Abstract

A new method for shift- and scale-invariant pattern recognition is based on a modification of the classical matched filtering technique. The nonsymmetrical Fourier spectrum of an input scene matches a filter made from the symmetrical FT of a target. The scale of the nonsymmetrical spectrum of a scene changes with the angle in the Fourier plane. Therefore a prototype filter can match the spectrum of an object having a different size in some direction. To reduce the cross-correlation noise, wedge masks are placed in the Fourier plane of a correlator. A scale search is possible by rotating the wedge masks. In the first variant of the system, a common VanderLugt filter is used and a simple threshold detection of the correlation signals is made in the output plane. In the second, a few circular harmonic filters of a target are used successively and a discrimination decision is made in feature space. Computer experiments were carried out for both variants.

© 1985 Optical Society of America