Rotationally invariant pattern recognition in a photorefractive joint transform correlator using circular harmonic filters and the wavelet transform

A photorefractive joint transform correlator using circular harmonic filter s and the wavelet transform for high discriminant and rotationally invarian t pattern recognition is reported. In the experimental implementation, a ph otorefractive crystal, BSO, is used as the dynamic holographic medium and a bank of wavelet functions, derived from a mother Mexican-hat wavelet have been selected to achieve a band-pass operation in the Fourier domain. The z ero-order and second-order circular harmonic components are used in the inv estigation. It is shown that, with the proper dilation factors, there is a trade-off between peak correlation intensity and signal-to-noise ratio (SNR ) with the wavelet transform filters. With the second-order circular harmon ic, an improvement of 63% in the SNR is achieved with only a 4% loss in the peak correlation intensity. (C) 2001 Elsevier Science B.V. All rights rese rved.