def fillsquares():
        """For each square of points stepsize apart,
           calculate middle value as mean of points + wibble"""
        cornerref = maparray[0:mapsize:stepsize, 0:mapsize:stepsize]
        squareaccum = cornerref + np.roll(cornerref, shift=-1, axis=0)
        squareaccum += np.roll(squareaccum, shift=-1, axis=1)
        maparray[stepsize // 2:mapsize:stepsize,
        stepsize // 2:mapsize:stepsize] = wibbledmean(squareaccum)
For each square of points stepsize apart,
           calculate middle value as mean of points + wibble
trocr/augmentation/ops.py