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 ColorspaceConversionEffect::ColorspaceConversionEffect()
22 : source_space(COLORSPACE_sRGB),
23 destination_space(COLORSPACE_sRGB)
25 register_int("source_space", (int *)&source_space);
26 register_int("destination_space", (int *)&destination_space);
29 Matrix3d get_xyz_matrix(Colorspace space)
31 if (space == COLORSPACE_XYZ) {
32 return Matrix3d::Identity();
39 case COLORSPACE_REC_709: // And sRGB.
40 x_R = rec709_x_R; x_G = rec709_x_G; x_B = rec709_x_B;
41 y_R = rec709_y_R; y_G = rec709_y_G; y_B = rec709_y_B;
43 case COLORSPACE_REC_601_525:
44 x_R = rec601_525_x_R; x_G = rec601_525_x_G; x_B = rec601_525_x_B;
45 y_R = rec601_525_y_R; y_G = rec601_525_y_G; y_B = rec601_525_y_B;
47 case COLORSPACE_REC_601_625:
48 x_R = rec601_625_x_R; x_G = rec601_625_x_G; x_B = rec601_625_x_B;
49 y_R = rec601_625_y_R; y_G = rec601_625_y_G; y_B = rec601_625_y_B;
55 // Recover z = 1 - x - y.
56 double z_R = 1.0 - x_R - y_R;
57 double z_G = 1.0 - x_G - y_G;
58 double z_B = 1.0 - x_B - y_B;
60 // We have, for each primary (example is with red):
62 // X_R / (X_R + Y_R + Z_R) = x_R
63 // Y_R / (X_R + Y_R + Z_R) = y_R
64 // Z_R / (X_R + Y_R + Z_R) = z_R
66 // Some algebraic fiddling yields (unsurprisingly):
68 // X_R = (x_R / y_R) Y_R
69 // Z_R = (z_R / y_R) Y_R
71 // We also know that since RGB=(1,1,1) should give us the
72 // D65 illuminant, we must have
74 // X_R + X_G + X_B = D65_X
75 // Y_R + Y_G + Y_B = D65_Y
76 // Z_R + Z_G + Z_B = D65_Z
78 // But since we already know how to express Y and Z by
79 // some constant multiple of X, this reduces to
81 // k1 Y_R + k2 Y_G + k3 Y_B = D65_X
82 // Y_R + Y_G + Y_B = D65_Y
83 // k4 Y_R + k5 Y_G + k6 Y_B = D65_Z
85 // Which we can solve for (Y_R, Y_G, Y_B) by inverting a 3x3 matrix.
88 temp(0,0) = x_R / y_R;
89 temp(0,1) = x_G / y_G;
90 temp(0,2) = x_B / y_B;
96 temp(2,0) = z_R / y_R;
97 temp(2,1) = z_G / y_G;
98 temp(2,2) = z_B / y_B;
100 Vector3d d65_XYZ(d65_X, d65_Y, d65_Z);
101 Vector3d Y_RGB = temp.inverse() * d65_XYZ;
103 // Now convert xyY -> XYZ.
104 double X_R = temp(0,0) * Y_RGB[0];
105 double Z_R = temp(2,0) * Y_RGB[0];
107 double X_G = temp(0,1) * Y_RGB[1];
108 double Z_G = temp(2,1) * Y_RGB[1];
110 double X_B = temp(0,2) * Y_RGB[2];
111 double Z_B = temp(2,2) * Y_RGB[2];
114 m(0,0) = X_R; m(0,1) = X_G; m(0,2) = X_B;
115 m(1,0) = Y_RGB[0]; m(1,1) = Y_RGB[1]; m(1,2) = Y_RGB[2];
116 m(2,0) = Z_R; m(2,1) = Z_G; m(2,2) = Z_B;
121 std::string ColorspaceConversionEffect::output_fragment_shader()
123 // Create a matrix to convert from source space -> XYZ,
124 // another matrix to convert from XYZ -> destination space,
125 // and then concatenate the two.
127 // Since we right-multiply the RGB column vector, the matrix
128 // concatenation order needs to be the opposite of the operation order.
129 Matrix3d source_space_to_xyz = get_xyz_matrix(source_space);
130 Matrix3d xyz_to_destination_space = get_xyz_matrix(destination_space).inverse();
131 Matrix3d m = xyz_to_destination_space * source_space_to_xyz;
133 return output_glsl_mat3("PREFIX(conversion_matrix)", m) +
134 read_file("colorspace_conversion_effect.frag");