Infinite loop in palettize

[Fabian Lippold]

In the palettize function when the PaletteCreationMode Uniform is used, in the corresponding function uniformQuantization when maxCols is less than 8 this causes bitDiv3 to return 0 as at least one element of the tuple (bg, br, bb) which then causes the corresponding list to evaluate to [0, 0 .. 255] which will never terminate.

Juicy.Pixels/src/Codec/Picture/ColorQuant.hs

Lines 157 to 173 in 8b16442

 uniformQuantization :: PaletteOptions -> Image PixelRGB8 -> (Image Pixel8, Palette) 
 uniformQuantization opts img 
   -- -| colorCount img <= maxCols = colorQuantExact img 
   | enableImageDithering opts = 
         (pixelMap paletteIndex (pixelMapXY dither img), palette) 
   | otherwise = (pixelMap paletteIndex img, palette) 
   where 
     maxCols = paletteColorCount opts 
     palette = listToPalette paletteList 
     paletteList = [PixelRGB8 r g b | r <- [0,dr..255] 
                                    , g <- [0,dg..255] 
                                    , b <- [0,db..255]] 
     (bg, br, bb) = bitDiv3 maxCols 
     (dr, dg, db) = (2^(8-br), 2^(8-bg), 2^(8-bb)) 
     paletteIndex (PixelRGB8 r g b) = fromIntegral $ fromMaybe 0 (elemIndex 
       (PixelRGB8 (r .&. negate dr) (g .&. negate dg) (b .&. negate db)) 
       paletteList) 

In my case, this causes the program to use 100% of the CPU filling up the RAM until the system hangs.

If values of less than 8 are not considered valid then this should be at least mentioned in the documentation or there should be a check of some sort.