Jython image manipulation problem.

Question

This program is supposed to take the outline of an image, then split it into different quadrants, then color it, such as the Andy Warhol Marilyn Monroe picture.

Every function up to the "Warholize" function works but it gets stuck on c=getPixel(picEdge,x,y) under the warholize function at which I'm not sure what to do. Any help would be greatly appreciated. It is supposed to do "let c be the color of the pixel in picEdge at location x,y "

def main():
  pic= makePicture( pickAFile() )
  show( pic )
  threshold= 10
  edgePic= makeOutline( pic, threshold )


  warholize(pic)

  show(warholize(pic))




def difference( a, b ):

  if a > b :
    return a - b
  else:
    return b - a


def intensity( px ) :

  r= getRed( px )
  g= getBlue( px )
  b= getGreen( px )
  avg= ( r + g + b ) / 3
  return avg


def makeOutline( pic, threshold ):

  w= getWidth( pic )
  h= getHeight( pic )
  edgePic= makeEmptyPicture( w, h )
  for x in range(2,w-1) :
    for y in range(2,h-1):
      px= getPixel( pic, x, y )
      pxLeft= getPixel( pic, x-1, y )
      pxUp= getPixel( pic, x, y-1 )
      leftDiff= difference( intensity(pxLeft), intensity(px) )
      upDiff= difference( intensity(pxUp), intensity(px) )
      if leftDiff > threshold or upDiff > threshold :

        setColor( getPixel(edgePic,x,y), black )


def warholize(pic):
    threshold=10
    picEdge=makeOutline(pic,threshold)
    w= getWidth( pic )
    h= getHeight( pic )
    picNew= makeEmptyPicture( w, h )


    for x in range(0,w,2):
        for y in range (0,h,2):
           c=getPixel(picEdge,x,y)
           px=getPixel(picNew,x/2,y/2)
           if c is black:
               setColor(px,blue)
           else:
               setColor(px,yellow)
    return picNew