def add(image1, image2, scale=1.0, offset=0):
    """
    Adds two images, dividing the result by scale and adding the
    offset. If omitted, scale defaults to 1.0, and offset to 0.0.
    At least one of the images must have mode "1".

    .. code-block:: python

        out = ((image1 + image2) / scale + offset)

    :rtype: :py:class:`~PIL.Image.Image`
    """
    image1.load()
    image2.load()
    return image1._new(image1.im.chop_add(image2.im, scale, offset))
