I needed something small for writing out png files and didn't see anything, so I wrote my own. It's not really large or general enough yet to warrant a full package. It wouldn't require much work to support other variant formats, such as color. ---- Png.hs ---- {- A small library for creating monochrome PNG files. This file is placed into the public domain. Dependencies: Zlib. -} module Png (png) where import Data.Array import Data.Bits import Data.List import Data.Word import qualified Codec.Compression.Zlib as Z import qualified Data.ByteString.Lazy as B be8 :: Word8 -> B.ByteString be8 x = B.singleton x be32 :: Word32 -> B.ByteString be32 x = B.pack [fromIntegral (x `shiftR` sh) | sh <- [24,16,8,0]] pack :: String -> B.ByteString pack xs = B.pack $ map (fromIntegral.fromEnum) xs unpack :: B.ByteString -> String unpack xs = map (toEnum.fromIntegral) (B.unpack xs) hdr, iHDR, iDAT, iEND :: B.ByteString hdr = pack "\137\80\78\71\13\10\26\10" iHDR = pack "IHDR" iDAT = pack "IDAT" iEND = pack "IEND" chunk :: B.ByteString -> B.ByteString -> [B.ByteString] chunk tag xs = [be32 (fromIntegral $ B.length xs), dat, be32 (crc dat)] where dat = B.append tag xs -- | Return a monochrome PNG file from a two dimensional bitmap -- stored in a list of lines represented as a list of booleans. png :: [[Bool]] -> String png dat = unpack $ B.concat $ hdr : concat [ihdr, imgdat, iend] where height = fromIntegral $ length dat width = fromIntegral $ length (head dat) ihdr = chunk iHDR (B.concat [ be32 width, be32 height, be8 1, be8 0, be8 0, be8 0, be8 0]) imgdat = chunk iDAT (Z.compress imgbits) imgbits = B.concat $ map scanline dat iend = chunk iEND B.empty scanline :: [Bool] -> B.ByteString scanline dat = 0 `B.cons` bitpack dat bitpack' :: [Bool] -> Word8 -> Word8 -> B.ByteString bitpack' [] n b = if b /= 0x80 then B.singleton n else B.empty bitpack' (x:xs) n b = if b == 1 then v `B.cons` bitpack' xs 0 0x80 else bitpack' xs v (b `shiftR` 1) where v = if x then n else n .|. b bitpack :: [Bool] -> B.ByteString bitpack xs = bitpack' xs 0 0x80 crc :: B.ByteString -> Word32 crc xs = updateCrc 0xffffffff xs `xor` 0xffffffff updateCrc :: Word32 -> B.ByteString -> Word32 updateCrc = B.foldl' crcStep crcStep :: Word32 -> Word8 -> Word32 crcStep crc ch = (crcTab ! n) `xor` (crc `shiftR` 8) where n = fromIntegral (crc `xor` fromIntegral ch) crcTab :: Array Word8 Word32 crcTab = array (0,255) $ zip [0..255] $ flip map [0..255] (\n -> foldl' (\c k -> if c .&. 1 == 1 then 0xedb88320 `xor` (c `shiftR` 1) else c `shiftR` 1) n [0..7])