As is known, a coherent optical data processing system can be used to perform convolution and correlation with ease. Recently it has been shown that the system with diffraction gratings in the spatial filtering plane can also add or subtract complex patterns displayed symmetrically in the input plane. A method is described here for synthesizing a spatial filter so that the coherent system can perform both correlation and subtraction simultaneously in real time. As a particular application of this technique, we present results of using such filters in optical feature extraction.
S. K. Yao and S. H. Lee, "Synthesis of a Spatial Filter for the Combined Operations of Subtraction and Correlation," Appl. Opt. 10, 1154-1156 (1971)