Void-and-cluster dither-matrix generation for better half-tone u

Details Void-and-cluster dither-matrix generation for better half-tone u Void-and-cluster dither-matrix generation for better half-tone u

1997-07-09

2000-07-11

Lee, Thomas D.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358456, 358457, 382270, B41B 1500, B41J 1500, H04N 140

Patent

active

060885122

ABSTRACT:
Dither thresholds are assigned one after the other to matrix locations in the process of generating a dither matrix used for printer half-toning. The matrix location to be assigned the next threshold is chosen by locating the tightest cluster or largest void in the dot pattern that will result from the gray level with which the threshold being assigned is associated. Measures of cluster tightness for low-range and high-range thresholds are based on the areas of Voronoi partitions associated with respective candidate locations. For mid-range thresholds, a Gaussian-filter output is used as the measure. In both cases, ties between candidate locations are resolved by applying a further criterion, which depends on the candidate locations' proximities to locations assigned thresholds the same as the one being assigned or differing from it by only one. If a tie still remains, the matrix is divided into blocks, a determination is made of the number of dots that will result from various blocks' thresholds at the gray level associated with the threshold being assigned, and a choice is made among the remaining candidate locations in accordance with the numbers of dots determined for the respective blocks in which they are located.

REFERENCES:
patent: 5201030 (1993-04-01), Carrie
patent: 5535020 (1996-07-01), Ulichney
patent: 5557709 (1996-09-01), Shu
Gotsman, Craig and Alleback, Jan P., "Bounds and Algorithms for Dither Screens," Conference on "Human Vision & Electronic Imaging," as part of EI-96, San Jose, CA Jan. 27-Feb. 2, 1996, SPIE vol. No. 2657.
Ulichney, Robert, "The Void-and-Cluster Method for Dither Array Generation," IS&T/SPIE Symposium on Electronic Imaging Science & Tech., San Jose, CA, Feb. 3, 1993.

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