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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.
-}
module Text.Pandoc.ImageSize ( ImageType(..), imageType, imageSize,
sizeInPixels, sizeInPoints ) where
import Data.ByteString (ByteString, unpack)
import qualified Data.ByteString.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
data ImageSize = ImageSize{
pxX :: Integer
, pxY :: Integer
, dpiX :: Integer
, dpiY :: Integer
} deriving (Read, Show, Eq)
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 ImageSize
imageSize img = do
t <- imageType img
case t of
Png -> pngSize img
Gif -> gifSize img
Jpeg -> jpegSize img
sizeInPixels :: ImageSize -> (Integer, Integer)
sizeInPixels s = (pxX s, pxY s)
sizeInPoints :: ImageSize -> (Integer, Integer)
sizeInPoints s = (pxX s * 72 `div` dpiX s, pxY s * 72 `div` dpiY s)
pngSize :: ByteString -> Maybe ImageSize
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"
let (sizes, rest'') = B.splitAt 8 rest'
(x,y) <- case map fromIntegral $ unpack $ sizes 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"
let (dpix, dpiy) = findpHYs rest''
return $ ImageSize { pxX = x, pxY = y, dpiX = dpix, dpiY = dpiy }
findpHYs :: ByteString -> (Integer, Integer)
findpHYs x =
if B.null x || "IDAT" `B.isPrefixOf` x
then (72,72) -- default, no pHYs
else if "pHYs" `B.isPrefixOf` x
then let [x1,x2,x3,x4,y1,y2,y3,y4,u] = map fromIntegral
$ unpack $ B.take 9 $ B.drop 4 x
factor = if u == 1 -- dots per meter
then \z -> z * 254 `div` 10000
else const 72
in ( factor $ (shift x1 24) + (shift x2 16) + (shift x3 8) + x4,
factor $ (shift y1 24) + (shift y2 16) + (shift y3 8) + y4 )
else findpHYs $ B.drop 1 x -- read another byte
gifSize :: ByteString -> Maybe ImageSize
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 ImageSize {
pxX = shift w1 8 + w2,
pxY = shift h1 8 + h2,
dpiX = 72,
dpiY = 72
}
_ -> fail "GIF parse error"
jpegSize :: ByteString -> Maybe ImageSize
jpegSize img = do
let (hdr, rest) = B.splitAt 4 img
guard $ hdr == "\xff\xd8\xff\xe0"
guard $ B.length rest >= 14
let [dpiDensity,dpix1,dpix2,dpiy1,dpiy2] = map fromIntegral
$ unpack $ B.take 5 $ B.drop 9 $ rest
let factor = case dpiDensity of
1 -> id
2 -> \x -> (x * 254 `div` 10)
_ -> const 72
let dpix = factor (shift dpix1 8 + dpix2)
let dpiy = factor (shift dpiy1 8 + dpiy2)
(w,h) <- findJpegSize rest
return $ ImageSize { pxX = w, pxY = h, dpiX = dpix, dpiY = dpiy }
findJpegSize :: ByteString -> Maybe (Integer,Integer)
findJpegSize 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
findJpegSize $ B.drop len bs''
_ -> fail "JPEG parse error"
Nothing -> fail "Did not find length record"
|
