Abstract: A system for converting an input bitmap image of one resolution to an output bitmap image of a different resolution. A mapping is defined between pixels in the input bitmap and pixels in the output bitmap. An error term is used to link successive output pixel determinations. For each output value determination, the values of the mapped input pixels are added to the error term to create a test value that determines what output is generated; the output value generated therefrom is then subtracted from the test value to create the next value of the error term. The conversion system is of particular advantage in converting an image having gray scale that is represented in a binary bitmap where gray scale is represented by the ratio of the number of "on" pixels to the number of "off" pixels. The present image conversion system performs a conversion such that the output bitmap represents such gray scale particularly well.