5 #include "colorspace_conversion_effect.h"
11 // Color coordinates from Rec. 709; sRGB uses the same primaries.
12 static const double rec709_x_R = 0.640, rec709_x_G = 0.300, rec709_x_B = 0.150;
13 static const double rec709_y_R = 0.330, rec709_y_G = 0.600, rec709_y_B = 0.060;
15 // Color coordinates from Rec. 601. (Separate for 525- and 625-line systems.)
16 static const double rec601_525_x_R = 0.630, rec601_525_x_G = 0.310, rec601_525_x_B = 0.155;
17 static const double rec601_525_y_R = 0.340, rec601_525_y_G = 0.595, rec601_525_y_B = 0.070;
18 static const double rec601_625_x_R = 0.640, rec601_625_x_G = 0.290, rec601_625_x_B = 0.150;
19 static const double rec601_625_y_R = 0.330, rec601_625_y_G = 0.600, rec601_625_y_B = 0.060;
21 // Color coordinates from Rec. 2020.
22 static const double rec2020_x_R = 0.708, rec2020_x_G = 0.170, rec2020_x_B = 0.131;
23 static const double rec2020_y_R = 0.292, rec2020_y_G = 0.797, rec2020_y_B = 0.046;
25 ColorspaceConversionEffect::ColorspaceConversionEffect()
26 : source_space(COLORSPACE_sRGB),
27 destination_space(COLORSPACE_sRGB)
29 register_int("source_space", (int *)&source_space);
30 register_int("destination_space", (int *)&destination_space);
33 Matrix3d ColorspaceConversionEffect::get_xyz_matrix(Colorspace space)
35 if (space == COLORSPACE_XYZ) {
36 return Matrix3d::Identity();
43 case COLORSPACE_REC_709: // And sRGB.
44 x_R = rec709_x_R; x_G = rec709_x_G; x_B = rec709_x_B;
45 y_R = rec709_y_R; y_G = rec709_y_G; y_B = rec709_y_B;
47 case COLORSPACE_REC_601_525:
48 x_R = rec601_525_x_R; x_G = rec601_525_x_G; x_B = rec601_525_x_B;
49 y_R = rec601_525_y_R; y_G = rec601_525_y_G; y_B = rec601_525_y_B;
51 case COLORSPACE_REC_601_625:
52 x_R = rec601_625_x_R; x_G = rec601_625_x_G; x_B = rec601_625_x_B;
53 y_R = rec601_625_y_R; y_G = rec601_625_y_G; y_B = rec601_625_y_B;
55 case COLORSPACE_REC_2020:
56 x_R = rec2020_x_R; x_G = rec2020_x_G; x_B = rec2020_x_B;
57 y_R = rec2020_y_R; y_G = rec2020_y_G; y_B = rec2020_y_B;
63 // Recover z = 1 - x - y.
64 double z_R = 1.0 - x_R - y_R;
65 double z_G = 1.0 - x_G - y_G;
66 double z_B = 1.0 - x_B - y_B;
68 // We have, for each primary (example is with red):
70 // X_R / (X_R + Y_R + Z_R) = x_R
71 // Y_R / (X_R + Y_R + Z_R) = y_R
72 // Z_R / (X_R + Y_R + Z_R) = z_R
74 // Some algebraic fiddling yields (unsurprisingly):
76 // X_R = (x_R / y_R) Y_R (so define k1 = x_R / y_R)
77 // Z_R = (z_R / y_R) Y_R (so define k4 = z_R / y_R)
79 // We also know that since RGB=(1,1,1) should give us the
80 // D65 illuminant, we must have
82 // X_R + X_G + X_B = D65_X
83 // Y_R + Y_G + Y_B = D65_Y
84 // Z_R + Z_G + Z_B = D65_Z
86 // But since we already know how to express X and Z by
87 // some constant multiple of Y, this reduces to
89 // k1 Y_R + k2 Y_G + k3 Y_B = D65_X
90 // Y_R + Y_G + Y_B = D65_Y
91 // k4 Y_R + k5 Y_G + k6 Y_B = D65_Z
93 // Which we can solve for (Y_R, Y_G, Y_B) by inverting a 3x3 matrix.
96 temp(0,0) = x_R / y_R;
97 temp(0,1) = x_G / y_G;
98 temp(0,2) = x_B / y_B;
104 temp(2,0) = z_R / y_R;
105 temp(2,1) = z_G / y_G;
106 temp(2,2) = z_B / y_B;
108 Vector3d d65_XYZ(d65_X, d65_Y, d65_Z);
109 Vector3d Y_RGB = temp.inverse() * d65_XYZ;
111 // Now convert xyY -> XYZ.
112 double X_R = temp(0,0) * Y_RGB[0];
113 double Z_R = temp(2,0) * Y_RGB[0];
115 double X_G = temp(0,1) * Y_RGB[1];
116 double Z_G = temp(2,1) * Y_RGB[1];
118 double X_B = temp(0,2) * Y_RGB[2];
119 double Z_B = temp(2,2) * Y_RGB[2];
122 m(0,0) = X_R; m(0,1) = X_G; m(0,2) = X_B;
123 m(1,0) = Y_RGB[0]; m(1,1) = Y_RGB[1]; m(1,2) = Y_RGB[2];
124 m(2,0) = Z_R; m(2,1) = Z_G; m(2,2) = Z_B;
129 std::string ColorspaceConversionEffect::output_fragment_shader()
131 // Create a matrix to convert from source space -> XYZ,
132 // another matrix to convert from XYZ -> destination space,
133 // and then concatenate the two.
135 // Since we right-multiply the RGB column vector, the matrix
136 // concatenation order needs to be the opposite of the operation order.
137 Matrix3d source_space_to_xyz = get_xyz_matrix(source_space);
138 Matrix3d xyz_to_destination_space = get_xyz_matrix(destination_space).inverse();
139 Matrix3d m = xyz_to_destination_space * source_space_to_xyz;
141 return output_glsl_mat3("PREFIX(conversion_matrix)", m) +
142 read_file("colorspace_conversion_effect.frag");