RedPNG.hs

-- RedPNG.hs
import qualified Codec.Picture as CP
import qualified Data.Vector.Storable as DV

writeRedPNG filename (width,height) =
 let
  imageVector = DV.generate (width * 3 * height) getPixel
  getPixel i =
   case i `mod` 3 of
    0 -> 255
    1 -> 0
    2 -> 0
  image = CP.Image width height imageVector
  imageRGB8 = CP.ImageRGB8 image
 in CP.writeDynamicPng filename imageRGB8

main = writeRedPNG "red.png" (200,50)