Intermodulation effects in pure phase-only correlation method

Abstract

Many problems related to optical pattern recognition nay be reduced to the detection and localization of search target. Various modifications of classical matched filte9 such as phase-only filters (POF) binary hase-only filters (Bi-POF) , and complex ternary matched filters (CTMF) providing the output peak sharpness minimalizaton are recently suggested in order to improve the detection quality. Among various matched filtering modifications leading5 to output peak sharpness minimalzation the inverse filtering (IF) , pure phase—only correlation (POC) , hard clipping nonlinear joint transform correlator (NJTC) and8 in some approximation , the optimum filter (OF) proposed by Jaroslawski provide the maximum sharp output signal (which is the diffraction limited delta function) . All procedures introduced to improve the detection quality have high pass characteristics and the high spatial frequencies are enhanced. Most of mentioned above methods (exept POC and NJTC) introduce only modification of the filter function keeping nonchanged spectrum of the input scene. The pure phase—only correlation method belongs to the class of nonlinear matched filtering such that both the filter transfer function and the input scene spectrum are modifed nonlinearly before they are multiplied in the spectral domn9 .Symmetric phase-only filter (SPOF) analyzed by Ersoy et all.9' as an example of the nonlinear matched filtering corresponds exactly to the POC method. Optical implementation of the POC method can be realized on the basis of the nonlinear joint transform correlator7. In this paper analysis of the properties of the phase-only correlation method applied p he multiobject input scenes is presented. Our initial results 1, obtained by digital simulation show that also in this case the method works well, but is sensitive to intermodulation noises. The study of the influence of the intermodulation noises on the recognition results is the main goal of our digital analysis.