Interpolation.hs

{-# LANGUAGE BangPatterns, ViewPatterns #-}
module Graphics.Image.Processing.Interpolation (
  Interpolation(..), Nearest(..), Bilinear(..)
  ) where

import Graphics.Image.Interface


class Interpolation method where
  interpolate :: (Elevator e, Num e, ColorSpace cs) =>
                 method (Pixel cs e) -- ^ Interpolation method
              -> (Int, Int)          -- ^ Image dimensions @m@ rows and @n@ columns.
              -> ((Int, Int) -> Pixel cs e)
                 -- ^ Lookup function that returns a pixel at @i@th and @j@th
                 -- location.
              -> (Double, Double) -- ^ real values of @i@ and @j@ index
              -> Pixel cs e


-- | Nearest Neighbor interpolation method.
data Nearest px = Nearest


-- | Bilinear interpolation method.
data Bilinear px = Bilinear (Border px)


instance Interpolation Nearest where
  interpolate _ !(m, n) !getPx !(round -> i, round -> j) =
    if i >= 0 && j >= 0 && i < m && j < n then getPx (i, j) else 0


instance Interpolation Bilinear where
  interpolate (Bilinear border) !sz !getPx !(i, j) = fi0 + jPx*(fi1-fi0) where
    getPx' = borderIndex border sz getPx
    !(i0, j0) = (floor i, floor j)
    !(i1, j1) = (i0 + 1, j0 + 1)
    !iPx = fromDouble $ fromChannel (i - fromIntegral i0)
    !jPx = fromDouble $ fromChannel (j - fromIntegral j0)
    !f00 = getPx' (i0, j0)
    !f10 = getPx' (i1, j0)
    !f01 = getPx' (i0, j1) 
    !f11 = getPx' (i1, j1) 
    !fi0 = f00 + iPx*(f10-f00)
    !fi1 = f01 + iPx*(f11-f01)
  {-# INLINE interpolate #-}