1. A processor-based method for reducing a binary input image to produce a reduced image wherein the input image is divided into M.times.N tiles, each tile has M pixels down and N pixels across, and each tile is mapped to a single pixel in the reduced image, comprising the steps, carried out once for each tile, of: applying a convolution window defined by a plurality of active pixel positions when registered to the tile, the number of active pixel positions in the tile being less than the number of pixels in the tile; determining, on the basis of pixel values at the active pixel positions, whether a particular condition is met; and turning ON the pixel in the reduced image if and only if the result of said determining step is affirmative.