Figure 2

Enhancement of the central ring.(a) Magnitude of the frequency spectrum \(|\mathcal {F}|\) for a typical image; only the central part is shown. (b) The image \(\mathcal {F}'\); the central peak has been removed, which enhances the ring. (c) Radial mean projections for \(|\mathcal {F}|\) (top) and \(\mathcal {F}'\) (bottom); note that the peak corresponding to the characteristic frequency is much more salient in the bottom graph. The vertical scaling in the two graphs is not the same.