In an image filtering system including an input device for inputting image data, a memory unit for storing an image data or the result derived by performing operation on the input image data, an arithmetic unit for performing operations between the image data inputted by the input device or between the input image data and the image data stored in the memory unit or between the image data stored in the memory unit, a loading unit for storing the results of the operation performed by the arithmetic unit in the memory, and an addressing device for designating the addresses of the memory in or from which the data is to be written or read out, an image filtering method in which a predetermined operation is performed 3(n-1) times on 2n inputs or input rows of the image data succeeding one another in a predetermined direction with a filter of a size n, to thereby determine (n+1) results or rows thereof.