COORDINATE-TRANSFORMED FILTER FOR SHIFT-INVARIANT AND SCALE-INVARIANTPATTERN-RECOGNITION

A variable radial coordinate transformation of the phase-only filter ( POF) that is dependent on the energy's angular distribution of the tar get spectrum is used to perform shift- and scale-invariant pattern rec ognition. The POF of a basic size target and the cumulative energy of its angular distribution are calculated. The filter function is then t ransformed by means of stretching along the radial coordinate so that the same energy contribution to the correlation peak is provided for a ny size target. The maximum ratio for recognizing scaled objects is 1: 1.5. Computer simulations and optical experiments showing the performa nces of the filter are presented. (C) 1997 Optical Society America.