mirror of
https://git.code.sf.net/p/libpng/code.git
synced 2025-07-10 18:04:09 +02:00
49 lines
1.2 KiB
C
49 lines
1.2 KiB
C
/*-
|
|
* 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;
|
|
}
|