Abstract: A convolver includes a plurality of multipliers for multiplying pixel values of a convolution window by corresponding coefficients of a convolution mask to provide products, a summer for summing the products to provide a result and a memory for storing intermediate results. The convolver may be used to perform an N.times.N convolution in two or more passes. A first subset of pixel values of an N.times.N convolution window and a first subset of corresponding coefficients of an N.times.N convolution mask are supplied to the multipliers during a first pass of the N.times.N convolution. The summer provides an intermediate result for the first pass and stores the intermediate result in the memory. A second subset of pixel values of the N.times.N convolution window and a second subset of corresponding coefficients of the N.times.N convolution mask are supplied to the multipliers during a second pass of the N.times.N convolution.