Screen generation for halftone screening of images using scan li

Details Screen generation for halftone screening of images using scan li Screen generation for halftone screening of images using scan li

1991-09-27

1994-04-26

Coles, Sr., Edward L.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358458, 358465, 358466, 358534, 358536, H04N 140

Patent

active

053071816

ABSTRACT:
A halftone screen pattern generation system for computing halftone screened images with rotated screens including multiple angle and ruling combinations, including irrational tangent angles, is disclosed. A screen pattern is generated by storing an oversized strip from an ideal angled screen pattern, and then assembling a sequence comprising selected scan line segments of the oversized strip. Each selected scan line segment corresponds to one of a plurality of offsets of the oversized strip. The error between the actual generated screen and ideal desired screen is computed. Each subsequent scan line segment is selected from the plurality of scan line segments corresponding to the plurality of offsets so as to minimize the accumulated error. In accordance with one aspect of the present invention, the measure of error between the actual generated screen and the ideal angled screen is the length of a vector in a transformed UV space between the actual screen sample point and the ideal screen sample point. The error is determined by vector addition of the accumulated error, from scan line to scan line, which is added to the present error contribution from the offset of the present scan line.

REFERENCES:
patent: 3657472 (1972-04-01), Taudt et al.
patent: 4149194 (1979-04-01), Holladay
patent: 4185304 (1980-01-01), Holladay
patent: 4413286 (1983-11-01), Boston
patent: 4456924 (1984-06-01), Rosenfeld
patent: 4499489 (1985-02-01), Gall et al.
patent: 5067025 (1991-11-01), Kitagawa

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