1/*-
 2 * sRGB.h
 3 *
 4 * Last changed in libpng 1.6.0 [February 14, 2013]
 5 *
 6 * COPYRIGHT: Written by John Cunningham Bowler, 2013.
 7 * To the extent possible under law, the author has waived all copyright and
 8 * related or neighboring rights to this work.  This work is published from:
 9 * United States.
10 *
11 * Utility file; not actually a header, this contains definitions of sRGB
12 * calculation functions for inclusion in those test programs that need them.
13 *
14 * All routines take and return a floating point value in the range
15 * 0 to 1.0, doing a calculation according to the sRGB specification
16 * (in fact the source of the numbers is the wikipedia article at
17 * https://en.wikipedia.org/wiki/SRGB).
18 */
19static double
20sRGB_from_linear(double l)
21{
22   if (l <= 0.0031308)
23      l *= 12.92;
24
25   else
26      l = 1.055 * pow(l, 1/2.4) - 0.055;
27
28   return l;
29}
30
31static double
32linear_from_sRGB(double s)
33{
34   if (s <= 0.04045)
35      return s / 12.92;
36
37   else
38      return pow((s+0.055)/1.055, 2.4);
39}
40
41static double
42YfromRGB(double r, double g, double b)
43{
44   /* Use the sRGB (rounded) coefficients for Rlinear, Glinear, Blinear to get
45    * the CIE Y value (also linear).
46    */
47   return 0.2126 * r + 0.7152 * g + 0.0722 * b;
48}