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33 ///////////////////////////////////////////////////////////////////////////
36 #ifndef INCLUDED_IMF_CHROMATICITIES_H
37 #define INCLUDED_IMF_CHROMATICITIES_H
39 //-----------------------------------------------------------------------------
41 // CIE (x,y) chromaticities, and conversions between
42 // RGB tiples and CIE XYZ tristimulus values.
44 //-----------------------------------------------------------------------------
47 #include "ImathMatrix.h"
59 Chromaticities (const Imath::V2f &red = Imath::V2f (0.6400f, 0.3300f),
60 const Imath::V2f &green = Imath::V2f (0.3000f, 0.6000f),
61 const Imath::V2f &blue = Imath::V2f (0.1500f, 0.0600f),
62 const Imath::V2f &white = Imath::V2f (0.3127f, 0.3290f));
67 // Conversions between RGB and CIE XYZ
71 // Given a set of chromaticities, c, and the luminance, Y, of the RGB
72 // triple (1,1,1), or "white", RGBtoXYZ(c,Y) computes a matrix, M, so
73 // that multiplying an RGB value, v, with M produces an equivalent
74 // XYZ value, w. (w == v * M)
78 // (Xr, Yr, Zr) == (1, 0, 0) * M
79 // (Xg, Yg, Zg) == (0, 1, 0) * M
80 // (Xb, Yb, Zb) == (0, 0, 1) * M
81 // (Xw, Yw, Zw) == (1, 1, 1) * M,
83 // then the following statements are true:
85 // Xr / (Xr + Yr + Zr) == c.red.x
86 // Yr / (Xr + Yr + Zr) == c.red.y
88 // Xg / (Xg + Yg + Zg) == c.red.x
89 // Yg / (Xg + Yg + Zg) == c.red.y
91 // Xb / (Xb + Yb + Zb) == c.red.x
92 // Yb / (Xb + Yb + Zb) == c.red.y
94 // Xw / (Xw + Yw + Zw) == c.red.x
95 // Yw / (Xw + Yw + Zw) == c.red.y
101 // YYZtoRGB(c,Y) returns RGBtoXYZ(c,Y).inverse().
105 // It would seem that RGBtoXYZ() and XYZtoRGB() are all you need
106 // to convert RGB values with one set of primary and white point
107 // chromaticities into perceptually equivalent RGB values with
108 // different primary and white point chromaticities:
110 // M44f M = RGBtoXYZ (chromaticities1, Y1) *
111 // XYZtoRGB (chromaticities2, Y2);
113 // However, this simple conversion does not account for white point
114 // adaptation, and produces undesirable results. The proper thing
115 // to do is to perform a Bradford or a von Kries transform, which
116 // moves the white point of the original color space to the white
117 // point of the destination color space, dragging other colors with
118 // it in a sensible fashion.
121 Imath::M44f RGBtoXYZ (const Chromaticities chroma, float Y);
122 Imath::M44f XYZtoRGB (const Chromaticities chroma, float Y);