Symbolic substitution operations can be realized optically on a correlator. This is a very
attractive and efficient architecture for symbolic substitution. It allows parallel multichannel
realization with a fixed set of filters (on film or easily realized on low space bandwidth product spatial
light modulators) using space and frequency-multiplexing or sequential filters. All basic logic,
numeric and morphological image processing functions can be achieved by symbolic substitution.
Moreover, all operations are possible on one multifunctional optical processor. Morphological
operations are felt to be essential for ATR and pattern recognition preprocessing in clutter. They
greatly improve the role for optics by allowing the same optical architecture to be used for low,
medium and high level vision.