source: downloads/Samples/Media/materials/programs/PosterizeFP.cg @ 3

sampler RT : register(s0);

float4 Posterize_ps (float2 iTexCoord : TEXCOORD0) : COLOR
{

        float nColors = 8;
        float gamma = 0.6;

        float4 texCol = tex2D(RT, iTexCoord);
        float3 tc = texCol.xyz;
        tc = pow(tc, gamma);
        tc = tc * nColors;
        tc = floor(tc);
        tc = tc / nColors;
        tc = pow(tc,1.0/gamma);
        return float4(tc,texCol.w);
}