Abstract: A filter for performing dilation and/or erosion operations associated with mathematical morphology using a W.times.H rectangular structuring element to a two-dimensional matrix of discrete values, the width of the matrix being x and the height being y, includes a horizontal portion for applying the selected operation to a W.times.1 local neighbourhood and a vertical portion for applying the selected operation to a 1.times.H local neighbourhood. According to one aspect of the filer, the portions are connected one after the other and the matrix elements are applied serially to the first portion, the output of one portion being connected to the input of the other portion. Each of the above-mentioned portions includes a multiplicity of delay devices, each device providing an equal delay, and a multiplicity of comparing devices for comparing two input values.