Digital halftoning, or dithering, is the technique commonly used to render a color or grayscale image on a printer, a computer monitor or other bi-level displays. A particular halftoning technique that has been used extensively in the past is the socalled error diffusion technique. For a number of years it was believed that this technique is inherently sequential and could not be parallelized. In this paper we present and analyze a simple, yet optimal, error-diffusion parallel algorithm for

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... tal halftoning and we discuss an implementation on a parallel machine. In particular, we describe implementations on data-parallel computers that contain linear arrays and two-dimensional meshes of processing elements. Our algorithm runs in 2·n+m parallel steps, a considerable improvement over the 10·m·n sequential algorithm. We expect that this research will lead to the development of faster printers and larger high-resolution monitors.