3 #include "colorspace_conversion_effect.h"
6 // Color coordinates from Rec. 709; sRGB uses the same primaries.
7 double rec709_x_R = 0.640, rec709_x_G = 0.300, rec709_x_B = 0.150;
8 double rec709_y_R = 0.330, rec709_y_G = 0.600, rec709_y_B = 0.060;
10 // Color coordinates from Rec. 601. (Separate for 525- and 625-line systems.)
11 double rec601_525_x_R = 0.630, rec601_525_x_G = 0.310, rec601_525_x_B = 0.155;
12 double rec601_525_y_R = 0.340, rec601_525_y_G = 0.595, rec601_525_y_B = 0.070;
13 double rec601_625_x_R = 0.640, rec601_625_x_G = 0.290, rec601_625_x_B = 0.150;
14 double rec601_625_y_R = 0.330, rec601_625_y_G = 0.600, rec601_625_y_B = 0.060;
16 double d65_x = 0.3127, d65_y = 0.3290;
18 ColorSpaceConversionEffect::ColorSpaceConversionEffect()
19 : source_space(COLORSPACE_sRGB),
20 destination_space(COLORSPACE_sRGB)
22 register_int("source_space", (int *)&source_space);
23 register_int("destination_space", (int *)&destination_space);
26 void get_xyz_matrix(ColorSpace space, Matrix3x3 m)
28 if (space == COLORSPACE_XYZ) {
29 m[0] = 1.0f; m[3] = 0.0f; m[6] = 0.0f;
30 m[1] = 0.0f; m[4] = 1.0f; m[7] = 0.0f;
31 m[2] = 0.0f; m[5] = 0.0f; m[8] = 1.0f;
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 // Find the XYZ coordinates of D65 (white point for both Rec. 601 and 709),
61 // normalized so that Y=1.
62 double d65_X = d65_x / d65_y;
64 double d65_Z = (1.0 - d65_x - d65_y) / d65_y;
66 // We have, for each primary (example is with red):
68 // X_R / (X_R + Y_R + Z_R) = x_R
69 // Y_R / (X_R + Y_R + Z_R) = y_R
70 // Z_R / (X_R + Y_R + Z_R) = z_R
72 // Some algebraic fiddling yields (unsurprisingly):
74 // X_R = (x_R / y_R) Y_R
75 // Z_R = (z_R / y_R) Z_R
77 // We also know that since RGB=(1,1,1) should give us the
78 // D65 illuminant, we must have
80 // X_R + X_G + X_B = D65_X
81 // Y_R + Y_G + Y_B = D65_Y
82 // Z_R + Z_G + Z_B = D65_Z
84 // But since we already know how to express Y and Z by
85 // some constant multiple of X, this reduces to
87 // k1 Y_R + k2 Y_G + k3 Y_B = D65_X
88 // Y_R + Y_G + Y_B = D65_Y
89 // k4 Y_R + k5 Y_G + k6 Y_B = D65_Z
91 // Which we can solve for (Y_R, Y_G, Y_B) by inverting a 3x3 matrix.
93 Matrix3x3 temp, inverted;
106 invert_3x3_matrix(temp, inverted);
108 multiply_3x3_matrix_float3(inverted, d65_X, d65_Y, d65_Z, &Y_R, &Y_G, &Y_B);
110 // Now convert xyY -> XYZ.
111 double X_R = temp[0] * Y_R;
112 double Z_R = temp[2] * Y_R;
113 double X_G = temp[3] * Y_G;
114 double Z_G = temp[5] * Y_G;
115 double X_B = temp[6] * Y_B;
116 double Z_B = temp[8] * Y_B;
118 m[0] = X_R; m[3] = X_G; m[6] = X_B;
119 m[1] = Y_R; m[4] = Y_G; m[7] = Y_B;
120 m[2] = Z_R; m[5] = Z_G; m[8] = Z_B;
123 std::string ColorSpaceConversionEffect::output_fragment_shader()
125 // Create a matrix to convert from source space -> XYZ,
126 // another matrix to convert from XYZ -> destination space,
127 // and then concatenate the two.
129 // Since we right-multiply the RGB column vector, the matrix
130 // concatenation order needs to be the opposite of the operation order.
133 Matrix3x3 source_space_to_xyz;
134 Matrix3x3 destination_space_to_xyz;
135 Matrix3x3 xyz_to_destination_space;
137 get_xyz_matrix(source_space, source_space_to_xyz);
138 get_xyz_matrix(destination_space, destination_space_to_xyz);
139 invert_3x3_matrix(destination_space_to_xyz, xyz_to_destination_space);
141 multiply_3x3_matrices(xyz_to_destination_space, source_space_to_xyz, m);
145 "const mat3 PREFIX(conversion_matrix) = mat3(\n"
146 " %.8f, %.8f, %.8f,\n"
147 " %.8f, %.8f, %.8f,\n"
148 " %.8f, %.8f, %.8f);\n\n",
152 return buf + read_file("colorspace_conversion_effect.frag");