def _interlace_passes(img):
    """
    Return the subimages of img that make up the seven Adam7 interlace passes.
    """
    pass1 = img[::8, ::8]
    pass2 = img[::8, 4::8]
    pass3 = img[4::8, ::4]
    pass4 = img[::4, 2::4]
    pass5 = img[2::4, ::2]
    pass6 = img[::2, 1::2]
    pass7 = img[1::2, :]
    return (pass1, pass2, pass3, pass4, pass5, pass6, pass7)