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3698so that it isn't written out again at the end (in case you are calling
3699png_write_end() with the same struct).
3700
3701The keywords that are given in the PNG Specification are:
3702
3703 Title Short (one line) title or
3704 caption for image
3705
3706 Author Name of image's creator
3707
3708 Description Description of image (possibly long)
3709
3710 Copyright Copyright notice
3711
3712 Creation Time Time of original image creation
3713 (usually RFC 1123 format, see below)
3714
3715 Software Software used to create the image
3716
3717 Disclaimer Legal disclaimer
3718
3719 Warning Warning of nature of content
3720
3721 Source Device used to create the image
3722
3723 Comment Miscellaneous comment; conversion
3724 from other image format
3725
3726The keyword-text pairs work like this. Keywords should be short
3727simple descriptions of what the comment is about. Some typical
3728keywords are found in the PNG specification, as is some recommendations
3729on keywords. You can repeat keywords in a file. You can even write
3730some text before the image and some after. For example, you may want
3731to put a description of the image before the image, but leave the
3732disclaimer until after, so viewers working over modem connections
3733don't have to wait for the disclaimer to go over the modem before
3734they start seeing the image. Finally, keywords should be full
3735words, not abbreviations. Keywords and text are in the ISO 8859-1
3736(Latin-1) character set (a superset of regular ASCII) and can not
3737contain NUL characters, and should not contain control or other
3738unprintable characters. To make the comments widely readable, stick
3739with basic ASCII, and avoid machine specific character set extensions
3740like the IBM-PC character set. The keyword must be present, but
3741you can leave off the text string on non-compressed pairs.
3742Compressed pairs must have a text string, as only the text string
3743is compressed anyway, so the compression would be meaningless.
3744
3745PNG supports modification time via the png_time structure. Two
3746conversion routines are provided, png_convert_from_time_t() for
3747time_t and png_convert_from_struct_tm() for struct tm. The
3748time_t routine uses gmtime(). You don't have to use either of
3749these, but if you wish to fill in the png_time structure directly,
3750you should provide the time in universal time (GMT) if possible
3751instead of your local time. Note that the year number is the full
3752year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3753that months start with 1.
3754
3755If you want to store the time of the original image creation, you should
3756use a plain tEXt chunk with the "Creation Time" keyword. This is
3757necessary because the "creation time" of a PNG image is somewhat vague,
3758depending on whether you mean the PNG file, the time the image was
3759created in a non-PNG format, a still photo from which the image was
3760scanned, or possibly the subject matter itself. In order to facilitate
3761machine-readable dates, it is recommended that the "Creation Time"
3762tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
3763although this isn't a requirement. Unlike the tIME chunk, the
3764"Creation Time" tEXt chunk is not expected to be automatically changed
3765by the software. To facilitate the use of RFC 1123 dates, a function
3766png_convert_to_rfc1123_buffer(buffer, png_timep) is provided to
3767convert from PNG time to an RFC 1123 format string. The caller must provide
3768a writeable buffer of at least 29 bytes.
3769
3770.SS Writing unknown chunks
3771
3772You can use the png_set_unknown_chunks function to queue up private chunks
3773for writing. You give it a chunk name, location, raw data, and a size. You
3774also must use png_set_keep_unknown_chunks() to ensure that libpng will
3775handle them. That's all there is to it. The chunks will be written by the
3776next following png_write_info_before_PLTE, png_write_info, or png_write_end
3777function, depending upon the specified location. Any chunks previously
3778read into the info structure's unknown-chunk list will also be written out
3779in a sequence that satisfies the PNG specification's ordering rules.
3780
3781Here is an example of writing two private chunks, prVt and miNE:
3782
3783 #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
3784 /* Set unknown chunk data */
3785 png_unknown_chunk unk_chunk[2];
3786 strcpy((char *) unk_chunk[0].name, "prVt";
3787 unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
3788 unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
3789 unk_chunk[0].location = PNG_HAVE_IHDR;
3790 strcpy((char *) unk_chunk[1].name, "miNE";
3791 unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
3792 unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
3793 unk_chunk[1].location = PNG_AFTER_IDAT;
3794 png_set_unknown_chunks(write_ptr, write_info_ptr,
3795 unk_chunk, 2);
3796 /* Needed because miNE is not safe-to-copy */
3797 png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
3798 (png_bytep) "miNE", 1);
3799 # if PNG_LIBPNG_VER < 10600
3800 /* Deal with unknown chunk location bug in 1.5.x and earlier */
3801 png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
3802 png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
3803 # endif
3804 # if PNG_LIBPNG_VER < 10500
3805 /* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
3806 * one before IDAT and another after IDAT, so don't use it; only use
3807 * PNG_HAVE_IHDR location. This call resets the location previously
3808 * set by assignment and png_set_unknown_chunk_location() for chunk 1.
3809 */
3810 png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
3811 # endif
3812 #endif
3813
3814.SS The high-level write interface
3815
3816At this point there are two ways to proceed; through the high-level
3817write interface, or through a sequence of low-level write operations.
3818You can use the high-level interface if your image data is present
3819in the info structure. All defined output
3820transformations are permitted, enabled by the following masks.
3821
3822 PNG_TRANSFORM_IDENTITY No transformation
3823 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
3824 PNG_TRANSFORM_PACKSWAP Change order of packed
3825 pixels to LSB first
3826 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
3827 PNG_TRANSFORM_SHIFT Normalize pixels to the
3828 sBIT depth
3829 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
3830 to BGRA
3831 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
3832 to AG
3833 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
3834 to transparency
3835 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
3836 PNG_TRANSFORM_STRIP_FILLER Strip out filler
3837 bytes (deprecated).
3838 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
3839 filler bytes
3840 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
3841 filler bytes
3842
3843If you have valid image data in the info structure (you can use
3844png_set_rows() to put image data in the info structure), simply do this:
3845
3846 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
3847
3848where png_transforms is an integer containing the bitwise OR of some set of
3849transformation flags. This call is equivalent to png_write_info(),
3850followed the set of transformations indicated by the transform mask,
3851then png_write_image(), and finally png_write_end().
3852
3853(The final parameter of this call is not yet used. Someday it might point
3854to transformation parameters required by some future output transform.)
3855
3856You must use png_transforms and not call any png_set_transform() functions
3857when you use png_write_png().
3858
3859.SS The low-level write interface
3860
3861If you are going the low-level route instead, you are now ready to
3862write all the file information up to the actual image data. You do
3863this with a call to png_write_info().
3864
3865 png_write_info(png_ptr, info_ptr);
3866
3867Note that there is one transformation you may need to do before
3868png_write_info(). In PNG files, the alpha channel in an image is the
3869level of opacity. If your data is supplied as a level of transparency,
3870you can invert the alpha channel before you write it, so that 0 is
3871fully transparent and 255 (in 8-bit or paletted images) or 65535
3872(in 16-bit images) is fully opaque, with
3873
3874 png_set_invert_alpha(png_ptr);
3875
3876This must appear before png_write_info() instead of later with the
3877other transformations because in the case of paletted images the tRNS
3878chunk data has to be inverted before the tRNS chunk is written. If
3879your image is not a paletted image, the tRNS data (which in such cases
3880represents a single color to be rendered as transparent) won't need to
3881be changed, and you can safely do this transformation after your
3882png_write_info() call.
3883
3884If you need to write a private chunk that you want to appear before
3885the PLTE chunk when PLTE is present, you can write the PNG info in
3886two steps, and insert code to write your own chunk between them:
3887
3888 png_write_info_before_PLTE(png_ptr, info_ptr);
3889 png_set_unknown_chunks(png_ptr, info_ptr, ...);
3890 png_write_info(png_ptr, info_ptr);
3891
3892After you've written the file information, you can set up the library
3893to handle any special transformations of the image data. The various
3894ways to transform the data will be described in the order that they
3895should occur. This is important, as some of these change the color
3896type and/or bit depth of the data, and some others only work on
3897certain color types and bit depths. Even though each transformation
3898checks to see if it has data that it can do something with, you should
3899make sure to only enable a transformation if it will be valid for the
3900data. For example, don't swap red and blue on grayscale data.
3901
3902PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
3903the library to strip input data that has 4 or 8 bytes per pixel down
3904to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
3905bytes per pixel).
3906
3907 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
3908
3909where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
3910PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
3911is stored XRGB or RGBX.
3912
3913PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
3914they can, resulting in, for example, 8 pixels per byte for 1 bit files.
3915If the data is supplied at 1 pixel per byte, use this code, which will
3916correctly pack the pixels into a single byte:
3917
3918 png_set_packing(png_ptr);
3919
3920PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
3921data is of another bit depth, you can write an sBIT chunk into the
3922file so that decoders can recover the original data if desired.
3923
3924 /* Set the true bit depth of the image data */
3925 if (color_type & PNG_COLOR_MASK_COLOR)
3926 {
3927 sig_bit.red = true_bit_depth;
3928 sig_bit.green = true_bit_depth;
3929 sig_bit.blue = true_bit_depth;
3930 }
3931
3932 else
3933 {
3934 sig_bit.gray = true_bit_depth;
3935 }
3936
3937 if (color_type & PNG_COLOR_MASK_ALPHA)
3938 {
3939 sig_bit.alpha = true_bit_depth;
3940 }
3941
3942 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
3943
3944If the data is stored in the row buffer in a bit depth other than
3945one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
3946this will scale the values to appear to be the correct bit depth as
3947is required by PNG.
3948
3949 png_set_shift(png_ptr, &sig_bit);
3950
3951PNG files store 16-bit pixels in network byte order (big-endian,
3952ie. most significant bits first). This code would be used if they are
3953supplied the other way (little-endian, i.e. least significant bits
3954first, the way PCs store them):
3955
3956 if (bit_depth > 8)
3957 png_set_swap(png_ptr);
3958
3959If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3960need to change the order the pixels are packed into bytes, you can use:
3961
3962 if (bit_depth < 8)
3963 png_set_packswap(png_ptr);
3964
3965PNG files store 3 color pixels in red, green, blue order. This code
3966would be used if they are supplied as blue, green, red:
3967
3968 png_set_bgr(png_ptr);
3969
3970PNG files describe monochrome as black being zero and white being
3971one. This code would be used if the pixels are supplied with this reversed
3972(black being one and white being zero):
3973
3974 png_set_invert_mono(png_ptr);
3975
3976Finally, you can write your own transformation function if none of
3977the existing ones meets your needs. This is done by setting a callback
3978with
3979
3980 png_set_write_user_transform_fn(png_ptr,
3981 write_transform_fn);
3982
3983You must supply the function
3984
3985 void write_transform_fn(png_structp png_ptr, png_row_infop
3986 row_info, png_bytep data)
3987
3988See pngtest.c for a working example. Your function will be called
3989before any of the other transformations are processed. If supported
3990libpng also supplies an information routine that may be called from
3991your callback:
3992
3993 png_get_current_row_number(png_ptr);
3994 png_get_current_pass_number(png_ptr);
3995
3996This returns the current row passed to the transform. With interlaced
3997images the value returned is the row in the input sub-image image. Use
3998PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
3999find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
4000
4001The discussion of interlace handling above contains more information on how to
4002use these values.
4003
4004You can also set up a pointer to a user structure for use by your
4005callback function.
4006
4007 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
4008
4009The user_channels and user_depth parameters of this function are ignored
4010when writing; you can set them to zero as shown.
4011
4012You can retrieve the pointer via the function png_get_user_transform_ptr().
4013For example:
4014
4015 voidp write_user_transform_ptr =
4016 png_get_user_transform_ptr(png_ptr);
4017
4018It is possible to have libpng flush any pending output, either manually,
4019or automatically after a certain number of lines have been written. To
4020flush the output stream a single time call:
4021
4022 png_write_flush(png_ptr);
4023
4024and to have libpng flush the output stream periodically after a certain
4025number of scanlines have been written, call:
4026
4027 png_set_flush(png_ptr, nrows);
4028
4029Note that the distance between rows is from the last time png_write_flush()
4030was called, or the first row of the image if it has never been called.
4031So if you write 50 lines, and then png_set_flush 25, it will flush the
4032output on the next scanline, and every 25 lines thereafter, unless
4033png_write_flush() is called before 25 more lines have been written.
4034If nrows is too small (less than about 10 lines for a 640 pixel wide
4035RGB image) the image compression may decrease noticeably (although this
4036may be acceptable for real-time applications). Infrequent flushing will
4037only degrade the compression performance by a few percent over images
4038that do not use flushing.
4039
4040.SS Writing the image data
4041
4042That's it for the transformations. Now you can write the image data.
4043The simplest way to do this is in one function call. If you have the
4044whole image in memory, you can just call png_write_image() and libpng
4045will write the image. You will need to pass in an array of pointers to
4046each row. This function automatically handles interlacing, so you don't
4047need to call png_set_interlace_handling() or call this function multiple
4048times, or any of that other stuff necessary with png_write_rows().
4049
4050 png_write_image(png_ptr, row_pointers);
4051
4052where row_pointers is:
4053
4054 png_byte *row_pointers[height];
4055
4056You can point to void or char or whatever you use for pixels.
4057
4058If you don't want to write the whole image at once, you can
4059use png_write_rows() instead. If the file is not interlaced,
4060this is simple:
4061
4062 png_write_rows(png_ptr, row_pointers,
4063 number_of_rows);
4064
4065row_pointers is the same as in the png_write_image() call.
4066
4067If you are just writing one row at a time, you can do this with
4068a single row_pointer instead of an array of row_pointers:
4069
4070 png_bytep row_pointer = row;
4071
4072 png_write_row(png_ptr, row_pointer);
4073
4074When the file is interlaced, things can get a good deal more complicated.
4075The only currently (as of the PNG Specification version 1.2, dated July
40761999) defined interlacing scheme for PNG files is the "Adam7" interlace
4077scheme, that breaks down an image into seven smaller images of varying
4078size. libpng will build these images for you, or you can do them
4079yourself. If you want to build them yourself, see the PNG specification
4080for details of which pixels to write when.
4081
4082If you don't want libpng to handle the interlacing details, just
4083use png_set_interlace_handling() and call png_write_rows() the
4084correct number of times to write all the sub-images
4085(png_set_interlace_handling() returns the number of sub-images.)
4086
4087If you want libpng to build the sub-images, call this before you start
4088writing any rows:
4089
4090 number_of_passes = png_set_interlace_handling(png_ptr);
4091
4092This will return the number of passes needed. Currently, this is seven,
4093but may change if another interlace type is added.
4094
4095Then write the complete image number_of_passes times.
4096
4097 png_write_rows(png_ptr, row_pointers, number_of_rows);
4098
4099Think carefully before you write an interlaced image. Typically code that
4100reads such images reads all the image data into memory, uncompressed, before
4101doing any processing. Only code that can display an image on the fly can
4102take advantage of the interlacing and even then the image has to be exactly
4103the correct size for the output device, because scaling an image requires
4104adjacent pixels and these are not available until all the passes have been
4105read.
4106
4107If you do write an interlaced image you will hardly ever need to handle
4108the interlacing yourself. Call png_set_interlace_handling() and use the
4109approach described above.
4110
4111The only time it is conceivable that you will really need to write an
4112interlaced image pass-by-pass is when you have read one pass by pass and
4113made some pixel-by-pixel transformation to it, as described in the read
4114code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
4115to determine the size of each sub-image in turn and simply write the rows
4116you obtained from the read code.
4117
4118.SS Finishing a sequential write
4119
4120After you are finished writing the image, you should finish writing
4121the file. If you are interested in writing comments or time, you should
4122pass an appropriately filled png_info pointer. If you are not interested,
4123you can pass NULL.
4124
4125 png_write_end(png_ptr, info_ptr);
4126
4127When you are done, you can free all memory used by libpng like this:
4128
4129 png_destroy_write_struct(&png_ptr, &info_ptr);
4130
4131It is also possible to individually free the info_ptr members that
4132point to libpng-allocated storage with the following function:
4133
4134 png_free_data(png_ptr, info_ptr, mask, seq)
4135
4136 mask - identifies data to be freed, a mask
4137 containing the bitwise OR of one or
4138 more of
4139 PNG_FREE_PLTE, PNG_FREE_TRNS,
4140 PNG_FREE_HIST, PNG_FREE_ICCP,
4141 PNG_FREE_PCAL, PNG_FREE_ROWS,
4142 PNG_FREE_SCAL, PNG_FREE_SPLT,
4143 PNG_FREE_TEXT, PNG_FREE_UNKN,
4144 or simply PNG_FREE_ALL
4145
4146 seq - sequence number of item to be freed
4147 (\-1 for all items)
4148
4149This function may be safely called when the relevant storage has
4150already been freed, or has not yet been allocated, or was allocated
4151by the user and not by libpng, and will in those cases do nothing.
4152The "seq" parameter is ignored if only one item of the selected data
4153type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
4154are allowed for the data type identified in the mask, such as text or
4155sPLT, only the n'th item in the structure is freed, where n is "seq".
4156
4157If you allocated data such as a palette that you passed in to libpng
4158with png_set_*, you must not free it until just before the call to
4159png_destroy_write_struct().
4160
4161The default behavior is only to free data that was allocated internally
4162by libpng. This can be changed, so that libpng will not free the data,
4163or so that it will free data that was allocated by the user with png_malloc()
4164or png_calloc() and passed in via a png_set_*() function, with
4165
4166 png_data_freer(png_ptr, info_ptr, freer, mask)
4167
4168 freer - one of
4169 PNG_DESTROY_WILL_FREE_DATA
4170 PNG_SET_WILL_FREE_DATA
4171 PNG_USER_WILL_FREE_DATA
4172
4173 mask - which data elements are affected
4174 same choices as in png_free_data()
4175
4176For example, to transfer responsibility for some data from a read structure
4177to a write structure, you could use
4178
4179 png_data_freer(read_ptr, read_info_ptr,
4180 PNG_USER_WILL_FREE_DATA,
4181 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4182
4183 png_data_freer(write_ptr, write_info_ptr,
4184 PNG_DESTROY_WILL_FREE_DATA,
4185 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4186
4187thereby briefly reassigning responsibility for freeing to the user but
4188immediately afterwards reassigning it once more to the write_destroy
4189function. Having done this, it would then be safe to destroy the read
4190structure and continue to use the PLTE, tRNS, and hIST data in the write
4191structure.
4192
4193This function only affects data that has already been allocated.
4194You can call this function before calling after the png_set_*() functions
4195to control whether the user or png_destroy_*() is supposed to free the data.
4196When the user assumes responsibility for libpng-allocated data, the
4197application must use
4198png_free() to free it, and when the user transfers responsibility to libpng
4199for data that the user has allocated, the user must have used png_malloc()
4200or png_calloc() to allocate it.
4201
4202If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
4203separately, do not transfer responsibility for freeing text_ptr to libpng,
4204because when libpng fills a png_text structure it combines these members with
4205the key member, and png_free_data() will free only text_ptr.key. Similarly,
4206if you transfer responsibility for free'ing text_ptr from libpng to your
4207application, your application must not separately free those members.
4208For a more compact example of writing a PNG image, see the file example.c.
4209
4210.SH V. Simplified API
4211
4212The simplified API, which became available in libpng-1.6.0, hides the details
4213of both libpng and the PNG file format itself.
4214It allows PNG files to be read into a very limited number of
4215in-memory bitmap formats or to be written from the same formats. If these
4216formats do not accommodate your needs then you can, and should, use the more
4217sophisticated APIs above - these support a wide variety of in-memory formats
4218and a wide variety of sophisticated transformations to those formats as well
4219as a wide variety of APIs to manipulate ancilliary information.
4220
4221To read a PNG file using the simplified API:
4222
4223 1) Declare a 'png_image' structure (see below) on the
4224 stack and memset() it to all zero.
4225
4226 2) Call the appropriate png_image_begin_read... function.
4227
4228 3) Set the png_image 'format' member to the required
4229 format and allocate a buffer for the image.
4230
4231 4) Call png_image_finish_read to read the image into
4232 your buffer.
4233
4234There are no restrictions on the format of the PNG input itself; all valid
4235color types, bit depths, and interlace methods are acceptable, and the
4236input image is transformed as necessary to the requested in-memory format
4237during the png_image_finish_read() step.
4238
4239To write a PNG file using the simplified API:
4240
4241 1) Declare a 'png_image' structure on the stack and memset()
4242 it to all zero.
4243
4244 2) Initialize the members of the structure that describe the
4245 image, setting the 'format' member to the format of the
4246 image in memory.
4247
4248 3) Call the appropriate png_image_write... function with a
4249 pointer to the image to write the PNG data.
4250
4251png_image is a structure that describes the in-memory format of an image
4252when it is being read or define the in-memory format of an image that you
4253need to write. The "png_image" structure contains the following members:
4254
4255 png_uint_32 version Set to PNG_IMAGE_VERSION
4256 png_uint_32 width Image width in pixels (columns)
4257 png_uint_32 height Image height in pixels (rows)
4258 png_uint_32 format Image format as defined below
4259 png_uint_32 flags A bit mask containing informational flags
4260 png_controlp opaque Initialize to NULL, free with png_image_free
4261 png_uint_32 colormap_entries; Number of entries in the color-map
4262 png_uint_32 warning_or_error;
4263 char message[64];
4264
4265In the event of an error or warning the following field warning_or_error
4266field will be set to a non-zero value and the 'message' field will contain
4267a '\0' terminated string with the libpng error or warning message. If both
4268warnings and an error were encountered, only the error is recorded. If there
4269are multiple warnings, only the first one is recorded.
4270
4271The upper 30 bits of this value are reserved; the low two bits contain
4272a two bit code such that a value more than 1 indicates a failure in the API
4273just called:
4274
4275 0 - no warning or error
4276 1 - warning
4277 2 - error
4278 3 - error preceded by warning
4279
4280The pixels (samples) of the image have one to four channels whose components
4281have original values in the range 0 to 1.0:
4282
4283 1: A single gray or luminance channel (G).
4284 2: A gray/luminance channel and an alpha channel (GA).
4285 3: Three red, green, blue color channels (RGB).
4286 4: Three color channels and an alpha channel (RGBA).
4287
4288The channels are encoded in one of two ways:
4289
4290 a) As a small integer, value 0..255, contained in a single byte. For the
4291alpha channel the original value is simply value/255. For the color or
4292luminance channels the value is encoded according to the sRGB specification
4293and matches the 8-bit format expected by typical display devices.
4294
4295The color/gray channels are not scaled (pre-multiplied) by the alpha
4296channel and are suitable for passing to color management software.
4297
4298 b) As a value in the range 0..65535, contained in a 2-byte integer, in
4299the native byte order of the platform on which the application is running.
4300All channels can be converted to the original value by dividing by 65535; all
4301channels are linear. Color channels use the RGB encoding (RGB end-points) of
4302the sRGB specification. This encoding is identified by the
4303PNG_FORMAT_FLAG_LINEAR flag below.
4304
4305When an alpha channel is present it is expected to denote pixel coverage
4306of the color or luminance channels and is returned as an associated alpha
4307channel: the color/gray channels are scaled (pre-multiplied) by the alpha
4308value.
4309
4310When a color-mapped image is used as a result of calling
4311png_image_read_colormap or png_image_write_colormap the channels are encoded
4312in the color-map and the descriptions above apply to the color-map entries.
4313The image data is encoded as small integers, value 0..255, that index the
4314entries in the color-map. One integer (one byte) is stored for each pixel.
4315
4316PNG_FORMAT_*
4317
4318The #defines to be used in png_image::format. Each #define identifies a
4319particular layout of channel data and, if present, alpha values. There are
4320separate defines for each of the two channel encodings.
4321
4322A format is built up using single bit flag values. Not all combinations are
4323valid: use the bit flag values below for testing a format returned by the
4324read APIs, but set formats from the derived values.
4325
4326When reading or writing color-mapped images the format should be set to the
4327format of the entries in the color-map then png_image_{read,write}_colormap
4328called to read or write the color-map and set the format correctly for the
4329image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly!
4330
4331NOTE: libpng can be built with particular features disabled, if you see
4332compiler errors because the definition of one of the following flags has been
4333compiled out it is because libpng does not have the required support. It is
4334possible, however, for the libpng configuration to enable the format on just
4335read or just write; in that case you may see an error at run time. You can
4336guard against this by checking for the definition of:
4337
4338 PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED
4339
4340 PNG_FORMAT_FLAG_ALPHA 0x01 format with an alpha channel
4341 PNG_FORMAT_FLAG_COLOR 0x02 color format: otherwise grayscale
4342 PNG_FORMAT_FLAG_LINEAR 0x04 png_uint_16 channels else png_byte
4343 PNG_FORMAT_FLAG_COLORMAP 0x08 libpng use only
4344 PNG_FORMAT_FLAG_BGR 0x10 BGR colors, else order is RGB
4345 PNG_FORMAT_FLAG_AFIRST 0x20 alpha channel comes first
4346
4347Supported formats are as follows. Future versions of libpng may support more
4348formats; for compatibility with older versions simply check if the format
4349macro is defined using #ifdef. These defines describe the in-memory layout
4350of the components of the pixels of the image.
4351
4352First the single byte formats:
4353
4354 PNG_FORMAT_GRAY 0
4355 PNG_FORMAT_GA PNG_FORMAT_FLAG_ALPHA
4356 PNG_FORMAT_AG (PNG_FORMAT_GA|PNG_FORMAT_FLAG_AFIRST)
4357 PNG_FORMAT_RGB PNG_FORMAT_FLAG_COLOR
4358 PNG_FORMAT_BGR (PNG_FORMAT_FLAG_COLOR|PNG_FORMAT_FLAG_BGR)
4359 PNG_FORMAT_RGBA (PNG_FORMAT_RGB|PNG_FORMAT_FLAG_ALPHA)
4360 PNG_FORMAT_ARGB (PNG_FORMAT_RGBA|PNG_FORMAT_FLAG_AFIRST)
4361 PNG_FORMAT_BGRA (PNG_FORMAT_BGR|PNG_FORMAT_FLAG_ALPHA)
4362 PNG_FORMAT_ABGR (PNG_FORMAT_BGRA|PNG_FORMAT_FLAG_AFIRST)
4363
4364Then the linear 2-byte formats. When naming these "Y" is used to
4365indicate a luminance (gray) channel. The component order within the pixel
4366is always the same - there is no provision for swapping the order of the
4367components in the linear format. The components are 16-bit integers in
4368the native byte order for your platform, and there is no provision for
4369swapping the bytes to a different endian condition.
4370
4371 PNG_FORMAT_LINEAR_Y PNG_FORMAT_FLAG_LINEAR
4372 PNG_FORMAT_LINEAR_Y_ALPHA
4373 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_ALPHA)
4374 PNG_FORMAT_LINEAR_RGB
4375 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR)
4376 PNG_FORMAT_LINEAR_RGB_ALPHA
4377 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR|
4378 PNG_FORMAT_FLAG_ALPHA)
4379
4380Color-mapped formats are obtained by calling png_image_{read,write}_colormap,
4381as appropriate after setting png_image::format to the format of the color-map
4382to be read or written. Applications may check the value of
4383PNG_FORMAT_FLAG_COLORMAP to see if they have called the colormap API. The
4384format of the color-map may be extracted using the following macro.
4385
4386 PNG_FORMAT_OF_COLORMAP(fmt) ((fmt) & ~PNG_FORMAT_FLAG_COLORMAP)
4387
4388PNG_IMAGE macros
4389
4390These are convenience macros to derive information from a png_image
4391structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the
4392actual image sample values - either the entries in the color-map or the
4393pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values
4394for the pixels and will always return 1 after a call to
4395png_image_{read,write}_colormap. The remaining macros return information
4396about the rows in the image and the complete image.
4397
4398NOTE: All the macros that take a png_image::format parameter are compile time
4399constants if the format parameter is, itself, a constant. Therefore these
4400macros can be used in array declarations and case labels where required.
4401Similarly the macros are also pre-processor constants (sizeof is not used) so
4402they can be used in #if tests.
4403
4404First the information about the samples.
4405
4406 PNG_IMAGE_SAMPLE_CHANNELS(fmt)
4407 Returns the total number of channels in a given format: 1..4
4408
4409 PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt)
4410 Returns the size in bytes of a single component of a pixel or color-map
4411 entry (as appropriate) in the image.
4412
4413 PNG_IMAGE_SAMPLE_SIZE(fmt)
4414 This is the size of the sample data for one sample. If the image is
4415 color-mapped it is the size of one color-map entry (and image pixels are
4416 one byte in size), otherwise it is the size of one image pixel.
4417
4418 PNG_IMAGE_COLORMAP_SIZE(fmt)
4419 The size of the color-map required by the format; this is the size of the
4420 color-map buffer passed to the png_image_{read,write}_colormap APIs, it is
4421 a fixed number determined by the format so can easily be allocated on the
4422 stack if necessary.
4423
4424#define PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt)\
4425 (PNG_IMAGE_SAMPLE_CHANNELS(fmt) * 256)
4426 /* The maximum size of the color-map required by the format expressed in a
4427 * count of components. This can be used to compile-time allocate a
4428 * color-map:
4429 *
4430 * png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)];
4431 *
4432 * png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
4433 *
4434 * Alternatively, use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
4435 * information from one of the png_image_begin_read_ APIs and dynamically
4436 * allocate the required memory.
4437 */
4438
4439
4440Corresponding information about the pixels
4441
4442 PNG_IMAGE_PIXEL_(test,fmt)
4443
4444 PNG_IMAGE_PIXEL_CHANNELS(fmt)
4445 The number of separate channels (components) in a pixel; 1 for a
4446 color-mapped image.
4447
4448 PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\
4449 The size, in bytes, of each component in a pixel; 1 for a color-mapped
4450 image.
4451
4452 PNG_IMAGE_PIXEL_SIZE(fmt)
4453 The size, in bytes, of a complete pixel; 1 for a color-mapped image.
4454
4455Information about the whole row, or whole image
4456
4457 PNG_IMAGE_ROW_STRIDE(image)
4458 Returns the total number of components in a single row of the image; this
4459 is the minimum 'row stride', the minimum count of components between each
4460 row. For a color-mapped image this is the minimum number of bytes in a
4461 row.
4462
4463 If you need the stride measured in bytes, row_stride_bytes is
4464 PNG_IMAGE_ROW_STRIDE(image) * PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)
4465 plus any padding bytes that your application might need, for example
4466 to start the next row on a 4-byte boundary.
4467
4468 PNG_IMAGE_BUFFER_SIZE(image, row_stride)
4469 Returns the size, in bytes, of an image buffer given a png_image and a row
4470 stride - the number of components to leave space for in each row. This
4471 macro takes care of multiplying row_stride by PNG_IMAGE_PIXEL_COMONENT_SIZE
4472 when the image has 2-byte components.
4473
4474 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
4475 This indicates the the RGB values of the in-memory bitmap do not
4476 correspond to the red, green and blue end-points defined by sRGB.
4477
4478 PNG_IMAGE_FLAG_COLORMAP == 0x02
4479 The PNG is color-mapped. If this flag is set png_image_read_colormap
4480 can be used without further loss of image information. If it is not set
4481 png_image_read_colormap will cause significant loss if the image has any
4482
4483READ APIs
4484
4485 The png_image passed to the read APIs must have been initialized by setting
4486 the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.)
4487
4488 int png_image_begin_read_from_file( png_imagep image,
4489 const char *file_name)
4490
4491 The named file is opened for read and the image header
4492 is filled in from the PNG header in the file.
4493
4494 int png_image_begin_read_from_stdio (png_imagep image,
4495 FILE* file)
4496
4497 The PNG header is read from the stdio FILE object.
4498
4499 int png_image_begin_read_from_memory(png_imagep image,
4500 png_const_voidp memory, png_size_t size)
4501
4502 The PNG header is read from the given memory buffer.
4503
4504 int png_image_finish_read(png_imagep image,
4505 png_colorp background, void *buffer,
4506 png_int_32 row_stride, void *colormap));
4507
4508 Finish reading the image into the supplied buffer and
4509 clean up the png_image structure.
4510
4511 row_stride is the step, in png_byte or png_uint_16 units
4512 as appropriate, between adjacent rows. A positive stride
4513 indicates that the top-most row is first in the buffer -
4514 the normal top-down arrangement. A negative stride
4515 indicates that the bottom-most row is first in the buffer.
4516
4517 background need only be supplied if an alpha channel must
4518 be removed from a png_byte format and the removal is to be
4519 done by compositing on a solid color; otherwise it may be
4520 NULL and any composition will be done directly onto the
4521 buffer. The value is an sRGB color to use for the
4522 background, for grayscale output the green channel is used.
4523
4524 For linear output removing the alpha channel is always done
4525 by compositing on black.
4526
4527 void png_image_free(png_imagep image)
4528
4529 Free any data allocated by libpng in image->opaque,
4530 setting the pointer to NULL. May be called at any time
4531 after the structure is initialized.
4532
4533When the simplified API needs to convert between sRGB and linear colorspaces,
4534the actual sRGB transfer curve defined in the sRGB specification (see the
4535article at http://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
4536approximation used elsewhere in libpng.
4537
4538WRITE APIS
4539
4540For write you must initialize a png_image structure to describe the image to
4541be written:
4542
4543 version: must be set to PNG_IMAGE_VERSION
4544 opaque: must be initialized to NULL
4545 width: image width in pixels
4546 height: image height in rows
4547 format: the format of the data you wish to write
4548 flags: set to 0 unless one of the defined flags applies; set
4549 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images
4550 where the RGB values do not correspond to the colors in sRGB.
4551 colormap_entries: set to the number of entries in the color-map (0 to 256)
4552
4553 int png_image_write_to_file, (png_imagep image,
4554 const char *file, int convert_to_8bit, const void *buffer,
4555 png_int_32 row_stride, const void *colormap));
4556
4557 Write the image to the named file.
4558
4559 int png_image_write_to_stdio(png_imagep image, FILE *file,
4560 int convert_to_8_bit, const void *buffer,
4561 png_int_32 row_stride, const void *colormap)
4562
4563 Write the image to the given (FILE*).
4564
4565With all write APIs if image is in one of the linear formats with
4566(png_uint_16) data then setting convert_to_8_bit will cause the output to be
4567a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise
4568a 16-bit linear encoded PNG file is written.
4569
4570With all APIs row_stride is handled as in the read APIs - it is the spacing
4571from one row to the next in component sized units (float) and if negative
4572indicates a bottom-up row layout in the buffer.
4573
4574Note that the write API does not support interlacing, sub-8-bit pixels,
4575and indexed (paletted) images.
4576
4577.SH VI. Modifying/Customizing libpng
4578
4579There are two issues here. The first is changing how libpng does
4580standard things like memory allocation, input/output, and error handling.
4581The second deals with more complicated things like adding new chunks,
4582adding new transformations, and generally changing how libpng works.
4583Both of those are compile-time issues; that is, they are generally
4584determined at the time the code is written, and there is rarely a need
4585to provide the user with a means of changing them.
4586
4587Memory allocation, input/output, and error handling
4588
4589All of the memory allocation, input/output, and error handling in libpng
4590goes through callbacks that are user-settable. The default routines are
4591in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4592these functions, call the appropriate png_set_*_fn() function.
4593
4594Memory allocation is done through the functions png_malloc(), png_calloc(),
4595and png_free(). The png_malloc() and png_free() functions currently just
4596call the standard C functions and png_calloc() calls png_malloc() and then
4597clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
4598is not the same as the calloc(number, size) function provided by stdlib.h.
4599There is limited support for certain systems with segmented memory
4600architectures and the types of pointers declared by png.h match this; you
4601will have to use appropriate pointers in your application. If you prefer
4602to use a different method of allocating and freeing data, you can use
4603png_create_read_struct_2() or png_create_write_struct_2() to register your
4604own functions as described above. These functions also provide a void
4605pointer that can be retrieved via
4606
4607 mem_ptr=png_get_mem_ptr(png_ptr);
4608
4609Your replacement memory functions must have prototypes as follows:
4610
4611 png_voidp malloc_fn(png_structp png_ptr,
4612 png_alloc_size_t size);
4613
4614 void free_fn(png_structp png_ptr, png_voidp ptr);
4615
4616Your malloc_fn() must return NULL in case of failure. The png_malloc()
4617function will normally call png_error() if it receives a NULL from the
4618system memory allocator or from your replacement malloc_fn().
4619
4620Your free_fn() will never be called with a NULL ptr, since libpng's
4621png_free() checks for NULL before calling free_fn().
4622
4623Input/Output in libpng is done through png_read() and png_write(),
4624which currently just call fread() and fwrite(). The FILE * is stored in
4625png_struct and is initialized via png_init_io(). If you wish to change
4626the method of I/O, the library supplies callbacks that you can set
4627through the function png_set_read_fn() and png_set_write_fn() at run
4628time, instead of calling the png_init_io() function. These functions
4629also provide a void pointer that can be retrieved via the function
4630png_get_io_ptr(). For example:
4631
4632 png_set_read_fn(png_structp read_ptr,
4633 voidp read_io_ptr, png_rw_ptr read_data_fn)
4634
4635 png_set_write_fn(png_structp write_ptr,
4636 voidp write_io_ptr, png_rw_ptr write_data_fn,
4637 png_flush_ptr output_flush_fn);
4638
4639 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4640 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4641
4642The replacement I/O functions must have prototypes as follows:
4643
4644 void user_read_data(png_structp png_ptr,
4645 png_bytep data, png_size_t length);
4646
4647 void user_write_data(png_structp png_ptr,
4648 png_bytep data, png_size_t length);
4649
4650 void user_flush_data(png_structp png_ptr);
4651
4652The user_read_data() function is responsible for detecting and
4653handling end-of-data errors.
4654
4655Supplying NULL for the read, write, or flush functions sets them back
4656to using the default C stream functions, which expect the io_ptr to
4657point to a standard *FILE structure. It is probably a mistake
4658to use NULL for one of write_data_fn and output_flush_fn but not both
4659of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4660It is an error to read from a write stream, and vice versa.
4661
4662Error handling in libpng is done through png_error() and png_warning().
4663Errors handled through png_error() are fatal, meaning that png_error()
4664should never return to its caller. Currently, this is handled via
4665setjmp() and longjmp() (unless you have compiled libpng with
4666PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4667but you could change this to do things like exit() if you should wish,
4668as long as your function does not return.
4669
4670On non-fatal errors, png_warning() is called
4671to print a warning message, and then control returns to the calling code.
4672By default png_error() and png_warning() print a message on stderr via
4673fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4674(because you don't want the messages) or PNG_NO_STDIO defined (because
4675fprintf() isn't available). If you wish to change the behavior of the error
4676functions, you will need to set up your own message callbacks. These
4677functions are normally supplied at the time that the png_struct is created.
4678It is also possible to redirect errors and warnings to your own replacement
4679functions after png_create_*_struct() has been called by calling:
4680
4681 png_set_error_fn(png_structp png_ptr,
4682 png_voidp error_ptr, png_error_ptr error_fn,
4683 png_error_ptr warning_fn);
4684
4685 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4686
4687If NULL is supplied for either error_fn or warning_fn, then the libpng
4688default function will be used, calling fprintf() and/or longjmp() if a
4689problem is encountered. The replacement error functions should have
4690parameters as follows:
4691
4692 void user_error_fn(png_structp png_ptr,
4693 png_const_charp error_msg);
4694
4695 void user_warning_fn(png_structp png_ptr,
4696 png_const_charp warning_msg);
4697
4698The motivation behind using setjmp() and longjmp() is the C++ throw and
4699catch exception handling methods. This makes the code much easier to write,
4700as there is no need to check every return code of every function call.
4701However, there are some uncertainties about the status of local variables
4702after a longjmp, so the user may want to be careful about doing anything
4703after setjmp returns non-zero besides returning itself. Consult your
4704compiler documentation for more details. For an alternative approach, you
4705may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
4706which is illustrated in pngvalid.c and in contrib/visupng.
4707
4708Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
4709You can use this to handle certain errors (normally handled as errors)
4710as warnings.
4711
4712 png_set_benign_errors (png_ptr, int allowed);
4713
4714 allowed: 0: treat png_benign_error() as an error.
4715 1: treat png_benign_error() as a warning.
4716
4717As of libpng-1.6.0, the default condition is to treat benign errors as
4718warnings while reading and as errors while writing.
4719
4720.SS Custom chunks
4721
4722If you need to read or write custom chunks, you may need to get deeper
4723into the libpng code. The library now has mechanisms for storing
4724and writing chunks of unknown type; you can even declare callbacks
4725for custom chunks. However, this may not be good enough if the
4726library code itself needs to know about interactions between your
4727chunk and existing `intrinsic' chunks.
4728
4729If you need to write a new intrinsic chunk, first read the PNG
4730specification. Acquire a first level of understanding of how it works.
4731Pay particular attention to the sections that describe chunk names,
4732and look at how other chunks were designed, so you can do things
4733similarly. Second, check out the sections of libpng that read and
4734write chunks. Try to find a chunk that is similar to yours and use
4735it as a template. More details can be found in the comments inside
4736the code. It is best to handle private or unknown chunks in a generic method,
4737via callback functions, instead of by modifying libpng functions. This
4738is illustrated in pngtest.c, which uses a callback function to handle a
4739private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4740libpng.
4741
4742If you wish to write your own transformation for the data, look through
4743the part of the code that does the transformations, and check out some of
4744the simpler ones to get an idea of how they work. Try to find a similar
4745transformation to the one you want to add and copy off of it. More details
4746can be found in the comments inside the code itself.
4747
4748.SS Configuring for gui/windowing platforms:
4749
4750You will need to write new error and warning functions that use the GUI
4751interface, as described previously, and set them to be the error and
4752warning functions at the time that png_create_*_struct() is called,
4753in order to have them available during the structure initialization.
4754They can be changed later via png_set_error_fn(). On some compilers,
4755you may also have to change the memory allocators (png_malloc, etc.).
4756
4757.SS Configuring zlib:
4758
4759There are special functions to configure the compression. Perhaps the
4760most useful one changes the compression level, which currently uses
4761input compression values in the range 0 - 9. The library normally
4762uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4763have shown that for a large majority of images, compression values in
4764the range 3-6 compress nearly as well as higher levels, and do so much
4765faster. For online applications it may be desirable to have maximum speed
4766(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4767specify no compression (Z_NO_COMPRESSION = 0), but this would create
4768files larger than just storing the raw bitmap. You can specify the
4769compression level by calling:
4770
4771 #include zlib.h
4772 png_set_compression_level(png_ptr, level);
4773
4774Another useful one is to reduce the memory level used by the library.
4775The memory level defaults to 8, but it can be lowered if you are
4776short on memory (running DOS, for example, where you only have 640K).
4777Note that the memory level does have an effect on compression; among
4778other things, lower levels will result in sections of incompressible
4779data being emitted in smaller stored blocks, with a correspondingly
4780larger relative overhead of up to 15% in the worst case.
4781
4782 #include zlib.h
4783 png_set_compression_mem_level(png_ptr, level);
4784
4785The other functions are for configuring zlib. They are not recommended
4786for normal use and may result in writing an invalid PNG file. See
4787zlib.h for more information on what these mean.
4788
4789 #include zlib.h
4790 png_set_compression_strategy(png_ptr,
4791 strategy);
4792
4793 png_set_compression_window_bits(png_ptr,
4794 window_bits);
4795
4796 png_set_compression_method(png_ptr, method);
4797
4798This controls the size of the IDAT chunks (default 8192):
4799
4800 png_set_compression_buffer_size(png_ptr, size);
4801
4802As of libpng version 1.5.4, additional APIs became
4803available to set these separately for non-IDAT
4804compressed chunks such as zTXt, iTXt, and iCCP:
4805
4806 #include zlib.h
4807 #if PNG_LIBPNG_VER >= 10504
4808 png_set_text_compression_level(png_ptr, level);
4809
4810 png_set_text_compression_mem_level(png_ptr, level);
4811
4812 png_set_text_compression_strategy(png_ptr,
4813 strategy);
4814
4815 png_set_text_compression_window_bits(png_ptr,
4816 window_bits);
4817
4818 png_set_text_compression_method(png_ptr, method);
4819 #endif
4820
4821.SS Controlling row filtering
4822
4823If you want to control whether libpng uses filtering or not, which
4824filters are used, and how it goes about picking row filters, you
4825can call one of these functions. The selection and configuration
4826of row filters can have a significant impact on the size and
4827encoding speed and a somewhat lesser impact on the decoding speed
4828of an image. Filtering is enabled by default for RGB and grayscale
4829images (with and without alpha), but not for paletted images nor
4830for any images with bit depths less than 8 bits/pixel.
4831
4832The 'method' parameter sets the main filtering method, which is
4833currently only '0' in the PNG 1.2 specification. The 'filters'
4834parameter sets which filter(s), if any, should be used for each
4835scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4836to turn filtering on and off, respectively.
4837
4838Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4839PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4840ORed together with '|' to specify one or more filters to use.
4841These filters are described in more detail in the PNG specification.
4842If you intend to change the filter type during the course of writing
4843the image, you should start with flags set for all of the filters
4844you intend to use so that libpng can initialize its internal
4845structures appropriately for all of the filter types. (Note that this
4846means the first row must always be adaptively filtered, because libpng
4847currently does not allocate the filter buffers until png_write_row()
4848is called for the first time.)
4849
4850 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4851 PNG_FILTER_UP | PNG_FILTER_AVG |
4852 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4853
4854 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4855 filters);
4856 The second parameter can also be
4857 PNG_INTRAPIXEL_DIFFERENCING if you are
4858 writing a PNG to be embedded in a MNG
4859 datastream. This parameter must be the
4860 same as the value of filter_method used
4861 in png_set_IHDR().
4862
4863It is also possible to influence how libpng chooses from among the
4864available filters. This is done in one or both of two ways - by
4865telling it how important it is to keep the same filter for successive
4866rows, and by telling it the relative computational costs of the filters.
4867
4868 double weights[3] = {1.5, 1.3, 1.1},
4869 costs[PNG_FILTER_VALUE_LAST] =
4870 {1.0, 1.3, 1.3, 1.5, 1.7};
4871
4872 png_set_filter_heuristics(png_ptr,
4873 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4874 weights, costs);
4875
4876The weights are multiplying factors that indicate to libpng that the
4877row filter should be the same for successive rows unless another row filter
4878is that many times better than the previous filter. In the above example,
4879if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4880"sum of absolute differences" 1.5 x 1.3 times higher than other filters
4881and still be chosen, while the NONE filter could have a sum 1.1 times
4882higher than other filters and still be chosen. Unspecified weights are
4883taken to be 1.0, and the specified weights should probably be declining
4884like those above in order to emphasize recent filters over older filters.
4885
4886The filter costs specify for each filter type a relative decoding cost
4887to be considered when selecting row filters. This means that filters
4888with higher costs are less likely to be chosen over filters with lower
4889costs, unless their "sum of absolute differences" is that much smaller.
4890The costs do not necessarily reflect the exact computational speeds of
4891the various filters, since this would unduly influence the final image
4892size.
4893
4894Note that the numbers above were invented purely for this example and
4895are given only to help explain the function usage. Little testing has
4896been done to find optimum values for either the costs or the weights.
4897
4898.SS Requesting debug printout
4899
4900The macro definition PNG_DEBUG can be used to request debugging
4901printout. Set it to an integer value in the range 0 to 3. Higher
4902numbers result in increasing amounts of debugging information. The
4903information is printed to the "stderr" file, unless another file
4904name is specified in the PNG_DEBUG_FILE macro definition.
4905
4906When PNG_DEBUG > 0, the following functions (macros) become available:
4907
4908 png_debug(level, message)
4909 png_debug1(level, message, p1)
4910 png_debug2(level, message, p1, p2)
4911
4912in which "level" is compared to PNG_DEBUG to decide whether to print
4913the message, "message" is the formatted string to be printed,
4914and p1 and p2 are parameters that are to be embedded in the string
4915according to printf-style formatting directives. For example,
4916
4917 png_debug1(2, "foo=%d", foo);
4918
4919is expanded to
4920
4921 if (PNG_DEBUG > 2)
4922 fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo);
4923
4924When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4925can still use PNG_DEBUG to control your own debugging:
4926
4927 #ifdef PNG_DEBUG
4928 fprintf(stderr, ...
4929 #endif
4930
4931When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
4932having level = 0 will be printed. There aren't any such statements in
4933this version of libpng, but if you insert some they will be printed.
4934
4935.SH VII. MNG support
4936
4937The MNG specification (available at http://www.libpng.org/pub/mng) allows
4938certain extensions to PNG for PNG images that are embedded in MNG datastreams.
4939Libpng can support some of these extensions. To enable them, use the
4940png_permit_mng_features() function:
4941
4942 feature_set = png_permit_mng_features(png_ptr, mask)
4943
4944 mask is a png_uint_32 containing the bitwise OR of the
4945 features you want to enable. These include
4946 PNG_FLAG_MNG_EMPTY_PLTE
4947 PNG_FLAG_MNG_FILTER_64
4948 PNG_ALL_MNG_FEATURES
4949
4950 feature_set is a png_uint_32 that is the bitwise AND of
4951 your mask with the set of MNG features that is
4952 supported by the version of libpng that you are using.
4953
4954It is an error to use this function when reading or writing a standalone
4955PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
4956in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
4957and the MHDR and MEND chunks. Libpng does not provide support for these
4958or any other MNG chunks; your application must provide its own support for
4959them. You may wish to consider using libmng (available at
4960http://www.libmng.com) instead.
4961
4962.SH VIII. Changes to Libpng from version 0.88
4963
4964It should be noted that versions of libpng later than 0.96 are not
4965distributed by the original libpng author, Guy Schalnat, nor by
4966Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
4967distributed versions 0.89 through 0.96, but rather by another member
4968of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
4969still alive and well, but they have moved on to other things.
4970
4971The old libpng functions png_read_init(), png_write_init(),
4972png_info_init(), png_read_destroy(), and png_write_destroy() have been
4973moved to PNG_INTERNAL in version 0.95 to discourage their use. These
4974functions will be removed from libpng version 1.4.0.
4975
4976The preferred method of creating and initializing the libpng structures is
4977via the png_create_read_struct(), png_create_write_struct(), and
4978png_create_info_struct() because they isolate the size of the structures
4979from the application, allow version error checking, and also allow the
4980use of custom error handling routines during the initialization, which
4981the old functions do not. The functions png_read_destroy() and
4982png_write_destroy() do not actually free the memory that libpng
4983allocated for these structs, but just reset the data structures, so they
4984can be used instead of png_destroy_read_struct() and
4985png_destroy_write_struct() if you feel there is too much system overhead
4986allocating and freeing the png_struct for each image read.
4987
4988Setting the error callbacks via png_set_message_fn() before
4989png_read_init() as was suggested in libpng-0.88 is no longer supported
4990because this caused applications that do not use custom error functions
4991to fail if the png_ptr was not initialized to zero. It is still possible
4992to set the error callbacks AFTER png_read_init(), or to change them with
4993png_set_error_fn(), which is essentially the same function, but with a new
4994name to force compilation errors with applications that try to use the old
4995method.
4996
4997Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
4998however, iTXt support was not enabled by default.
4999
5000Starting with version 1.0.7, you can find out which version of the library
5001you are using at run-time:
5002
5003 png_uint_32 libpng_vn = png_access_version_number();
5004
5005The number libpng_vn is constructed from the major version, minor
5006version with leading zero, and release number with leading zero,
5007(e.g., libpng_vn for version 1.0.7 is 10007).
5008
5009Note that this function does not take a png_ptr, so you can call it
5010before you've created one.
5011
5012You can also check which version of png.h you used when compiling your
5013application:
5014
5015 png_uint_32 application_vn = PNG_LIBPNG_VER;
5016
5017.SH IX. Changes to Libpng from version 1.0.x to 1.2.x
5018
5019Support for user memory management was enabled by default. To
5020accomplish this, the functions png_create_read_struct_2(),
5021png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
5022png_malloc_default(), and png_free_default() were added.
5023
5024Support for the iTXt chunk has been enabled by default as of
5025version 1.2.41.
5026
5027Support for certain MNG features was enabled.
5028
5029Support for numbered error messages was added. However, we never got
5030around to actually numbering the error messages. The function
5031png_set_strip_error_numbers() was added (Note: the prototype for this
5032function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
5033builds of libpng-1.2.15. It was restored in libpng-1.2.36).
5034
5035The png_malloc_warn() function was added at libpng-1.2.3. This issues
5036a png_warning and returns NULL instead of aborting when it fails to
5037acquire the requested memory allocation.
5038
5039Support for setting user limits on image width and height was enabled
5040by default. The functions png_set_user_limits(), png_get_user_width_max(),
5041and png_get_user_height_max() were added at libpng-1.2.6.
5042
5043The png_set_add_alpha() function was added at libpng-1.2.7.
5044
5045The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
5046Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
5047tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
5048deprecated.
5049
5050A number of macro definitions in support of runtime selection of
5051assembler code features (especially Intel MMX code support) were
5052added at libpng-1.2.0:
5053
5054 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
5055 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
5056 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
5057 PNG_ASM_FLAG_MMX_READ_INTERLACE
5058 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
5059 PNG_ASM_FLAG_MMX_READ_FILTER_UP
5060 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
5061 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
5062 PNG_ASM_FLAGS_INITIALIZED
5063 PNG_MMX_READ_FLAGS
5064 PNG_MMX_FLAGS
5065 PNG_MMX_WRITE_FLAGS
5066 PNG_MMX_FLAGS
5067
5068We added the following functions in support of runtime
5069selection of assembler code features:
5070
5071 png_get_mmx_flagmask()
5072 png_set_mmx_thresholds()
5073 png_get_asm_flags()
5074 png_get_mmx_bitdepth_threshold()
5075 png_get_mmx_rowbytes_threshold()
5076 png_set_asm_flags()
5077
5078We replaced all of these functions with simple stubs in libpng-1.2.20,
5079when the Intel assembler code was removed due to a licensing issue.
5080
5081These macros are deprecated:
5082
5083 PNG_READ_TRANSFORMS_NOT_SUPPORTED
5084 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
5085 PNG_NO_SEQUENTIAL_READ_SUPPORTED
5086 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
5087 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
5088 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
5089
5090They have been replaced, respectively, by:
5091
5092 PNG_NO_READ_TRANSFORMS
5093 PNG_NO_PROGRESSIVE_READ
5094 PNG_NO_SEQUENTIAL_READ
5095 PNG_NO_WRITE_TRANSFORMS
5096 PNG_NO_READ_ANCILLARY_CHUNKS
5097 PNG_NO_WRITE_ANCILLARY_CHUNKS
5098
5099PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
5100deprecated since libpng-1.0.16 and libpng-1.2.6.
5101
5102The function
5103 png_check_sig(sig, num)
5104was replaced with
5105 !png_sig_cmp(sig, 0, num)
5106It has been deprecated since libpng-0.90.
5107
5108The function
5109 png_set_gray_1_2_4_to_8()
5110which also expands tRNS to alpha was replaced with
5111 png_set_expand_gray_1_2_4_to_8()
5112which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
5113
5114.SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
5115
5116Private libpng prototypes and macro definitions were moved from
5117png.h and pngconf.h into a new pngpriv.h header file.
5118
5119Functions png_set_benign_errors(), png_benign_error(), and
5120png_chunk_benign_error() were added.
5121
5122Support for setting the maximum amount of memory that the application
5123will allocate for reading chunks was added, as a security measure.
5124The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
5125were added to the library.
5126
5127We implemented support for I/O states by adding png_ptr member io_state
5128and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
5129
5130We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
5131input transforms.
5132
5133Checking for and reporting of errors in the IHDR chunk is more thorough.
5134
5135Support for global arrays was removed, to improve thread safety.
5136
5137Some obsolete/deprecated macros and functions have been removed.
5138
5139Typecasted NULL definitions such as
5140 #define png_voidp_NULL (png_voidp)NULL
5141were eliminated. If you used these in your application, just use
5142NULL instead.
5143
5144The png_struct and info_struct members "trans" and "trans_values" were
5145changed to "trans_alpha" and "trans_color", respectively.
5146
5147The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
5148were removed.
5149
5150The PNG_1_0_X and PNG_1_2_X macros were eliminated.
5151
5152The PNG_LEGACY_SUPPORTED macro was eliminated.
5153
5154Many WIN32_WCE #ifdefs were removed.
5155
5156The functions png_read_init(info_ptr), png_write_init(info_ptr),
5157png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
5158have been removed. They have been deprecated since libpng-0.95.
5159
5160The png_permit_empty_plte() was removed. It has been deprecated
5161since libpng-1.0.9. Use png_permit_mng_features() instead.
5162
5163We removed the obsolete stub functions png_get_mmx_flagmask(),
5164png_set_mmx_thresholds(), png_get_asm_flags(),
5165png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
5166png_set_asm_flags(), and png_mmx_supported()
5167
5168We removed the obsolete png_check_sig(), png_memcpy_check(), and
5169png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
5170and memset(), respectively.
5171
5172The function png_set_gray_1_2_4_to_8() was removed. It has been
5173deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
5174png_set_expand_gray_1_2_4_to_8() because the former function also
5175expanded any tRNS chunk to an alpha channel.
5176
5177Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
5178were added and are used by default instead of the corresponding
5179functions. Unfortunately,
5180from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5181function) incorrectly returned a value of type png_uint_32.
5182
5183We changed the prototype for png_malloc() from
5184 png_malloc(png_structp png_ptr, png_uint_32 size)
5185to
5186 png_malloc(png_structp png_ptr, png_alloc_size_t size)
5187
5188This also applies to the prototype for the user replacement malloc_fn().
5189
5190The png_calloc() function was added and is used in place of
5191of "png_malloc(); memset();" except in the case in png_read_png()
5192where the array consists of pointers; in this case a "for" loop is used
5193after the png_malloc() to set the pointers to NULL, to give robust.
5194behavior in case the application runs out of memory part-way through
5195the process.
5196
5197We changed the prototypes of png_get_compression_buffer_size() and
5198png_set_compression_buffer_size() to work with png_size_t instead of
5199png_uint_32.
5200
5201Support for numbered error messages was removed by default, since we
5202never got around to actually numbering the error messages. The function
5203png_set_strip_error_numbers() was removed from the library by default.
5204
5205The png_zalloc() and png_zfree() functions are no longer exported.
5206The png_zalloc() function no longer zeroes out the memory that it
5207allocates. Applications that called png_zalloc(png_ptr, number, size)
5208can call png_calloc(png_ptr, number*size) instead, and can call
5209png_free() instead of png_zfree().
5210
5211Support for dithering was disabled by default in libpng-1.4.0, because
5212it has not been well tested and doesn't actually "dither".
5213The code was not
5214removed, however, and could be enabled by building libpng with
5215PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
5216was re-enabled, but the function was renamed png_set_quantize() to
5217reflect more accurately what it actually does. At the same time,
5218the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
5219PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
5220was renamed to PNG_READ_QUANTIZE_SUPPORTED.
5221
5222We removed the trailing '.' from the warning and error messages.
5223
5224.SH XI. Changes to Libpng from version 1.4.x to 1.5.x
5225
5226From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5227function) incorrectly returned a value of type png_uint_32.
5228The incorrect macro was removed from libpng-1.4.5.
5229
5230Checking for invalid palette index on write was added at libpng
52311.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
5232a benign error. This is enabled by default because this condition is an
5233error according to the PNG specification, Clause 11.3.2, but the error can
5234be ignored in each png_ptr with
5235
5236 png_set_check_for_invalid_index(png_ptr, allowed);
5237
5238 allowed - one of
5239 0: disable benign error (accept the
5240 invalid data without warning).
5241 1: enable benign error (treat the
5242 invalid data as an error or a
5243 warning).
5244
5245If the error is ignored, or if png_benign_error() treats it as a warning,
5246any invalid pixels are decoded as opaque black by the decoder and written
5247as-is by the encoder.
5248
5249Retrieving the maximum palette index found was added at libpng-1.5.15.
5250This statement must appear after png_read_png() or png_read_image() while
5251reading, and after png_write_png() or png_write_image() while writing.
5252
5253 int max_palette = png_get_palette_max(png_ptr, info_ptr);
5254
5255This will return the maximum palette index found in the image, or "\-1" if
5256the palette was not checked, or "0" if no palette was found. Note that this
5257does not account for any palette index used by ancillary chunks such as the
5258bKGD chunk; you must check those separately to determine the maximum
5259palette index actually used.
5260
5261There are no substantial API changes between the non-deprecated parts of
5262the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
5263members of the main libpng control structures, png_struct and png_info,
5264deprecated in earlier versions of libpng, has been completely removed from
5265libpng 1.5.
5266
5267We no longer include zlib.h in png.h. The include statement has been moved
5268to pngstruct.h, where it is not accessible by applications. Applications that
5269need access to information in zlib.h will need to add the '#include "zlib.h"'
5270directive. It does not matter whether this is placed prior to or after
5271the '"#include png.h"' directive.
5272
5273The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
5274and were removed.
5275
5276We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
5277macros into a private header file (pngpriv.h) that is not accessible to
5278applications.
5279
5280In png_get_iCCP, the type of "profile" was changed from png_charpp
5281to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
5282
5283There are changes of form in png.h, including new and changed macros to
5284declare parts of the API. Some API functions with arguments that are
5285pointers to data not modified within the function have been corrected to
5286declare these arguments with PNG_CONST.
5287
5288Much of the internal use of C macros to control the library build has also
5289changed and some of this is visible in the exported header files, in
5290particular the use of macros to control data and API elements visible
5291during application compilation may require significant revision to
5292application code. (It is extremely rare for an application to do this.)
5293
5294Any program that compiled against libpng 1.4 and did not use deprecated
5295features or access internal library structures should compile and work
5296against libpng 1.5, except for the change in the prototype for
5297png_get_iCCP() and png_set_iCCP() API functions mentioned above.
5298
5299libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
5300interlaced images. The macros return the number of rows and columns in
5301each pass and information that can be used to de-interlace and (if
5302absolutely necessary) interlace an image.
5303
5304libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
5305the application-provided png_longjmp_ptr on the internal, but application
5306initialized, longjmp buffer. It is provided as a convenience to avoid
5307the need to use the png_jmpbuf macro, which had the unnecessary side
5308effect of resetting the internal png_longjmp_ptr value.
5309
5310libpng 1.5.0 includes a complete fixed point API. By default this is
5311present along with the corresponding floating point API. In general the
5312fixed point API is faster and smaller than the floating point one because
5313the PNG file format used fixed point, not floating point. This applies
5314even if the library uses floating point in internal calculations. A new
5315macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
5316uses floating point arithmetic (the default) or fixed point arithmetic
5317internally for performance critical calculations such as gamma correction.
5318In some cases, the gamma calculations may produce slightly different
5319results. This has changed the results in png_rgb_to_gray and in alpha
5320composition (png_set_background for example). This applies even if the
5321original image was already linear (gamma == 1.0) and, therefore, it is
5322not necessary to linearize the image. This is because libpng has *not*
5323been changed to optimize that case correctly, yet.
5324
5325Fixed point support for the sCAL chunk comes with an important caveat;
5326the sCAL specification uses a decimal encoding of floating point values
5327and the accuracy of PNG fixed point values is insufficient for
5328representation of these values. Consequently a "string" API
5329(png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
5330arbitrary sCAL chunks in the absence of either the floating point API or
5331internal floating point calculations. Starting with libpng-1.5.0, both
5332of these functions are present when PNG_sCAL_SUPPORTED is defined. Prior
5333to libpng-1.5.0, their presence also depended upon PNG_FIXED_POINT_SUPPORTED
5334being defined and PNG_FLOATING_POINT_SUPPORTED not being defined.
5335
5336Applications no longer need to include the optional distribution header
5337file pngusr.h or define the corresponding macros during application
5338build in order to see the correct variant of the libpng API. From 1.5.0
5339application code can check for the corresponding _SUPPORTED macro:
5340
5341#ifdef PNG_INCH_CONVERSIONS_SUPPORTED
5342 /* code that uses the inch conversion APIs. */
5343#endif
5344
5345This macro will only be defined if the inch conversion functions have been
5346compiled into libpng. The full set of macros, and whether or not support
5347has been compiled in, are available in the header file pnglibconf.h.
5348This header file is specific to the libpng build. Notice that prior to
53491.5.0 the _SUPPORTED macros would always have the default definition unless
5350reset by pngusr.h or by explicit settings on the compiler command line.
5351These settings may produce compiler warnings or errors in 1.5.0 because
5352of macro redefinition.
5353
5354Applications can now choose whether to use these macros or to call the
5355corresponding function by defining PNG_USE_READ_MACROS or
5356PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
5357only supported from 1.5.0; defining PNG_NO_USE_READ_MACROS prior to 1.5.0
5358will lead to a link failure.
5359
5360Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
5361when compressing the IDAT data and textual data such as zTXt and iCCP.
5362In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
5363We added five png_set_text_*() functions for setting the parameters to
5364use with textual data.
5365
5366Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5367option was off by default, and slightly inaccurate scaling occurred.
5368This option can no longer be turned off, and the choice of accurate
5369or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
5370API for accurate scaling or the old png_set_strip_16_to_8() API for simple
5371chopping. In libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5372macro became PNG_READ_SCALE_16_TO_8_SUPPORTED, and the PNG_READ_16_TO_8
5373macro became PNG_READ_STRIP_16_TO_8_SUPPORTED, to enable the two
5374png_set_*_16_to_8() functions separately.
5375
5376Prior to libpng-1.5.4, the png_set_user_limits() function could only be
5377used to reduce the width and height limits from the value of
5378PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
5379that it could be used to override them. Now this function will reduce or
5380increase the limits.
5381
5382Starting in libpng-1.5.10, the user limits can be set en masse with the
5383configuration option PNG_SAFE_LIMITS_SUPPORTED. If this option is enabled,
5384a set of "safe" limits is applied in pngpriv.h. These can be overridden by
5385application calls to png_set_user_limits(), png_set_user_chunk_cache_max(),
5386and/or png_set_user_malloc_max() that increase or decrease the limits. Also,
5387in libpng-1.5.10 the default width and height limits were increased
5388from 1,000,000 to 0x7ffffff (i.e., made unlimited). Therefore, the
5389limits are now
5390 default safe
5391 png_user_width_max 0x7fffffff 1,000,000
5392 png_user_height_max 0x7fffffff 1,000,000
5393 png_user_chunk_cache_max 0 (unlimited) 128
5394 png_user_chunk_malloc_max 0 (unlimited) 8,000,000
5395
5396The png_set_option() function (and the "options" member of the png struct) was
5397added to libpng-1.5.15.
5398
5399The library now supports a complete fixed point implementation and can
5400thus be used on systems that have no floating point support or very
5401limited or slow support. Previously gamma correction, an essential part
5402of complete PNG support, required reasonably fast floating point.
5403
5404As part of this the choice of internal implementation has been made
5405independent of the choice of fixed versus floating point APIs and all the
5406missing fixed point APIs have been implemented.
5407
5408The exact mechanism used to control attributes of API functions has
5409changed, as described in the INSTALL file.
5410
5411A new test program, pngvalid, is provided in addition to pngtest.
5412pngvalid validates the arithmetic accuracy of the gamma correction
5413calculations and includes a number of validations of the file format.
5414A subset of the full range of tests is run when "make check" is done
5415(in the 'configure' build.) pngvalid also allows total allocated memory
5416usage to be evaluated and performs additional memory overwrite validation.
5417
5418Many changes to individual feature macros have been made. The following
5419are the changes most likely to be noticed by library builders who
5420configure libpng:
5421
54221) All feature macros now have consistent naming:
5423
5424#define PNG_NO_feature turns the feature off
5425#define PNG_feature_SUPPORTED turns the feature on
5426
5427pnglibconf.h contains one line for each feature macro which is either:
5428
5429#define PNG_feature_SUPPORTED
5430
5431if the feature is supported or:
5432
5433/*#undef PNG_feature_SUPPORTED*/
5434
5435if it is not. Library code consistently checks for the 'SUPPORTED' macro.
5436It does not, and libpng applications should not, check for the 'NO' macro
5437which will not normally be defined even if the feature is not supported.
5438The 'NO' macros are only used internally for setting or not setting the
5439corresponding 'SUPPORTED' macros.
5440
5441Compatibility with the old names is provided as follows:
5442
5443PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
5444
5445And the following definitions disable the corresponding feature:
5446
5447PNG_SETJMP_NOT_SUPPORTED disables SETJMP
5448PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
5449PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
5450PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
5451PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
5452PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
5453
5454Library builders should remove use of the above, inconsistent, names.
5455
54562) Warning and error message formatting was previously conditional on
5457the STDIO feature. The library has been changed to use the
5458CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
5459the library no longer uses the printf(3) functions, even though the
5460default read/write implementations use (FILE) style stdio.h functions.
5461
54623) Three feature macros now control the fixed/floating point decisions:
5463
5464PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
5465
5466PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
5467practice these are normally required internally anyway (because the PNG
5468file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
5469merely stops the function from being exported.
5470
5471PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
5472point implementation or the fixed point one. Typically the fixed point
5473implementation is larger and slower than the floating point implementation
5474on a system that supports floating point; however, it may be faster on a
5475system which lacks floating point hardware and therefore uses a software
5476emulation.
5477
54784) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
5479functions to read and write ints to be disabled independently of
5480PNG_USE_READ_MACROS, which allows libpng to be built with the functions
5481even though the default is to use the macros - this allows applications
5482to choose at app buildtime whether or not to use macros (previously
5483impossible because the functions weren't in the default build.)
5484
5485.SH XII. Changes to Libpng from version 1.5.x to 1.6.x
5486
5487A "simplified API" has been added (see documentation in png.h and a simple
5488example in contrib/examples/pngtopng.c). The new publicly visible API
5489includes the following:
5490
5491 macros:
5492 PNG_FORMAT_*
5493 PNG_IMAGE_*
5494 structures:
5495 png_control
5496 png_image
5497 read functions
5498 png_image_begin_read_from_file()
5499 png_image_begin_read_from_stdio()
5500 png_image_begin_read_from_memory()
5501 png_image_finish_read()
5502 png_image_free()
5503 write functions
5504 png_image_write_to_file()
5505 png_image_write_to_stdio()
5506
5507Starting with libpng-1.6.0, you can configure libpng to prefix all exported
5508symbols, using the PNG_PREFIX macro.
5509
5510We no longer include string.h in png.h. The include statement has been moved
5511to pngpriv.h, where it is not accessible by applications. Applications that
5512need access to information in string.h must add an '#include <string.h>'
5513directive. It does not matter whether this is placed prior to or after
5514the '#include "png.h"' directive.
5515
5516The following API are now DEPRECATED:
5517 png_info_init_3()
5518 png_convert_to_rfc1123() which has been replaced
5519 with png_convert_to_rfc1123_buffer()
5520 png_malloc_default()
5521 png_free_default()
5522 png_reset_zstream()
5523
5524The following have been removed:
5525 png_get_io_chunk_name(), which has been replaced
5526 with png_get_io_chunk_type(). The new
5527 function returns a 32-bit integer instead of
5528 a string.
5529 The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
5530 png_memset() macros are no longer used in the libpng sources and
5531 have been removed. These had already been made invisible to applications
5532 (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
5533
5534The signatures of many exported functions were changed, such that
5535 png_structp became png_structrp or png_const_structrp
5536 png_infop became png_inforp or png_const_inforp
5537where "rp" indicates a "restricted pointer".
5538
5539The support for FAR/far types has been eliminated and the definition of
5540png_alloc_size_t is now controlled by a flag so that 'small size_t' systems
5541can select it if necessary.
5542
5543Error detection in some chunks has improved; in particular the iCCP chunk
5544reader now does pretty complete validation of the basic format. Some bad
5545profiles that were previously accepted are now accepted with a warning or
5546rejected, depending upon the png_set_benign_errors() setting, in particular
5547the very old broken Microsoft/HP 3144-byte sRGB profile. Starting with
5548libpng-1.6.11, recognizing and checking sRGB profiles can be avoided by
5549means of
5550
5551 #if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && \
5552 defined(PNG_SET_OPTION_SUPPORTED)
5553 png_set_option(png_ptr, PNG_SKIP_sRGB_CHECK_PROFILE,
5554 PNG_OPTION_ON);
5555 #endif
5556
5557It's not a good idea to do this if you are using the "simplified API",
5558which needs to be able to recognize sRGB profiles conveyed via the iCCP
5559chunk.
5560
5561The PNG spec requirement that only grayscale profiles may appear in images
5562with color type 0 or 4 and that even if the image only contains gray pixels,
5563only RGB profiles may appear in images with color type 2, 3, or 6, is now
5564enforced. The sRGB chunk is allowed to appear in images with any color type
5565and is interpreted by libpng to convey a one-tracer-curve gray profile or a
5566three-tracer-curve RGB profile as appropriate.
5567
5568Prior to libpng-1.6.0 a warning would be issued if the iTXt chunk contained
5569an empty language field or an empty translated keyword. Both of these
5570are allowed by the PNG specification, so these warnings are no longer issued.
5571
5572The library now issues an error if the application attempts to set a
5573transform after it calls png_read_update_info() or if it attempts to call
5574both png_read_update_info() and png_start_read_image() or to call either
5575of them more than once.
5576
5577The default condition for benign_errors is now to treat benign errors as
5578warnings while reading and as errors while writing.
5579
5580The library now issues a warning if both background processing and RGB to
5581gray are used when gamma correction happens. As with previous versions of
5582the library the results are numerically very incorrect in this case.
5583
5584There are some minor arithmetic changes in some transforms such as
5585png_set_background(), that might be detected by certain regression tests.
5586
5587Unknown chunk handling has been improved internally, without any API change.
5588This adds more correct option control of the unknown handling, corrects
5589a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
5590it possible to skip IDAT chunks in the sequential reader.
5591
5592The machine-generated configure files are no longer included in branches
5593libpng16 and later of the GIT repository. They continue to be included
5594in the tarball releases, however.
5595
5596Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
5597stream to set the size of the sliding window for reading instead of using the
5598default 32-kbyte sliding window size. It was discovered that there are
5599hundreds of PNG files in the wild that have incorrect CMF bytes that caused
5600zlib to issue the "invalid distance too far back" error and reject the file.
5601Libpng-1.6.3 and later calculate their own safe CMF from the image dimensions,
5602provide a way to revert to the libpng-1.5.x behavior (ignoring the CMF bytes
5603and using a 32-kbyte sliding window), by using
5604
5605 png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
5606 PNG_OPTION_ON);
5607
5608and provide a tool (contrib/tools/pngfix) for rewriting a PNG file while
5609optimizing the CMF bytes in its IDAT chunk correctly.
5610
5611Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong
5612length, which resulted in PNG files that cannot be read beyond the bad iTXt
5613chunk. This error was fixed in libpng-1.6.3, and a tool (called
5614contrib/tools/png-fix-itxt) has been added to the libpng distribution.
5615
5616.SH XIII. Detecting libpng
5617
5618The png_get_io_ptr() function has been present since libpng-0.88, has never
5619changed, and is unaffected by conditional compilation macros. It is the
5620best choice for use in configure scripts for detecting the presence of any
5621libpng version since 0.88. In an autoconf "configure.in" you could use
5622
5623 AC_CHECK_LIB(png, png_get_io_ptr, ...
5624
5625.SH XV. Source code repository
5626
5627Since about February 2009, version 1.2.34, libpng has been under "git" source
5628control. The git repository was built from old libpng-x.y.z.tar.gz files
5629going back to version 0.70. You can access the git repository (read only)
5630at
5631
5632 git://git.code.sf.net/p/libpng/code
5633
5634or you can browse it with a web browser by selecting the "code" button at
5635
5636 https://sourceforge.net/projects/libpng
5637
5638Patches can be sent to glennrp at users.sourceforge.net or to
5639png-mng-implement at lists.sourceforge.net or you can upload them to
5640the libpng bug tracker at
5641
5642 http://libpng.sourceforge.net
5643
5644We also accept patches built from the tar or zip distributions, and
5645simple verbal discriptions of bug fixes, reported either to the
5646SourceForge bug tracker, to the png-mng-implement at lists.sf.net
5647mailing list, or directly to glennrp.
5648
5649.SH XV. Coding style
5650
5651Our coding style is similar to the "Allman" style
5652(See http://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
5653braces on separate lines:
5654
5655 if (condition)
5656 {
5657 action;
5658 }
5659
5660 else if (another condition)
5661 {
5662 another action;
5663 }
5664
5665The braces can be omitted from simple one-line actions:
5666
5667 if (condition)
5668 return (0);
5669
5670We use 3-space indentation, except for continued statements which
5671are usually indented the same as the first line of the statement
5672plus four more spaces.
5673
5674For macro definitions we use 2-space indentation, always leaving the "#"
5675in the first column.
5676
5677 #ifndef PNG_NO_FEATURE
5678 # ifndef PNG_FEATURE_SUPPORTED
5679 # define PNG_FEATURE_SUPPORTED
5680 # endif
5681 #endif
5682
5683Comments appear with the leading "/*" at the same indentation as
5684the statement that follows the comment:
5685
5686 /* Single-line comment */
5687 statement;
5688
5689 /* This is a multiple-line
5690 * comment.
5691 */
5692 statement;
5693
5694Very short comments can be placed after the end of the statement
5695to which they pertain:
5696
5697 statement; /* comment */
5698
5699We don't use C++ style ("//") comments. We have, however,
5700used them in the past in some now-abandoned MMX assembler
5701code.
5702
5703Functions and their curly braces are not indented, and
5704exported functions are marked with PNGAPI:
5705
5706 /* This is a public function that is visible to
5707 * application programmers. It does thus-and-so.
5708 */
5709 void PNGAPI
5710 png_exported_function(png_ptr, png_info, foo)
5711 {
5712 body;
5713 }
5714
5715The return type and decorations are placed on a separate line
5716ahead of the function name, as illustrated above.
5717
5718The prototypes for all exported functions appear in png.h,
5719above the comment that says
5720
5721 /* Maintainer: Put new public prototypes here ... */
5722
5723We mark all non-exported functions with "/* PRIVATE */"":
5724
5725 void /* PRIVATE */
5726 png_non_exported_function(png_ptr, png_info, foo)
5727 {
5728 body;
5729 }
5730
5731The prototypes for non-exported functions (except for those in
5732pngtest) appear in pngpriv.h above the comment that says
5733
5734 /* Maintainer: Put new private prototypes here ^ */
5735
5736To avoid polluting the global namespace, the names of all exported
5737functions and variables begin with "png_", and all publicly visible C
5738preprocessor macros begin with "PNG". We request that applications that
5739use libpng *not* begin any of their own symbols with either of these strings.
5740
5741We put a space after the "sizeof" operator and we omit the
5742optional parentheses around its argument when the argument
5743is an expression, not a type name, and we always enclose the
5744sizeof operator, with its argument, in parentheses:
5745
5746 (sizeof (png_uint_32))
5747 (sizeof array)
5748
5749Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
5750though it were a function.
5751
5752Control keywords if, for, while, and switch are always followed by a space
5753to distinguish them from function calls, which have no trailing space.
5754
5755We put a space after each comma and after each semicolon
5756in "for" statements, and we put spaces before and after each
5757C binary operator and after "for" or "while", and before
5758"?". We don't put a space between a typecast and the expression
5759being cast, nor do we put one between a function name and the
5760left parenthesis that follows it:
5761
5762 for (i = 2; i > 0; \-\-i)
5763 y[i] = a(x) + (int)b;
5764
5765We prefer #ifdef and #ifndef to #if defined() and #if !defined()
5766when there is only one macro being tested. We always use parentheses
5767with "defined".
5768
5769We prefer to express integers that are used as bit masks in hex format,
5770with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
5771
5772We prefer to use underscores in variable names rather than camelCase, except
5773for a few type names that we inherit from zlib.h.
5774
5775We prefer "if (something != 0)" and "if (something == 0)"
5776over "if (something)" and if "(!something)", respectively.
5777
5778We do not use the TAB character for indentation in the C sources.
5779
5780Lines do not exceed 80 characters.
5781
5782Other rules can be inferred by inspecting the libpng source.
5783
5784.SH XVI. Y2K Compliance in libpng
5785
5786March 26, 2015
5787
5788Since the PNG Development group is an ad-hoc body, we can't make
5789an official declaration.
5790
5791This is your unofficial assurance that libpng from version 0.71 and
5792upward through 1.6.17 are Y2K compliant. It is my belief that earlier
5793versions were also Y2K compliant.
5794
5795Libpng only has two year fields. One is a 2-byte unsigned integer
5796that will hold years up to 65535. The other, which is deprecated,
5797holds the date in text format, and will hold years up to 9999.
5798
5799The integer is
5800 "png_uint_16 year" in png_time_struct.
5801
5802The string is
5803 "char time_buffer[29]" in png_struct. This is no longer used
5804in libpng-1.6.x and will be removed from libpng-1.7.0.
5805
5806There are seven time-related functions:
5807
5808 png_convert_to_rfc_1123_buffer() in png.c
5809 (formerly png_convert_to_rfc_1152() in error, and
5810 also formerly png_convert_to_rfc_1123())
5811 png_convert_from_struct_tm() in pngwrite.c, called
5812 in pngwrite.c
5813 png_convert_from_time_t() in pngwrite.c
5814 png_get_tIME() in pngget.c
5815 png_handle_tIME() in pngrutil.c, called in pngread.c
5816 png_set_tIME() in pngset.c
5817 png_write_tIME() in pngwutil.c, called in pngwrite.c
5818
5819All appear to handle dates properly in a Y2K environment. The
5820png_convert_from_time_t() function calls gmtime() to convert from system
5821clock time, which returns (year - 1900), which we properly convert to
5822the full 4-digit year. There is a possibility that applications using
5823libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5824function, or that they are incorrectly passing only a 2-digit year
5825instead of "year - 1900" into the png_convert_from_struct_tm() function,
5826but this is not under our control. The libpng documentation has always
5827stated that it works with 4-digit years, and the APIs have been
5828documented as such.
5829
5830The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5831integer to hold the year, and can hold years as large as 65535.
5832
5833zlib, upon which libpng depends, is also Y2K compliant. It contains
5834no date-related code.
5835
5836
5837 Glenn Randers-Pehrson
5838 libpng maintainer
5839 PNG Development Group
5840
5841.SH NOTE
5842
5843Note about libpng version numbers:
5844
5845Due to various miscommunications, unforeseen code incompatibilities
5846and occasional factors outside the authors' control, version numbering
5847on the library has not always been consistent and straightforward.
5848The following table summarizes matters since version 0.89c, which was
5849the first widely used release:
5850
5851 source png.h png.h shared-lib
5852 version string int version
5853 ------- ------ ----- ----------
5854 0.89c ("beta 3") 0.89 89 1.0.89
5855 0.90 ("beta 4") 0.90 90 0.90
5856 0.95 ("beta 5") 0.95 95 0.95
5857 0.96 ("beta 6") 0.96 96 0.96
5858 0.97b ("beta 7") 1.00.97 97 1.0.1
5859 0.97c 0.97 97 2.0.97
5860 0.98 0.98 98 2.0.98
5861 0.99 0.99 98 2.0.99
5862 0.99a-m 0.99 99 2.0.99
5863 1.00 1.00 100 2.1.0
5864 1.0.0 1.0.0 100 2.1.0
5865 1.0.0 (from here on, the 100 2.1.0
5866 1.0.1 png.h string is 10001 2.1.0
5867 1.0.1a-e identical to the 10002 from here on, the
5868 1.0.2 source version) 10002 shared library is 2.V
5869 1.0.2a-b 10003 where V is the source
5870 1.0.1 10001 code version except as
5871 1.0.1a-e 10002 2.1.0.1a-e noted.
5872 1.0.2 10002 2.1.0.2
5873 1.0.2a-b 10003 2.1.0.2a-b
5874 1.0.3 10003 2.1.0.3
5875 1.0.3a-d 10004 2.1.0.3a-d
5876 1.0.4 10004 2.1.0.4
5877 1.0.4a-f 10005 2.1.0.4a-f
5878 1.0.5 (+ 2 patches) 10005 2.1.0.5
5879 1.0.5a-d 10006 2.1.0.5a-d
5880 1.0.5e-r 10100 2.1.0.5e-r
5881 1.0.5s-v 10006 2.1.0.5s-v
5882 1.0.6 (+ 3 patches) 10006 2.1.0.6
5883 1.0.6d-g 10007 2.1.0.6d-g
5884 1.0.6h 10007 10.6h
5885 1.0.6i 10007 10.6i
5886 1.0.6j 10007 2.1.0.6j
5887 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
5888 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
5889 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
5890 1.0.7 1 10007 2.1.0.7
5891 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
5892 1.0.8rc1 1 10008 2.1.0.8rc1
5893 1.0.8 1 10008 2.1.0.8
5894 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
5895 1.0.9rc1 1 10009 2.1.0.9rc1
5896 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
5897 1.0.9rc2 1 10009 2.1.0.9rc2
5898 1.0.9 1 10009 2.1.0.9
5899 1.0.10beta1 1 10010 2.1.0.10beta1
5900 1.0.10rc1 1 10010 2.1.0.10rc1
5901 1.0.10 1 10010 2.1.0.10
5902 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
5903 1.0.11rc1 1 10011 2.1.0.11rc1
5904 1.0.11 1 10011 2.1.0.11
5905 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
5906 1.0.12rc1 2 10012 2.1.0.12rc1
5907 1.0.12 2 10012 2.1.0.12
5908 1.1.0a-f - 10100 2.1.1.0a-f abandoned
5909 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
5910 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
5911 1.2.0rc1 3 10200 3.1.2.0rc1
5912 1.2.0 3 10200 3.1.2.0
5913 1.2.1beta-4 3 10201 3.1.2.1beta1-4
5914 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
5915 1.2.1 3 10201 3.1.2.1
5916 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
5917 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
5918 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
5919 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
5920 1.0.13 10 10013 10.so.0.1.0.13
5921 1.2.2 12 10202 12.so.0.1.2.2
5922 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
5923 1.2.3 12 10203 12.so.0.1.2.3
5924 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
5925 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
5926 1.0.14 10 10014 10.so.0.1.0.14
5927 1.2.4 13 10204 12.so.0.1.2.4
5928 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
5929 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
5930 1.0.15 10 10015 10.so.0.1.0.15
5931 1.2.5 13 10205 12.so.0.1.2.5
5932 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
5933 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
5934 1.0.16 10 10016 10.so.0.1.0.16
5935 1.2.6 13 10206 12.so.0.1.2.6
5936 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
5937 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
5938 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
5939 1.0.17 10 10017 12.so.0.1.0.17
5940 1.2.7 13 10207 12.so.0.1.2.7
5941 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
5942 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
5943 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
5944 1.0.18 10 10018 12.so.0.1.0.18
5945 1.2.8 13 10208 12.so.0.1.2.8
5946 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
5947 1.2.9beta4-11 13 10209 12.so.0.9[.0]
5948 1.2.9rc1 13 10209 12.so.0.9[.0]
5949 1.2.9 13 10209 12.so.0.9[.0]
5950 1.2.10beta1-7 13 10210 12.so.0.10[.0]
5951 1.2.10rc1-2 13 10210 12.so.0.10[.0]
5952 1.2.10 13 10210 12.so.0.10[.0]
5953 1.4.0beta1-6 14 10400 14.so.0.0[.0]
5954 1.2.11beta1-4 13 10210 12.so.0.11[.0]
5955 1.4.0beta7-8 14 10400 14.so.0.0[.0]
5956 1.2.11 13 10211 12.so.0.11[.0]
5957 1.2.12 13 10212 12.so.0.12[.0]
5958 1.4.0beta9-14 14 10400 14.so.0.0[.0]
5959 1.2.13 13 10213 12.so.0.13[.0]
5960 1.4.0beta15-36 14 10400 14.so.0.0[.0]
5961 1.4.0beta37-87 14 10400 14.so.14.0[.0]
5962 1.4.0rc01 14 10400 14.so.14.0[.0]
5963 1.4.0beta88-109 14 10400 14.so.14.0[.0]
5964 1.4.0rc02-08 14 10400 14.so.14.0[.0]
5965 1.4.0 14 10400 14.so.14.0[.0]
5966 1.4.1beta01-03 14 10401 14.so.14.1[.0]
5967 1.4.1rc01 14 10401 14.so.14.1[.0]
5968 1.4.1beta04-12 14 10401 14.so.14.1[.0]
5969 1.4.1 14 10401 14.so.14.1[.0]
5970 1.4.2 14 10402 14.so.14.2[.0]
5971 1.4.3 14 10403 14.so.14.3[.0]
5972 1.4.4 14 10404 14.so.14.4[.0]
5973 1.5.0beta01-58 15 10500 15.so.15.0[.0]
5974 1.5.0rc01-07 15 10500 15.so.15.0[.0]
5975 1.5.0 15 10500 15.so.15.0[.0]
5976 1.5.1beta01-11 15 10501 15.so.15.1[.0]
5977 1.5.1rc01-02 15 10501 15.so.15.1[.0]
5978 1.5.1 15 10501 15.so.15.1[.0]
5979 1.5.2beta01-03 15 10502 15.so.15.2[.0]
5980 1.5.2rc01-03 15 10502 15.so.15.2[.0]
5981 1.5.2 15 10502 15.so.15.2[.0]
5982 1.5.3beta01-10 15 10503 15.so.15.3[.0]
5983 1.5.3rc01-02 15 10503 15.so.15.3[.0]
5984 1.5.3beta11 15 10503 15.so.15.3[.0]
5985 1.5.3 [omitted]
5986 1.5.4beta01-08 15 10504 15.so.15.4[.0]
5987 1.5.4rc01 15 10504 15.so.15.4[.0]
5988 1.5.4 15 10504 15.so.15.4[.0]
5989 1.5.5beta01-08 15 10505 15.so.15.5[.0]
5990 1.5.5rc01 15 10505 15.so.15.5[.0]
5991 1.5.5 15 10505 15.so.15.5[.0]
5992 1.5.6beta01-07 15 10506 15.so.15.6[.0]
5993 1.5.6rc01-03 15 10506 15.so.15.6[.0]
5994 1.5.6 15 10506 15.so.15.6[.0]
5995 1.5.7beta01-05 15 10507 15.so.15.7[.0]
5996 1.5.7rc01-03 15 10507 15.so.15.7[.0]
5997 1.5.7 15 10507 15.so.15.7[.0]
5998 1.6.0beta01-40 16 10600 16.so.16.0[.0]
5999 1.6.0rc01-08 16 10600 16.so.16.0[.0]
6000 1.6.0 16 10600 16.so.16.0[.0]
6001 1.6.1beta01-09 16 10601 16.so.16.1[.0]
6002 1.6.1rc01 16 10601 16.so.16.1[.0]
6003 1.6.1 16 10601 16.so.16.1[.0]
6004 1.6.2beta01 16 10602 16.so.16.2[.0]
6005 1.6.2rc01-06 16 10602 16.so.16.2[.0]
6006 1.6.2 16 10602 16.so.16.2[.0]
6007 1.6.3beta01-11 16 10603 16.so.16.3[.0]
6008 1.6.3rc01 16 10603 16.so.16.3[.0]
6009 1.6.3 16 10603 16.so.16.3[.0]
6010 1.6.4beta01-02 16 10604 16.so.16.4[.0]
6011 1.6.4rc01 16 10604 16.so.16.4[.0]
6012 1.6.4 16 10604 16.so.16.4[.0]
6013 1.6.5 16 10605 16.so.16.5[.0]
6014 1.6.6 16 10606 16.so.16.6[.0]
6015 1.6.7beta01-04 16 10607 16.so.16.7[.0]
6016 1.6.7rc01-02 16 10607 16.so.16.7[.0]
6017 1.6.7 16 10607 16.so.16.7[.0]
6018 1.6.8beta01-02 16 10608 16.so.16.8[.0]
6019 1.6.8rc01-02 16 10608 16.so.16.8[.0]
6020 1.6.8 16 10608 16.so.16.8[.0]
6021 1.6.9beta01-04 16 10609 16.so.16.9[.0]
6022 1.6.9rc01-02 16 10609 16.so.16.9[.0]
6023 1.6.9 16 10609 16.so.16.9[.0]
6024 1.6.10beta01-03 16 10610 16.so.16.10[.0]
6025 1.6.10rc01-03 16 10610 16.so.16.10[.0]
6026 1.6.10 16 10610 16.so.16.10[.0]
6027 1.6.11beta01-06 16 10611 16.so.16.11[.0]
6028 1.6.11rc01-02 16 10611 16.so.16.11[.0]
6029 1.6.11 16 10611 16.so.16.11[.0]
6030 1.6.12rc01 16 10612 16.so.16.12[.0]
6031 1.6.12 16 10612 16.so.16.12[.0]
6032 1.6.13beta01-04 16 10613 16.so.16.13[.0]
6033 1.6.13rc01-02 16 10613 16.so.16.13[.0]
6034 1.6.13 16 10613 16.so.16.13[.0]
6035 1.6.14beta01-07 16 10614 16.so.16.14[.0]
6036 1.6.14rc01-02 16 10614 16.so.16.14[.0]
6037 1.6.14 16 10614 16.so.16.14[.0]
6038 1.6.15beta01-08 16 10615 16.so.16.15[.0]
6039 1.6.15rc01-03 16 10615 16.so.16.15[.0]
6040 1.6.15 16 10615 16.so.16.15[.0]
6041 1.6.16beta01-03 16 10616 16.so.16.16[.0]
6042 1.6.16rc01-02 16 10616 16.so.16.16[.0]
6043 1.6.16 16 10616 16.so.16.16[.0]
6044 1.6.17beta01-06 16 10617 16.so.16.17[.0]
6045 1.6.17rc01-06 16 10617 16.so.16.17[.0]
6046 1.6.17 16 10617 16.so.16.17[.0]
6047
6048Henceforth the source version will match the shared-library minor
6049and patch numbers; the shared-library major version number will be
6050used for changes in backward compatibility, as it is intended. The
6051PNG_PNGLIB_VER macro, which is not used within libpng but is available
6052for applications, is an unsigned integer of the form xyyzz corresponding
6053to the source version x.y.z (leading zeros in y and z). Beta versions
6054were given the previous public release number plus a letter, until
6055version 1.0.6j; from then on they were given the upcoming public
6056release number plus "betaNN" or "rcN".
6057
6058.SH "SEE ALSO"
6059.BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
6060
6061.LP
6062.IR libpng :
6063.IP
6064http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
6065http://www.libpng.org/pub/png
6066
6067.LP
6068.IR zlib :
6069.IP
6070(generally) at the same location as
6071.I libpng
6072or at
6073.br
6074ftp://ftp.info-zip.org/pub/infozip/zlib
6075
6076.LP
6077.IR PNG specification: RFC 2083
6078.IP
6079(generally) at the same location as
6080.I libpng
6081or at
6082.br
6083ftp://ds.internic.net/rfc/rfc2083.txt
6084.br
6085or (as a W3C Recommendation) at
6086.br
6087http://www.w3.org/TR/REC-png.html
6088
6089.LP
6090In the case of any inconsistency between the PNG specification
6091and this library, the specification takes precedence.
6092
6093.SH AUTHORS
6094This man page: Glenn Randers-Pehrson
6095<glennrp at users.sourceforge.net>
6096
6097The contributing authors would like to thank all those who helped
6098with testing, bug fixes, and patience. This wouldn't have been
6099possible without all of you.
6100
6101Thanks to Frank J. T. Wojcik for helping with the documentation.
6102
6103Libpng version 1.6.17 - March 26, 2015:
6104Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
6105Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
6106
6107Supported by the PNG development group
6108.br
6109png-mng-implement at lists.sf.net
6110(subscription required; visit
6111png-mng-implement at lists.sourceforge.net (subscription required; visit
6112https://lists.sourceforge.net/lists/listinfo/png-mng-implement
6113to subscribe).
6114
6115.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
6116
6117(This copy of the libpng notices is provided for your convenience. In case of
6118any discrepancy between this copy and the notices in the file png.h that is
6119included in the libpng distribution, the latter shall prevail.)
6120
6121If you modify libpng you may insert additional notices immediately following
6122this sentence.
6123
6124This code is released under the libpng license.
6125
6126libpng versions 1.2.6, August 15, 2004, through 1.6.17, March 26, 2015, are
6127Copyright (c) 2004,2006-2015 Glenn Randers-Pehrson, and are
6128distributed according to the same disclaimer and license as libpng-1.2.5
6129with the following individual added to the list of Contributing Authors
6130
6131 Cosmin Truta
6132
6133libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
6134Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
6135distributed according to the same disclaimer and license as libpng-1.0.6
6136with the following individuals added to the list of Contributing Authors
6137
6138 Simon-Pierre Cadieux
6139 Eric S. Raymond
6140 Gilles Vollant
6141
6142and with the following additions to the disclaimer:
6143
6144 There is no warranty against interference with your
6145 enjoyment of the library or against infringement.
6146 There is no warranty that our efforts or the library
6147 will fulfill any of your particular purposes or needs.
6148 This library is provided with all faults, and the entire
6149 risk of satisfactory quality, performance, accuracy, and
6150 effort is with the user.
6151
6152libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
6153Copyright (c) 1998, 1999 Glenn Randers-Pehrson
6154Distributed according to the same disclaimer and license as libpng-0.96,
6155with the following individuals added to the list of Contributing Authors:
6156
6157 Tom Lane
6158 Glenn Randers-Pehrson
6159 Willem van Schaik
6160
6161libpng versions 0.89, June 1996, through 0.96, May 1997, are
6162Copyright (c) 1996, 1997 Andreas Dilger
6163Distributed according to the same disclaimer and license as libpng-0.88,
6164with the following individuals added to the list of Contributing Authors:
6165
6166 John Bowler
6167 Kevin Bracey
6168 Sam Bushell
6169 Magnus Holmgren
6170 Greg Roelofs
6171 Tom Tanner
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
61971. The origin of this source code must not be misrepresented.
6198
61992. Altered versions must be plainly marked as such and
6200 must not be misrepresented as being the original source.
6201
62023. This Copyright notice may not be removed or altered from
6203 any 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
6211
6212A "png_get_copyright" function is available, for convenient use in "about"
6213boxes and the like:
6214
6215 printf("%s",png_get_copyright(NULL));
6216
6217Also, the PNG logo (in PNG format, of course) is supplied in the
6218files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
6219
6220Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
6221certification mark of the Open Source Initiative.
6222
6223Glenn Randers-Pehrson
6224glennrp at users.sourceforge.net
6225March 26, 2015
6226
6227.\" end of man page
6228