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Proceedings Paper

Boundary stitching algorithm for parallel implementation of error diffusion
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Paper Abstract

Error diffusion1{3 is a popular halftoning algorithm extensively used in digital printing. It renders di erent tone levels by adaptively modulating local dot density. Moreover, because of its random dot placement nature, error di usion is free of Moir e artifacts when rendering an image with strong periodic components. This makes it very attractive to render scanned images which often have strong embedded periodic screen frequencies. However, one potential drawback of error di usion for high speed printing applications is its computation load. Unlike screening algorithms4, 5 which only require one threshold operation per pixel, error di usion also must compute and di use the ltered pixel errors to the neighboring pixels. In practice, it may be desirable to implement error di usion in parallel to speed up the computation. One scenario is shown in Figure 1. The input image is rst equally split into four stripes. Each image stripe is then fed to a DSP chip programmed to run error di usion. Each DSP chip runs error di usion independently without synchronization or communication between processors. The halftone outputs from four DSP chips are nally merged to form the whole halftone image. While this can speed up the algorithm by a factor of four, one potential problem with this parallel implementation is that dot clusters or holes can be very visible along the stripe boundaries in the merged halftone image. This is because the pixel error can not be di used across the stripe boundary, so the \blue noise" characteristics of the halftone texture are destroyed near the stripe boundaries. These artifacts are most visible in midtone areas, and somewhat less visible in the shadow areas. In highlight areas the dots are sparse, so these boundary artifacts are much less visible.

Paper Details

Date Published: 18 December 2003
PDF: 12 pages
Proc. SPIE 5293, Color Imaging IX: Processing, Hardcopy, and Applications, (18 December 2003); doi: 10.1117/12.538667
Show Author Affiliations
Zhen He, Xerox Corp. (United States)
Tichiun Chang, Purdue Univ. (United States)
Jan P. Allebach, Purdue Univ. (United States)
Charles A. Bouman, Purdue Univ. (United States)


Published in SPIE Proceedings Vol. 5293:
Color Imaging IX: Processing, Hardcopy, and Applications
Reiner Eschbach; Gabriel G. Marcu, Editor(s)

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