Optimally pipelined error diffusion architecture for converting scanned

Abstract

A color copier machine includes a conventional image scanner for scanning successive swaths of an original document into an image memory and a conventional high quality four-color inkjet printing mechanism for printing each swath as an array of pixels each covered with up to two types of ink (black, or one primary color, or a secondary color combining two primary colors) and an optional color overprint mode in which the blackest pixels may be covered with op to three types of ink (black and one color or three colors). The processing time for the error diffusion and color overprint algorithms is reduced to a minimum time associated with the required number of memory access cycles; to that end, the required memory access and computational operations are organized as pipelined sequences in which multiple computations are performed on previously accessed data while other data from prior computations are being stored in a remote storage or while data required for future computations are being retrieved from the remote storage. A table lookup operation is used to randomize four correction ratios for each pixel; the retrieved 8-bit correction ratio is multiplied by a 10-bit signal representing the remaining error, thereby using one byte read operation (rather than two byte read operations) to obtain a 10-bit accumulated error. The individual pixels are processed in sequential fashion from left to right of the page, one row at a time, with local registers storing the accumulated error for the current pixel and a temporary accumulated error for the four not yet fully processed adjacent pixels in the current row and the next row.