Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Patent
1985-04-17
1986-12-23
Faber, Alan
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
360 331, 360 60, 360 15, 358120, 358335, H04N 591
Patent
active
046316035
ABSTRACT:
A video signal is modified so that a television receiver will still provide a normal color picture from the modified video signal while a videotape recording of the modified video signal produces generally unacceptable pictures. This invention relies on the fact that typical videocassette recorder automatic gain control systems cannot distinguish between the normal sync pulses (including equalizing or broad pulses) of a conventional video signal and added pseudo-sync pulses. Pseudo-sync pulses are defined here as any other pulses which extend down to a normal sync tip level and which have a duration of at least 0.5 microseconds. A plurality of such pseudo-sync pulses is added to the conventional video signal during the vertical blanking interval, and each of such pseudo-sync pulses is followed by a positive pulse of suitable amplitude and duration. As a result, the automatic gain control system in a videotape recorder will make a false measurement of video level which causes an improper recording of the video signal. The result is unacceptable picture quality during playback. This approach utilizes positive-going pulses which occur at a time not ordinarily used for black-level restoration in typical television receivers, and therefore does not give rise to black level depression in such typical television sets.
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Faber Alan
Macrovision
Zimmerman C. Michael
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