Library for PPM images
Revision as of 14:18, 18 April 2007
Here's a trivial little thing I wrote for saving PPM images.
For those that don't know, PPM is probably the simplest possible image file format that other software will actually read! For example, IrfanView will read it. Thus, this is a simple, light-weight way to write programs that will output graphics files, using only pure Haskell 98 I/O.
The code is actually designed to work with my Library for colours - but you can supply something of your own if you prefer.
1 ASCII PPM
This is the 'P3' PPM format. The entire thing is plain ASCII. This makes it very easy to read and write, and extremely inefficient. Don't be surprised if a 800x800 pixel image takes up a couple of MB of space!
module PPM (make_ppm, save_ppm) where import Colour save_ppm :: FilePath -> [[Colour]] -> IO () save_ppm f css = writeFile f $ make_ppm css make_ppm :: [[Colour]] -> String make_ppm css = "P3\n" ++ (show $ length $ head css) ++ " " ++ (show $ length css) ++ " 255\n" ++ (unlines $ map unwords $ group 15 $ map show $ concatMap colour $ concat css) group _  =  group n xs = let (xs0,xs1) = splitAt n xs in xs0 : group n xs1 colour (Colour r g b) = [channel r, channel g, channel b] channel :: Double -> Int channel = floor . (255*) . min 1 . max 0
2 Binary PPM
This is the 'P6' PPM format. The header is still plain ASCII, but the actual raster data is binary. This makes the file roughly 10x smaller. I suspect it also makes it go faster too. This library is a drop-in replacement for the one above; include whichever one you want depending on what output you want.
module Fast_PPM (make_ppm, save_ppm) where import Data.Word import qualified Data.ByteString as BIN import Colour quant8 :: Double -> Word8 quant8 x = floor $ x * 0xFF cquant8 :: Colour -> [Word8] cquant8 (Colour r g b) = [quant8 r, quant8 g, quant8 b] string_to_bin :: String -> BIN.ByteString string_to_bin = BIN.pack . map (fromIntegral . fromEnum) header :: [[Colour]] -> BIN.ByteString header pss = let nx = length $ head pss ny = length pss in string_to_bin $ "P6\n" ++ show nx ++ " " ++ show ny ++ " 255\n" body :: [[Colour]] -> BIN.ByteString body pss = BIN.pack $ concatMap (cquant8 . cclip) $ concat pss make_ppm :: [[Colour]] -> BIN.ByteString make_ppm pss = BIN.append (header pss) (body pss) save_ppm :: FilePath -> [[Colour]] -> IO () save_ppm f pss = BIN.writeFile f (make_ppm pss)