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TWO-DIMENSIONAL ADDITIVE NALF- TONE SCREEN IMPLEMENTATION

IP.com Disclosure Number: IPCOM000024142D
Original Publication Date: 1979-Oct-31
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 237K

Publishing Venue

Xerox Disclosure Journal

Abstract

One-dimensional additive halftone screens cannot achieve linear TRC (tone reproduction curve) over a density range larger than unity. To increase the linear density range, two basic methods have been proposed; one is to image on the xerographic drum a two-dimensional halftone screen by flashing on and off a halftone pattern as the drum rotates, and the second method is to use an addressable screen whose amplitude is made dependent on the image content. It can be produced by a scanning laser beam whose irradiance is modulated by the image content The beam either produces the halftone pattern directly, or it is used to scan a halftone mask. The second method can also be used to perform low-resolution image corrections like color masking or unsharp masking.

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XEROX DISCLOSURE JOURNAL

TWO-DIMENSIONAL ADDITIVE NALF- Proposed Classification TONE SCREEN IMPLEMENTATION U.S. Cl. 355/3

mt. CL G03g 15/00

One-dimensional additive halftone screens cannot achieve linear TRC (tone reproduction curve) over a density range larger than unity. To increase the linear

density range, two basic methods have been proposed; one is to image on the xerographic drum a two-dimensional halftone screen by flashing on and off a halftone pattern as the drum rotates, and the second method is to use an addressable screen whose amplitude is made dependent on the image content. It can be produced by a scanning laser beam whose irradiance is modulated by the image content The beam either produces the halftone pattern directly, or it is used to scan a halftone mask. The second method can also be used to perform low- resolution image corrections like color masking or unsharp masking.

Both methods have the disadvantage that they are highly sensitive to small changes in the drum velocity; the second method is also highly sensitive to 60 cycle noise in the laser beam. We propose to reduce this sensitivity by producing the halftone screen on the drum from two separate, one-dimensional patterns. The main one is produced by a continuously illuminated, one-dimensional halftone mask, as done in

sequential screen implementation except that it is under exposed and it creates a

TRC with a gamma larger than unity. In the first implementation, a second pattern is fla...