// Color coordinates from Rec. 709; sRGB uses the same primaries.
double rec709_x_R = 0.640, rec709_x_G = 0.300, rec709_x_B = 0.150;
double rec709_y_R = 0.330, rec709_y_G = 0.600, rec709_y_B = 0.060;
-double rec709_Y_R = 0.2126, rec709_Y_G = 0.7152, rec709_Y_B = 0.0722;
// Color coordinates from Rec. 601. (Separate for 525- and 625-line systems.)
double rec601_525_x_R = 0.630, rec601_525_x_G = 0.310, rec601_525_x_B = 0.155;
double rec601_525_y_R = 0.340, rec601_525_y_G = 0.595, rec601_525_y_B = 0.070;
double rec601_625_x_R = 0.640, rec601_625_x_G = 0.290, rec601_625_x_B = 0.150;
double rec601_625_y_R = 0.330, rec601_625_y_G = 0.600, rec601_625_y_B = 0.060;
-double rec601_Y_R = 0.299, rec601_Y_G = 0.587, rec601_Y_B = 0.114;
+
+// The D65 white point. Given in both Rec. 601 and 709.
+double d65_x = 0.3127, d65_y = 0.3290;
ColorSpaceConversionEffect::ColorSpaceConversionEffect()
: source_space(COLORSPACE_sRGB),
void get_xyz_matrix(ColorSpace space, Matrix3x3 m)
{
+ if (space == COLORSPACE_XYZ) {
+ m[0] = 1.0f; m[3] = 0.0f; m[6] = 0.0f;
+ m[1] = 0.0f; m[4] = 1.0f; m[7] = 0.0f;
+ m[2] = 0.0f; m[5] = 0.0f; m[8] = 1.0f;
+ return;
+ }
+
double x_R, x_G, x_B;
double y_R, y_G, y_B;
- double Y_R, Y_G, Y_B;
switch (space) {
case COLORSPACE_REC_709: // And sRGB.
x_R = rec709_x_R; x_G = rec709_x_G; x_B = rec709_x_B;
y_R = rec709_y_R; y_G = rec709_y_G; y_B = rec709_y_B;
- Y_R = rec709_Y_R; Y_G = rec709_Y_G; Y_B = rec709_Y_B;
break;
case COLORSPACE_REC_601_525:
x_R = rec601_525_x_R; x_G = rec601_525_x_G; x_B = rec601_525_x_B;
y_R = rec601_525_y_R; y_G = rec601_525_y_G; y_B = rec601_525_y_B;
- Y_R = rec601_Y_R; Y_G = rec601_Y_G; Y_B = rec601_Y_B;
break;
case COLORSPACE_REC_601_625:
x_R = rec601_625_x_R; x_G = rec601_625_x_G; x_B = rec601_625_x_B;
y_R = rec601_625_y_R; y_G = rec601_625_y_G; y_B = rec601_625_y_B;
- Y_R = rec601_Y_R; Y_G = rec601_Y_G; Y_B = rec601_Y_B;
break;
default:
assert(false);
}
- // Convert xyY -> XYZ.
- double X_R, X_G, X_B;
- X_R = Y_R * x_R / y_R;
- X_G = Y_G * x_G / y_G;
- X_B = Y_B * x_B / y_B;
-
- double Z_R, Z_G, Z_B;
- Z_R = Y_R * (1.0f - x_R - y_R) / y_R;
- Z_G = Y_G * (1.0f - x_G - y_G) / y_G;
- Z_B = Y_B * (1.0f - x_B - y_B) / y_B;
+ // Recover z = 1 - x - y.
+ double z_R = 1.0 - x_R - y_R;
+ double z_G = 1.0 - x_G - y_G;
+ double z_B = 1.0 - x_B - y_B;
+
+ // Find the XYZ coordinates of D65 (white point for both Rec. 601 and 709),
+ // normalized so that Y=1.
+ double d65_X = d65_x / d65_y;
+ double d65_Y = 1.0;
+ double d65_Z = (1.0 - d65_x - d65_y) / d65_y;
+
+ // We have, for each primary (example is with red):
+ //
+ // X_R / (X_R + Y_R + Z_R) = x_R
+ // Y_R / (X_R + Y_R + Z_R) = y_R
+ // Z_R / (X_R + Y_R + Z_R) = z_R
+ //
+ // Some algebraic fiddling yields (unsurprisingly):
+ //
+ // X_R = (x_R / y_R) Y_R
+ // Z_R = (z_R / y_R) Z_R
+ //
+ // We also know that since RGB=(1,1,1) should give us the
+ // D65 illuminant, we must have
+ //
+ // X_R + X_G + X_B = D65_X
+ // Y_R + Y_G + Y_B = D65_Y
+ // Z_R + Z_G + Z_B = D65_Z
+ //
+ // But since we already know how to express Y and Z by
+ // some constant multiple of X, this reduces to
+ //
+ // k1 Y_R + k2 Y_G + k3 Y_B = D65_X
+ // Y_R + Y_G + Y_B = D65_Y
+ // k4 Y_R + k5 Y_G + k6 Y_B = D65_Z
+ //
+ // Which we can solve for (Y_R, Y_G, Y_B) by inverting a 3x3 matrix.
+
+ Matrix3x3 temp, inverted;
+ temp[0] = x_R / y_R;
+ temp[3] = x_G / y_G;
+ temp[6] = x_B / y_B;
+
+ temp[1] = 1.0;
+ temp[4] = 1.0;
+ temp[7] = 1.0;
+
+ temp[2] = z_R / y_R;
+ temp[5] = z_G / y_G;
+ temp[8] = z_B / y_B;
+
+ invert_3x3_matrix(temp, inverted);
+ float Y_R, Y_G, Y_B;
+ multiply_3x3_matrix_float3(inverted, d65_X, d65_Y, d65_Z, &Y_R, &Y_G, &Y_B);
+
+ // Now convert xyY -> XYZ.
+ double X_R = temp[0] * Y_R;
+ double Z_R = temp[2] * Y_R;
+ double X_G = temp[3] * Y_G;
+ double Z_G = temp[5] * Y_G;
+ double X_B = temp[6] * Y_B;
+ double Z_B = temp[8] * Y_B;
m[0] = X_R; m[3] = X_G; m[6] = X_B;
m[1] = Y_R; m[4] = Y_G; m[7] = Y_B;
" %.8f, %.8f, %.8f,\n"
" %.8f, %.8f, %.8f,\n"
" %.8f, %.8f, %.8f);\n\n",
- m[0], m[3], m[6],
- m[1], m[4], m[7],
- m[2], m[5], m[8]);
- return buf + read_file("colorspace_conversion_effect.glsl");
+ m[0], m[1], m[2],
+ m[3], m[4], m[5],
+ m[6], m[7], m[8]);
+ return buf + read_file("colorspace_conversion_effect.frag");
}
projects / movit / blobdiff