EXPERIMENTAL ASSESSMENT OF A PHOTOREFRACTIVE BANDPASS JOINT TRANSFORMCORRELATOR

An experimental implementation of a joint transform correlator based o n a nondegenerate four-wave mixing interaction in the photorefractive material bismuth silicon oxide is described. An investigation is made of the pattern recognition performance of the correlator by assessing its ability to maintain a correlation response despite orientation cha nges of a model road vehicle while simultaneously discriminating again st a similar vehicle. The full-bandwidth performance, essentially impl ementing an inverse filtering operation, was found to give good discri mination but to be highly sensitive to changes of the vehicle orientat ion from that of the reference function. A bandpass filtering strategy , based on the difference of Gaussian wavelet filter, was implemented in the correlator by exploiting the Gaussian amplitude profile of the TEM00 made of the helium neon readout laser. An extensive experimental evaluation of the performance of the modified filtering scheme is pre sented, demonstrating considerably enhanced intraclass distortion tole rance while maintaining goad interclass discrimination ability. (C) 19 97 Society of Photo-Optical Instrumentation Engineers.