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GLSL color functions

RGB - YUB

mat3 yuv2rgb = mat3(1.0, 0.0, 1.28033, 1.0, -0.21482, -0.38059, 1.0, 2.12798, 0.0);
mat3 rgb2yuv = mat3(0.2126, 0.7152, 0.0722, -0.09991, -0.33609, 0.43600, 0.615, -0.5586, -0.05639);

RGB - HSV

vec3 rgb2hsv(vec3 c){
	vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
    	vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
    	vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));

    	float d = q.x - min(q.w, q.y);
    	float e = 1.0e-10;
    	return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
}

vec3 hsv2rgb(vec3 c){
	vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
	vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
	return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}

RGB - HSV

From https://www.shadertoy.com/view/MsS3Wc

// Official HSV to RGB conversion 
vec3 hsv2rgb( in vec3 c ){
    vec3 rgb = clamp( abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),6.0)-3.0)-1.0, 0.0, 1.0 );
    return c.z * mix( vec3(1.0), rgb, c.y);
}

// Smooth HSV to RGB conversion 
vec3 hsv2rgb_smooth( in vec3 c ){
    vec3 rgb = clamp( abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),6.0)-3.0)-1.0, 0.0, 1.0 );
    rgb = rgb*rgb*(3.0-2.0*rgb); // cubic smoothing
    return c.z * mix( vec3(1.0), rgb, c.y);
}
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