New approaches to 3D image recognition

We describe a number of new optoelectronic approaches to three-dimensional (3D) image recognition. In all the cases, digital holography is used to record the complex amplitude distribution of Fresnel diffraction patterns generated by 3D scenes illuminated with coherent light. This complex information is compared with that from a similar digital hologram of a 3D reference object using correlation methods. Pattern recognition techniques that are shift-variant or shift-invariant along the optical axis are described. In the latter case it is possible to detect the 3D position of the reference in the input scene with high accuracy. We use also a nonlinear composite correlation filter to achieve distortion tolerance. Experiments are presented to illustrate the recognition of a 3D object in the presence of out-of-plane rotation