kernel Levels
<   nameSpace : "anttikupila";
    vendor : "Antti Kupila";
    version : 1;
    description : "Levels filter";
>
{

    parameter float2 red
    <
        minValue: float2(0,0);
        maxValue: float2(1,1);
        defaultValue: float2(0,1);
    >;

    parameter float2 green
    <
        minValue: float2(0,0);
        maxValue: float2(1,1);
        defaultValue: float2(0,1);
    >;

    parameter float2 blue
    <
        minValue: float2(0,0);
        maxValue: float2(1,1);
        defaultValue: float2(0,1);
    >;

    parameter float2 RGB
    <
        minValue: float2(0,0);
        maxValue: float2(1,1);
        defaultValue: float2(0.1,0.9);
    >;

    void
    evaluatePixel(in image3 src, out pixel3 dst)
    {
    
        pixel3 p = sampleNearest(src,outCoord());
        
        float rgbdiff = RGB[1] - RGB[0];
        
        p.r = ( (p.r - red[0])/(red[1] - red[0]) - RGB[0])/rgbdiff;
        p.g = ( (p.g - green[0])/(green[1] - green[0]) - RGB[0])/rgbdiff;
        p.b = ( (p.b - blue[0])/(blue[1] - blue[0]) - RGB[0])/rgbdiff;
        
        dst = p;
    }
}