F. Turon

Nonlinearity effects in the pure phase correlation method in multiobject scenes

The nonlinearity used in the pure phase correlation method can improve pattern recognition, but it causes high-order harmonics in the correlation plane in the case of multiobject scenes. High-order harmonics and the presence of aliasing may cause false alarms. We show that these effects are strongly diminished when the periodicity in the scene is broken (by different objects, random distribution, etc.).

Performance of the pure phase-only correlation method for pattern recognition

The implementation of nonlinear procedures in optical inforraation processing systems is the recently studied proruising step in the optical correlators development . Optical correlators with phase-only filters and binary phase-only filters belong to the class of such a nonlinear systems with the nonlinearity in the Fourier transfornt plane. The generalization of nonlinear matched filtering such that both the filter transfer function and the Fourier transform of the input objec are processed nonlinearly are recently under investigation. Pattern recognition by using phase nomation only is the particular case of nonlinear matched filtering. As a result of the nonlinear procedure one keeps only phase information about both the target and the input scene, and the pure phase-only correlation is realized. The discrimination capability of the phase-only correlation method is enhanced, even in comparison with the results obtained in the case of the phase-only filtering, and the autocorrelation signal is the diffraction limited delta function.

Phase-only filters codified with Burckhardt's method.

We show that Burckhardt’s method is available to codify phase-only filters with amplitude-only variations. Correlation experimental results are given.

Correlation methods in polychromatic objects recognition: application of lithographic filters

A review of the multichannel correlation methods applied to discriminate color objects with the logical operation AND is presented. The effects of the color CCD camera as the acquisition system are studied. A preprocessing method is proposed to increase the discrimination. The generation of the filters is improved by applying lithographic techniques. Finally an approach of the optimal filter proposed by Yaroslavsky is applied to each channel in the correlation process. Computer and experimental results are given.

Pattern recognition with quantized computer-generated filters

The influence of the quantization levels used in the computer-generated filter on the correlation is studied. Two types of objects, binary characters and gray-tone objects, are used in the scene and in the test. The filters are codified by the method proposed by Burckhardt. Three different filters (a classical matched filter, a high-frequency-enhanced filter, and an amplitude-encoded phase-only filter) are generated, and the influence of the quantization levels in such cases is studied. Numerical and experimental results are obtained.

Filter quanitization effects on the correlation

The computer generated holograms must be registered after the codification, and all the output devices (TV, laser printer,...) involve a quantisation to discreet values. There are losses of information in the quantisation due to the considerable dynamic range of the FT of the object and the limited spatial or grey levels resolution.