import ndimage, datasets
    >>> import numpy.fft
    >>> import matplotlib.pyplot as plt
    >>> fig, (ax1, ax2) = plt.subplots(1, 2)
    >>> plt.gray()  # show the filtered result in grayscale
    >>> ascent = datasets.ascent()
    >>> input_ = numpy.fft.fft2(ascent)
    >>> result = ndimage.fourier_ellipsoid(input_, size=20)
    >>> result = numpy.fft.ifft2(result)
    >>> ax1.imshow(ascent)
    >>> ax2.imshow(result.real)  # the imaginary part is an artifact
    >>> plt.show()
    