g :: YCbCr -> Pixel8
g (y, cb, cr) = (assertBounded . round) (y - 0.395 * cb - 0.581 * cr)
g :: YCbCr -> Pixel8
g (y, cb, cr) = (assertBounded . round) (y - 0.395 * cb - 0.581 * cr)
g (y, cb, cr) = (assertBounded . round) (y - 0.395 * cb - 0.581 * cr)