This paper brings forward a new algorithm for gray image edge detection using the Pulse Coupled Neural Network(PCNN)which features parallel running.And the algorithm is analyzed and discussed the- oretically.Grayscale image edge is corresponding to a non-synchronous firing matrix of neurons in neighbor- ing field in PCNN.According to the gray level of the gray image and using the monolayer PCNN,the edges in a 256 colors gray image by doubly or once processed based on the gray scale levels are detected,and t...