Methods and apparatus for providing digital halftone images with random error diffusion dithering

摘要

A process for performing error diffusion to print an image with reduced visually apparent artifacts. The process involves a step of encoding selected pixels as binary values, and calculating error values corresponding to differences between modified intensity values of the pixels and predetermined threshold values. The calculated error values are diffused among four neighbors of each pixel in accordance with a predetermined ordered set of weighting factors. The set of weighting values dictates that 4/8 of the error is diffused to one of the pixel neighbors, 1/8 of the error is diffused to a second pixel neighbor, 2/8 of the error is diffused to a third pixel neighbor, and 1/8 of the error is diffused to a fourth pixel neighbor. A random selection is made of one of the predetermined set of weight values as a starting weight value. The starting weight value is assigned to a predetermined one of the pixel neighbors. Based on the starting weight value, the process then involves selecting in an ordered fashion weight values of the predetermined set of weight values until all the predetermined weight values have been selected, and assigning each selected weight value to a predetermined one of the pixel neighbors. This process continues for all pixels of an input image.