1 ///////////////////////////////////////////////////////////////////////////
2 //
3 // Copyright (c) 2003, Industrial Light & Magic, a division of Lucas
4 // Digital Ltd. LLC
5 //
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32 //
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 #include "ImfNamespace.h"
45 #include <string.h>
46
47 OPENEXR_IMF_INTERNAL_NAMESPACE_SOURCE_ENTER
48
49
Chromaticities(const IMATH_NAMESPACE::V2f & red,const IMATH_NAMESPACE::V2f & green,const IMATH_NAMESPACE::V2f & blue,const IMATH_NAMESPACE::V2f & white)50 Chromaticities::Chromaticities (const IMATH_NAMESPACE::V2f &red,
51 const IMATH_NAMESPACE::V2f &green,
52 const IMATH_NAMESPACE::V2f &blue,
53 const IMATH_NAMESPACE::V2f &white)
54 :
55 red (red),
56 green (green),
57 blue (blue),
58 white (white)
59 {
60 // empty
61 }
62
63
64 bool
operator ==(const Chromaticities & c) const65 Chromaticities::operator == (const Chromaticities & c) const
66 {
67 return red == c.red && green == c.green && blue == c.blue;
68 }
69
70
71 bool
operator !=(const Chromaticities & c) const72 Chromaticities::operator != (const Chromaticities & c) const
73 {
74 return red != c.red || green != c.green || blue != c.blue;
75 }
76
77
78 IMATH_NAMESPACE::M44f
RGBtoXYZ(const Chromaticities chroma,float Y)79 RGBtoXYZ (const Chromaticities chroma, float Y)
80 {
81 //
82 // For an explanation of how the color conversion matrix is derived,
83 // see Roy Hall, "Illumination and Color in Computer Generated Imagery",
84 // Springer-Verlag, 1989, chapter 3, "Perceptual Response"; and
85 // Charles A. Poynton, "A Technical Introduction to Digital Video",
86 // John Wiley & Sons, 1996, chapter 7, "Color science for video".
87 //
88
89 //
90 // X and Z values of RGB value (1, 1, 1), or "white"
91 //
92
93 float X = chroma.white.x * Y / chroma.white.y;
94 float Z = (1 - chroma.white.x - chroma.white.y) * Y / chroma.white.y;
95
96 //
97 // Scale factors for matrix rows
98 //
99
100 float d = chroma.red.x * (chroma.blue.y - chroma.green.y) +
101 chroma.blue.x * (chroma.green.y - chroma.red.y) +
102 chroma.green.x * (chroma.red.y - chroma.blue.y);
103
104 float Sr = (X * (chroma.blue.y - chroma.green.y) -
105 chroma.green.x * (Y * (chroma.blue.y - 1) +
106 chroma.blue.y * (X + Z)) +
107 chroma.blue.x * (Y * (chroma.green.y - 1) +
108 chroma.green.y * (X + Z))) / d;
109
110 float Sg = (X * (chroma.red.y - chroma.blue.y) +
111 chroma.red.x * (Y * (chroma.blue.y - 1) +
112 chroma.blue.y * (X + Z)) -
113 chroma.blue.x * (Y * (chroma.red.y - 1) +
114 chroma.red.y * (X + Z))) / d;
115
116 float Sb = (X * (chroma.green.y - chroma.red.y) -
117 chroma.red.x * (Y * (chroma.green.y - 1) +
118 chroma.green.y * (X + Z)) +
119 chroma.green.x * (Y * (chroma.red.y - 1) +
120 chroma.red.y * (X + Z))) / d;
121
122 //
123 // Assemble the matrix
124 //
125
126 IMATH_NAMESPACE::M44f M;
127
128 M[0][0] = Sr * chroma.red.x;
129 M[0][1] = Sr * chroma.red.y;
130 M[0][2] = Sr * (1 - chroma.red.x - chroma.red.y);
131
132 M[1][0] = Sg * chroma.green.x;
133 M[1][1] = Sg * chroma.green.y;
134 M[1][2] = Sg * (1 - chroma.green.x - chroma.green.y);
135
136 M[2][0] = Sb * chroma.blue.x;
137 M[2][1] = Sb * chroma.blue.y;
138 M[2][2] = Sb * (1 - chroma.blue.x - chroma.blue.y);
139
140 return M;
141 }
142
143
144 IMATH_NAMESPACE::M44f
XYZtoRGB(const Chromaticities chroma,float Y)145 XYZtoRGB (const Chromaticities chroma, float Y)
146 {
147 return RGBtoXYZ (chroma, Y).inverse();
148 }
149
150
151 OPENEXR_IMF_INTERNAL_NAMESPACE_SOURCE_EXIT
152