Automatic reference control for image scanners

Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry

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Details

358461, 358406, H04N 140

Patent

active

052670538

ABSTRACT:
A system for calibration and closed loop feedback control of image signals from charge coupled imaging devices. During periodic iterative calibration, sampling the output of dark reference cells on a CCD nets an initial D.C. restoration voltage (black) level. A white reference strip is scanned and the system gain is adjusted. The process continues until the scanned values equal the expected values, whereat the calibration process is concluded and the offset value becomes fixed for subsequent scanning. During each scan line of regular scanning, black and white signal levels are adjusted to provide full dynamic range of system operation. Dark cells are sampled and produce a voltage that is modified by the offset voltage, that was determined during calibration. The white reference strip is scanned and the system gain is adjusted.

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