Browse Prior Art Database

Four Level Dark And Light Compensation

IP.com Disclosure Number: IPCOM000048907D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Gillingham, RD: AUTHOR [+2]

Abstract

In linear array CCD (charge-coupled device)-type scanners, it is desirable to compensate the signal from each diode for black and white variances. This is typically done by scanning a dark reference and storing a dark compensation value for a diode and subsequently scanning a white reference and storing a white compensation value for each diode. These values may then be used to adjust the signal from that diode as it scans video information. The system described herein simplifies this technique by utilizing only 4-values of dark compensation and 4-values of white compensation, and placing these values near the normal levels for the white reference value and the dark reference value (Fig. 1).

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Four Level Dark And Light Compensation

In linear array CCD (charge-coupled device)-type scanners, it is desirable to compensate the signal from each diode for black and white variances. This is typically done by scanning a dark reference and storing a dark compensation value for a diode and subsequently scanning a white reference and storing a white compensation value for each diode. These values may then be used to adjust the signal from that diode as it scans video information. The system described herein simplifies this technique by utilizing only 4-values of dark compensation and 4-values of white compensation, and placing these values near the normal levels for the white reference value and the dark reference value (Fig. 1).

To understand the operation, reference is now made to Fig. 2. The signal from the CCD scanning array is amplified by the preamplifier 10 and passed through filter 12 to a DC restore circuit 14. Once during each line scan, the video signal is restored to a base reference level, usually the dark level. From the DC restore, the video signal for each diode passes to a level-shift circuit which is used to compensate for dark variances peculiar to the diode producing the video signal. From the level shift circuit 16, the signal passes to a variable gain amplifier 18 which compensates the diode signal for white variances.

Initially, level shift 16 and variable gain amplifier 18 will pass the signal directly through to threshold circuit 20, whit...