Browse Prior Art Database

A DIGITAL TECHNIQUE OF ADAPTIVE THRESHOLDING/QUANTIZING

IP.com Disclosure Number: IPCOM000024365D
Original Publication Date: 1980-Jun-30
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 97K

Publishing Venue

Xerox Disclosure Journal

Abstract

In the application of using a CCD or other type of image scanner to generate an accurate gray-scale response, the lampshading (cosine) effect in the CCD direction (X-direction) and the time-varying, lamp illumination effect in the time direction (Y-direction) will cause video amplitude variations as high as 30 to 50%.

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This is the abbreviated version, containing approximately 58% of the total text.

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XEROX DISCLOSURE JOURNAL

VIDEO SIGNAL 8BlTS 256x6

A/D I RAM

A DIGITAL TECHNIQUE OF ADAPTIVE THRES HOLDING/Q u ANTIZING
Henry J. Liao

Proposed Classification US. C1. 355/8
Int. C1. G03g 15/28

6 BITS

L I

71

TABLE LOADING

  8 BITS 255

N

0

0

1

MANY TO ONE MAPPING

In the application of using a CCD or other type of image scanner to generate an accurate gray-scale response, the lampshading (cosine) effect in the CCD direction (X-direction) and the time-varying, lamp illumination effect in the time direction (Y-direction) will cause video amplitude variations as high as 30 to 50%.

This disclosure proposes an all-digital technique to correct the video amplitude response due to X or Y direction nonuniformity. The major advantage of this technique is the all-digital feature, which will be easier to implement and correct more accurately.

The block diagram is described as follows: The A/D converter converts the analog video signal to 8 bits regardless of the illumination effect. The absolute range of the digital signal can vary as much as 30 to 50%. If the maximum number 255 is made to correspond to the CCD dark current, then the minimum number obtained from a white strip reference can be from 0 to as high as 128.

Volume 5 Number 3 May/June 1980 273

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A DIGITAL TECHNIQUE OF ADAPTIVE THRESHOLDING/QUANTIZING (Cont'd)

The technique proposed is to convert the 8-bit signal to a 6-bit signal by table look- up on a page-by-page basis to correct the time-varying illumination effect or in a section-by-section basis in the Xdirection to correct the cosine shading effect.

A reasonably small amount of time is required to generate and load the RAM table on a page-by-page basis but special hardware or software and section wi...