Amplitude-modulated radial harmonic filters

An amplitude-modulated radial harmonic filter is introduced to improve the discrimination of the radial harmonic filter for shift- and scale-invariant pattern recognition. The improvement of discrimination is achieved by Four ier-domain amplitude modulation, which places more emphasis on the high-fre quency terms. The gain of better discrimination, however, is at the cost of poorer noise robustness since the amplitude-modulated radial harmonic filt er is an optimal trade-off filter for noise robustness and discrimination. To compensate for the loss of noise robustness, we apply the technique of F ourier-domain amplitude truncation to the proposed filter. With a given siz e of bandpass, the amplitude truncation approach results in the lowest sign al energy loss, thus yielding a better SNR and discrimination than with a l ow-pass amplitude-modulated radial harmonic filter. (C) 2000 Society of Pho to-Optical Instrumentation Engineers. [S0091-3286(00)00405-0].