Cryptography – Video cryptography – Copy protection or prevention
Reexamination Certificate
1997-10-13
2002-06-11
Peeso, Thomas R. (Department: 2132)
Cryptography
Video cryptography
Copy protection or prevention
C380S201000, C380S204000, C380S210000, C380S221000
Reexamination Certificate
active
06404889
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to video signal protection and more specifically to such protection for component video.
BACKGROUND OF THE INVENTION
With the advent of the Digital Video Disc (DVD) format, manufacturers and users of personal computers are incorporating the ability to playback movies or other recorded material recorded on DVD's via the personal computer. Copy protection measures are being incorporated within these computers to protect the analog (NTSC or PAL television) video output from such a device. This is being done by incorporating bits within the digital stream on the DVD to instruct a digital to analog converter and NTSC (or PAL) encoder integrated circuit to incorporate copy protection pulses onto the analog video output signal. The copy protection techniques being used on the analog output include e.g. those in U.S. Pat. Nos. 4,631,603; 4,819,098; 4,577,216; and U.S. patent applications Ser. No. 08/784,876 filed Jan. 16, 1996; and International applications PCT/US96/17719, filed Nov. 5, 1996, and PCT/US97/05095 filed Mar. 25, 1997, all assigned to Macrovision Corporation and incorporated herein by reference.
A computer display uses a VGA (or similar or equivalent) output signal of the computer. This VGA output signal (“component video”) is provided on a multiwire bus that provides separately a red video signal, a green video signal, a blue video signal, a set of vertical synchronizing pulses and a set of horizontal synchronizing pulses. The frame rate (refresh rate) is usually 60 frames per second. VGA does not require any one format (resolution) in terms of pixels per line or lines per frame or refresh rate; a variety of pixels per line and lines per frame are accommodated within the VGA standard.
There has been a growing after market for VGA to NTSC (or PAL) converters that take the VGA signal described above and convert it into an NTSC or PAL (composite) video signal for display on a regular TV monitor, TV set or video projector. With such a converter device connected to receive a VGA output signal, a user converts the VGA output signal to an NTSC or PAL output signal and then can record the NTSC/PAL output signal using a conventional VCR (video cassette recorder), thus circumventing the analog copy protection described above. While the video quality of such a conversion may be inferior, that may not deter a determined pirate.
SUMMARY
Therefore there is a need for protection of a VGA video signal that meets the usual requirements for an effective video protection system. A useful video protection system meets two basic requirements. First any copy made must result in an inferior quality picture. This is called effectiveness. In this case, a user who connects a video cassette recorder to a VGA to NTSC (PAL) converter must get a signal therefrom of inferior entertainment quality. Tearing of the picture, amplitude variation or loss of color are examples of inferior entertainment quality. The counterbalancing requirement is that the VGA signal when viewed on a VGA monitor must be totally “playable”, e.g. not display any artifacts in the picture. The present protection technique balances these two requirements.
The present VGA protection method modifies at least one of the synchronization (“sync”) pulse trains that are part of the VGA video signal. These modifications include deletion and/or addition of certain sync pulses, changing of the duty cycle of certain pulses, and switching between one or more of the above methods on a fixed, psuedo-random or random basis on various frames of the video signal. The additions and/or deletions can be in the vertical blanking intervals or the horizontal blanking intervals of the VGA video signal.
Thus in accordance with this invention, VGA video signals are protected from copying (or even from viewing) after being subject to NTSC/PAL conversion by modifying at least one of the horizontal and/or synchronization pulse trains that are part of the VGA video signal. In this context “VGA” refers to the well known Video Graphics Array video standard commonly used in the computer field and also to the associated SVGA and IBM's XVGA standards, which for purpose of this invention are the same.
Moreover, while one embodiment is directed to VGA signals provided from a DVD player installed in a computer, clearly the invention is not so limited and generally applies to VGA video signals whether output from a DVD player installed in a computer, other types of digital video players, or to any type of component computer video output. Of course, it is to be understood that a typical application is to copy protect copyrighted material, which is typically movies provided on DVD, but the invention is not so limited.
Hence in accordance with the invention, in one embodiment the horizontal sync pulses in the vertical blanking interval of a VGA signal are modified. The resulting modified VGA signal is readily viewable on any VGA monitor. However, if this signal is converted to an NTSC/PAL signal by one of the well known commercially available VGA to NTSC/PAL converters, the resulting signal is relatively unviewable on a NTSC/PAL television or television monitor. Also, if an attempt is made to copy this signal for instance using a conventional NTSC/PAL VCR (video cassette recorder), the resulting recording is also unviewable. By unviewable is meant a picture exhibiting artifacts, as described above, which substantially degrade the resulting picture when displayed on the television set.
It has been found that the most advantageous modifications to the sync pulses in accordance with this invention are to modify the horizontal sync pulse in the first part of the vertical blanking interval, e.g. prior to the occurrence of the vertical sync pulse. This typically means in the first 10 lines of the vertical blanking interval (VBI). Also, it has been found that in general it is undesirable to have a net increase in the total number of horizontal sync pulses in the VBI in any one video frame since this tends to adversely affect some VGA monitors.
Hence in one embodiment, one or more horizontal sync pulses are deleted from the first part of the vertical blanking interval. For increased effectiveness of the copy protection, one horizontal sync pulse is added, but in a place where such a horizontal sync pulse is not normally present, e.g. in the middle of a particular horizontal video line. The pattern by which horizontal sync pulses are deleted and/or added may be the same in every frame, or may vary from frame-to-frame. If it varies, the variation may be a fixed pattern, a pseudo-randomly varying pattern, or a randomly varying pattern. The varying patterns have been found to increase copy protection effectiveness. In another embodiment, the number of horizontal sync pulses is increased by adding several horizontal sync pulses to each line, for instance in the first portion of the vertical blanking interval. As mentioned above, with some VGA monitors, this degrades playability.
Other patterns for removal and/or addition of horizontal sync pulses are also possible.
Also in accordance with other embodiment, the vertical sync signal is altered, but this has been found to affect some VGA monitors adversely.
Also in accordance with the invention, a particular modification pattern to the sync pulses is dependent upon the characteristics of the attached VGA monitor. This is possible because in the computer environment, it is possible for the computer to “know” the characteristics of the attached VGA monitor as supplied by the user. In this case, the particular modification pattern may be set adaptively to accommodate the particular VGA monitor so as to minimize adverse affects on playability. Also, the present VGA copy protection scheme may be turned on or off either by content present in the source video material, e.g. on the DVD, or otherwise. This turning on and off may be either only to protect certain (copyrighted) material or may be done to increase the effectiveness of the anti-copy protection scheme by periodically switching
Kurowski Kordian J.
Quan Ronald
Ryan John O.
Jack Todd
Klivans Norman R.
Macrovision Corporation
Peeso Thomas R.
Skjerven Morrill & MacPherson LLP
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