Cells i corresponding to pixels are initialized into a non-excitation state, to calculate coupling weights W.sub.ik between the eight cells k adjacent to the cells i, thereby determining leader cells p.sub.i=1 based on calculation results. Next, one leader cell yet to be excited is selected as a self-excitable cell. The selected cell is put into the excitation state, the excitable cells are selected based on the coupling weights between the adjacent cells, and the selected cells are put into the excitation state. These operations are repeated until no excitable cell is detected any more and, if there no excitable cell is detected any more, inhibition processing is performed, thereby completing image segmentation of one region. These operations are repeated until there is no non-excited and non-inhibited leader cell any more, thereby pinpointing regions belonging to the same category from an input image and identifying them as an image segmentation regions.