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AUTOMATIC GAIN CORRECTION (AGC) VIDEO CORRECTION

IP.com Disclosure Number: IPCOM000026659D
Original Publication Date: 1993-Feb-28
Included in the Prior Art Database: 2004-Apr-06
Document File: 2 page(s) / 78K

Publishing Venue

Xerox Disclosure Journal

Abstract

In a raster input scanner of the type having a transparent platen on which the document to be scanned rests, a movable carriage bearing a scanning array such as a CCD for scanning the platen and the document thereon line by line, and a scan lamp to illuminate the document line being scanned, automatic gain correction or AGC typically performs two functions. In addition to dynamically correcting for short term and long term variations in the light output of the scan lamp, AGC circuitry also compensates for component variations which remain fixed in any particular scanner.

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XEROX DISCLOSURE JOURNAL

VIDEO IN

AUTOMATIC GAIN CORRECTION Proposed Classification (AGC) VIDEO CORRECTION U.S. C1.358/406 Irshad H. Qureshi Int. C1. H04N 1/00

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XEROX DISCLOSURE JOURNAL - Vol. 18, No. 1 January/February 1993 75

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AUTOMATIC GAIN CORRECTION (AGC) VIDEO C ORRE CTION(Cont'd)

In a raster input scanner of the type having a transparent platen on which the document to be scanned rests, a movable carriage bearing a scanning array such as a CCD for scanning the platen and the document thereon line by line, and a scan lamp to illuminate the document line being scanned, automatic gain correction or AGC typically performs two functions. In addition to dynamically correcting for short term and long term variations in the light output of the scan lamp, AGC circuitry also compensates for component variations which remain fixed in any particular scanner.

To provide AGC, a reference patch near the edge of the platen is imaged onto a group of photosites of the CCD sensor array reserved for this purpose. Referring to the drawing Figure, the signal from these photosites (VIDEO IN) is then compared to a suitable reference value 3 and the difference used to set the gain of an analog multiplier 4. This same gain value is then held for the entire scanline.

It is apparent that there are two ways to change the multiplier gain: (1) change t...