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Task/Bitmap/Haskell/bitmap-2.hs

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+module Bitmap.RGB(module Bitmap.RGB) where
+
+import Bitmap
+import Control.Monad.ST
+
+newtype RGB = RGB (Int, Int, Int) deriving (Eq, Ord)
+
+instance Color RGB where
+    luminance (RGB (r, g, b)) = round x
+      where x = 0.2126*r' + 0.7152*g' + 0.0722*b'
+            (r', g', b') = (toEnum r, toEnum g, toEnum b)
+    black = RGB (0,   0,   0)
+    white = RGB (255, 255, 255)
+    toNetpbm = concatMap f
+      where f (RGB (r, g, b)) = [toEnum r, toEnum g, toEnum b]
+    fromNetpbm [] = []
+    fromNetpbm (r : g : b : rest) = RGB (r, g, b) : fromNetpbm rest
+    netpbmMagicNumber _ = "P6"
+    netpbmMaxval _ = "255"
+
+toRGBImage :: Color c => Image s c -> ST s (Image s RGB)
+toRGBImage = mapImage $ f . luminance
+  where f x = RGB (x, x, x)