luminosity :: Color -> Double
luminosity (fenceColor -> RGBA r g b _) = (lo + hi) / 2
  where
    hi = max r (max g b)
    lo = min r (min g b)
luminosity :: Color -> Double
luminosity (fenceColor -> RGBA r g b _) = (lo + hi) / 2
  where
    hi = max r (max g b)
    lo = min r (min g b)
luminosity (fenceColor -> RGBA r g b _) = (lo + hi) / 2
  where
    hi = max r (max g b)
    lo = min r (min g b)