OPTICAL CIRCULAR SAMPLING SYSTEM FOR TRANSLATION AND ROTATION-INVARIANT PATTERN-RECOGNITION

A simple but effective rotation invariant pattern recognition method b ased on optical circular sampling of the input pattern is described. T he object is decomposed by a set of concentric rings. The distribution of energy between those rings is independent of the orientation of th e object and characterizes it sufficiently to allow its classification . A computer generated hologram formed of concentric diffraction grati ng rings of suitable spatial frequencies may perform the sampling in p arallel. In combination with a lens, each ring is then focused to a gi ven position on a CCD detector where the intensity distribution may be found. Translation invariance is added to the system by sampling the intensity of the Fourier transform of the input object in combination with a liquid crystal light valve. A phototypesetter is used to write the hologram whose quality is demonstrated by optical experiments.