Hybrid calculation of invariant moments

A hybrid system for computing a position-, scale-, and rotation-invariant (PSRI) feature set is investigated for use in automatic pattern recognition. Specifically, the first four (p+ q)th (zeroth, first, second, and third) ordinary moments of a set of six objects are optically calculated. The process begins with the creation of computer-generated detour phase holograms, which are used to produce wavefronts of the form x^py^q . Each wavefront is imaged onto the object plane, and the Fourier transform of this product is optically calculated. A camera records the intensity pattern in the Fourier transform plane. A normalization technique is used to account for the wide variation in beam intensities. The center value of this pattern is found using a frame grabber and image analyzer. When scaled according to the power meter readings, the center value is the ordinary moment of the object. All of the moment values are processed digitally to form a PSRI feature set, and the Euclidean distance separations between the object´s PSRI features are calculated. The resulting invariant moments can be used for pattern recognition