Optical Pattern Recognition Using Normalized Invariant Moments

A novel approach to coherent optical pattern recognition is described. It does not utilize matched spatial filters and optical correlation methods. Rather, a 2-dimensional input function is described in terms of its absolute normalized invariant moments. Comparison of these moments enables one to determine the presence of a given object independent of geometrical distortions. A parallel optical processor with a special mask is used to generate all moments for a 2-D scene in parallel. A simple digital post processor calculates the actual absolute normalized invariant moments with the high dynamic range necessary. Our initial work reported upon here has concentrated on: the optical generation of individual moments, how the individual moments vary, the dynamic range requirements of the system and how they may best be met in a hybrid optical digital topology,and methods to generate all moments optically in parallel.