/
sRGB.h
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/
sRGB.h
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/*-
* sRGB.h
*
* Last changed in libpng 1.6.0 [February 14, 2013]
*
* COPYRIGHT: Written by John Cunningham Bowler, 2013.
* To the extent possible under law, the author has waived all copyright and
* related or neighboring rights to this work. This work is published from:
* United States.
*
* Utility file; not actually a header, this contains definitions of sRGB
* calculation functions for inclusion in those test programs that need them.
*
* All routines take and return a floating point value in the range
* 0 to 1.0, doing a calculation according to the sRGB specification
* (in fact the source of the numbers is the wikipedia article at
* https://en.wikipedia.org/wiki/SRGB).
*/
static double
sRGB_from_linear(double l)
{
if (l <= 0.0031308)
l *= 12.92;
else
l = 1.055 * pow(l, 1/2.4) - 0.055;
return l;
}
static double
linear_from_sRGB(double s)
{
if (s <= 0.04045)
return s / 12.92;
else
return pow((s+0.055)/1.055, 2.4);
}
static double
YfromRGB(double r, double g, double b)
{
/* Use the sRGB (rounded) coefficients for Rlinear, Glinear, Blinear to get
* the CIE Y value (also linear).
*/
return 0.2126 * r + 0.7152 * g + 0.0722 * b;
}