'Returns the pixel at x,y. The pixel is returned as a single
value for single band images or a tuple for multiple band
images
:param xy: The pixel coordinate, given as (x, y).
:returns: a pixel value for single band images, a tuple of
pixel values for multiband images.'

def __getitem__(self, xy):

    (x, y) = self.check_xy(xy)
    return self.get_pixel(x, y)
