| Method and apparatus for modifying a video signal or for providing a copy protection signal by adding selected negative going and positive going pulses -> Monitor Keywords |
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Method and apparatus for modifying a video signal or for providing a copy protection signal by adding selected negative going and positive going pulsesRelated Patent Categories: Television Signal Processing For Dynamic Recording Or Reproducing, Processing Of Television Signal For Dynamic Recording Or Reproducing, Record Protection (e.g., Anti-copying)Method and apparatus for modifying a video signal or for providing a copy protection signal by adding selected negative going and positive going pulses description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070242930, Method and apparatus for modifying a video signal or for providing a copy protection signal by adding selected negative going and positive going pulses. Brief Patent Description - Full Patent Description - Patent Application Claims
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. Pat. No. 4,631,603 issued to J. Ryan in Dec. 23, 1986, and herein incorporated by reference, which capitalizes on the fact that a typical video cassette recorder's (V7CR) automatic gain control (AGC) system cannot distinguish between the normal sync pulses of a conventional video signal (including equalizing or broad pulses) and added pseudo-sync pulses. Pseudo-sync pulses are defined here as any other pulses which extend down to a normal sync tip level and which have a duration of at least 0.5 microseconds. A plurality of such pseudo-sync pulses is added to the conventional video signal during the vertical blanking interval, and each of such pseudo-sync pulses is followed by a positive pulse of suitable amplitude and duration. As a result, the automatic gain control system in a videotape recorder will make a false measurement of video level which causes an improper recording of the video signal. The result is unacceptable picture quality during playback. However, this approach utilizes positive-going pulses which occur at a time not ordinarily used for black-level restoration in typical television receivers and therefore does not give rise to black level depression in such typical television sets, whereby a television set (TV) displays a picture of fully acceptable quality. [0004] Another copy protection process is disclosed in U.S. Pat. No. 4,819,098 issued to J. Ryan on Apr. 4, 1989 and incorporated herein by reference, which capitalizes on the fact that VCRs include the AGC system which here measures the sync pulse level in a video signal and develops a gain correction signal for keeping the video level applied to an FM modulator in the VCR system at a fixed, predetermined value. A plurality of positive pulses are added to the video signal with each immediately following a respective trailing edge of a normally occurring sync pulse. These added pulses are clustered at the vertical blanking interval of each field to minimize the affect of the same on the watchability of the picture defined by the signal, but still cause the automatic level control circuit in a VCR to assess the video level at many times its actual value thereby providing a copy of unacceptable picture quality. The sync pulses themselves can also be at a reduced level, in order to enhance the effectiveness of the copy protection process. [0005] A further copy protection process is disclosed in U.S. Pat. No. 4,163,253 issued to M. Morio et al. on Jul. 31, 1979, wherein the AGC circuit of a VCR again prevents recording an acceptable copy of a copy protected video signal. A pulse whose amplitude is substantially equal to the peak white level of the video signal is inserted into respective horizontal blanking intervals of the video signal. If this modified video signal is recorded on a conventional type of video signal recorder, the presence of the inserted pulse signal is detected by the AGC detector which, in turn, controls an AGC amplifier to substantially attenuate the modified video signal which then is recorded. The resulting recording is of unacceptable picture quality. [0006] It has been found that the copy protection signals of various copy protection processes which employ positive-going pulses, such as AGC pulses, in the back porch region of the HBI, may experience various degrees of playability problems such as for example black level depression. In the field of copy protection, it obviously is necessary to maximize the effectiveness of the copy protection of a recorded video signal. However, it is equally necessary to maintain the playability of the copy protected video signal by reducing the amount of side effects such as darkening of the TV set monitor during playback of the video signal, playback of a legal copy of the video signal, etc. It follows that it would be advantageous to maximize not only the effectiveness of a copy protection process against illegal copying but also the playability of the video signal by a legitimate TV set. SUMMARY OF THE INVENTION [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. [0008] To this end, the various embodiments of the invention add selected special pulses to selected regions in the HBI of the video signal. In one embodiment, a modified horizontal sync (H sync) pulse is added in the front porch region of the HBI. The modified H sync pulse is a relatively narrow negative-going pulse, hereinafter also termed a "presync" pulse for ease of description. A positive-going pulse of even narrower width is added following the negative-going modified presync pulse within the front porch region. Both pulses are inserted immediately before the normal horizontal sync (H sync) signal of normal duration, for example, 4.7 microseconds (.mu.s) width. The negative-going presync and positive-going pulses have a combined time duration about equal to the duration of the front porch. [0009] In another embodiment, a latter portion of the amplitude of the H sync signal is increased to below its normal or clipped H sync tip level. For example, the H sync tip level of the latter portion can be extended by an amplitude of about 10 to 50 IRE. Thus, if normal H sync signals are 4.7 .mu.s in width, the invention process provides an additional amplitude extending pulse of for example about 1.0 .mu.s width and about -40 IRE, superimposed onto a latter 1.0 .mu.s portion of the H sync signal to provide an amplitude augmented H sync signal of about -80 IRE during the last 1.0 .mu.s of the pulse. The amplitude extending pulse can also be added to the latter portion of pseudo sync pulses as well. The H sync and/or pseudo sync signals also may be clipped. An example of the clipped H sync tip level and/or the pseudo sync level of previous mention is about -30 IRE. [0010] 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. However, the added pulses do not affect the determination of the black level in the TV set since the samples taken by the circuit in the TV set average out and cause the black level to be sampled at a preferred point in the back porch region. BRIEF DESCRIPTION OF THE DRAWINGS [0011] FIG. 1 is a block diagram illustrating various embodiments of the invention wherein respective modifications are applied to a normal video signal or to a copy protected video signal. [0012] FIG. 2A-2G is a chart illustrating waveforms generated via respective embodiments of the invention such as depicted for example in the block diagram of FIG. 1. [0013] FIG. 3A-3D is a chart illustrating waveforms generated via other respective embodiments of the invention depicted in the block diagram of FIG. 1. [0014] FIG. 4 is a block diagram illustrating an embodiment of the invention for generating and applying a negative-going presync and positive-going pulse pair to a normal or copy protected video signal. [0015] FIG. 5 is a block diagram illustrating another embodiment of the invention for generating and applying amplitude extending pulses to the H sync and/or pseudo sync signals, time extending color burst signals and/or extra post H sync pulses to a normal or copy protected video signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0016] FIG. 1 is a basic block diagram illustrating various modifications and associated apparatus corresponding to the several embodiments of the invention, and the manner of applying one, or a combination, of the modifications to an incoming video signal which may or may not be a copy protected video signal. That is, the input video signal may contain a basic copy protection signal such as automatic gain control, (AGC) pulses or pseudo sync/AGC pulses, as depicted in a block 12 of FIG. 1 which receives the input video signal. The output of the basic copy protection process 12 is supplied to one input of a jumper J1, while the input video signal is also supplied directly to a second input of the jumper J1. The output of jumper J1 then supplies several blocks each of which comprises a respective modification which can be applied to the normal or copy protected video signal supplied via the jumper J1. The several blocks are each coupled to a combining circuit 14 such as, for example, a summing amplifier, via respective jumpers J2 through J7, as further described below. The normal or copy protected video signal from the jumper J1 also is supplied to the combining circuit 14 via one input of the jumper J7. [0017] More particularly, the different modifications are selectively supplied to the combining circuit 14, along with the video signal via the jumper J7, by closure of one or more of the respective jumpers J2-J6. One such modification, a process 16 for adding a special narrow negative-going presync and very narrow positive-going pulse pair prior to the normal horizontal sync (H sync), is illustrated by a respective block. This embodiment of the invention is supplied to the combining circuit 14 by closing jumper J2, whereupon the presync/positive-going pulse pair is combined with the normal or copy protected video signal in the combining circuit 14 by closure of jumper J7. [0018] The video signal supplied via the jumper J7 may be the normal or copy protected video signal from the jumper J1, which, however, has the color bursts therein removed by a color burst blanker process 18 if the respective input to the jumper J7 is closed. The color burst blanker process 18 is activated for example in a modification, described hereinafter, in which a new extended color burst is to be added, to the video signal. [0019] Another modification, a process 20 for extending an amplitude of a portion of an H sync signal whereby the AGC circuit in a respective VCR will be affected, is illustrated by a respective block. The resulting process 20 of an extended H sync amplitude portion is supplied to the combining circuit 14 by closure of the jumper J5, whereupon the extended H sync amplitude portion is combined with the video signal from the jumper J7 via the combining circuit 14. [0020] A further modification, a process 22 for extending the amplitude of a portion of a pseudo sync pulse to affect the AGC circuit of respective VCRs, is illustrated by a respective block. Obviously, since a pseudo sync pulse is being extended, the basic copy protection process includes pseudo sync signals in the video signal, and is provided by the basic copy protection process 12 to the process 22. The process 22 supplies an amplitude extending pseudo sync portion to the combining circuit 14 via closure of the jumper J6, whereby the pseudo sync signal with the extended pseudo sync portion is combined with the video signal from jumper J7 via the combining circuit 14. Continue reading about Method and apparatus for modifying a video signal or for providing a copy protection signal by adding selected negative going and positive going pulses... 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