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AUTOMATIC GAIN CONTROL SYSTEM FOR IMAGE INPUT MODULE

IP.com Disclosure Number: IPCOM000024795D
Original Publication Date: 1982-Feb-28
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 113K

Publishing Venue

Xerox Disclosure Journal

Abstract

It is desirable that Image Input Models (IIM) deliver uniform video output despite variations in illumination and sensitivity of the image scanning device being used, typically one or more Charge Coupled Devices (CCD) and amplifier drift. In fact, the gain of the IIMb video amplifier must be adjusted scan line by scan line to compensate for slow (warmup) and fast (60 Hz) variations in the document illumination intensity.

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XEROX DISCLOSURE JOURNAL

AUTOMATIC GAIN CONTROL SYSTEM FOR
IMAGE INPUT MODULE
Glenn M. Mehalek

Proposed Classification
U.S. C1. 358/284 Int. CI. H04n 1/40

DRIVER AGC VOLTAGE

             TO MULTIPLIER AMPLIFIER
6 VOLTAGE GAIN -2

I

I

HIGH EVERY SCAN DURING AGC TARGET PIXELS

It is desirable that Image Input Models (IIM) deliver uniform video output despite variations in illumination and sensitivity of the image scanning device being used, typically one or more Charge Coupled Devices (CCD) and amplifier drift. In fact, the gain of the IIMb video amplifier must be adjusted scan line by scan line to compensate for slow (warmup) and fast (60 Hz) variations in the document illumination intensity.

The CCD scans the input document one raster line at a time, each line consisting of many pixels and outputs each scan line pixel by pixel to the video amplifier. The video amplifier increases the magnitude of the signal and performs a DC restoration on the signal. This restoration clamps the level of the video corresponding to black to 0 volts. The "black" video occurs when inactive pixels are clocked out of the CCD.

Volume 7 Number 1 January/February 1982 55

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AUTOMATIC GAIN CONTROL SYSTEM FOR IMAGE INPUT MODULE (Cont'd)

The Automatic Gain Control (AGC) system proposed here includes a multiplier which facilitates the adjustment of the overall system gain. For this purposet a 50% reflectance AGC target is scanned by the CCD for the first several pixels of each scan line. A feedback system is then used to adjust the overall gain of the video amplifier so that the video output voltage is -3 volts for the pixel corresponding to the AGC target. This ensures that the video output voltage corresponding to white is -1 volt.

In the Figure, a schematic representation of the AGC system is sho...