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IMAGE SIGNAL PROCESSING METHOD AND APPARATUS

IP.com Disclosure Number: IPCOM000024857D
Original Publication Date: 1982-Jun-30
Included in the Prior Art Database: 2004-Apr-04
Document File: 6 page(s) / 268K

Publishing Venue

Xerox Disclosure Journal

Abstract

The need for halftone detection comes about from the methods used to process binary images. To have the best copy quality possible, an image containing halftone areas must be processed in a different manner than line copy. Par-ticularly, there is a need to detect the areas of halftone images in real time. This detection not only must detect halftone areas but also must include a low level detector for detecting line copy areas. This is needed because an error in identifying a line copy region will result in a copy with ragged edges and holes which will rapidly reduce copy quality.

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L 'EROX DISCLOSURE JOURNAL

IMAGE SIGNAL PROCESSING METHOD AND APPARATUS
Ronald S. Tomory
James M. Odorczyk

Proposed Classification
U.S. C1. 358/283 Int. CI. H04n 1/40

Introduction:

The need for halftone detection comes about from the methods used to process binary images. To have the best copy quality possible, an image containing halftone areas must be processed in a different manner than line copy. Par- ticularly, there is a need to detect the areas of halftone images in real time. This detection not only must detect halftone areas but also must include a low level detector for detecting line copy areas. This is needed because an error in identifying a line copy region will result in a copy with ragged edges and holes which will rapidly reduce copy quality.

Description of idea:

In order to segment the image, which may for example comprise a page and designate halftone and text areas on the page, a 12-bit table look up procedure is used. However, because of varying tints, noise and arbitrary threshold levels, many bit patterns may be representative of both halftone and text. Therefore, a post processing technique is used which will further delineate these areas. This scheme called llNeighborhood Logic" is used to fill in the areas where halftone is present as well as eliminate any false detections which may have occurred in areas which are not half tone.

To accomplish this task, a series of 4-bit counters is used to hold information about the current scanline as well as previous scanlines. Each counter is associated with a 4-bit wide column on the page being processed. By making additions and subtractions to these counters depending on the current scanline, the presence of a halftone area and its location may be determined. In this manner, each counter contains information in the vertical direction for a certain location on the page. To obtain information in the horizontal direction as well, the counters are taken in groups of 16 called a block. The counters in each block are processed to decide whether the entire block should be classified as halftone or text. The result is then output and the next block is processed.

Simulation of Haftone Detection Process:

I. Table Look Up

A. Window Logic

Volume 7 Number 3 May/June 1982 191

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IMAGE SIGNAL PROCESSING METHOD AND APPARATUS (Cont'd)

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The original halftone detection is 12ccomplished with a RAM look up procedure. The RAM is a 12-bit table with 2 or 4096 locations. A 12-bit, 1-dimensional window is used to take samples, in shifts of 4, across each incoming scan. After the 12 bits are selected, the location in the RAM designated by these 12 bits is referenced to see if it contains a 1 (designating halftone). If this is the case then the presence of halftone is indicated by injecting llll's into the output stream. The window is then shifted 4 bits to the right and the next 12 bits are selected.

110001 10001...