Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1991-12-24
1994-01-04
Coles, Sr., Edward L.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358458, H04N 140
Patent
active
052765350
ABSTRACT:
Internal moire artifacts found in digital halftoning of photographic images are diffused by rearranging the order of grayscale levels in an original screen pattern cell to generate a new screen pattern cell having a different grayscale order of stored screen pattern pixels. The grayscale order of the original cell is modified by the addition of a bump function at each point in the original cell in order of grayscale. The new grayscale order is stored in the new cell. Adding the bump function at the chosen point in the original cell influences the choice of the next pixel in the grayscale so that the grayscale order in the new cell is, in general, somewhat different from the grayscale order in the original cell. Errors caused by internal moire effects are thus both diffused in the grayscale dimension, and also diffused isotropically in the spatial dimension. The effect of rearranging the order of the grayscale levels in the screen pattern cell is to diffuse the internal moire artifacts in the final halftone to nearby pixels, thereby rendering the internal moire artifacts less noticeable.
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Digital Halftones by Dot Diffusion Donald E. Knuth, ACM Transactions on Graphics 1987.
Coles Sr. Edward L.
Jacobson Allan
Rogers Scott A.
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