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