def _initial_image_sum(width, height, channels):
 if (channels == 1):
  return np.zeros((height, width), np.float64)
 else:
  return np.zeros((height, width, channels), np.float64)

def _initial_image_sum ( width , height , channels ) : if ( channels == 1 ) : return np . zeros ( ( height , width ) , np . float64 ) else : return np . zeros ( ( height , width , channels ) , np . float64 )
returns an array of zeros that will be used to store the accumulated sum of images .