Abstract:
An improved television scrambling signal is achieved by adding erroneous clamp pulses into a television signal after the signal may have been previously scrambled, for example, by prior art position modulated horizontal sync pulses. Prior art scrambling systems such as those using position modulated sync pulses cause tearing in an unauthorized displayed television picture. The addition of the erroneous clamp pulses of the present invention causes both tearing and darkening of the picture. This darkening can completely shut off the display on some TV sets, thus yielding complete concealment of the television signal. In an alternative embodiment, an erroneous color “rainbow” effect is provided by modifying a portion of a color burst signal, to cause the color subcarrier system in a TV set to unlock. In another embodiment, an improved television vertical scrambling overlay method is achieved by using fewer lines for the insertion of fake vertical sync pulses in a vertical blanking interval and by turning on the fewer fake vertical pulses in a selected specific manner. This improvement provides greater vertical displacement for enhanced picture concealment while providing additional lines for other purposes.

Description:
This application claims the benefit of Provisional Application No. 60/076,087, filed Feb. 26, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to scrambling television signals transmitted over air or via a cable or satellite environment. The invention is most effective as an improvement of the subject matter of the provisional patent application, “METHOD AND APPARATUS FOR IMPROVED HORIZONTAL AND VERTICAL OVERLAY SIGNALS FOR HIGHER CONCEALMENT IN MODERN TV SETS”, Ser. No. 60/069815 (&#39;815) filed on Dec. 16, 1997. However, the present invention can be used alone to provide concealment in the form of prohibitive darkening and/or lightening of the signal. 
     In the previous concealment systems, the concealment is done by causing a television picture being viewed on an unauthorized television (TV) set to tear horizontally and/or jitter vertically. In general, these effects are effective in creating an unviewable picture unless the viewing is authorized and the signal is descrambled. In a population of modern television sets, however, effectiveness is not always at the highest levels when applying the scrambling signal of such prior art techniques. 
     OBJECTS OF THE INVENTION 
     An object of this invention is to improve existing concealment systems by using an erroneous clamp pulse. This erroneous clamp pulse is removed and thus ignored by a decoder of an authorized playback device, i.e. TV set, but will produce excessive darkening (or lightening) of a picture supplied by unauthorized television sets. Because today&#39;s modern television sets now use some form of back porch clamping (for example, a clamp pulse to reference a black level starts 4.7 microseconds after the leading edge of sync), modification of the clamping signal during the horizontal blanking interval can cause a desired darkening scrambling effect. 
     In the preferred embodiments, this erroneous clamp pulse or signal is distinguished from the copy protection signal described in U.S. Pat. 4,631,603 (&#39;603) and/or 5,130,810 (&#39;810) to J. O. Ryan, both incorporated by reference, by the following distinguishing features: 
     1) A narrowed and/or position modulated horizontal sync pulse. 
     2) A modified color burst signal which may include a narrowed or widened color burst envelope. 
     3) The timing of the erroneous clamp pulse in the present invention is based on the TV set&#39;s clamp pulse (not a video cassette recorder&#39;s (VCR&#39;s) automatic gain control (AGC) sample pulse as generally the case), and the TV set&#39;s clamp pulse is generally timed from the leading edge of sync. In the Ryan references, the copy protection signal is based on the timing after the trailing edge of sync. That is, in copy protection signals for VCRs, an AGC pulse is timed from the trailing edge of sync or pseudo sync and the VCR&#39;s AGC sample pulse likewise is timed from the trailing edge of sync. 
     Another object of this invention is to improve on the effect of a vertical overlay signal by taking up fewer television lines in the vertical blanking interval (VBI) for added “fake” vertical sync pulses. By taking up fewer lines in the vertical blanking interval, more data lines in the VBI are available for other purposes. 
     A further object of the invention is to disclose a simpler way of inducing more vertical jitter and or rolling effects utilizing the “fake” vertical sync pulses. 
     To help clarify the invention over the above mentioned references, it is worthwhile to differentiate video “copy protection” techniques, such as disclosed in the &#39;603 and &#39;810 patents, from video “scrambling” techniques such as that of the present invention. To one skilled in the art of video engineering, video copy protection is defined as a system wherein a copy protected video signal is viewable with a minimum of or no visible artifacts, but where the playback of a recording of such a signal is not possible or produces a signal that has significantly degraded entertainment value. On the other hand, video scrambling is defined as a system wherein a video signal is made unviewable. A scrambled signal may be recordable, but unless it has been descrambled the playback of such a recording is still unviewable. 
     SUMMARY OF THE INVENTION 
     A primary feature of the present invention includes the technique of adding a pulse or signal, having a level around peak white, during or after the color burst signal, or a portion of the color burst signal. In this example, the color burst signal preferably has a narrower envelope than normal. In an embodiment in which the input video signal is previously scrambled as, for example, by horizontal sync modulation, the position modulated horizontal sync pulse preceding the narrower color burst is also narrowed. These techniques of the invention are predicated on the fact that most modern television sets use back porch clamping and use a horizontal oscillator and/or high voltage flyback pulse to form the clamp pulse. The clamp pulse is triggered by the leading edge of horizontal sync pulse and generally starts around 4.7 microseconds later. However, in a standard video signal, the back porch blanking level is approximately 4.7 microseconds after the leading edge of a horizontal sync pulse. Thus, if a pulse other than blanking level is placed around 4.7 microseconds after a leading edge of sync, then the television set will trigger (or clamp) on, and thus will display, an erroneous black level. This erroneous black level can cause the picture to darken abnormally when the pulse is higher than the normal blanking level, or brighten abnormally when the pulse is lower than the normal blanking level. Since extra concealment in a scrambled TV signal is the goal of the present invention, the abnormal or excessive darkening or lightening of the displayed scrambled picture caused by the present invention provides a highly effective scrambling technique wherein a displayed TV picture not only is torn horizontally and jittered vertically, but also is excessively darkened or lightened. 
     Therefore, a preferred embodiment of the invention includes the narrowing of both the horizontal sync and color burst envelope and then the adding of an erroneous clamp pulse (ECP) around peak white level after the narrowed color burst. Note that in one embodiment, the narrowed sync pulse and color burst, along with the added erroneous clamp pulse (ECP), are all being position shifted or modulated. In an alternative embodiment, the color burst envelope does not need to be shortened, but rather can be of normal or longer length. This is done by including at least a part of the color burst superimposed on the erroneous clamp pulse. In this instance, a decoder of the TV set can be made to have a shortened back porch clamp pulse not coincident with the erroneous pulse. To recover color burst, the decoder&#39;s color burst gate pulse can occur after the trailing edge of sync because the associated chroma band pass filter will reject the erroneous pulse portion of the signal and will only pass through the color subcarrier frequency. 
     The present invention can be implemented alone as an effective scrambling system, or preferably can be combined with the techniques as described for example, in the &#39;815 provisional application of previous mention, or in U.S. Pat. Nos. 5,504,815, 5,438,620 or 5,058,157 (all incorporated by reference) for an even more enhanced scrambling signal. In the latter combinations, the invention causes darkening (or lightening) that is combined with horizontal tearing and vertical instability along with horizontal picture displacement and inverted video as described in the above patents. That is, the resulting scrambled signal will have horizontal tearing due to position (or shift) modulated horizontal sync edge or edges, vertical jittering due to deleting standard vertical sync pulses and replacing them with modulating vertical sync pulses, inverted video, and line position modulating on the video, as well as the darkening (or lightening) of the scrambled signal via the erroneous clamp pulse signals in the horizontal blanking interval, in accordance with the present invention. 
     Another alternative embodiment of this invention includes modifying a last portion of the color burst signal so as to cause the color subcarrier system in an unauthorized TV set to unlock and cause an erroneous color display. 
     Yet another alternative feature of this invention includes the generation of a known location for a decoder&#39;s clamping system for example, a dedicated black level interval or a sync tip interval, and to incorporate sync/AGC pulse pair signals as disclosed in the Ryan &#39;603 and/or &#39;810 patents of previous mention, for even more darkening when combined with a scrambled signal. The use of position modulated (or shifted) sync/AGC pulse pair signals is motivated by the fact that certain TV sets respond to this type of signal by darkening completely (not to mention the horizontal tearing that also is present). 
     Another modification of the &#39;815 provisional application of previous mention, includes a unique method of utilizing fewer lines in the vertical blanking interval for the vertical overlay signal while providing more concealment by increased vertical instability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a waveform showing a standard video signal primarily in the horizontal blanking interval. 
     FIG. 1B is a waveform illustrating a pulse turned on 4.7 microseconds after the leading edge of horizontal sync in FIG.  1 A and which is used in TV sets for clamping to a blanking level and for gating in the color burst for the color subcarrier oscillator in the TV set. 
     FIG. 2A is a waveform illustrating an embodiment of the invention where the horizontal sync pulse is moved close to the front porch (pre-sync position) to allow maximum horizontal tearing when the sync pulse is position modulated. The horizontal sync is also narrowed to about 3.1 microseconds (μs). A color burst portion A is about 4 to 5 cycles of subcarrier (about 1.4 μs) and is added to the normal clamp level. The B and C portions of FIG. 2A include an erroneous clamp pulse (ECP) such as a positive pedestal voltage, with color burst added. In this example, both portions A and B have the correct color subcarrier frequency while the portion C has incorrect color subcarrier frequency and/or phase. However, if an erroneous color display is not desired, the portion C can have the correct color burst frequency or phase. The duration of portion B is about 2 μs (or more) and the duration of portion C preferably varies by modulation. In the pre-sync position as shown here, portion C is about 5 μs duration. Note that the pulse in FIG. 1B is coincident with portion C for burst gate and is a feature of the invention which causes an erroneous color display. 
     FIG. 2B is a waveform illustrating a narrowed clamp pulse for FIG. 2A waveform, for use by a decoder in the descrambler system to correctly clamp the scrambled video to blanking level. The pulse in FIG. 2B can also be used as the burst gate for the decoder&#39;s burst phase loop oscillator. 
     FIG. 2C is a waveform illustrating a burst gate pulse for the decoder that gates through the correct chroma burst for the FIG. 2A color burst portions A and B, but not C, for the decoder. 
     FIG. 3A is a waveform illustrating a post-sync pulse position of the modified horizontal sync pulse and the erroneous clamp pulse (ECP) with color subcarrier in portion B. Note that the sync pulse is now moved toward the beginning of the following active TV line for maximum horizontal tearing and that the burst portion C has collapsed. The sync position of FIG. 2A moves or shifts to the position of FIG. 3A with a displacement of about 5 μs or more, at a rate, for example, of 665 Hz for maximum tearing. 
     FIG. 3B is a waveform illustrating a narrowed clamp pulse of the decoder of a descrambler for correctly clamping the video to the blanking level for the FIG. 3A waveform. 
     FIG. 3C is a waveform illustrating a burst gate pulse for the decoder for gating the correct burst phase for the FIG. 3A waveform. 
     FIG. 4A is a waveform illustrating a more effective erroneous clamp pulse (ECP) signal which occurs immediately after the trailing edge (TE) of the horizontal sync. Color subcarrier is added after the trailing edge of sync as well. FIG. 4A also includes a dedicated blanking level location (BLVL) for a modified decoder clamp pulse for clamping to the correct blanking level. The horizontal sync in FIG. 4A is in the pre-sync position. 
     FIG. 4B is a waveform illustrating a more effective erroneous clamp pulse (ECP) signal similar to that of FIG. 4A, but where the horizontal sync pulse is now in the post-sync position and the burst portion C is collapsed. 
     FIG. 4C is a waveform illustrating an alternate location of the decoder&#39;s clamp pulse for the waveforms of FIGS. 4A and 4B. 
     FIG. 5 is a waveform illustrating a double sync scrambled TV signal used optionally in conjunction with added fake vertical sync pulses such as provided by the circuitry of FIG. 6, which may or may not include ECP signals. 
     FIG. 6 is a block diagram illustrating an embodiment of the invention for inducing vertical jitter more effectively than does the prior art while also using fewer TV lines in the vertical blanking interval (VBI). 
     FIG. 7 is a block diagram illustrating circuitry of the &#39;815 provisional application for generating a scrambled video program signal using video line position modulation, video inversion and horizontal sync overlay techniques. The output also may include a vertical sync overlay signal (not shown here). 
     FIG. 8 is a block diagram illustrating an embodiment of the present invention. 
     FIG. 9 is a resultant waveform of the circuit of FIG. 8 for providing modifications in the horizontal blanking interval. The waveform also illustrates that the ECP can be amplitude modulated to cause the darkening effect to flicker. The ECP can also be pulse width or position modulated to create the same type of effect as caused by the amplitude modulation, that is, causing the darkening effect to flicker. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 7 is a block diagram of the general implementation of the &#39;815 provisional application of previous mention. Program (unscrambled) video is supplied on input  178  to a timing circuit  180  to generate a horizontal blanking interval (HBI) signal for a switch  188  and for a sync modulation circuit  185 . The first level of scrambling is done by a video line position modulator circuit  181  which receives the program video on input  178  and which position modulates the video on a line by line basis. Circuit  181  is coupled to an inverter circuit  189  which inverts only the active video portion. The output of circuit  189  is inverted active video that is line position modulated and is supplied to a switch  188  which replaces the horizontal sync from the inverter circuit  189  with new sync and color burst. The new sync is position modulated within the HBI or switched between a number of relative positions in the HBI. The sync modulation circuit  185  provides the various sync (edge) positions. A color subcarrier is regenerated by a circuit  182  also coupled to the program video input  178 , and the subcarrier is gated through an AND gate  183  by a gate signal from a burst gate circuit  186 . The circuit  186  triggers off the trailing sync edge of the sync modulation circuit  185 . The output of AND gate  183  is supplied to a chroma band pass filter  184 . The output of circuit  184  is summed in an adder circuit  187  with the output of the sync modulation circuit  185  in negative fashion. The output of the adder circuit  187  then has new sync (position modulated and the like) and new burst. The switch  188  inserts the new sync and burst into the position modulated video from the inverter circuit  189 . The combined video signal then is supplied to an amplifier  190 . The output of the amplifier  190  then may be supplied to the circuit of FIG. 8 as an initially scrambled video signal from for example the &#39;815 provisional application. 
     The embodiments of the present invention are particularly useful in enhancing the teachings of the &#39;815 provisional application; that is, to add to the concealment provided by the scrambled signal described in FIG.  7 . For certain types of program material such as adult viewing, maximum scrambling concealment is desired. The preferred embodiments of the invention thus add darkening effects that can effectively blank out the TV set. It is these embodiments that cause a TV set to lock onto a horizontal sync signal which has been position modulated, for example, and then cause the TV set to erroneously clamp not to blanking level but for example to a white level to cause the picture to darken abnormally. This is achieved due to the fact that many TV sets use the horizontal flyback pulse and/or a horizontal oscillator to generate a clamp pulse approximately 4.7 microseconds after the leading edge of the horizontal sync pulse. Since the horizontal sync pulse is narrowed to about 3 microseconds (μs) and the color burst to about 1.5 μs, and the ECP signal occurs after the narrowed burst, a TV set will generate a clamp pulse coincident with the ECP signal. The reason is that the duration from the leading edge of the narrowed sync to the end of the narrowed burst is about 4.5 μs. Since the ECP signal follows the narrowed color burst, it is readily apparent that the ECP signal will be in the 4.7 μs interval after the leading edge of (narrowed) sync. Typically the ECP signal is at least 1 or 2 μs long. However, the longer the ECP signal used, the more effective is the darkening. For example, in FIG. 2A the longer ECP pulse provides maximum darkening effect. Likewise, in FIG. 4A, extending the ECP over the width of the portion C also will increase the darkening effect. As shown in FIGS. 2A,  3 A and  9  these modified signals will cause darkening of the television picture. Again, for example, it should be noted that the narrowed sync, narrowed burst and ECP signal may all be position modulated or shifted to also induce the horizontal tearing scrambling effect of previous discussion. 
     The teachings of FIGS. 4A and 4B when combined with the teachings of the &#39;815 provisional application, i.e., FIG. 7, cause the most effective darkening on TV sets during unauthorized viewing. The reason is that there are also some TV sets that generate video clamp pulses after the trailing edge of sync. FIGS. 4A and 4B depict an alternative embodiment wherein the ECP signal occurs immediate after the trailing edge (TE) of sync. In the case of FIG. 4A, the ECP signal should be as long as possible in the pre-sync location to provide maximum darkening. That is, the ECP can be at least 3 to 5 μs. For instance in FIG. 4A, the ECP can extend or widen from TE to just the beginning of the reference blanking level location, (BLVL). The BLVL is a dedicated blanking reference level location for the decoder of the descrambler to allow it to properly clamp the input video to blanking level. 
     The defeat or descrambling of the scrambled signal generated by the present invention may be accomplished by replacing or modifying the horizontal blanking interval that modifies the ECP signal so that the TV set clamps the video satisfactorily with minimal darkening effects. The methods for modifying the ECP signal can include removal, attenuation, narrowing, delaying and/or level shifting of the ECP signal. For example, removal schemes such as disclosed in U.S. Pat. Nos. 4,695,901, 4,336,554, 5,157,510, 5,194,965 or 5,625,691 (all incorporated by reference) can be used to reduce the effectiveness of the ECP signal of the present invention. U.S. Pat. No. 4,626,890 also can be used to reduce the incorrect color effects of the incorrect frequency of the portion C (see FIG. 2A for example) and is incorporated by reference. 
     The embodiment shown in FIG. 8 then is capable of creating the ECP signals as illustrated in the figures described above, i.e., FIGS. 2A,  3 A,  4 A,  4 B and  9 . 
     The enhanced scrambling effects attained by the present invention are illustrated via the circuitry of FIG.  8 . To this end, in one embodiment the scrambled video from, for example, FIG. 7 is coupled to a sync separator circuit  205  via an input  200 . The resulting position modulated sync output of circuit  205  is supplied to a one shot timing circuit  206  which forms a first burst gate. The first burst gate from circuit  206  is timed to the input&#39;s burst so that a phase locked loop (PLL) circuit  213  can regenerate the color subcarrier in the form of a continuous wave (c.w.). The output of the sync separator circuit  205  also is coupled to a timing circuit  204  which generates a horizontal blanking interval (HBI) signal. This HBI signal controls a switch  202  which receives the scrambled video via the input  200 . The output of switch  202  is then the scrambled video described in FIG. 7 with the color burst removed via a chroma notch filter  201 . The position modulated sync from sync separator  205  is also fed to a one shot timing circuit  209  and a burst gate circuit  208 . One shot timing circuit  209  sets the delay of the ECP signal relative to the trailing edge of sync, that is, sets the duration of the gap in which the burst portion A, FIGS. 2A,  3 A and  9 , is inserted. A one shot timing circuit  210  sets the duration of the ECP signal. Circuit  209  can be modulated in time to form a varying blanking level gap or duration between the trailing edge of sync and the beginning of ECP. Varying this blanking level gap between the trailing edge of sync and the leading edge of the ECP signal can alter the television picture darkening response of a TV set. By varying the ECP pulse width in circuit  210 , the darkening will vary as well when a television picture is displayed on a TV set. Finally, an ECP amplitude modulation circuit  214  can also vary the amount of darkening of a picture displayed on the TV set. Varying the darkening effect over time can be a further annoyance to the unauthorized viewer. The output of modulation circuit  214  then supplies the ECP signal to a summing amplifier  203 , which also receives the scrambled signal with color burst removed from the switch  202 . 
     Regenerated burst such as the A and B portions of FIGS. 2A,  3 A,  4 A,  4 B and  9  is generated by a second burst gate from a burst gate circuit  208 , which gate is supplied to an AND circuit  211  which also receives the continuous wave regenerated subcarrier from the PLL circuit  213 . The output of the AND circuit  211  is supplied to a summing chroma filter  212 . 
     An “incorrect” burst of incorrect color burst frequency or phase, which will cause a rainbow color effect, for example, is generated by an AND circuit  216  coupled to the burst gate circuit  208  via a burst gate circuit  207 . The burst gate circuit  207  generates a third burst gate which follows the second burst gate generated by the circuit  208 . The second  20  burst gate forms the burst portion B and the third burst gate forms the burst portion C. An “incorrect subcarrier” signal having a selected incorrect frequency or phase is supplied to the AND gate  216 . The output of AND gate  216  is supplied to the summing chroma filter  212 . The B and C type burst portions are illustrated in FIGS. 2A,  3 A,  4 A, and  9 . The output of the chroma filter  212  is coupled to the summing amplifier  203 . The output of amplifier  203  then contains the scrambled signal of the input  200  plus the new ECP darkening signals and/or the erroneous color “rainbow” effect from the ECP amplitude modulation circuit  214  and the chroma filter  212 . As shown in FIG. 8, the HBI signal from the timing circuit  204  also is supplied to the ECP amplitude modulation circuit  214  and the chroma filter  212  to keep the ECP and burst signals within the HBI (in the video signal output by the summing amplifier  203 . 
     FIG. 6 illustrates a circuit and associated method for providing improved vertical scrambling for an unscrambled or previously scrambled video signal, while taking up fewer TV lines that then may be used for data, closed caption, test signals and the like. That is, instead of alternating correct and fake vertical sync signals between two or more sets of lines in the vertical blanking interval (VBI) (i.e., lines  1 ,  2 ,  3  in even fields and lines  19 ,  20 ,  21  in odd TV fields) to make the TV set jump or jitter a displacement of about 20 lines vertically, it was found that a more effective vertical scrambling can be achieved by the following: 
     1) the use of at least 1 line in the VBI (three lines for example which is the number of lines required for most TV sets to recognize the fake vertical sync as a “vertical trigger”) to cause the vertical jumping. 
     2) the insertion of fake vertical pulses as mentioned in #1 above and as illustrated in FIG.  6 . That is, fake vertical pulses are inserted via a generator  92  into a D flip flop  93 . The clock input of flip flop  93  is clocked by vertical or frame rate frequency. The output of the flip flop  93  then allows the insertion of fake vertical pulses during the VBI or multiples of a VBI. The output of the flip flop  93  is supplied to an AND gate  94  whose other input defines lines  1 ,  2  and  3  supplied by a timing circuit  97  which derives timing signals from a video signal received via an input  91 . As previously mentioned, the video signal on input  91  may be unscrambled program video or previously scrambled video. The output of the AND gate  94  then controls insertion of the fake vertical sync signals via a sync insertion circuit  96 . As a result, the fake vertical syncs are inserted in a somewhat random manner that causes the TV sets to jitter vertically more effectively (i.e., jitter more than 20 lines of displacement) in the vertical direction. 
     3) preferably cause the addition of multiple horizontal sync pulses to some TV lines to cause the counter circuits in the horizontal oscillators of modem TV sets to miscount. FIG. 5 illustrates an example of multiple horizontal syncs in the HBI. In FIG. 6, a circuit  95 , which receives the video signal via the input  91 , adds multiple (i.e. double) horizontal syncs in response to the timing circuit  97 . A circuit  98  removes the standard vertical sync signals from the respective lines of the input video prior to the insertion of the fake vertical sync signals. The output of circuit  96  may contain horizontal sync, for example, in the VBI. As shown in dashed lines in FIG. 5, the color burst signals may be superimposed on ECL signals to add the darkening effect to the scrambled signal. The whole burst, or portions of the burst, can be raised. 
     4) by way of example, very effective vertical scrambling is observed when the generator  92  is set to about 11 Hz and the clock frequency into flip flop  93  is set at field rate frequency. Note the clock input at flip flop  93  preferably starts either before or after the fake vertical sync pulses (i.e. before line  1  or after line  3 ). It is also found if the clock frequency is at frame rate or half of the vertical frequency, then the generator  98  is set to 5.5 Hz or around 18 Hz for maximum vertical scrambling. Of course other combinations are possible with varying clock frequencies supplied to flip flop  93  and varying frequencies generated by the generator  92 . 
     Although a previously scrambled video signal is illustrated herein by way of example as the input  200  to the embodiment of the invention of FIG. 8, it is to be understood that the video signal supplied to the circuit of FIG. 8 may be an unscrambled video signal which is to be scrambled in accordance with the present invention. That is, the present invention may be used alone to provide a scrambled video signal which is prohibitively darkened or lightened, which flickers from excessive darkness to lightness and/or which includes an erroneous color “rainbow” effect which also can flicker on and off such as when the burst portion C increases and collapses. 
     While the preferred forms of the invention have been shown in the drawings and described herein, the invention should not be construed as limited to the specific forms shown and described since variations of the preferred forms will be apparent to those skilled in the art. Thus the scope of the invention is defined by the following claims and their equivalents.