<title>Adapting the input scene and the filter to the operating curves of the modulators in real-time correlators</title>

Abstract

In this paper we present some results on the research line of real-time correlation applied to optical pattern recognition. We present a real time optical correlator that uses two twisted nematic liquid crystal spatial light modulators (SLM). This kind of SLM produces phase and amplitude coupled modulation. Phase modulation is useful for the implementation of phase only filters (POF), but the coupled amplitude modulation affects its performance. We present a model to evaluate the response of the phase-only filter (POF) implemented on a modulator with a restricted modulation and we show results on the optimal implementation of POF on this restricted coding domain. The phase modulation is also used for the implementation of the scene by means of a phase-encoding algorithm. The performance of the phase-only filter has been improved for several performance criteria by the design of binary amplitude masks. We present a technique for the implementation of these optimized binary amplitude phase-only filters (BAPOF) using phase-mostly SLMs. Results obtained for the optimization of different criteria are presented. Finally, we present results on the application of these methods to color pattern recognition problems by a multichannel correlation.

<title>Implementation of phase-only coded ternary filters for filtering-based optical processors</title>

“…The correlation planes obtained are sometimes so noisy that detection is impossible. To improve the performance of the BPOF, many authors [6][7][8][9][10][11][12][13][14][15][16][17] have proposed optimization techniques globally involving an amplitude filtering of the frequencies which deteriorate the correlation performance. It could also be interesting to extend these techniques to any kind of amplitude filtering in addition to a phase filter, such as wavelets [18][19][20] for instance.…”