/src/FreeImage/Source/OpenEXR/IlmImf/ImfChromaticities.cpp

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 33///////////////////////////////////////////////////////////////////////////
 34
 35
 36//-----------------------------------------------------------------------------
 37//
 38//	CIE (x,y) chromaticities, and conversions between
 39//	RGB tiples and CIE XYZ tristimulus values.
 40//
 41//-----------------------------------------------------------------------------
 42
 43#include <ImfChromaticities.h>
 44
 45namespace Imf {
 46
 47   
 48Chromaticities::Chromaticities (const Imath::V2f &red,
 49				const Imath::V2f &green,
 50				const Imath::V2f &blue,
 51				const Imath::V2f &white)
 52:
 53    red (red),
 54    green (green),
 55    blue (blue),
 56    white (white)
 57{
 58    // empty
 59}
 60
 61
 62Imath::M44f
 63RGBtoXYZ (const Chromaticities chroma, float Y)
 64{
 65    //
 66    // For an explanation of how the color conversion matrix is derived,
 67    // see Roy Hall, "Illumination and Color in Computer Generated Imagery",
 68    // Springer-Verlag, 1989, chapter 3, "Perceptual Response"; and 
 69    // Charles A. Poynton, "A Technical Introduction to Digital Video",
 70    // John Wiley & Sons, 1996, chapter 7, "Color science for video".
 71    //
 72
 73    //
 74    // X and Z values of RGB value (1, 1, 1), or "white"
 75    //
 76
 77    float X = chroma.white.x * Y / chroma.white.y;
 78    float Z = (1 - chroma.white.x - chroma.white.y) * Y / chroma.white.y;
 79
 80    //
 81    // Scale factors for matrix rows
 82    //
 83
 84    float d = chroma.red.x   * (chroma.blue.y  - chroma.green.y) +
 85	      chroma.blue.x  * (chroma.green.y - chroma.red.y) +
 86	      chroma.green.x * (chroma.red.y   - chroma.blue.y);
 87
 88    float Sr = (X * (chroma.blue.y - chroma.green.y) -
 89	        chroma.green.x * (Y * (chroma.blue.y - 1) +
 90		chroma.blue.y  * (X + Z)) +
 91		chroma.blue.x  * (Y * (chroma.green.y - 1) +
 92		chroma.green.y * (X + Z))) / d;
 93
 94    float Sg = (X * (chroma.red.y - chroma.blue.y) +
 95		chroma.red.x   * (Y * (chroma.blue.y - 1) +
 96		chroma.blue.y  * (X + Z)) -
 97		chroma.blue.x  * (Y * (chroma.red.y - 1) +
 98		chroma.red.y   * (X + Z))) / d;
 99
100    float Sb = (X * (chroma.green.y - chroma.red.y) -
101		chroma.red.x   * (Y * (chroma.green.y - 1) +
102		chroma.green.y * (X + Z)) +
103		chroma.green.x * (Y * (chroma.red.y - 1) +
104		chroma.red.y   * (X + Z))) / d;
105
106    //
107    // Assemble the matrix
108    //
109
110    Imath::M44f M;
111
112    M[0][0] = Sr * chroma.red.x;
113    M[0][1] = Sr * chroma.red.y;
114    M[0][2] = Sr * (1 - chroma.red.x - chroma.red.y);
115
116    M[1][0] = Sg * chroma.green.x;
117    M[1][1] = Sg * chroma.green.y;
118    M[1][2] = Sg * (1 - chroma.green.x - chroma.green.y);
119
120    M[2][0] = Sb * chroma.blue.x;
121    M[2][1] = Sb * chroma.blue.y;
122    M[2][2] = Sb * (1 - chroma.blue.x - chroma.blue.y);
123
124    return M;
125}
126
127
128Imath::M44f
129XYZtoRGB (const Chromaticities chroma, float Y)
130{
131    return RGBtoXYZ (chroma, Y).inverse();
132}
133
134
135} // namespace Imf