def METHOD_NAME(cls):
    yc = cls.shape[0] // 2
    xc = cls.shape[0] // 2
    y, x = numpy.ogrid[:cls.shape[0],:cls.shape[1]]
    r = 0.4 * min(cls.shape)
    r2 = r * r
    y -= yc
    x -= xc
    cls.img = (x * x + y * y < r2).astype(numpy.int8)