cr :: RGB8 -> Double
cr rgb@(r, g, b) = 0.877 * (r' - y rgb) 
  where r' = fromIntegral r
cr :: RGB8 -> Double
cr rgb@(r, g, b) = 0.877 * (r' - y rgb) 
  where r' = fromIntegral r
cr rgb@(r, g, b) = 0.877 * (r' - y rgb) 
  where r' = fromIntegral r