WO1998042130A1

WO1998042130A1 - Method and apparatus for adaptively enhancing a scrambled television signal

Info

Publication number: WO1998042130A1
Application number: PCT/US1998/005163
Authority: WO
Inventors: John O Ryan; Ronald Quan
Original assignee: Macrovision Corporation
Priority date: 1997-03-17
Filing date: 1998-03-17
Publication date: 1998-09-24
Also published as: AU6864898A

Abstract

An enhancement system is disclosed for enhancing the signal scrambling effects generated by, for example, a sync suppression scrambling system, while at the same time providing for compatibility with sync suppression scrambled signal decoding circuits of existing television sets. To this end, first and last portions of selected television lines in a field of video are modified by the selective application at various times of a signal of about blanking level to provide horizontal enhancement via fake horizontal sync pulses. In a modified technique, a selected number of the first and last television lines in the video field are modified by the selective application of a signal from about blanking level to about gray level to also provide vertical enhancement via resulting fake vertical sync pulses during the scrambling process.

Description

METHOD AND APPARATUS FOR ADAPTIVELY ENHANCING A SCRAMBLED TELEVISION SIGNAL

BACKGROUND OF THE INVENTION

The present invention relates to the scrambling of television signals transmitted via air or via cable, and particularly to a system for enhancing the scrambling effect when desired without the need for modifying the existing scrambling system, or the descrambling system in existing television sets. Currently, the technique of prior art television scrambling utilizes primarily a sync suppression system. In addition, there may be variations of the sync suppression scrambling system such as techniques for also applying video inversion, inverting the sync pulses, and level shifting the vertical blanking interval. In the current prior art sync suppression systems, generally the horizontal blanking interval is level shifted and or inverted thereby yielding horizontal sync suppression. In some prior art scrambling systems, the vertical blanking interval including the vertical sync pulses also are level shifted and or inverted to thus yield suppressed vertical sync pulses. When the prior art sync suppression technique is applied, the program video signal, depending on scene content, falsely triggers the scan circuits such as the sync separator and/or horizontal oscillator, in the television (TV) set. As a result, the TV set will display distorted pictures most of the time. Generally, the distorted pictures are displayed as a somewhat random horizontal displacement or "'tearing" from one television line to another.

Compatible prior art descrambling sync suppression systems utilize for example a technique for identifying the horizontal blanking interval of the video signal and restoring the horizontal sync and color burst to the proper relationship with the active television line (video portion). If the prior art sync suppression scrambling system includes a modified vertical blanking interval, descrambling is done by identifying the sync in the vertical blanking area and restoring the syncs in the vertical blanking area to their proper relationship in the television signal. In order to restore the proper relationship of sync to video, for example, a level shifting of the horizontal and/or other sync pulses back down to DC level (i.e. level shifting in an opposite fashion to that which is done in scrambling) is performed such that a TV set displays proper video. SUMMARY OF THE INVENTION The present invention provides a technique for improving upon the scrambling effects produced by typical prior art sync suppression scrambler systems. Accordingly, it is an object and corresponding advantage of the present invention to enhance the concealment provided by an existing suppression scrambling system while at the same time providing for compatibility with existing TV set sync suppression decoder circuits. Thus, the invention selectively modifies an existing sync suppression scrambled signal without requiring that new or modified descrambler systems be installed in existing TV sets.

In a preferred embodiment of the invention, portions of the TV set's overscan areas are modified by the application of a blanking level which is turned on and off at various selected times. As an example, the first and/or last 2 microseconds (μs) of each line are switched to a voltage level about blanking level at various times to thereby act as additional fake horizontal sync pulses along with the sync suppressed scrambled program video, to further scramble the video signal received by the TV set. Additionally, the end and beginning of the television field may include television lines which are modified to generate fake vertical sync pulses during the scramble mode. These fake vertical sync pulses are the last and beginning few lines of the video field and vary from blanking level to above blanking level (i.e. 20-60 IRE units, that is, 20-60% of peak white).

It is to be understood that for maximum enhancement to take place in accordance with the invention, the above mentioned modifications preferably are controlled by an adaptive circuit which senses the picture content of the program video and applies the present enhancement technique at optimal times, as further explained below. Although there are many ways to analyze the picture content, a representative technique supplies the unenhanced sync suppression scrambled video signal to a combination sync separator (sync sep)-horizontal phase lock loop oscillator (HPLL) circuit that is representative of similar circuits present in existing TV sets. It follows that the output of the HPLL circuit supplies output pulses that are phase shifted in relation to the program video's original horizontal sync pulses. Likewise the output of the sync sep during a scrambled sync suppressed signal will be a horizontal pulse which is phase shifted with respect to the program video's original horizontal sync pulse. This phase shift information then is used to determine for example whether or not, and/or when, to turn on the enhancement system of the present invention. For instance, if the phase shift is determined to be about 20 μs to 40 μs from the input video's original sync pulse, the enhancement system is turned off. Such action is preferable because 20 μs to 40 μs of phase shift in itself causes a huge tearing effect on the picture displayed on the TV set. Thus there is no need to add the enhancements generated by the enhancement system of the invention. In fact, under such conditions, application of the enhancement system may actually reduce the amount of tearing. It follows that selective application of the present enhancement system via the integral adaptive circuitry maximizes the advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a waveform depicting a typical horizontal line of unscrambled video signal such as is coupled to the input of a prior art sync suppression scrambler circuit, or to the circuit of the invention;

FIG. 2 is a waveform illustrating a level shift voltage such as applied to the signal of FIG. 1 to generate a prior art sync suppressed scrambled signal;

FIG. 3 is a waveform depicting the output of a prior art sync suppression scrambler circuit wherein the horizontal blanking interval (HBI) is generally level shifted by adding the level shift pedestal voltage of FIG. 2 to horizontal sync and/or color burst. It is understood that in some sync suppression scrambler circuits, the HBI includes level shifting and inversion of horizontal syncs. Either way, the circuit of the invention is compatible with both the level shifting and inversion of sync processes; FIG. 4 is a waveform depicting selected blanking signals in accordance with the invention for blanking selected portions at the front and/or back porch of the signal, which results in horizontal enhancements (i.e. extra tearing) in the scrambling effects generated by a prior art sync suppression scrambler circuit. The portions or locations "A" and "B" are blanked separately at different times or can be blanked all the time with pulses varying from about blanking level (i.e. -10% to 0%) to a gray level (i.e. 20% to 80% peak white) which are inserted at the A and B locations;

FIG. 5 is a waveform depicting the combination of the sync suppressed scrambled signal of FIG. 3 and the horizontally enhanced modification of the invention depicted in FIG 4; FIG. 6 is a waveform of a typical video signal and vertical sync signal before scrambling;

FIG. 7 is a waveform illustrating selected blanking signals of the invention for blanking selected lines in a field of video; FIG. 8 is a waveform depicting the modification of a video signal by application of the waveform of FIG. 7 to that of FIG. 6 to modify the first and last few lines of the active video field by blanking and inserting signals from about blanking level to gray level. This results in vertical enhancement of the prior art scrambled signal by causing extra vertical jitter;

FIG. 9 is a diagram illustrating an example of the relative locations of the portions of the video signal which are modified on an underscanned television screen (i.e. blanked out portions and/or inserted signals) in accordance with the invention;

FIG. 10 is a block diagram illustrating a basic embodiment of the present invention; FIG. 11 is a block diagram illustrating the location of the invention in the environment of an existing prior art sync suppression scrambling circuit;

FIG. 12 is a block diagram illustrating an alternative embodiment of the invention employing an adaptive technique for improving the concealment process of for example FIGs. 11, 12 by enabling or disabling the enhancement process as a function of picture level or content; and

FIG. 13 is a block diagram illustrating in further detail an embodiment of the adaptive technique illustrated in FIG. 12, configured to increase concealment effects by detecting the phase or timing difference between a sync pulse of a sync suppressed scrambled signal (as seen by a typical TV set) and a sync pulse of a nonscrambled video signal; and

FIGs. 14 and 15 are schematic/block diagrams of a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method and apparatus described herein comprise a combination of elements and features that selectively enhance the concealment produced by a typical sync suppression scrambling system. Typical of such a system is for example the system employed in the Jerrold Staφack service encoder, Model SSE-200AN manufactured by General Instruments. Advantageously, the invention further is compatible with the same television set circuits that detect the scrambled signal and produce the concealment in existing typical sync suppression scrambling systems. Thus the present invention selectively enhances the scrambling effects produced by prior art sync suppression scrambling systems but does not require that new or modified descrambling circuitry be added to existing television sets.

FIG. 1 illustrates the configuration and parameters of a standard waveform of a horizontal line of video, exemplifying a horizontal blanking interval (HBI) and including a conventional horizontal sync pulse, front and back porches, color burst and the various associated white, black, blanking and sync levels. FIG. 1 also illustrates a fictitious curve corresponding to a horizontal line of television, i.e. active video, preceding a second HBI interval.

FIG. 3 illustrates a waveform configuration and parameters of a television line produced by a typical prior art sync suppression scrambling system such as utilized for example in the General Instrument's encoder of previous mention. In this example, the standard horizontal blanking interval of FIG. 1 is level shifted by application of a level shift voltage depicted as pulses 20 in FIG. 2. Prior art sync suppression scrambling systems also may include inversion of the horizontal syncs (not shown). The present invention is described here relative to an NTSC color television standard, but can be used in other television standards as well. The invention adds concealment to an existing prior art sync suppressed signal by selectively blanking out selected edges or portions of the television lines or selected lines themselves. The blanking of the edges or lines generally is hidden in the TV set's overscan areas. FIG. 4 illustrates blanking pulses A and B which are applied in accordance with the invention to a prior art sync suppression scrambled signal (such as shown in FIG. 3) to further enhance the scrambling effects of the prior art scrambled signal. To this end, the blanking pulse A which occurs during a television line time interval corresponding to the width of the pulse A, is applied to the prior art sync suppression signal of FIG. 3 during approximately 2 μs at the beginning of the active video line. Likewise, the blanking pulse B occurs during a line time integral corresponding to the width of pulse B, and is applied to the prior art signal during approximately 2 μs at the end of the active video line. The pulses A and B may be blanked separately at different times, or can be blanked all the time with respective pulses varying from about blanking level (i.e. -10% to 0%) to a gray level (i.e. 20%) to 80% of peak white) inserted to define the A and B pulses.

FIG. 5 illustrates by way of example only, a waveform of a prior art sync suppression scrambled signal, such as that of FIG. 3, which is enhanced by the technique of the invention, that is, by the selective application of the blanking pulses A and B during the corresponding beginning and end portions of the active video line. A pulse A corresponding to the applied blanking pulse A occurs at the beginning of the active video, and a pulse B corresponding to the applied blanking pulse B occurs at the end of the active video. As depicted in solid and phantom lines, the level of the pulses A, B may vary from - 10% to 80%) peak white, although it is preferable to apply a negative level of about -7.5% as shown.

By blanking out the edges of the television lines selectively, existing TV sets will be fed a signal as depicted in FIG. 5. The blanked out areas or portions A and B will cause the TV set's scan circuit to start scanning after the horizontal sync pulse at the beginning of a line followed later at the end of the line by scanning before the horizontal sync pulse. As a result the picture is torn with a horizontal displacement of about 2 μs plus 10.9 μs = 13 μs. The blanking pulses A and B are selectively turned on randomly, pseudo randomly or periodically to thereby cause the maximum concealment.

It should be noted that the blanking levels of A and B can be lower than 0% peak white to increase effectiveness, but not so low as to cause problems when the signal is descrambled. Thus the blanking level should not go below -10 to -20% peak white. To insure proper descrambling, A and B levels generally are set at about -7.5% peak white as depicted in phantom line in FIG. 5. It is also possible to add a pedestal to the input video signal such that black level is never lower than +10% for example (by NTSC color television standards, black level is defined as +7.5% peak white). By adjusting the blanking levels of A and B and the black levels of the input video, the TV set will sense the modifications better and cause more effective "tearing" of the scrambled picture. In practice, however, existing TV sets will respond to the sync suppressed video signal as well. As a matter of fact, the suppressed video scrambling may cause the TV set to start its scan about in the middle of the television line, causing the TV set to display the level shifted or inverted horizontal sync pulse in the middle portion of the screen, thereby providing ample concealment.

FIGs. 6-8 illustrate an alternative embodiment of the invention wherein vertical enhancement of a prior art sync suppression scrambled signal is provided alone or is added to the horizontal enhancement described in FIG. 5. FIG. 6 illustrates a standard vertical blanking interval and retrace interval. FIG. 7 illustrates the application of vertical blanking pulses C and D during several active television lines at the beginning and end respectively, of an active television field. FIG. 8 then illustrates the occurrence of pulses C and D, corresponding to the applied pulses C and D of FIG. 7, within the waveform of FIG. 6 at the beginning and end of a vertical blanking and retrace interval. As depicted in phantom line, the level of the pulses may vary from below through above blanking level. The addition of the pulses C and D provides the vertical enhancement by causing extra vertical jitter in the television picture.

More particularly, if the first and last few lines of the active TV field are modified with a signal that pulsates, vertical jitter can be induced to further increase the concealment. This is especially true when combined with the horizontal modifications (i.e. the A and B pulses). For example, in the NTSC standard, the invention inserts a signal in lines 259 through 261 that goes from about blanking level to a middle gray level in a random, pseudo random, and/or periodic manner. A further insertion of a pulse is provided at another time with a signal from about blanking level to middle gray level for lines 20 through 22. Because the value of the lines drops to about blanking level longer than about 4.7 μs to at least 1/2 television line, these lines will be inteφreted by existing TV set circuits as vertical sync pulses which, in turn, causes the TV set to scan vertically incorrectly.

There may be situations such as in television standards where there is very limited overscan intervals at the edges of the television picture, where shaving the approximately 2 μs intervals at the beginning and/or end of the television lines, as done in the horizontal enhancement technique of the invention, is not acceptable. In such situations, the vertical enhancement technique of the invention may be applied alone to the scrambled video signal to enhance the scrambling effect, as described below.

FIG. 9 illustrates by way of example only, relative locations of the enhancement pulses applied in accordance with the invention on an underscanned television screen 22. Thus, for example, blanked out portions and/or inserted signal levels are depicted as the pulses A and B at the beginning and end respectively of a selected plurality of horizontal television lines, while the pulses C and D are shown over two to several lines at the beginning and end respectively of a television field.

It should be noted that the horizontal enhancements A and B can be further modified as follows: Selected portions may be blanked in the front and back porch areas of every line associated with the horizontal sync suppression scrambling process. For example, from lines 23 through 258 and lines 280 through 522, a gray level is inserted during the first and last 2 μs of the active television lines. Then blanking to around blanking level is applied in a random, pseudo random, and/or periodic manner in the first and last 2 μs of each of these active television lines, as illustrated in FIG. 9. The occurrence of the blanking pulses in FIG. 9 is by way of example only, and thus pulses A and B need not be symmetrical and can be random in frequency, duty cycle, and the like. The pulses A and/or B also can be turned on or off via pulse width modulation. For example, if pulse A needs to be turned off, the 2 μs back porch blanking and/or insertion portion is simply reduced to 0 μs.

FIG. 10 depicts a generalized version of circuitry 28 which provides enhancement of a sync suppressed scrambled signal in accordance with the invention, and which is situated to essentially pre-process the program video signal relative to a sync suppression scrambler system 26 (see FIG. 11). Thus, the output of the circuit of FIG. 10 is supplied to the input of the prior art sync suppression scrambler system 26.

More particularly, FIG. 10 illustrates an embodiment of an enhancement system 28 in accordance with the invention. The circuit as shown in FIG. 10 is not adaptive. However, in combination with for example the adaptive circuit of FIG. 13, the circuit of FIG. 10 becomes an adaptive enhancement system, as is further described below. In particular, program video is supplied to a sync separator circuit 30 via an input lead 32. A composite sync signal from the sync separator circuit 30 is supplied to a horizontal (H) timing circuit 34 which generates pulses A and B both during an active television field. The pulse A is coincident with the beginning of the active television line immediately after the horizontal blanking interval and is about 2 μs in width. The pulse B is about 2 μs wide and is coincident with the last 2 μs of the active television line. The pulses A and B are supplied to AND gates (ANDs) 36 and 38, respectively. The second input of AND 36 is VgenA. a random, pseudo random and/or periodic in signal source. The second input of AND 38 is VgenB which generally is similar to VgenA, but which can be an independent signal source. The output of AND 36 is a signal A' which drives the switching of an analog multiplexor circuit (MUX) 40. In turn, MUX 40 supplies a voltage E_BA (blanking level for signal A) when signal A' is high and a voltage E_GA (gray level for signal A) when signal A' is low. Similarly, AND 38 supplies a signal B' which drives the switching of an analog multiplexor circuit (MUX) 42 to provide a voltage E_BB (blanking level for signal B) when signal B' is high and a voltage E_GB (gray level for signal B) when signal B' is low. Generally, and E_GA = E_GB- The outputs of the MUX 40 and MUX 42 are supplied on respective leads 44, 46. For adding the vertical enhancements, composite sync from the sync separator circuit 30 drives the input of a V timing circuit 48 which supplies signals C and D. The signals C and D are logic pulses turned on high coincident with a selected number of active television lines at the beginning and end of the active television field. A signal source VgenC gates an AND 50 which in turn controls the switching of an analog multiplexor circuit (MUX) 52. The output of the MUX 52 is a voltage E_Bc when signal C is high and voltage EC_JC when signal C is low. Similarly, in response to an AND 54, the output of a MUX 56 is a voltage E_BD when the signal D' is high and is a voltage E_GD when signal D' is low. The outputs of the MUXs 52, 56 are supplied on leads 58, 60 respectively and are toggling voltage sources to enable voltage levels of about blanking level to about a middle gray level to occur during a selected number of active line periods near the end and the beginning of a television field. The output of the MUX 56 is gated by a source VgenD which can be equal to VgenC but also can be an independent source. In general, both VgenC and VgenD preferably may be a swept signal source which is swept from about 2 Hz to 20 Hz.

The input program video also is supplied to clamp and blanking amplifiers 62 and 64, which clamp the input video to for example, 0 voltage as blanking level. Amplifier 62 passes most of the input video while also blanking the active lines near the beginning and end of the television field (vertical enhancement), as well as blanking the back and front porch areas of the input video's active television lines as a function of VgenA and VgenB (horizontal enhancement). The signals A', B', C, D' are supplied via leads 65 to respective inputs A', B¹, C, D' of the blanking amplifier 62 and provide the timing for selectively blanking the video signal at the beginning and/or end of a television line or at a number of lines at the beginning or end of a video field. The output of the amplifier 62 is summed with pulsation signals on leads 58 and 60 from MUX 52 and MUX 56 via a summing amplifier 66. The output of the amplifier 66 then couples to the prior art sync suppression scrambler system 26 as illustrated in FIG. 11.

Similarly, the clamp and blanking amplifier 64 clamps and passes the input video in response to the signals A', B', C, D' on leads 65 the same way as amplifier 62, and also blanks the front and back porch areas during the active television field as a function of

VgenA and/or VgenB. The blanking amplifier 64 also blanks the active lines near the beginning and end of the active television field the same way as amplifier 62. The output of the summing amplifier 64 then is summed in a summing amplifier 68 with pulsation signals from MUXs 52, 56, 40 and 42 on respective leads 58, 60, 44 and 46. The output of the amplifiers 66 and 68 on respective output leads 70, 72 results in "blinking" levels between around blanking level and around gray level at the back and front porch portions of the active video signal, as well as blinking levels between around blanking level and around a gray level at the active lines of a selected number of lines near the beginning and end of the active field.

It is to be understood that the blanking amplifier 62 and summing amplifier 66 comprise an auxiliary channel and could be deleted with corresponding functions provided by the blanking and summing amplifiers 64, 68. FIG. 12 illustrates an example of an adaptive control circuit of the present invention for use with the prior art sync suppression system 26. Essentially, an enhancement system of the present invention, such as for example, the circuit 28 of FIG. 10, has the blanking controls of the enhancement system (for example, blanking amplifiers 62, 64) turned on or off depending on the scene content of the video image. To this end, an adaptive circuit 80 generates a control signal on a lead 81 that is a function of the phase shift in a TV set's scanning system when the latter is subjected to a sync suppressed signal produced by for example the prior art scrambler system 26. The adaptive embodiment of FIG. 12 maximizes the concealment by reducing or turning off the control pulses (e.g. blanking) supplied to, for example, the blanking amplifiers 62 and 64 in FIG. 10, any time that the TV set generates horizontal line scanning beginning in a general region of the middle third of the active television line. Such action is taken because of the successful scrambling effects of the prior art sync suppression system when scanning is forced to start around the middle of the television lines. Such successful effects result for example, in the video picture being torn, i.e. horizontally displaced, about 30 μs resulting in the displaced H sync pulse being displayed around the middle of the picture. Such tearing adequately scrambles the signal so that further enhancement by the present invention is not as necessary.

More particularly, FIG. 13 illustrates an implementation of the adaptive control circuit 80 of FIG. 12 for controlling the blanking pulses supplied for example to the blanking amplifiers 62, 64 of FIG. 10. The circuit 80 receives nonscrambled program video into a sync separator 82. The output of the sync separator 82 is supplied to one input of a phase detector circuit, PHI det 84. The output of a prior art sync suppression scrambler system, such as system 26, FIG. 12, is supplied via an input lead 83 to one input of a switch

86 whose other input is a voltage level of middle gray or white voltage, i.e. 50% white level. The switch 86 is switched to the gray or white voltage during the times when it is desirable to enhance the sync suppression scrambled signal in response to, for example, the timing signals A, B, C, D derived from the timing circuits 34, 48 of FIG. 10 and applied via an OR gate 87. Conversely, in the event that the scrambling effects are optimal, the OR 87 causes the output of the switch 86 to supply the sync suppressed video signal without any of the invention's enhancements, such as blanking by pulses A, B, C, D, etc. In turn, the output of the switch 86 is coupled to a sync separator 88 such as used in a TV set. The output of the sync separator 88 is the scrambled video sensed or separated at the darkest portions of the sync suppressed video, and is supplied to a horizontal phase lock loop oscillator (H PLL) 90 also such as used in a TV set. The output of H PLL 90 is then a timing pulse representative of how a TV set would respond to a prior art sync suppression scrambled video signal such as generated by the scrambler system 26 of FIG. 12. In short, due to sync suppression, the H PLL 90 generates a pulse that is varying in phase or time with reference to a normal sync pulse of the input program video signal of, for example, lead 32. The output of the H PLL 90 is supplied to the second input of the phase detector 84. The output of detector 84 generates a voltage proportional to the phase shift or timing difference between the input program video's sync pulses and the erroneous or fake "sync" pulses produced by passing the sync suppressed scrambled video through the sync separator 88, H PLL 90. In a modification of the circuit of FIG. 13, the switch 86 and OR gate 87 can be deleted and the sync suppression scrambled signal on lead 83 can be supplied directly to the sync separator 88, as is illustrated in FIG. 15 below.

A window detector 92 then uses the output of the phase detector 84 to generate logic pulses indicative of different scanning zones corresponding to different amounts of phase shift. The output of the window detector 92 then is indicative of a first third of a television line (1/3 BOL), a last third of a line (1/3 EOL) or a middle third of a line (1/3 MOL). The output is supplied to a control circuit 94 which also receives timing via H sync V sync pulses on a lead 95 and which shuts off or reduces the enhancement provided by the invention, as a function of the amount of phase shift caused by scrambling, via control signals A', B', C, D' (similar to those in FIG. 10) on leads 96. In an adaptive enhancement embodiment of the invention, the signals A', B', C, D' supplied by the leads 65 to the blanking amplifiers 62, 64, FIG. 10, are replaced by the adaptively generated signals A', B',

C, D' on the leads 96 of FIG. 13. Thus the combination of the FIGs. 10 and 13 illustrate an adaptive enhancement system of the invention. There are cable sync suppression decoders that rely on burst, and therefore could compromise the effects of the, invention. Such sync suppression decoders are defeated by moving the gap, which exists between last and first color bursts during the vertical blanking interval, around where burst is not present or by adding burst of the vertical blanking interval on a line by line basis so there is no gap or loss of burst. In this way, the invention remains resistant to unauthorized decoding.

FIGs. 14 and 15 illustrate a preferred embodiment of an adaptive enhancement system of the present invention, including enhancement circuitry comparable to the circuitry 28 of FIG. 10, and adaptive control circuitry comparable to the circuitry 80 of FIG. 13, but in further detail. Similar components in the FIGs. 14, 15 are generally similarly numbered to those in FIGs. 10 and 13.

Referring to FIG. 14 (and portions of FIG. 10) the unscrambled program video is supplied via the input lead 32 to the sync separator 30, which supplies horizontal (H) and vertical (V) sync signals to the H timing generator 34. Generator 34 supplies two types of pulses; namely, end of line (EOL) and beginning of line (BOL) via respective leads 102 and 100. The pulses, or signals, BOL and EOL are the equivalent of the signals A and B of previous description in for example FIGs. 4, 9, 10 and 13. The signal EOL is logic high during approximately the last 2 microseconds of the active video line while the signal BOL is logic high approximately the first 2 microseconds of the active video line. The leads 100, 102 and thus the signals BOL and EOL are supplied to further circuits shown in FIG. 15.

Referring now to FIG. 15, the signals EOL and BOL are coupled to a switching circuit (indicated at 103) consisting of logic gates 104 through 110. This switching circuit has two outputs which are turned on and off alternately as determined by an input to an inverting gate 104. In response to the BOL signal and an FM signal indicated at 112 and supplied via the inverting gate 104 and an inverting gate 106, an AND 110 supplies one output of the switching circuit 103 as the BOL pulses modulated by the FM signal indicated at 112. The FM signal waveform may vary from about 90 to 340 Hz over periods of 200 and 25 milliseconds (ms). Another output is supplied by an AND 108 as the EOL signal modulated by the complement of the FM signal 112 via the inverting gate 104. To insert the BOL and EOL pulses in a modulated manner and in an adaptive mode, a switching circuit 1 14 consisting of logic gates 116 through 124 is used.

To this end, a sync suppressed scrambled signal such as produced by the scrambler system 26. FIG. 12, is supplied to a typical television scanning system of a TV set and is then compared to the true horizontal sync position. This way the actual scanning location of a scrambled television signal supplied to a sync separator circuit and/or an H PLL of a TV set can be identified. If the scanning system of a TV set begins scanning in the first third of the active television line, then a resulting signal BOLCONT on a lead 126 will be logic high while a resulting signal EOLCONT on a lead 128 will be logic low. As a result, an OR 124 of the switching circuit 114 will output EOL pulses that are frequency modulated via the FM signal 112. If the scanning system of a TV set begins scanning in the last third of the active television line, then the situation is reversed and the OR 124 outputs a BOL signal that is frequency modulated by the FM signal 112. If however, the television scanning system begins the scans in the middle third of the television lines, or picture, the OR 124 outputs for the most part no EOL and no BOL pulses, i.e. signals. In general, when the scanning system already is scanning in the middle of the picture, maximum concealment is being produced. Therefore, as previously described, the enhancement system may be adaptively disabled. Alternatively, however, under these conditions, EOL and BOL signals can be added in a complementary fashion at a frequency modulated rate for about 30% of the time to enhance the concealment by tearing the picture from time to time with the BOL and EOL pulses. To this end, program video on the input lead 32 is replaced during the BOL and EOL locations with a 50% peak white signal via a switch 132 controlled by an OR gate (OR) 130. The switch 132 also may replace the end and beginning of field (EOF and BOF) lines with 50% white. This is to insure that the BOL and EOL locations do not cause the TV set to scan or trigger. Which portions of lines or which groups of lines in a field are replaced with 50% peak white is determined by the BOL, EOL signals on the leads 100, 102, or by BOF, EOF signals supplied on leads 133, 135, respectively, from the timing generator 48, FIG. 14 (further discussed below). The output of the OR 124 then replaces the output of the switch 132 with a signal around blanking level via a switch 134. The output of switch 134 then has an adaptive blanking (based on a television scanning circuit's response to a scrambled television signal) which acts as fake horizontal sync signals (via blanking) to cause maximum tearing in a sync suppressed scrambled video signal. The output of the switch 134 is then coupled to a summing amplifier 136 which provides an output on a lead 138. Amplifier 136 also may have added and/or individual vertical enhancements provided in accordance with the invention via a lead 140 from the FIG. 14. The output of the amplifier 136 is coupled via the output lead 138 to the input of, for example, the sync suppression scrambler system 26 of previous discussion.

The BOLCONT and EOLCONT signals are obtained as follows. Program video on the lead 32 from for example FIG. 14 is input to a sync suppression scrambler system 142 such as system 26, FIG. 12, or other system which emulates a similar scrambling effect. The system should be at least very similar in scrambling characteristics to the scrambler system coupled to the output of the summing amplifier 136. The output of the scrambler system 142 is supplied to a "typical" television sync separator and horizontal oscillator (H PLL) circuit 144. The output of circuit 144 then is a signal denoting the start of horizontal scan. Under scrambled conditions, such as sync suppressed scrambled video, the circuit 144 will output pulses at different times over the entire active television line location, since the content of the scrambled video acts like horizontal sync pulses. The circuit 144 is the equivalent of the sync separator and H PLL circuits 88, 90 of FIG. 13. The output of the circuit 144 then is coupled to one input of a phase comparator circuit 146 which is generally equivalent to the comparator circuit 84 of FIG. 13. The reference input of circuit 146 is the horizontal sync from the normal or unscrambled video such as supplied via a lead 148 from the sync separator 30 of FIG. 14. The output of the phase comparator circuit 146 is supplied to an H phase location circuit 150 generally equivalent to the window detector 92 of FIG. 13. Location circuit 150 then outputs, for example, three zones or locations of the beginning of scan for the output of circuit 144. It is to be understood that although the scanning interval is described herein by way of example only as three zones, other numbers of zones may be used instead.

The circuit 150 generates a high at only one of its three outputs at any given time. Therefore, if the output of the circuit 144 shows the start of scanning at the last third of a television line, the circuit 150 will supply a logic high on a lead 152 during the last third and a logic low on two other leads 154, 156. If the output of circuit 144 is high during the start of scanning at the first third of a line then the output of circuit 150 is logic high on the lead 154 during the first third of the line and the other leads 152, 156 are logic low. If the output of circuit 144 is high during the middle of a line then the output of circuit 150 is logic high on the lead 156 for the mid third of the line and the other leads 152, 145 are logic low. The signals on the leads 152, 154, 156 herein are labeled 1/3EOL, 1/3BOL, 1/3MOL, respectively, and generally are the equivalent of the signals 1/3 EOL, 1/3 BOL and 1/3 MOL of FIG. 13. An AND 158 and ORs 160, 162 logically combine the outputs of the circuit 150.

The OR 162 supplies the signal BOLCONT on the lead 126 and the OR 160 supplies the signal EOLCONT on the lead 128. The BOLCONT signal is high when the circuit 150 outputs a logic high for the first third of a line. This turns off AND 120 of the switching circuit 114 to allow modulated EOL pulses to be inserted in the program video as a blanking level via the switch 134. It follows that when the scanning is identified to be in the first third of the television line, the adaptive scrambler enhancement system of the invention (28 of FIG. 12) adds fake sync pulses (via blanking) at the end of the television line for maximum tearing. Similarly if the output EOLCONT of the circuit 150 is logic high as when the scan starts during the last third of the television line, the output of the OR 160 is high and the output of OR 162 is low, allowing beginning of line fake sync pulses (via blanking) to be added via the switch 134 for maximum tearing. Thus, it may be said that in accordance with the invention if scanning begins in one zone, the adaptive system enables the enhancement system in a complementary zone.

Referring now back to FIG. 14, there is illustrated a vertical enhancement system of the invention, generally indicated by number 170, wherein the H sync and V sync signals from the sync separator 30 also are supplied to a vertical timing generator 48 similar to that of FIG. 10. Although the FIG. 15 does not include specific circuitry for adding the fake vertical pulses generated by the system 170 in an adaptive mode, an adaptive vertical enhancement mode is derived by employing the adaptive techniques and circuitry of FIG. 15. This is accomplished by modifying the sync separator/H PLL circuit 144 with a vertical oscillator instead of a horizontal oscillator, and then also modifying the phase comparator circuit 146 with an input vertical sync on the lead 148 instead of an input horizontal sync. The zones of identification in this example of the invention then are the first, mid and last third of a television field instead of a television line. Although optimal enhancement is provided by adding the vertical enhancement effects to the horizontal enhancement effects, it is found that with the frequency modulated insertion of fake vertical sync, adequate vertical concealment under given conditions is obtained by the vertical enhancement system.

FIG. 14 illustrates circuitry for adding fake vertical syncs to the program video signal with the fake horizontal sync signals or for supplying fake vertical syncs alone. To this end, a frequency modulated waveform 172, for example, a square wave that varies from about 7 to 17 Hertz (Hz) over a period of 4 seconds, is used to multiplex beginning of field (BOF) and end of field (EOF) signals to thus add fake vertical sync pulses (via blanking). The V timing generator 48 supplies the pulses BOF that are for example high during the active line portions of for example television lines 19 through 21 (in an NTSC color television standard). Similarly, the pulses EOF are high for example during the active line of television lines 260 through 262, in NTSC. The BOF pulse and EOF pulse related vertical fake sync signals are added in a complementary manner via the frequency modulated source which supplies the FM signal 172 on a lead 174 to ANDs 176, 178, as well as to an inverting gate 180 and ANDs 182, 184. The EOF and BOF signals also are disabled from time to time via a gating signal 186 supplied to the input of an inverting gate 190 via a lead 188. The gating signal 186 is illustrated by way of example as 650 ms pulses turned off for 150 ms. The resulting EOF and BOF pulses are used to control a switch 192 and a switch 194, respectively. When either switch 192 or 194 is activated, a negative 50% signal is supplied to a summing circuit 196. The negative 50% signal is used to subtract the plus 50%ι signal level which was applied to the video by the switch 132, FIG. 15, which results in a blanking level signal being supplied to the summing amplifier 136, FIG. 15. Thus the output of the summing circuit 196, FIG. 14, is a gated, frequency modulated, complementary (alternating) BOF, EOF signal for adding fake vertical pulses (via blanking) into the program video signal prior to its introduction to a television scrambler system such as system 26. FIGs. 11, 12.

The above description of the invention is illustrative and not limiting: other modifications in accordance with the invention will be apparent to one of ordinary skill in the art in light of this disclosure. For example, in such a modification of the vertical enhancement technique, fake horizontal sync signals are added during about the last and first 10 to 15 lines of the active video field. Doing this provides more control of the concealment process when applying the fake vertical sync pulses,

the addition of fake horizontal sync pulses in the top and bottom portion of the video may reduce the amount of horizontal tearing, it is not critical to conceal the picture information at these locations horizontally. A more effective effect for concealment is to jerk the picture up and down via the fake vertical syncs added just outside the viewable area. By putting in the fake horizontal pulses of previous mention before and/or after the HBI in the top and bottom 10 to 15 lines of the field, dark areas due to sync suppression will prevent the occurrence of vertical sync near the real vertical syncs. Instead, the dark areas will cause vertical synchronizing in the middle portion of the picture. The vertical enhancement process of the invention thus has a better chance to define other vertical synchronizing points elsewhere by pulsing at different times near the end of the field and/or the beginning of the field.

Thus the scope of the invention is defined by the appended claims and their equivalents.

Claims

What is claimed is:

1. A method of enhancing the scrambling effects of a scrambled television signal formed of successive television lines in a video field, comprising the steps of: blanking first and/or last portions of selected television lines in the video field; and inserting selected levels of signals in the blanked first and last portions of the lines to produce erroneous sync pulses which are subsequently incorrectly detected.

2. The method of claim 1 wherein: the inserted signal levels are measured in percent (%) of peak white, and the levels vary from blanking levels of about -10 to 0% and gray levels of about 20 to 80%, of peak white; and the blanking and inserting are applied randomly, pseudo randomly or periodically.

3. The method of claim 1 wherein the portions are about two to several microseconds in duration at the beginning and/or at the end of a television line.

4. The method of claim 3 wherein the step of blanking includes blanking the first and last portions of selected numbers of television lines.

5. The method of claim 4 wherein the numbers of lines with first portions blanked are alternated with the number of lines with last portions blanked.

6. The method of claim 3 wherein the step of blanking includes blanking first or last portions of selected lines in the field.

7. The method of claim 3 wherein the inserted signal levels are measured in percent (%) of peak white, and the levels vary from blanking levels of about -10 to 0% and gray levels of about 20 to 80%>, of peak white.

8. The method of claim 1 including the steps of: detecting the scene content of a video image corresponding to the video field; and selectively enabling or disabling the steps of blanking and inserting in response to the step of detecting.

9. The method of claim 8 wherein: the step of detecting includes detecting the phase shift between horizontal sync pulses of the television signal before and after scrambling; and generating control signals, in response to the step of detecting, for enabling or disabling the steps of blanking and inserting.

10. The method of claim 9 wherein: the signal levels vary from selected blanking levels and selected gray levels; and the selected portions are about two to several microseconds at the beginning and/or end of a television line.

11. The method of claim 8 wherein the step of detecting includes: determining if horizontal line scanning begins in a middle third of a horizontal line; and providing a control signal, in response to the step of determining, for disabling the steps of blanking and inserting.

12. The method of claim 1 including the steps of: blanking a selected number of first and last television lines in the video field; and inserting signals from about blanking level to gray level in the blanked number of first and last television lines.

13. The method of claim 12 wherein the inserted signals are applied randomly, pseudo randomly and/or periodically.

14. A method of enhancing the scrambling effects of a scrambled television signal formed of successive television lines in a video field, comprising the steps of: detecting the scene content of a video image corresponding to the video field; generating a control signal which identifies whether the detected scene content indicates that the television signal is or is not sufficiently scrambled; blanking first and/or last portions of selected television lines in the video field to selected voltage levels in response to the control signal when the television signal is not sufficiently scrambled, wherein the selected voltage levels subsequently cause erroneous detection.

15. The method of claim 14 including the step of: disabling the step of blanking when the control signal indicates that the television signal is sufficiently scrambled.

16. The method of claim 14 wherein: the step of detecting includes determining if scanning begins in generally a middle third of a horizontal line; and the step of generating includes providing the control signal as a disabling signal which disables the step of blanking in response to the step of determining that the scanning begins in generally the middle third of the horizontal line.

17. The method of claim 14 wherein: the step of detecting includes determining if scanning begins in about a first third or a last third of a horizontal line; and the step of generating includes providing the control signal as an enabling signal which enables the step of blanking in response to the step of determining that the scanning begins in about the first or last third of the horizontal line.

18. The method of claim 17 wherein: the steps of blanking and inserting are enabled during the last third of the line when the start of scanning is detected in about the first third of the line, and vice versa.

19. The method of claim 14 including the steps of: blanking a selected number of first and last television lines in the video field when the television signal is not sufficiently scrambled; and inserting signals from about blanking level to gray level in the blanked number of first and last television lines.

20. The method of claim 19 including the step of: blanking first and last portions of a selected number of lines of from 10 through 15 lines while also blanking the selected number of first and last television lines in a video field.

21. The method of claim 19 wherein the inserted signals are applied randomly, pseudo randomly and/or periodically, to cause incorrectly detected vertical sync pulses in the respective lines.

22. The method of claim 19 wherein the inserted signal levels are measured in percent (%) of peak white; wherein the levels vary from selected blanking levels of about - 10 to 0% and selected gray levels of about 20 to 80%, of peak white; and wherein the first and/or last portions of a television line are about two to several microseconds at the corresponding beginning and/or end of the line.

23. Apparatus for enhancing the scrambling of a standard television signal, wherein the scrambled signal is displayed as successive television lines of a video field, comprising: means for generating horizontal signals of respective voltage levels during selected first and/or last portions of the television lines; means for selectively blanking the television signal during the selected first and/or last portions; and means for inserting the horizontal signals of respective voltage levels in the selected blanked first and/or last portions of the television lines.

24. The apparatus of claim 23 including: means for selectively modulating the horizontal signals so that they are applied randomly, pseudo randomly or periodically.

25. The apparatus of claim 24 wherein the levels are measured in percent (%) of peak white and vary from blanking levels of about -10 to plus a few % and gray levels of about 20 to 80% peak white.

26. The apparatus of claim 23 including: means for detecting the scene content of a video image corresponding to the video field; and means responsive to the detecting means for enabling, disabling or partially disabling the blanking means depending upon the detected scene content.

27. Apparatus for enhancing the scrambling of a standard television signal which has been scrambled by a sync suppression scrambler system, wherein the scrambled signal is displayed as successive television lines of a video field, comprising: means for providing timing signals during first and last portions of selected television lines; and means for blanking the first and last portions to selected voltage levels in response to the timing signals, to produce erroneous sync pulses via the selected voltage levels which are subsequently erroneously detected.

28. The apparatus of claim 27 including: means for determining when the television signal is or is not sufficiently scrambled; and said blanking means being responsive to the determining means for selectively blanking the first and last portions when the signal is not sufficiently scrambled.

29. The apparatus of claim 28 wherein the determining means includes: means responsive to the scrambled television signal for detecting the scene content of a displayed video image corresponding to the video field; and means responsive to the detecting means for producing a control signal which enables or disables the blanking means depending upon the detected scene content.

30. The apparatus of claim 29 wherein: the detecting means includes means for determining if scanning of a television line begins at about a first zone, a middle zone or a last zone of the line; and the producing means provides a control signal, in response to the zone in which the scanning begins, which enables the enhancement apparatus in a complementary zone.

31. The apparatus of claim 29 wherein: the detecting means includes; first means for detecting the phase or timing of a horizontal sync pulse of the scrambled television signal; second means for detecting the phase or timing of a horizontal sync pulse of the standard television signal; and phase detector means responsive to the first and second means for generating a voltage proportional to the phase or timing difference between the first and second means; and the producing means includes control means responsive to the voltage for producing the control signal in the form of enabling or disabling control signals.

32. The apparatus of claim 28 including: means for generating vertical signals of respective voltage levels which occur during a selected number of first and last television lines in the video field; means for selectively blanking the television signal to selected voltage levels during the selected number of first and last television lines.

33. The apparatus of claim 32 including: means responsive to the scrambled television signal for detecting the scene content of the scrambled image; and means responsive to the detecting means for enabling or disabling the blanking means depending upon the scene content.

34. The apparatus of claim 28 wherein the generating means includes: timing means receiving the standard television signal for providing timing signals indicative of the first and last portions of the television line; and logic means responsive to the timing signals for generating horizontal pulsation signals of selected blanking and/or gray levels during the first and last portions.

35. Apparatus for enhancing the scrambling of a standard television signal which has been scrambled, wherein the scrambled signal is displayed on a television set as successive television lines of a video field, comprising. a horizontal blanking circuit disposed to selectively blank the standard television signal at selected first and last portions of the television lines; first means for inserting signals of selected voltage levels in the selected first and last portions when the portions are blanked; and an adaptive circuit for detecting the scene content of an image corresponding to the video field and for enabling or disabling the blanking circuit in response to the detected scene content.

36. The apparatus of claim 35 wherein the first means for inserting includes first means for selectively modulating the inserted signals to provide the selected voltage levels.

37. The apparatus of claim 35 including: a vertical blanking circuit disposed to selectively blank the standard television signal at a selected number of first and last lines of the video field; and second means for inserting signals of selected voltage levels in the selected number of first and last lines when the lines are blanked.

38. The apparatus of claim 37 wherein the second means for inserting includes second means for selectively modulating the inserted signals to provide the selected voltage levels.

39. A method of enhancing the scrambling effects of a scrambled television signal which is to be displayed on a television set in the form of successive television lines of a field of video, comprising the steps of: determining the occurrence of first and last portions of selected television lines in the video field; and blanking said first and/or last portions to selected voltage levels to produce erroneous sync pulses in the respective lines, which erroneous sync pulses are subsequently incorrectly detected in the television set.

40. The method of claim 39 wherein: the step of determining includes providing beginning of line and end of line signals indicative of said first and last portions; and the step of blanking includes selectively modulating the beginning of line and end of line signals to produce the selected blanking voltage levels.

41. The method of claim 40 wherein the beginning of line and end of line signals are frequency modulated at a frequency of about 94 through 333 Hertz.

42. The method of claim 39 including the steps of: detecting the scene content of the scrambled television signal; and selectively enabling or disabling the step of blanking in response to the detected scene content.

43. The method of claim 42 wherein: the step of detecting includes determining if scanning of a television line begins during a middle third of the line; and the step of enabling or disabling includes supplying a control signal for enabling or disabling the step of blanking in response to determining that scanning does not begin, or does begin, respectively, during the middle third of the line.

44. A method of enhancing the scrambling effects of a scrambled television signal formed of successive television lines in a video field, comprising the steps of: blanking a selected number of first and last television lines in the video field; and inserting signals from about blanking level to gray level in the blanked number of first and last television lines; wherein the inserted signals are applied randomly, pseudo randomly and/or periodically.