Self regulating microfilm frame detection circuit
US4219737A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 18, 1978 |
| Grant date | Aug 26, 1980 |
| Priority date | — |
| Expiry date | Dec 18, 1998 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06K17/0019
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A system for optically detecting the presence of indicating markers on microfilm frames and for ignoring stray marks and smudges. As light shines through the microfilm and is detected by a photo-transistor, the system self regulates to provide an absolute baseline value, called a prescaler, for each frame of microfilm. Then, as each mark appears on the microfilm and interrupts the light path to the photo-transistor, the degree or extent of light blockage is measured as a deviation from the baseline for that frame. If the deviation exceeds a predetermined threshold, the mark is counted as a marker; otherwise the mark is ignored as a stray spot or smudge. The threshold is also self regulated based on a percentage of the amount that the light blockage of the marker in the immediately preceding frame deviated from the baseline for that frame.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.