Optical processor for zero-crossing edge detection

Abstract An optical processor for zero-crossing edge detection is presented, which consists of two defocusedimaging systems to perform the Gaussian convolutions and a VLSI, ferroelectric liquid crystal spatiallight modulator (SLM) to determine the zero-crossings. The zero-crossing SLM is a 32 x 32 arrayof pixels located on 100pm centers. Each pixels contains a phototransistor, an auto-scaling ampli-fier, a zero-crossing detection circuit, and a liquid crystal modulating pad. Electrical and opticalcharacteristics of the zero-crossing SLM are presented along with experimental results of the system. 1. Introduction. In 1980, Marr and Hildreth [1] proposed a method of edge detection based upon locating the zero-crossings inan image convolved with the Laplacian of a Gaussian. The second derivative of an edge produces a zero-crossing.The edges in the image can be determined by locating the zero-crossings of the second derivative. This method ofedge detection differs from convolving an image with different orientational kernels such as the Sobel filter. Withthe Marr and Hildreth method, the single, non-directional, Laplacian operator needs to be applied to the image.