PrimeImage.hs

{-# LANGUAGE DeriveDataTypeable #-}
import Codec.Picture
import Data.Numbers.Primes
import System.Console.CmdArgs.Implicit
import Prelude hiding (exponent)
import System.IO
import System.Exit
 
data Options = Options
    { exponent :: Double
    , input    :: FilePath
    , output   :: FilePath
    } deriving (Show, Data, Typeable)
 
options = Options
    { exponent = 1.0 &= help "Exponent argument"
    , input    = def &= argPos 0 &= typ "INPUT"
    , output   = def &= argPos 1 &= typ "OUTPUT"
    } &= summary "PrimeImage v1"
 
main = do
    o <- cmdArgs options
    (Right di) <- readImage $ input o
    case di of
        (ImageRGB8 i) -> writePng (output o)
            $ pixelMap (colorMap (largestPrimeExp $ exponent o)) i
        _ -> hPutStrLn stderr "Input must be 8-bit RGB PNG" >> exitFailure
 
largestPrimeExp :: Integral a => Double -> a -> a
largestPrimeExp e x = -- 251 manually checked for due to a bug (?)
    if x == 1 || x == 251 || isPrime x
    then x
    else min 255 (truncate $ fromIntegral (maximum . primeFactors $ x) ** e)