kernel FadeToHistory
<   nameSpace : "Kevin's Tutorial Filters";
    vendor : "Kevin's Filters, Inc";
    version : 1;
    description : "Fade from color to B&W to sepia";
>
{
    parameter float crossfade;
    const float3 lumMult = float3(0.3, 0.59, 0.11);
    
    void
    evaluatePixel(in image4 src, out pixel4 dst)
    {
        dst = sampleNearest(src,outCoord());
        float luminance = dot(dst.rgb, lumMult);
        dst.rgb = mix(dst.rgb, float3(luminance), crossfade);
    }
}