Accession Number:

ADA125316

Title:

Automatic Threshold Design for a Bound Document Scanner.

Descriptive Note:

Master's thesis,

Corporate Author:

AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH

Personal Author(s):

Report Date:

1982-12-01

Pagination or Media Count:

223.0

Abstract:

Research was carried out on an electro-optical bound document scanner using a charge-coupled device CCD as a sensing element. The goal was to develop a means whereby the voltage threshold level of the video analog-to-digital converter could be set automatically to provide optimum hard-copy output over a range of lighting conditions and document background colors and qualities. To determine an acceptable component of the analog video signal as a thresholding reference, an extensive study of the signal behavior was conducted over a variety of conditions. An Automatic Threshold Control ATC was designed that exploited the modulation transfer function of the CCDs analog signal. A CALIBRATION PATTERN is superimposed at the left-hand margin of the page being scanned. This pattern contains various discrete spatial frequencies. The threshold voltage is varied automatically until the number of blackwhite zeroone transitions is maximized for the CALIBRATION PATTERN. The threshold voltage producing this maximum number of transitions is equivalent to the threshold required to produce optimum resolution in the scanner hard-copy output. This threshold value is then locked in for the duration of the page being scanned.

Subject Categories:

  • Information Science
  • Non-Radio Communications

Distribution Statement:

APPROVED FOR PUBLIC RELEASE