All-optical Subtracted Joint Transform Correlator

Abstract

When the classical joint transform correlator (CJTC) was applied to pattern recognition, one of the most well known disadvantages was that the cross correlation signals between the object and the reference patterns as well as those between the reference patterns themselves would join closely in the same output plane. This fact causes inconvenience to identify the necessary output correlation signals between the object and the references, especially when a large number of references was used in the input image. Q.Zhan and T.Minemoto(1) proposed the subtracted joint transform correlator (SJTC) to remove the correlation signals between the references from the output plane, and the binnary subtracted joint transform correlator (BSJTC) to improve furthermore the output correlation results. According to the SJTC and BSJTC, the cross correlations between the references had been successfully removed from the output plane by subtracting the Fourier power spectrum of the references from the joint Fourier power spectrum of the input image. Thus far, the subtraction processing was performed by a computer. In this paper, a new all-optical SJTC system is proposed. In this system, a holographic interference was introduced to perform the subtraction of the Fourier power spectrum of reference patterns. There is not any digital processing by a computer in the system, it is possible to achieve the real time SJTC. The experimental arrangement of the system, the shift-invariant characteristics and the dscriminability of input patterns are described in the following.