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Video copy protection process enhancement to introduce horizontal and vertical picture distortions
| Details |
Inventors: Wonfor, Peter J.; Knox, Alistair J.; Corcoran, Jeremy J.; Ryan, John O.; Quan, Ronald;
Assignee: Macrovision Corporation (Sunnyvale, CA)
Primary Examiner: Barron, Jr.; Gilberto
Assistant Examiner:
Attorney, Agent or Firm: Brill; Gerow D.
Enhancements to a video anticopying process that causes an abnormally low amplitude video signal to be recorded on an illegal copy. The enhancements in one version introduce into the overscan portion of the television picture, just prior to the horizontal or vertical sync signals but in active video, a negative going waveform that appears to the television receiver or videotape recorder to be a sync signal, thereby causing an early horizontal or vertical retrace. One version provides (in the right overscan portion of the picture), a checker pattern of alternating gray and black areas which causes the TV set on which the illegal copy is played to horizontally retrace earlier than normal in selected lines with a consequential horizontal shift of the picture information on those lines. This substantially degrades picture viewability. In another version a gray pattern at the bottom overscan portion of the picture causes vertical picture instability. In another version selected horizontal sync signals are narrowed, causing irregular vertical retraces. Also provided is apparatus for removing or attenuating these enhancements from the video signal, to allow copying. |
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DETAILED DESCRIPTION In accordance with the present invention, the above-described prior art "basic" copy protection process is enhanced by further modifying the video signal in several ways to ensure that the necessary picture content requirement is met to maximize effectiveness of the basic copy protection process.
The further modifications include blanking a portion of the active video in the overscan area of the picture just prior to the occurrence of the (1) horizontal or (2) vertical synchronization (sync) signals, and inserting into the blanked portion a waveform that (for a video signal having reduced amplitude) is perceived by the TV receiver or videotape recorder as a sync signal, and so causes incorrect synchronization of the VCR or TV receiver.
Using this modification especially only on certain video lines or fields causes substantial picture degradation of an unauthorized copy.
Another modification narrows the horizontal sync pulses to cause sensing of a spurious vertical sync signal in a TV set and will also affect certain videotape recorders.
In the horizontal modification, the right edge of the picture is replaced by a "checker" pattern appearing (like a checker board) of black and gray rectangles.
The width of this checker pattern is chosen to be within the overscan (not viewed) part of the picture when displayed on a standard television receiver.
It will be understood that with an abnormally low signal amplitude, when the picture content is light (such as mid gray), the left edge of the black rectangle in certain video lines will trigger an early horizontal retrace as being a negative-going (towards blanking level) transition.
When the picture content is dark, the right edge of the gray rectangle (adjacent to a dark picture area), in certain video lines will trigger an early retrace on each line as also being a negative-going transition.
(The description of video waveforms herein follows the convention of positive amplitude being white and negative amplitude being black)
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TV Signal 
