Optical means of performing pattern recognition possessing shift-, rotation- and limited size-invariance is demonstrated. The experimental set-up is a standard Fourier transform correlator with a binary circular harmonic (CGH) filter. The filtering function of the filter is obtained by the synthetic discriminant functions (SDF) method. In the process of synthesizing the filtering function, circular harmonic functions are chosen as the basic functions. Both optical results and computer simulation results demonstrate that the filter is able to recognize the target in every rotational orientation and in the relative size range of 1-1.82.
