Abstract

Optical correlation can be done in spatially incoherent light. Such correlators are advantageous compared with coherent correlators because diffuse or self-luminous objects can be used directly as inputs without converting them to coherent light inputs. Moreover, incoherent light systems are less sensitive to the lateral positioning of the filter. For the coherent correlator, it has been shown¹ that by using a single circular harmonic (CH) function as a reference object, rotation invariant pattern recognition can be achieved. Unfortunately, these functions are usually complex (having phase and amplitude information) and cannot be used directly with the incoherent correlator. In this work² the real-positive implementation of a CH function in an in-coherent correlator has been investigated. We propose to use a conventional incoherent correlator scheme with two filters simultaneously in order to implement the real and imaginary parts of information contained in a single CH. By using these two filters followed by some post-processing steps, rotation invariant pattern recognition was achieved. In addition, partial information about the angular orientation of the input object can be also obtained. Computer simulations and experiments were performed.

© 1992 Optical Society of America