Optical EngineeringAmplitude-modulated radial harmonic filters
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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 Fourier-domain amplitude modulation, which places more emphasis on the high-frequency terms. The gain of better discrimination, however, is at the cost of poorer noise robustness since the amplitude- modulated radial harmonic filter is an optimal trade-off filter for noise robustness and discrimination. To compensate for the loss of noise robustness, we apply the technique of Fourier-domain amplitude truncation to the proposed filter. With a given size of bandpass, the amplitude truncation approach results in the lowest signal energy loss, thus yielding a better SNR and discrimination than with a low-pass amplitude-modulated radial harmonic filter.