# Fourier transform artifacts

My starting point in what follows is a radially symmetric random field. Taking the Fourier transform of this (and plotting it in logarithm to highlight the patterns), I obtain the following image in Fourier space:

As you can see, there is a radially symmetric part of concentric circles, superimposed with a cross-pattern. Now, I do not understand this last part, but I highly suspect this to be an artifact that is not supposed to be there...

It would not surprise me if this is a problem that more people have run into this problem, but I have not been able to find an answer yet.

So, bottom line: Why is there a cross-pattern in my image?

• Please include a picture of the random field too. – Olli Niemitalo Sep 19 '15 at 21:24
• not saying that this was done with MATLAB, but if the fftshift() has already been done with this (so DC is in the middle and not at the corners), i would say that you get what you have because of DC and low frequency components that exist purely in the left-right and top-down directions and not diagonally. maybe there is a checkerboard or similar pattern that is square with the two spacial axes.  just a guess. – robert bristow-johnson Sep 20 '15 at 0:56