diff --git a/Codec/Picture/Repa.hs b/Codec/Picture/Repa.hs
--- a/Codec/Picture/Repa.hs
+++ b/Codec/Picture/Repa.hs
@@ -20,6 +20,7 @@
        , ToRGBAChannels(..)
        ) where
 import qualified Data.Array.Repa as R
+import qualified Data.Array.Repa.Unsafe as RU
 import qualified Data.Array.Repa.Repr.ForeignPtr as RF
 import Data.Array.Repa.Repr.ForeignPtr (F)
 import Data.Array.Repa ((:.), Array, (:.)(..), Z(..), DIM3, backpermute, extent)
@@ -154,20 +155,20 @@
 
 instance Collapsable RGBA (Word8,Word8,Word8,Word8) where
     collapseColorChannel (Img a) =
-        R.traverse4 a a a a
-             (\_ _ _ (Z:.r:.c:._) -> Z:.r:.c)
-             (\l1 l2 l3 l4 idx -> (l1 (idx:.0)
-                               ,l2 (idx:.1)
-                               ,l3 (idx:.2)
-                               ,l4 (idx:.3)))
+        R.traverse a
+             (\(Z:.r:.c:._) -> Z:.r:.c)
+             (\l idx -> (l (idx:.0)
+                        ,l (idx:.1)
+                        ,l (idx:.2)
+                        ,l (idx:.3)))
 
 instance Collapsable RGBA (Word8,Word8,Word8) where
     collapseColorChannel (Img a) =
-        R.traverse3 a a a
-             (\_ _ (Z:.r:.c:._) -> Z:.r:.c)
-             (\l1 l2 l3 idx -> (l1 (idx:.0)
-                               ,l2 (idx:.1)
-                               ,l3 (idx:.2)))
+        R.traverse a
+             (\(Z:.r:.c:._) -> Z:.r:.c)
+             (\l idx -> (l (idx:.0)
+                        ,l (idx:.1)
+                        ,l (idx:.2)))
 
 -- Helper functions --
 getChannel :: Int -> PixelRGBA8 -> Word8
@@ -307,7 +308,7 @@
   (Z :. ha :. _ :. _) = R.extent a
   (Z :. hb :. _ :. _) = R.extent b
   stack fa fb (Z :. h :. w :. d)
-	| h < hb    = fb (Z :. h :. w :. d)
+        | h < hb    = fb (Z :. h :. w :. d)
         | otherwise = fa (Z :. h - hb :. w :. d)
 
 vConcat :: [Array F DIM3 Word8] -> Array F DIM3 Word8
@@ -326,5 +327,21 @@
     = Z :. min r1 r2 :. c1 + c2 :. min d1 d2
   (Z :. _ :. ca :. _) = R.extent a
   stack fa fb (Z :. r :. c :. d)
-	| c < ca    = fa (Z :. r :. c :. d)
-	| otherwise = fb (Z :. r :. c - ca :. d)
+        | c < ca    = fa (Z :. r :. c :. d)
+        | otherwise = fb (Z :. r :. c - ca :. d)
+
+type Histogram = R.Array R.D R.DIM1 Word8
+
+histograms :: Img a -> (Histogram, Histogram, Histogram, Histogram)
+histograms (Img arr) =
+    let (Z:.nrRow:.nrCol:._) = R.extent arr
+        zero = R.fromFunction (Z:.256) (\_ -> 0 :: Word8)
+        incElem idx x = RU.unsafeTraverse x id (\l i -> l i + if i==(Z:.fromIntegral idx) then 1 else 0)
+    in Prelude.foldl (\(hR, hG, hB, hA) (row,col) ->
+             let r = R.unsafeIndex arr (Z:.row:.col:.0)
+                 g = R.unsafeIndex arr (Z:.row:.col:.1)
+                 b = R.unsafeIndex arr (Z:.row:.col:.2)
+                 a = R.unsafeIndex arr (Z:.row:.col:.3)
+             in (incElem r hR, incElem g hG, incElem b hB, incElem a hA))
+          (zero,zero,zero,zero)
+          [ (row,col) | row <- [0..nrRow-1], col <- [0..nrCol-1] ]
diff --git a/JuicyPixels-repa.cabal b/JuicyPixels-repa.cabal
--- a/JuicyPixels-repa.cabal
+++ b/JuicyPixels-repa.cabal
@@ -1,5 +1,5 @@
 Name:                JuicyPixels-repa
-Version:             0.6
+Version:             0.6.1
 Synopsis:            Convenience functions to obtain array representations of images.
 Description:         This wraps the Juicy.Pixels library to convert into 'Repa' and 
                      'Data.Vector.Storable' formats.