19. The method of claim 15 wherein: the processor-based method is performed in a computer capable of testing whether a word has a value of 2.sup.N -1; the particular plurality of pixels is a horizontal 1.times.N array in the tile and corresponds to a word in the computer; the threshold number is N; and said evaluating and determining steps are carried out by testing whether the word has a value of 2.sup.N -1.
15. A processor-based method for reducing a binary input image to produce a reduced image wherein the 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: evaluating a particular plurality of the pixels in the tile, the particular plurality being smaller in number than the number of pixels in the tile; determining whether at least a threshold number of the evaluated pixels are ON; and turning ON the pixel in the reduced image if and only if the result of said determining step is affirmative.