The first step of processing is to extract structure factors (including amplitude and phase) from an selected portion of the image. For this purpose, the selected portion should first be Fourier transformed. To do this, make the image (the left sub widow) the current window, then click the 'FT' button on the toolbar. The result appears in the right sub window. To set the resolution limit for extracting structure factors, click the "max sinQ/l" button  (see the pointer in the figure below). A green ring will appear. You can point at the ring, drag it in and out and set it at a proper position as shown in the right window.