[Haskell-cafe] Hsmagick crash

[Ron de Bruijn]

Hi,

I am trying to extract the image data from various file formats and it appeared 
that hsmagick would be the right package to use.

However, it doesn't actually work or I use it incorrectly. If you have installed 
hsmagick and change the value of some_png_file to some existing png file, you 
should see that it crashes at some random pixel. For the particular 256*256 
image I had, it crashed on pixel_nr `elem` [54,56,57].

I am open to suggestions for better ways to get a Array (Int,Int) RGB from e.g. 
a png file.

import Graphics.Transform.Magick.Images
import Graphics.Transform.Magick.Types
import Foreign.Storable
import Control.Monad

image_file_name_to_2d_array file =   do
     himage <- readImage file
     let ptr_to_image = image himage
     himage_ <- peekElemOff ptr_to_image 0
     let bounds@(_rows, _cols) = (rows himage_,columns himage_)
         number_of_pixels  = fromIntegral _rows * fromIntegral _cols
     mapM (\pixel_nr -> do
            putStrLn ("Pixel: " ++ show pixel_nr)
            pixel_packet <- liftM background_color_  $
              peekElemOff
               ptr_to_image
               pixel_nr
            let red_component = red pixel_packet
            putStrLn ("Pixel packet: " ++ show red_component)
            return red_component)
       [0.. number_of_pixels - 1]

some_png_file = "foo.png"

t = do
   initialize_image_library
   image_file_name_to_2d_array some_png_file

initialize_image_library = initializeMagick

Best regards,
  Ron de Bruijn