Abstract

Median filtering can be performed optically on a gray-scale input by decomposing the input into a seriesof binary cross sections, convolving each cross section with a binary kernel of the desired shape, thresholding the convolution output, and summing the filtered cross sections to form the gray-scale output. A potential problem in the optical implementation of this method is finding a spatial light modulator to perform the thresholding. We studied whether it is possible to obtain adequate results with nonideal (soft) thresholding. A numerical simulation was used to evaluate the effects of soft transfer curves with different slopes. The simulation produced a startling conclusion: It is better not to have ideal thresholding when performing median filtering. Better grayscale outputs were obtained with transfer curves that had a finite transition region rather than an ideal step response. This bodes well for the possibility of a real-time optical implementation of median filtering with real devices.

© 1990 Optical Society of America