Shrink an Image

def shrink (source):
  #set up target picture
  target = makeEmptyPicture( getWidth(source)/2, getHeight(source)/2)
 
  #do the actual copying
  sourceX = 0
  for targetX in range (0, getWidth(source)/2):
    sourceY = 0
    for targetY in range (0, getHeight(source)/2):
      color = getColor (getPixel (source, sourceX, sourceY))
      setColor (getPixel (target, targetX, targetY), color)
      sourceY = sourceY + 2
    sourceX = sourceX + 2
  return (target)