Browse Prior Art Database

DIGITAL HALFTONE SCREENER AND RESCREENER

IP.com Disclosure Number: IPCOM000024287D
Original Publication Date: 1980-Feb-29
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 96K

Publishing Venue

Xerox Disclosure Journal

Abstract

When multiple bit per pixel digital data is halftoned for printing, it is common for text, line drawings and previously halftoned pictures to be significantly degraded by the halftoning process. A method of performing the halftoning which reduces these degradations is suggested.

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(EROX DISCLOWRE JOURNAL

Proposed Classification
U.S. C1. 358/283
Int. CI. H04n 3/10

When multiple bit per pixel digital data is halftoned for printing, it is common for text, line drawings and previously halftoned pictures to be significantly degraded by the halftoning process. A method of performing the halftoning which reduces these degradations is suggested.

The scanned page is broken into rectangular blocks for computation. For example, if a 45 degree screen pattern is desired, the page would be broken into blocks of height ltn'l pixels and width 112n11 pixels with trnrr being an even number. Blocks above and below the current block would end at the middle of the current block, the resulting appearance being much like a typical brick wall. Two computations are performed on each rectangular image region. Firstly, the region is thresholded. With proper choice of threshold, the result will be the best for text or line drawings. Secondly, the average grey scale and centroid of the intensity distribution of the region is computed. The result of this second computation indicates the proper placement and size of a halftone dot to represent the region. This representation would be better if the region of the picture covered by the rectangle is either a continuous toner picture or a halftoned picture. The decision must be made which of the two versions, thresholded or halftoned, is proper for this rectangular region of the picture.

The decision is made by attempting to determine what type of material is present in each rectangular region of the picture. The decision is made independently for each region, so regions of the image containing text are treated differently than regions containing pictorial information. The decision is made on the basis of some observations about the computations already performed on...