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{-# LANGUAGE OverloadedStrings, ScopedTypeVariables #-}
{-
Copyright (C) 2011 John MacFarlane <jgm@berkeley.edu>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
-}
{- |
Module : Text.Pandoc.ImageSize
Copyright : Copyright (C) 2011 John MacFarlane
License : GNU GPL, version 2 or above
Maintainer : John MacFarlane <jgm@berkeley.edu>
Stability : alpha
Portability : portable
Functions for determining the size of a PNG, JPEG, or GIF image.
Algorithms borrowwed from wwwis.pl (c) 2005 Alex K, released
under the GPL.
-}
module Text.Pandoc.ImageSize ( ImageType(..), imageType, imageSize, readImageSize ) where
import Data.ByteString.Lazy (ByteString, unpack)
import qualified Data.ByteString.Lazy.Char8 as B
import Control.Monad
import Data.Bits
-- quick and dirty functions to get image sizes
-- algorithms borrowed from wwwis.pl
data ImageType = Png | Gif | Jpeg deriving Show
type Height = Integer
type Width = Integer
readImageSize :: FilePath -> IO (Maybe (Width,Height))
readImageSize fp = imageSize `fmap` B.readFile fp
imageType :: ByteString -> Maybe ImageType
imageType img = case B.take 4 img of
"\x89\x50\x4e\x47" -> return Png
"\x47\x49\x46\x38" -> return Gif
"\xff\xd8\xff\xe0" -> return Jpeg
_ -> fail "Unknown image type"
imageSize :: ByteString -> Maybe (Width,Height)
imageSize img = do
t <- imageType img
case t of
Png -> pngSize img
Gif -> gifSize img
Jpeg -> jpegSize img
pngSize :: ByteString -> Maybe (Width,Height)
pngSize img = do
let (h, rest) = B.splitAt 8 img
guard $ h == "\x8a\x4d\x4e\x47\x0d\x0a\x1a\x0a" ||
h == "\x89\x50\x4e\x47\x0d\x0a\x1a\x0a"
let (i, rest') = B.splitAt 4 $ B.drop 4 rest
guard $ i == "MHDR" || i == "IHDR"
case map fromIntegral $ unpack $ B.take 8 rest' of
([w1,w2,w3,w4,h1,h2,h3,h4] :: [Integer]) -> return
((shift w1 24) + (shift w2 16) + (shift w3 8) + w4,
(shift h1 24) + (shift h2 16) + (shift h3 8) + h4)
_ -> fail "PNG parse error"
gifSize :: ByteString -> Maybe (Width,Height)
gifSize img = do
let (h, rest) = B.splitAt 6 img
guard $ h == "GIF87a" || h == "GIF89a"
case map fromIntegral $ unpack $ B.take 4 rest of
[w2,w1,h2,h1] -> return (shift w1 8 + w2, shift h1 8 + h2)
_ -> fail "GIF parse error"
jpegSize :: ByteString -> Maybe (Width,Height)
jpegSize img = do
let (h, rest) = B.splitAt 2 img
guard $ h == "\xff\xd8"
findJpegLength rest
findJpegLength :: ByteString -> Maybe (Width,Height)
findJpegLength bs = do
let bs' = B.dropWhile (=='\xff') $ B.dropWhile (/='\xff') bs
case B.uncons bs' of
Just (c,bs'') | c >= '\xc0' && c <= '\xc3' -> do
case map fromIntegral $ unpack $ B.take 4 $ B.drop 3 bs'' of
[h1,h2,w1,w2] -> return (shift w1 8 + w2, shift h1 8 + h2)
_ -> fail "JPEG parse error"
Just (_,bs'') -> do
case map fromIntegral $ unpack $ B.take 2 bs'' of
[c1,c2] -> do
let len = shift c1 8 + c2
-- skip variables
findJpegLength $ B.drop len bs''
_ -> fail "JPEG parse error"
Nothing -> fail "Did not find length record"
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