Manipulating images in parallel using Repa

Repa is a powerful library for manipulating high-dimensional arrays in parallel. We will use it to read and edit the pixels of an image.

Getting ready

Install Developer's Image Library (DevIL), a cross-platform image manipulation toolkit. It can be downloaded from http://openil.sourceforge.net/download.php or through apt-get on Debian systems as follows:

$ sudo apt-get install libdevil-dev

Install the Repa package from cabal for the DevIL toolkit as follows:

$ cabal install repa-devil

Create two images named image1.png and image2.png that have the same dimensions, which are shown as follows:

Here comes the second image:

How to do it…

1. Import the following libraries as follows:

   import System.Environment (getArgs)
   import Data.Word (Word8)
   import qualified Data.Array.Repa as R
   import Data.Array.Repa hiding ((++))
   import Data.Array.Repa.IO.DevIL (runIL, readImage, 
     writeImage, IL, Image(RGB))
   import Data.Array.Repa.Repr.ForeignPtr (F)

2. Read the...