Method and apparatus for clustering modifications made to a video signal to inhibit the making of acceptable videotape recordings
US4819098A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Apr 14, 1987 |
| Grant date | Apr 4, 1989 |
| Priority date | — |
| Expiry date | Apr 14, 2007 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N2005/91314
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A video signal is modified so that a television monitor/receiver still produces a normal picture from the modified signal, whereas a videotape recording of this signal produces generally unacceptable pictures. Videotape recorders have an automatic gain control circuit which measures the sync pulse level in a video signal and develops a gain correction signal for keeping the video level applied to an FM modulator in the videotape recording system at a fixed, predetermined value. A plurality of positive pulses are added to the video signal with each immediately following a respective trailing edge of a normally occuring sync pulse. These added pulses are clustered at the vertical blanking interval of each field to minimize the affect of the same on the viewability of the picture defined by the signal while still causing the automatic level control circuit in a recorder to assess the video level at many times its actual value. The sync pulses themselves can also be at a reduced level, in order to enhance the effectiveness of the process.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.