5 #include "colorspace_conversion_effect.h"
10 // Color coordinates from Rec. 709; sRGB uses the same primaries.
11 double rec709_x_R = 0.640, rec709_x_G = 0.300, rec709_x_B = 0.150;
12 double rec709_y_R = 0.330, rec709_y_G = 0.600, rec709_y_B = 0.060;
14 // Color coordinates from Rec. 601. (Separate for 525- and 625-line systems.)
15 double rec601_525_x_R = 0.630, rec601_525_x_G = 0.310, rec601_525_x_B = 0.155;
16 double rec601_525_y_R = 0.340, rec601_525_y_G = 0.595, rec601_525_y_B = 0.070;
17 double rec601_625_x_R = 0.640, rec601_625_x_G = 0.290, rec601_625_x_B = 0.150;
18 double rec601_625_y_R = 0.330, rec601_625_y_G = 0.600, rec601_625_y_B = 0.060;
20 // The D65 white point. Given in both Rec. 601 and 709.
21 double d65_x = 0.3127, d65_y = 0.3290;
23 ColorspaceConversionEffect::ColorspaceConversionEffect()
24 : source_space(COLORSPACE_sRGB),
25 destination_space(COLORSPACE_sRGB)
27 register_int("source_space", (int *)&source_space);
28 register_int("destination_space", (int *)&destination_space);
31 Matrix3d get_xyz_matrix(Colorspace space)
33 if (space == COLORSPACE_XYZ) {
34 return Matrix3d::Identity();
41 case COLORSPACE_REC_709: // And sRGB.
42 x_R = rec709_x_R; x_G = rec709_x_G; x_B = rec709_x_B;
43 y_R = rec709_y_R; y_G = rec709_y_G; y_B = rec709_y_B;
45 case COLORSPACE_REC_601_525:
46 x_R = rec601_525_x_R; x_G = rec601_525_x_G; x_B = rec601_525_x_B;
47 y_R = rec601_525_y_R; y_G = rec601_525_y_G; y_B = rec601_525_y_B;
49 case COLORSPACE_REC_601_625:
50 x_R = rec601_625_x_R; x_G = rec601_625_x_G; x_B = rec601_625_x_B;
51 y_R = rec601_625_y_R; y_G = rec601_625_y_G; y_B = rec601_625_y_B;
57 // Recover z = 1 - x - y.
58 double z_R = 1.0 - x_R - y_R;
59 double z_G = 1.0 - x_G - y_G;
60 double z_B = 1.0 - x_B - y_B;
62 // Find the XYZ coordinates of D65 (white point for both Rec. 601 and 709),
63 // normalized so that Y=1.
67 (1.0 - d65_x - d65_y) / d65_y
70 // We have, for each primary (example is with red):
72 // X_R / (X_R + Y_R + Z_R) = x_R
73 // Y_R / (X_R + Y_R + Z_R) = y_R
74 // Z_R / (X_R + Y_R + Z_R) = z_R
76 // Some algebraic fiddling yields (unsurprisingly):
78 // X_R = (x_R / y_R) Y_R
79 // Z_R = (z_R / y_R) Y_R
81 // We also know that since RGB=(1,1,1) should give us the
82 // D65 illuminant, we must have
84 // X_R + X_G + X_B = D65_X
85 // Y_R + Y_G + Y_B = D65_Y
86 // Z_R + Z_G + Z_B = D65_Z
88 // But since we already know how to express Y and Z by
89 // some constant multiple of X, this reduces to
91 // k1 Y_R + k2 Y_G + k3 Y_B = D65_X
92 // Y_R + Y_G + Y_B = D65_Y
93 // k4 Y_R + k5 Y_G + k6 Y_B = D65_Z
95 // Which we can solve for (Y_R, Y_G, Y_B) by inverting a 3x3 matrix.
98 temp(0,0) = x_R / y_R;
99 temp(0,1) = x_G / y_G;
100 temp(0,2) = x_B / y_B;
106 temp(2,0) = z_R / y_R;
107 temp(2,1) = z_G / y_G;
108 temp(2,2) = z_B / y_B;
110 Vector3d Y_RGB = temp.inverse() * d65_XYZ;
112 // Now convert xyY -> XYZ.
113 double X_R = temp(0,0) * Y_RGB[0];
114 double Z_R = temp(2,0) * Y_RGB[0];
116 double X_G = temp(0,1) * Y_RGB[1];
117 double Z_G = temp(2,1) * Y_RGB[1];
119 double X_B = temp(0,2) * Y_RGB[2];
120 double Z_B = temp(2,2) * Y_RGB[2];
123 m(0,0) = X_R; m(0,1) = X_G; m(0,2) = X_B;
124 m(1,0) = Y_RGB[0]; m(1,1) = Y_RGB[1]; m(1,2) = Y_RGB[2];
125 m(2,0) = Z_R; m(2,1) = Z_G; m(2,2) = Z_B;
130 std::string ColorspaceConversionEffect::output_fragment_shader()
132 // Create a matrix to convert from source space -> XYZ,
133 // another matrix to convert from XYZ -> destination space,
134 // and then concatenate the two.
136 // Since we right-multiply the RGB column vector, the matrix
137 // concatenation order needs to be the opposite of the operation order.
138 Matrix3d source_space_to_xyz = get_xyz_matrix(source_space);
139 Matrix3d xyz_to_destination_space = get_xyz_matrix(destination_space).inverse();
140 Matrix3d m = xyz_to_destination_space * source_space_to_xyz;
142 return output_glsl_mat3("PREFIX(conversion_matrix)", m) +
143 read_file("colorspace_conversion_effect.frag");