Three-Dimensional Optical Correlator with General Complex Filters

Introduction Three-dimensional #3-D# spatial correlations can be made fast and in parallel by the use of optics. In 1997 Rosen extended the optical correlator's operation from two dimensions to three. 1 This correlation involves fusing images of objects from a few different points of view and allows objects to be identified and located in 3-D space. This process has been demonstrated in a 3-D joint transform correlator #JTC#,in which a reference and tested objects are observed together from a distance. 2,3 The reference object and the tested objects are projected a few times from different points of view onto a spatial light modulator #SLM#, and the projected images are electro-optically processed to yield the desired 3-D correlation. Recently two other attempts at 3-D optical pattern recognition were reported. 4,5 Although these creative proposals contribute original ideas to the reservoir of image-processing techniques, none of them has permitted complete spatial correlatio