Optimised Hue shift function in GLSL

Webgl shader Hue Shift function

vec3 hueShift( vec3 color, float hueAdjust ){

    const vec3  kRGBToYPrime = vec3 (0.299, 0.587, 0.114);
    const vec3  kRGBToI      = vec3 (0.596, -0.275, -0.321);
    const vec3  kRGBToQ      = vec3 (0.212, -0.523, 0.311);

    const vec3  kYIQToR     = vec3 (1.0, 0.956, 0.621);
    const vec3  kYIQToG     = vec3 (1.0, -0.272, -0.647);
    const vec3  kYIQToB     = vec3 (1.0, -1.107, 1.704);

    float   YPrime  = dot (color, kRGBToYPrime);
    float   I       = dot (color, kRGBToI);
    float   Q       = dot (color, kRGBToQ);
    float   hue     = atan (Q, I);
    float   chroma  = sqrt (I * I + Q * Q);

    hue += hueAdjust;

    Q = chroma * sin (hue);
    I = chroma * cos (hue);

    vec3    yIQ   = vec3 (YPrime, I, Q);

    return vec3( dot (yIQ, kYIQToR), dot (yIQ, kYIQToG), dot (yIQ, kYIQToB) );

}

vmedea, thank you for the code.

How to adapt your code fro RGBA (alpha) image, vec4?

@l375cd It doesn't do anything with alpha channel, so just use GLSL swizzling to only pass in the RGB channels, and then re-apply the alpha channel to the result. Something like the pseudo-code below.

in vec2 texCoord;
out vec4 outFrag;

uniform sampler2D image;
uniform float hue

void main()
    vec4 color = texture(image, texCoord);
    outFrag = vec4(hueShift(color.rgb, hue), color.a);
}

@ForeverZer0, thank you so much!

Will it work with sRGB color format, or should I convert my color to RGB before using this function?

My version of hue shift I did for some codegolf shader.

vec3 h(vec3 c, float s){  
    return c * mat3(c = .66 * cos(s + vec3(0, 2.09, 4.18)) + .33, c.zxy, c.yzx);
}