#Scale picture to half size and display
def scale_half():
  pic=makePicture(pickAFile())
  show(pic)
  w=getWidth(pic)
  h=getHeight(pic)
  pic2=makeEmptyPicture(w/2,h/2)
  for px in getPixels(pic2):
    x=getX(px)
    y=getY(px)
    sourcepx=getPixel(pic,2*x ,2*y )
    c=getColor(sourcepx)
    setColor(px,c)
  show(pic2)