Colorspace Conversions

colorspaces.glsl

#version 330

// Colorspace conversions, I haven't checked the validity of this stuff.
// Some of them cause discolorations when transformed to and back so I'm
// probably doing wrong things that I don't understand -- Caveat emptor.

// CIELab XYZ
// ----------
// Matrices borrowed from Fundamentals Of Computer Graphics (3rd edition).

vec3 RGBtoLAB(vec3 rgb) {
	mat3 toLAB = {
		{0.4124, 0.3576, 0.1805},
		{0.2126, 0.7152, 0.0722},
		{0.0193, 0.1192, 0.9505}
	};
	return toLAB * rgb;
}

vec3 LABtoRGB(vec3 xyz) {
	mat3 toRGB = {
		{ 3.2405, -1.5371, -0.4985},
		{-0.9693,  1.8706,  0.0416},
		{ 0.0556, -0.2040,  1.0572}
	};
	return toRGB * xyz;
}

// YCoCg
// -----
// Borrowed from the Wikipedia article.

vec3 RGBtoYCoCg(vec3 rgb) {

	float R = rgb.r;
	float G = rgb.g;
	float B = rgb.b;

	float Co  = R - B;
	float tmp = B + Co / 2;
	float Cg  = G - tmp;
	float Y   = tmp + Cg / 2;

	return vec3(Y, Co, Cg);
}

vec3 YCoCgToRGB(vec3 YCoCg) {
	
	float Y  = YCoCg.r;
	float Co = YCoCg.g;
	float Cg = YCoCg.b;
	
	float tmp = Y - Cg/2;
	float G   = Cg + tmp;
	float B   = tmp - Co/2;
	float R   = B + Co;

	return vec3(R, G, B);
}

// Grayscale
// ---------

float Grayscale(vec3 x) {
	return (x.r * 0.299) + (x.g * 0.587) + (x.b * 0.114);
}

float MaxRGB(vec3 x) {
	return max(max(x.r, x.g), x.b);
}