prototype. reads test.jpg, creates test.png with the filter applied, prints inverted image onto console

img2ascii.cabal

@@ -20,6 +20,8 @@ executable img2ascii
   main-is:             Main.hs
   -- other-modules:       
   -- other-extensions:    
-  build-depends:       base >=4.8 && <4.9
+  build-depends:       base >=4.8 && <4.9,
+                       JuicyPixels,
+                       vector
   hs-source-dirs:      src
-  default-language:    Haskell2010
+  default-language:    Haskell2010

src/Main.hs

@@ -0,0 +1,89 @@
+module Main where
+
+import Codec.Picture
+import Codec.Picture.Types
+import Data.Maybe (fromJust)
+import Data.Word (Word8)
+import Data.List (transpose)
+
+targetWidth :: Int
+targetWidth = 80
+targetHeight :: Int
+targetHeight = 50
+
+main :: IO ()
+main = do
+       img' <- readImage "test.jpg"
+       case img' of
+         Left err -> putStrLn err
+         Right img -> do
+            src <- return $ extractDynImage img
+            case src of
+              (Just s) -> do
+                 pix <- return $ pixelize s targetWidth targetHeight
+                 case pix of
+                   Nothing -> return ()
+                   Just c -> do
+                     savePngImage "test.png" (ImageRGB8 c)
+                     str <- return $ img2ascii conv c
+                     mapM_ putStrLn (transpose $ chunksof targetHeight str)
+              Nothing -> return ()
+
+chunksof :: Int -> [a] -> [[a]]
+chunksof _ [] = []
+chunksof c xs = take c xs : chunksof c (drop c xs)
+
+conv :: Word8 -> Char
+conv x 
+  | x > 225 = '@'
+  | x > 180 = 'O'
+  | x > 150 = 'o'
+  | x > 50 = '.'
+  | otherwise = ' '
+
+img2ascii :: (Word8 -> Char) -> Image PixelRGB8 -> String
+img2ascii c im@(Image w h _) = do
+   x <- [0..w-1]
+   y <- [0..h-1]
+   return $ c (255-computeLuma (pixelAt im x y))
+
+pixelize :: Image PixelRGB8 -> Int -> Int -> Maybe (Image PixelRGB8)
+pixelize im@(Image iw ih id) tw th =
+      if windoww == 0 || windowh == 0 then
+          Nothing
+      else Just $ snd $ generateFoldImage (folder windoww windowh) im tw th
+     where
+       windoww = iw `div` tw
+       windowh = ih `div` th
+
+folder :: Int -> Int -> Image PixelRGB8 -> Int -> Int -> (Image PixelRGB8, PixelRGB8)
+folder ww wh im@(Image iw ih id) x y = (im,(\(a,_,_) -> a) $ foldl1 filterfun
+    [ (pixelAt im (x'+dx) (y'+dy),dx,dy)
+    | dx <- [-(ww `div` 2)..ww - (ww `div`2)]
+    , dy <- [-(ww `div` 2)..ww - (ww `div`2)]
+    , x'+dx > 0 && x'+dx < iw
+    , y'+dy > 0 && y'+dy < ih
+    ])
+    where
+     x' = x*ww
+     y' = y*wh
+
+filterfun :: (PixelRGB8,Int,Int) -> (PixelRGB8, Int, Int) -> (PixelRGB8,Int,Int)
+filterfun (x@(PixelRGB8 r g b),_,_) (y@(PixelRGB8 r' g' b'),_,_) = if computeLuma x > computeLuma y then (x,0,0) else (y,0,0)
+
+extractDynImage :: DynamicImage -> Maybe (Image PixelRGB8)
+extractDynImage image =
+         case image of
+                ImageY8 img     -> Just $ promoteImage img
+                ImageY16 img    -> Nothing
+                ImageYF img     -> Nothing
+                ImageYA8 img    -> Just $ promoteImage img
+                ImageYA16 img   -> Nothing
+                ImageRGB8 img   -> Just img
+                ImageRGB16 img  -> Nothing
+                ImageRGBF img   -> Nothing
+                ImageRGBA8 img  -> Just $ pixelMap dropTransparency img
+                ImageRGBA16 img -> Nothing
+                ImageYCbCr8 img -> Just $ convertImage img
+                ImageCMYK8 img  -> Just $ convertImage img
+                ImageCMYK16 img -> Nothing