X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=colorspace_conversion_effect.cpp;h=89123d313e861802faaeb19e04f8e900f73fdfbe;hp=fe8119ae76ce3a8741d106bbfc41ba9f33807d3f;hb=4625d0a9601e33201f257c68392c4b1830388a79;hpb=a88f299483ffe5068cd2828513078b9103325da8

diff --git a/colorspace_conversion_effect.cpp b/colorspace_conversion_effect.cpp
index fe8119a..89123d3 100644
--- a/colorspace_conversion_effect.cpp
+++ b/colorspace_conversion_effect.cpp
@@ -1,4 +1,19 @@
+#include <assert.h>
+
 #include "colorspace_conversion_effect.h"
+#include "util.h"
+
+// 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;
+
+// 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 d65_x = 0.3127, d65_y = 0.3290;
 
 ColorSpaceConversionEffect::ColorSpaceConversionEffect()
 	: source_space(COLORSPACE_sRGB),
@@ -7,3 +22,132 @@ ColorSpaceConversionEffect::ColorSpaceConversionEffect()
 	register_int("source_space", (int *)&source_space);
 	register_int("destination_space", (int *)&destination_space);
 }
+
+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;
+
+	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;
+		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;
+		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;
+		break;
+	default:
+		assert(false);
+	}
+
+	// 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;
+	m[2] = Z_R; m[5] = Z_G; m[8] = Z_B;
+}
+
+std::string ColorSpaceConversionEffect::output_fragment_shader()
+{
+	// Create a matrix to convert from source space -> XYZ,
+	// another matrix to convert from XYZ -> destination space,
+	// and then concatenate the two.
+	//
+	// Since we right-multiply the RGB column vector, the matrix
+	// concatenation order needs to be the opposite of the operation order.
+	Matrix3x3 m;
+
+	Matrix3x3 source_space_to_xyz;
+	Matrix3x3 destination_space_to_xyz;
+	Matrix3x3 xyz_to_destination_space;
+
+	get_xyz_matrix(source_space, source_space_to_xyz);
+	get_xyz_matrix(destination_space, destination_space_to_xyz);
+	invert_3x3_matrix(destination_space_to_xyz, xyz_to_destination_space);
+	
+	multiply_3x3_matrices(xyz_to_destination_space, source_space_to_xyz, m);
+
+	char buf[1024];
+	sprintf(buf,
+		"const mat3 PREFIX(conversion_matrix) = mat3(\n"
+		"    %.8f, %.8f, %.8f,\n"
+		"    %.8f, %.8f, %.8f,\n"
+		"    %.8f, %.8f, %.8f);\n\n",
+		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");
+}