Digital halftoning on the IBM 4250 Printer

A method of reproducing high-quality continuous-tone images via the IBM 4250 Printer is presented. The approach is modeled on the halftone process used in conventional lithography but is adapted to discrete bilevel printing and digital processing. We use a combination of standard and novel techniques. These include generation and calibration of a set of halftone dot patterns, randomized error propagation in pattern selection, and resolution enhancement in areas of high intensity gradients. The resultant images have good gray-scale rendition and sharp edges without the problems of contouring and worminess often associated with digital image reproduction. We have named this approach PREPRESS: Picture Rendition using Error Propagation and Resolution Enhancement in Simulated Screening.