code: def rebin2x2(a):
      
      inshape = np.array(a.shape)
      if not (inshape % 2 == np.zeros(2)).all(): # Modulo check to see if size is even
          raise RuntimeError, "I want even image shapes !"
          
      return rebin(a, inshape/2)
docs: Wrapper around rebin that actually rebins 2 by 2