rgb2lab.fsh

rgb2lab.fsh

varying vec2 textureCoordinate;

uniform sampler2D inputImageTexture;

vec3 rgb2xyz(vec3 c) {
    vec3 tmp;
    tmp.x = (c.r > 0.04045) ? pow( (c.r + 0.055) / 1.055, 2.4) : c.r / 12.92;
    tmp.y = (c.g > 0.04045) ? pow( (c.g + 0.055) / 1.055, 2.4) : c.g / 12.92;
    tmp.z = (c.b > 0.04045) ? pow( (c.b + 0.055) / 1.055, 2.4) : c.b / 12.92;
    
    return 100.0 * tmp * mat3(0.4124, 0.3576, 0.1805,
                              0.2126, 0.7152, 0.0722,
                              0.0193, 0.1192, 0.9505);
}

vec3 xyz2lab(vec3 c) {
    vec3 n = c / vec3(95.047, 100, 108.883);
    vec3 v;
    v.x = (n.x > 0.008856) ? pow(n.x, 1.0 / 3.0) : (7.787 * n.x) + (16.0 / 116.0);
    v.y = (n.y > 0.008856) ? pow(n.y, 1.0 / 3.0) : (7.787 * n.y) + (16.0 / 116.0);
    v.z = (n.z > 0.008856) ? pow(n.z, 1.0 / 3.0) : (7.787 * n.z) + (16.0 / 116.0);
    
    return vec3((116.0 * v.y) - 16.0, 500.0 * (v.x - v.y), 200.0 * (v.y - v.z));
}

vec3 rgb2lab(vec3 c) {
   vec3 lab = xyz2lab(rgb2xyz(c));
   return vec3(lab.x / 100.0, 0.5 + 0.5 * (lab.y / 127.0), 0.5 + 0.5 * (lab.z / 127.0));
}

void main() {
    vec4 c = texture2D(inputImageTexture, textureCoordinate);
    gl_FragColor = vec4(rgb2lab(c.rgb), c.a);
}