2013-02-13 23:49:19 -05:00
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/*-
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* sRGB.h
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*
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* Last changed in libpng 1.6.0 [February 14, 2013]
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*
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2013-03-27 21:31:36 -04:00
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* COPYRIGHT: Written by John Cunningham Bowler, 2013.
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2013-02-13 23:49:19 -05:00
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* To the extent possible under law, the author has waived all copyright and
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* related or neighboring rights to this work. This work is published from:
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* United States.
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*
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* Utility file; not actually a header, this contains definitions of sRGB
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* calculation functions for inclusion in those test programs that need them.
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*
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* All routines take and return a floating point value in the range
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* 0 to 1.0, doing a calculation according to the sRGB specification
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* (in fact the source of the numbers is the wikipedia article at
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2017-06-28 14:46:04 -04:00
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* https://en.wikipedia.org/wiki/SRGB).
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2013-02-13 23:49:19 -05:00
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*/
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static double
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sRGB_from_linear(double l)
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{
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if (l <= 0.0031308)
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l *= 12.92;
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else
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l = 1.055 * pow(l, 1/2.4) - 0.055;
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return l;
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}
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static double
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linear_from_sRGB(double s)
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{
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if (s <= 0.04045)
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return s / 12.92;
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else
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return pow((s+0.055)/1.055, 2.4);
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}
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static double
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YfromRGB(double r, double g, double b)
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{
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/* Use the sRGB (rounded) coefficients for Rlinear, Glinear, Blinear to get
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* the CIE Y value (also linear).
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*/
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return 0.2126 * r + 0.7152 * g + 0.0722 * b;
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}
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