source: NonGTP/OpenEXR/include/IlmImf/ImfChromaticities.h @ 855

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[855]1///////////////////////////////////////////////////////////////////////////
2//
3// Copyright (c) 2003, Industrial Light & Magic, a division of Lucas
4// Digital Ltd. LLC
5//
6// All rights reserved.
7//
8// Redistribution and use in source and binary forms, with or without
9// modification, are permitted provided that the following conditions are
10// met:
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12// notice, this list of conditions and the following disclaimer.
13// *       Redistributions in binary form must reproduce the above
14// copyright notice, this list of conditions and the following disclaimer
15// in the documentation and/or other materials provided with the
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18// its contributors may be used to endorse or promote products derived
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20//
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33///////////////////////////////////////////////////////////////////////////
34
35
36#ifndef INCLUDED_IMF_CHROMATICITIES_H
37#define INCLUDED_IMF_CHROMATICITIES_H
38
39//-----------------------------------------------------------------------------
40//
41//      CIE (x,y) chromaticities, and conversions between
42//      RGB tiples and CIE XYZ tristimulus values.
43//
44//-----------------------------------------------------------------------------
45
46#include <ImathVec.h>
47#include <ImathMatrix.h>
48
49namespace Imf {
50
51   
52struct Chromaticities
53{
54    Imath::V2f  red;
55    Imath::V2f  green;
56    Imath::V2f  blue;
57    Imath::V2f  white;
58
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));
63};
64
65
66//
67// Conversions between RGB and CIE XYZ
68//
69// RGB to XYZ:
70//
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)
75//
76//      If we define that
77//
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,
82//
83//      then the following statements are true:
84//
85//         Xr / (Xr + Yr + Zr) == c.red.x
86//         Yr / (Xr + Yr + Zr) == c.red.y
87//
88//         Xg / (Xg + Yg + Zg) == c.red.x
89//         Yg / (Xg + Yg + Zg) == c.red.y
90//
91//         Xb / (Xb + Yb + Zb) == c.red.x
92//         Yb / (Xb + Yb + Zb) == c.red.y
93//
94//         Xw / (Xw + Yw + Zw) == c.red.x
95//         Yw / (Xw + Yw + Zw) == c.red.y
96//
97//         Yw == Y.
98//
99// XYZ to RGB:
100//
101//      YYZtoRGB(c,Y) returns RGBtoXYZ(c,Y).inverse().
102//
103// Warning:
104//
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:
109//
110//          M44f M = RGBtoXYZ (chromaticities1, Y1) *
111//                   XYZtoRGB (chromaticities2, Y2);
112//
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. 
119//
120
121Imath::M44f     RGBtoXYZ (const Chromaticities chroma, float Y);
122Imath::M44f     XYZtoRGB (const Chromaticities chroma, float Y);
123
124
125} // namespace Imf
126
127#endif
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