Composite harmonic filters for scale-, projection-, and shift-invariant pattern recognition.

The Mellin radial harmonic filter and the logarithmic harmonic filter are useful for performing optical scale- and projection-invariant pattern recognition, respectively. To our knowledge, on the basis of the harmonic-function method, no one has been able to obtain more than one invariant property (in addition to the shift invariance) when using the matched-filter approach. A new method of combining the scale-, the projection-, and the shift-invariance properties is proposed, based on two decomposition stages of the input pattern. Computer simulations are presented as well as preliminary experimental results.