#A modification of our original program for drawing a white
#square in the center of a picture allows you to draw a rather
#large one.  Note how we use looping over a range.
def setCenterWhite2():
  f=pickAFile()
  pic=makePicture(f)
  height=getHeight(pic)
  width=getWidth(pic)
  startx=width/4
  endx=3*width/4
  starty=height/4
  endy=3*height/4
  for x in range(startx,endx):
    for y in range(starty,endy):
      px=getPixel(pic,x,y)
      setColor(px,white)
  show(pic)