A method of encoding intensity images as phase-only images will be presented. This method is suitable for implementation in a variety of devices to be used as the input to an optical correlator. Continuous and discrete phase-only filters can be designed to recognize a variety of target aspects of such encoded images. Moreover, there appears to be a distinct advantage in using such an encoding scheme for filters designed to give a fairly stable response over quite large training sets. This advantage appears to be more than four- to-one when compared to filters designed to recognize the standard amplitude inputs. The advantage is particularly pronounced when the phase-only filters are designed to given an optimal response over the detector in the correlation plane. Complete results of computer simulations are given for realistic training sets containing up to ninety-one targets. The performance of the phase-only filters against targets not in the training set is presented, along with results for stability with respect to additive zero mean Gaussian noise.
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