Abstract: A technique for producing a dithered halftoned pattern for reproduction on a binary printer having a limited resolution where the halftoned pattern has a relatively fine screen ruling and, for a given size dither matrix, can depict an increased number of gray levels. Specifically, with this technique, gray level error is propagated from tile to tile and based upon the total gray level value for a current tile, which includes both the gray value for that tile itself and the gray level error propagated thereto, one of a number of different threshold matrices is selected. The selected matrix is then used to generate a dithered halftone pattern within the corresponding tile in an output halftoned image in order to depict a desired intermediate gray level in a corresponding area of that image. The threshold matrices produce corresponding dither patterns that illustratively differ by one darkened pel.

Abstract: A system for producing improved halftone images from continuous tone input images, the pixels of which have been digitized as gray scale values, using a printer having the capability to print a set of output pel patterns producing a respective set of discrete gray scale values, is disclosed. Blocks of pel patterns with discrete gray scale values approximating the gray scale values of the input pixels are selected for printing, and the error in a first block due to the difference between the gray scale value associated with the block and the gray scale value of the corresponding input pixel, is determined. To diffuse this error it is distributed to at least two adjacent blocks using a random number generator to determine the distribution such that a random fraction of said error is distributed to one block and the remainder is distributed to the other block. This error diffusion process is carried through the adjacent blocks taking into account the error fraction already assigned.

Abstract: A multi-stage, multi-function, arithmetic and logic unit for a data processing system is formed with only a small number of components. Some of the functions (Sum and Exclusive OR) are performed within each stage. For other functions (AND and OR), some of the components of one stage cooperate with different components of the next stage in an arrangement that reduces the total number of components for each stage. For these functions, the output appears shifted one bit position to the left and is then re-shifted one bit position to the right by a conventionally available shifter.