Optical pattern comparison by interferometry

By placing two similar input transparencies adjacent to each other in the same plane, and illuminating them with coherent light, it is possible to create parallel fringes that will modulate the composite Fraunhofer diffraction pattern of the two input objects. The power spectrum of the combined inputs, i.e. test and reference signal Fourier transform, is analyzed for regularity of the fringe pattern. The method of interference used on input with small rotational errors and on relatively large displacements of the input does not affect the recognition capabilities of the system. This optical method is useful for making rapid pattern comparisons, where the signal to noise ratio is large.