Fourier tools.

FFT, Inverse FFT, convolution (blurring by point spread function).

Note that some arithmetic operations such as

 Arithmetic / Logarithm

work on complex images, giving a complex result.



To get the real-space Levy psf - swap quads first so that real part

image is the same as the magnitude image.  Otherwise, the real part

image oscillates every other pixel, and the phase oscillates -pi pi.