OPTIMUM REDUCED-RESOLUTION PHASE-ONLY FILTERS FOR EXTENDED TARGET RECOGNITION

The effect of reducing the resolution of a phase-only filter (POF) wit h respect to the target Fourier transform, while maintaining a constan t filter bandwidth, is investigated. An existing procedure for the opt imal design of filters with constrained complex amplitude values is mo dified by imposing an additional constraint on the filter resolution, and is used to design an optimal POF under such restrictions. A simple analysis is performed for an idealized target, which shows that the c orrelation peak magnitude significantly decreases when the filter reso lution, in terms of number of subregions (pixels), falls below the tar get size, measured in terms of the number of smallest resolvable eleme nts (pixels), in the input. The applicability of this analysis for rea l IR imagery is verified by simulation. The dependence of the correlat ion peak degradation, with filter resolution, on the nature of the ima gery is also investigated, and it is shown that, for a given image siz e, high-pass filtered images are marginally more robust to filter reso lution reduction than normal imagery. Finally, the effectiveness of th e optimizing procedure is demonstrated by comparing the amount of filt er resolution reduction that can be achieved by this procedure with th at achieved by an existing nonoptimal technique.