| 摘要 |
PURPOSE: A method is provided for modifying a video signal so that a conventional television monitor/receiver product a normal picture from the modified signal, whereas a videotape recording made from the modified signal is rendered unacceptable. CONSTITUTION: By adding pulses to selected lines of the video signal during the back porch interval, a portion of the back porch intervals following the trailing edges of a substantial number of sync pulses are significantly raised and lowered to improve the playability of the original signal without reducing the effectiveness of the copy protection of the copied signal. and pulses significantly raise or lower the voltage amplitude during the blanking interval to provide a signal where the average value is approximately equal to the blanking interval. The sync level and the sync duration on the selected lines are reduced.
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