example.

kernel Grayscale
<   namespace : "YourNamespace";
    vendor : "YourVendor";
    version : 1;
    description : "Converts an image to grayscale.";
>
{
    input image4 src;
    output pixel4 dst;

    void evaluatePixel()
    {
        // Get the RGBA color values of the source pixel
        float4 color = sampleNearest(src, outCoord());

        // Calculate the grayscale value
        float gray = dot(color.rgb, float3(0.299, 0.587, 0.114));

        // Set the grayscale value for each color channel
        dst = float4(gray, gray, gray, color.a);
    }
}