public void AddFunction <TPixel>(TestPixel <TPixel> back, TestPixel <TPixel> source, float amount, TestPixel <TPixel> expected)
            where TPixel : struct, IPixel <TPixel>
        {
            TPixel actual = PorterDuffFunctions.AddSrcOver(back.AsPixel(), source.AsPixel(), amount);

            VectorAssert.Equal(expected.AsPixel(), actual, 2);
        }