'Modifies the pixel at x,y. The color is given as a single
numerical value for single band images, and a tuple for
multi-band images
:param xy: The pixel coordinate, given as (x, y).
:param value: The pixel value.'

def __setitem__(self, xy, color):

    if self.readonly:
        raise ValueError('Attempt    to    putpixel    a    read    only    image')
    (x, y) = self.check_xy(xy)
    return self.set_pixel(x, y, color)
