[Haskell-cafe] Image processing using Repa
I'm playing a bit with Repa library and its DevIL bindings. I tried to modify
one of the examples
from tutorial on HaskellWiki. I want to load an image, rotate it and save it to
disk. I managed
to write something like this:
import Foreign.Ptr
import System.Environment
import Data.Array.Repa as R hiding ((++))
import qualified Data.Array.Repa.Repr.ForeignPtr as RFP
import Data.Array.Repa.IO.DevIL
main = do
[f] <- getArgs
(RGB v) <- runIL $ readImage f
RFP.computeIntoP (RFP.toForeignPtr v) (rot180 v)
runIL $ writeImage ("flip-"++f) (RGB v)
return ()
rot180 g = backpermute e flop g
where
e@(Z :. x :. y :. _) = extent g
flop (Z :. i :. j :. k) =
(Z :. x - i - 1 :. y - j - 1 :. k)
This is obviously wrong, because the foreign pointer used as a data source is
at the same time
used as destination, so the data gets overwritten before it is used. Does this
mean that I have
to allocate foreign memory buffers on my own? If so, than it feels kind of
painfull to go through
the hassle of allocating foreign pointers, converting between many different
representations and
so on. Am I doing something wrong and if not is there a more painless way of
working with images
and repa in Haskell?
Jan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Image processing using Repa
You do not have to use computeIntoP. You can just use computeP followed by
toForeignPtr (i don't remember the exact name for that and am on my phone
so it would be awkward to look up). So Repa can create the buffer for you.
Coincidentally, I didn't realize computeIntoP even existed, and I want it
for what I'm doing!
On Oct 10, 2012 7:55 AM, "Janek S." wrote:
> I'm playing a bit with Repa library and its DevIL bindings. I tried to
> modify one of the examples
> from tutorial on HaskellWiki. I want to load an image, rotate it and save
> it to disk. I managed
> to write something like this:
>
> import Foreign.Ptr
> import System.Environment
> import Data.Array.Repa as R hiding ((++))
> import qualified Data.Array.Repa.Repr.ForeignPtr as RFP
> import Data.Array.Repa.IO.DevIL
>
> main = do
> [f] <- getArgs
> (RGB v) <- runIL $ readImage f
> RFP.computeIntoP (RFP.toForeignPtr v) (rot180 v)
> runIL $ writeImage ("flip-"++f) (RGB v)
> return ()
>
> rot180 g = backpermute e flop g
> where
> e@(Z :. x :. y :. _) = extent g
> flop (Z :. i :. j :. k) =
> (Z :. x - i - 1 :. y - j - 1 :. k)
>
> This is obviously wrong, because the foreign pointer used as a data source
> is at the same time
> used as destination, so the data gets overwritten before it is used. Does
> this mean that I have
> to allocate foreign memory buffers on my own? If so, than it feels kind of
> painfull to go through
> the hassle of allocating foreign pointers, converting between many
> different representations and
> so on. Am I doing something wrong and if not is there a more painless way
> of working with images
> and repa in Haskell?
>
> Jan
>
> ___
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Image processing using Repa
> You do not have to use computeIntoP. You can just use computeP followed by
> toForeignPtr (i don't remember the exact name for that and am on my phone
> so it would be awkward to look up). So Repa can create the buffer for you.
> Coincidentally, I didn't realize computeIntoP even existed, and I want it
> for what I'm doing!
I managed to fix my code - thanks! The main function now reads:
main = do
[f] <- getArgs
(RGB v) <- runIL $ readImage f
rotated <- (computeP $ rot180 v) :: IO (Array RFP.F DIM3 Word8)
runIL $ writeImage ("flip-"++f) (RGB rotated)
Jan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
