METHOD TO CONVERT BITMAPS TO MONOCHROME DATA

A peripheral unit converts source color image data to a rasterized monochrome bit map and includes a random access memory, a storage memory containing a gray scale conversion table, dithering matrices, procedures for determining destination image dithering tiling locations, scaling conversion procedures and sub routines for establishing a gray scale value array index to a bit mask array. The peripheral unit performs a method of converting color source image data to a rasterized compressed monochrome bit map which involves a conversion cycle for converting source pixels to gray scale value and output position bits within the two arrays. Testing is performed to determine all of the source pixels converted to the same gray scale value, and if so, a read ahead cycle commences, reading ahead in the source pixel row for as long as the unconverted source image color data bytes are the same as for those converted in the conversion cycle. The converted output position bits of the converted source pixels are dithered, and an attempt is made to generate a compressed data repeated run entry with a default to a literal run entry based upon dithering of only the converted source pixel output position bits and a count of repeating source pixels.