TUNABLE EDGE ENHANCEMENT FILTERS FOR OPTICAL CORRELATION

Difference of Gaussian (DOG) filters, a form of wavelet filter, are an extremely useful preprocessing tool for the enhancement of image edge data. The DOG filter is highly tuneable by control of the standard de viations of its constituent Gaussian distributions. These can be used in the frequency plane of optical correlators and implemented in the f orm of a static non-updateable filter This article reports on a simple optical technique using photorefractive materials whereby a filter, u pdateable in real time and very similar to the DOG filter, is implemen ted by tuning the intensity of the hologram reference wave to give enh anced modulation in a selectable frequency band. This is called a tune able photorefractive (TPR) filter. The results of the DOG and TPR filt ers are compared with those of the phase-only filter and classical mar ched spatial filter with respect to the criteria of signal-to-noise ra tio, Horner efficiency and discrimination capability.