Adjustable read level threshold for optical mark scanning
US5420407A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 17, 1993 |
| Grant date | May 30, 1995 |
| Priority date | — |
| Expiry date | Sep 17, 2013 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06K17/0032
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
To determine a read level threshold for discriminating those response bubbles on a scannable answer sheet intended to be marked from those response bubbles not intended to be marked, an adjustable read level threshold is dynamically determined based on the read levels of a designated pool of response bubbles. In an optical scanner the darkness (read level) of each response mark entered for a particular question is determined to make a profile. From this profile showing the various read levels present for the response marks, the system determines read level "gaps," i.e., read levels in the profile for which there are no marks present, and adjusts the threshold for discriminating intended marks based on the read level(s) comprising the gaps.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.