Improved holographic matched filter systems for pattern recognition using a correlation method

Abstract

A multi-channel correlator for holographic matched filtering is described. The two-dimensional channels are separated spatially in the Fourier plane. This arrangement allows individual filters to be realized for each channel for different spatial frequency ranges etc. The multi-channel correlator is addressed by a generator of multiple object waves, i.e. by different directions of object illumination. Parallel and sequential evaluation of the correlation signals is possible. The efficiency and signal-to-noise ratio for both modes of operation are discussed. In each channel, linear superimposed multiple Vander-Lugt filters may be introduced to increase the over-all capacity of learning steps. The risk of over-exposure is small because the centres of the frequency spectra are separated on the hologram filter plate. With a multi-channel correlator, combined matched and feature filtering may be performed. Preliminary experimental results show that this method can be succesfully used in some cases where the results of simple matched filtering remain unsatisfactory. The results and discussions are presented from a more general point of view with some remarks concerning comparable methods and possible future aspects.