How to interpret diffractograms

A diffractogram is a 2-D Fourier transform of a gray scale microscopy image modulated by a 2-D window function (also called windowed FFT). Below is an explanation of some artifacts present in a diffractogram of a STEM image.

Simulation of the effect of scan noise in a STEM image and its FFT; (a) a simulated ADF-STEM image of an ideal square lattice. The slight streaking of the Fourier spots in both the horizontal and the vertical directions is due to fact that the image dimension is not an integer times the lattice constant. By applying a Hanning window to the image before Fourier transform, the streaking can be removed; (b) shot noise (Poisson noise) is included to simulate a realistic image; (c) random scan noise, resulting from scanning without synchronization to the external field, is included in the simulated image. The vertical streaking in the FFT is more pronounced than in the other two cases and cannot be removed by applying a Hanning window.