The joint transform correlator (JTC) is a robust architecture for optical object recognition or verification and has been investigated intensively for a number of years. In order to improve its performance digital processing, such as binarization to an appropriate threshold, has been proposed at the recording stage of the joint power spectrum (JPS), this of course to some extent negates the benefits of an optical system. We propose to employ a third beam which is coherent to the beams forming the JPS and is the Fourier transform of an appropriate third input image and thus can be used to modify the JPS so as to implement a phase only filtering action for example. The triple joint transform correlator thus consists of three Fourier spectra incident simultaneously on a photorefractive crystal and can exhibit improved discrimination over the conventional JTC without an intermediate digital processing stage. Computer simulations and experimental results are presented.
Colin M. Cartwright,
G. Allan Gillespie,
"Triple joint transform correlator", Proc. SPIE 3715, Optical Pattern Recognition X, (9 March 1999); doi: 10.1117/12.341300; https://doi.org/10.1117/12.341300