TransparentizeGreenChannel

TransparentizeGreenChannel.pbk

<languageVersion: 1.0;>

kernel TransparentizeGreenChannel
<   namespace : "Sgss";
    vendor : "Matsuda Shota";
    version : 1;
    description : "Recovers transparency of grayscale image with key channel"; >
{
    input image4 sourceImage;
    output float4 destinationColor;
    
    void evaluatePixel()
    {
        float4 sourceColor = sample(sourceImage, outCoord());
        
        destinationColor.a = 1.0;
        
        float keyChannel = sourceColor.g;
        float baseChannel = sourceColor.r;
        float outputAlpha = (1.0 - keyChannel) + baseChannel;
        float outputChannel = baseChannel / outputAlpha;
        
        if (keyChannel == baseChannel) {
            outputChannel = baseChannel;
            outputAlpha = 1.0;
        } 
        destinationColor.rgb = float3(outputChannel, outputChannel, outputChannel);
        destinationColor.a = outputAlpha;
    }
}