Method and apparatus for modifying a video signal or for providing a copy protection signal by adding selected negative going and positive going pulses

Abstract

The horizontal blanking interval (HBI) of a normal video signal is modified to enhance the playability of the applied copy protected video signal while maintaining the copy protection effectiveness. As generally known, a copy protected video signal with positive-going pulses in a back porch region causes possible black level depression. The addition of a negative-going pulse and / or negative-going and positive-going pulse pair immediately prior to the H sync signal in the front porch region causes a reduction in such black level depression while resulting in enhanced playability. In other embodiments, an amplitude extending pulse is added to a latter portion of the H sync pulse or to a latter portion of a pseudo sync pulse, to increase the negative-going amplitude of the respective pulse. Various combinations of the added pulses also are possible.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to a video signal copy protection process and apparatus, and more particularly to a technique for providing or enhancing copy protection of video signals via the addition of special negative-going pulses as well as special positive-going pulses in some embodiments, within selected portions of front porch regions in the video signal horizontal blanking interval (HBI). [0002] In the field of video signal copy protection, copy protection processes are well known for modifying a video signal so that a normal color picture may be produced by a television receiver receiving the copy protected video signal, but wherein videotape recording of the copy protected video signal is inhibited and / or is so degraded in quality as to be unwatchable. In addition, many processes have been developed which enhance or otherwise improve upon the many basic copy protection processes. [0003] Typical of such processes is that disclosed in U.S. ...

AI Technical Summary

Benefits of technology

[0007] The present invention provides a process and apparatus for maximizing video signal copy protection while also enhancing the playability of a legitimate playback of the copy protected video signal.

Problems solved by technology

In either of the above embodiments the sampling circuits of a VCR sample the signal in the HBI at other than the normal time thereby resulting in an erroneous AGC gain level that in turn will turn the gain down.

Thus, a subsequent recording made by the VCR will be darkened and unacceptable for watching.

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