Two coherent optical systems are described that can realize local nonlinear preprocessing operators such as the Sobel edge-enhancement function in parallel on a 2-D input image. By local, we refer to the size of the image region rather than a nonstationary process. Realization of such operators using a multiple-exposure matched spatial filter and a computer-generated hologram is discussed. Experimental results using these techniques for 3 × 3 and 5 × 5 Sobel operators, respectively, are presented. Our techniques can be extended to larger window sizes and other edge-enhancement operators. These new operators are achieved by novel coherent systems using complex arithmetic with magnitude evaluation of the output pattern.
© 1983 Optical Society of America
David Casasent and Jiabi Chen, "Nonlinear local image preprocessing using coherent optical techniques," Appl. Opt. 22, 808-814 (1983)