Method and apparatus for modifying the color burst to prohibit videotape recording
AssigneeMacrovision Corporation
InventorJohn O. Ryan
Life of this patent
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Abstract
A method and apparatus which modifies a color video signal in such a manner that a conventional television receiver produces a normal color picture from the modified signal, whereas a videotape recording made from the modified signal exhibits annoying color interference. This is achieved by phase modulating the color burst component of the video signal with a noise signal. A videotape recorder interprets the phase variation as a velocity error and alters the chrominance signal, giving rise to color noise in the videotape recording. The characteristics of the noise signal are chosen to preclude interfering with the receiver's subcarrier regenerator.
Claims14
A method for modifying a color video signal of the type wherein color information is transmitted on a subcarrier, the color video signal also including a color burst signal for generating in a television receiver a subcarrier signal at a reference phase for use in demodulating the color information, the method comprising the step of phase modulating the color burst signal with a noise signal to produce a modified color video signal, whereby the modified signal produces a normal color picture on a television receiver while a videotape recording made from the modified signal exhibits color interference.
Apparatus for modifying a color video signal of the type wherein color information is transmitted on a subcarrier, the color video signal also including a color burst signal for generating in a television receiver a subcarrier signal at a reference phase for use in demodulating the color information, comprising means coupling the video signal in parallel along two signals paths to an output terminal, switch means for selectively coupling one or the other of the signal paths to said output terminal, one of said signal paths including a phase modulator, a noise generator for driving said phase, modulator, means controlling said switch means to couple the color burst portion of the video signal to said output terminal through said signal path containing a phase modulator, and the other portions of the video signal through the other of said signal paths to said output terminal.
Apparatus for modifying a color video signal of the type wherein color information is transmitted on a subcarrier, the color video signal also including a color burst signal for generating in a television receiver a subcarrier signal at a reference phase for use in demodulating the color information, comprising an input video terminal and an output video terminal, a first switching means having an output connected to the output video terminal and having first and second inputs alternatively connectable to said output, a first signal path between said input video terminal and said first input of said first switch means, a second signal path between said input video terminal and said second input of said first switch means, means coupled to said input video terminal and said first switch means for coupling said second input of said first switch means to said output of said first switch means during color burst portions of the video signal and coupling the first input of said first switch means to said output during other portions of the video signal, said second signal path including means for phase modulating the color burst portions of the video signal.
Dependencies are inferred from the claim text.