Phase-only filter solution based on fuzzy logic for reducing the defocus problem

One of the main problems in imaging systems is the difficulty in placing the output CCD exactly at the imaging plane. This causes the so-called defocus effect in which the optical transfer function in the output plane is worse than expected. This leads to loss of detail and possible contrast conversion. A good solution for solving the defocus problem in a specific plane would be to place a phase-only filter right after (or before) the lens of the imaging setup. This filter can be designed to cancel the defocusing effect in the specific plane. The design of a filter that will yield good images for a range of planes at different distances from the actual imaging plane requires a more complex approach. In this work the authors introduce a novel method for designing the filter using Fuzzy Logic principles. The Fuzzy Logic inference engine accepts as input data a set of filters; each designed for good results in a specific region, and collaborates them to produce a single phase-only filter. The optical transfer function of the combined filter in the various regions is presented to demonstrate the improvement in limiting defocus.