contrast.metal

kernel void contrast(
                     texture2d<float, access::write> outTex [[texture(0)]],
                     texture2d<float, access::read> inTex [[texture(1)]],
                     uint2 gid [[thread_position_in_grid]]) {
    //HIGH: More than 1, LOW: Less than 1
    float filterLevel = 1.2;
    float4 c = inTex.read(gid).rgba;
    c = float4((c.rgb - float3(0.5)) * filterLevel + float3(0.5), 1.0);
    outTex.write(c.rgba, gid);
}