Video copy protection process enhancement to introduce horizontal and vertical picture distortions

IS 2 136 200 T5

DESCRIPTION

Improved video copy protection procedure to introduce horizontal and vertical image distortions.

The present invention relates to a method and apparatus for modifying a video signal subjected to copy protection.

Video anti-copying processes are well known. An example is US Patent No. 4,631,603 which describes modifying a video signal so that a television receiver will continue to provide a normal color image from the modified video signal while videotape recording the video signal. modified produces generally unacceptable images.

To achieve this, a plurality of pseudo-sync pulses are added to the conventional video signal during the vertical decay interval, and each of the pseudo-sync pulses is followed by a positive pulse of suitable amplitude and duration. As a result, the automatic gain control system in a VCR will make a false measurement of the video signal level, causing an inappropriate recording of the video signal. The result is unacceptable image quality during playback.

Thus, this prior art "basic anti-copy process" causes an abnormally low amplitude video signal to be recorded when a copy is attempted. Some of the effects seen when illegal copy is played are horizontal tearing (position shift) and vertical image shift. Whether or not this happens depends a lot on the content of the image, that is, the presence of white (light) and black (dark) areas in the image. Thus, this prior art process, while generally providing excellent copy protection, with some combinations of VCRs (such as VCRs) and television receivers provides an image viewable by persons willing to tolerate a poor quality image.

WO-A-91/16791 describes a method and apparatus for preventing unauthorized dubbing of video signals on tape. A number of image lines with their corresponding line sync pulses are extracted and additional pulses are replaced. A tape recording apparatus does not recognize the inserted pulses and thus the sync frame is disturbed. Also, an additional pulse is added after a color sync signal. This can adversely affect the amplitude control of a tape recording apparatus. An amplification of this effect can be obtained by supplying in addition an additional pulse in the opposite direction to the said additional pulse and also after the color synchronization signal.

An object of the invention is to seek to improve known copy protection.

According to a first aspect of the present invention, there is provided a method for modifying a copy-protected video signal to improve copy protection, wherein the unmodified copy-protected video signal is arranged to cause a reduced amplitude video signal to be recorded on the copy, the method comprising the step of:

add to said unmodified copy-protected video signal a waveform to provide a video signal with improved copy protection that can be displayed on a TV receiver or monitor, the waveform is arranged to cause a video return, when in combination with the low amplitude video signal is recorded in the copy, in which said waveform is added in the overscan portion of the video signal, and wherein said waveform is replaced by active video at one end of a horizontal line and is immediately prior to a horizontal sync signal, or wherein said waveform is replaced by active video at end lines of a video field and is immediately before a vertical sync signal.

In one embodiment, said waveform is added to said video signal by extinguishing a portion of the video signal and adding the waveform to said extinguished portion.

In a preferred embodiment, only active video is extinguished.

In one embodiment of the invention where the waveform is added to horizontal lines of the video signal, the right edge of the image is replaced by a "checkered" pattern that appears as a checkerboard of black and gray rectangles. . The width of this checkered pattern is chosen to be within the overscan (not viewed) portion of the image when viewed on a standard television receiver. It will be understood that at abnormally low signal amplitude, when the image content is light (such as mid gray), the left edge of the black rectangle on certain video lines will trigger an anticipated horizontal return since it is a variable transition in the negative direction. (towards extinction level). When the image content is dark, the right edge of the gray rectangle (adjacent to a dark image area) in certain video lines will trigger an early return on each line since it is also a variable transition in the negative sense (the description of these video waveforms follow the convention that positive amplitude is white and negative amplitude is black).

The horizontally shifting checkered pattern can be generated at a rate slightly asynchronous with the repetition rate of the video field, so that the checkered pattern appears to slowly move up or down in the image, at a rate of about 1 second for any point. since it scrolls from the bottom to the top of the image or vice versa. The checkered pattern has no effect on the picture when an original (licensed) cassette is played back since signal states that are abnormal in any way are not present in the television receiver.

However, when an illegal (unauthorized or pirated) copy of the cassette is played back using a VCR, the signal attenuation produced by the prior art copy protection process described above, in combination with the checkered pattern, causes the horizontal return of the television receiver occurs in advance on each video line where the black or gray rectangle is present, depending on the picture content and the characteristics of the VTR and TV receiver. Each of the black rectangles and the rec2

EN 2 136 200 T5 gray angles may cause a transition of sufficient width depending on the previous active video image content. If the image content is light (white), the left edge of the black rectangle causes a negative transition to black; if the image content is dark, the right edge of the gray rectangle causes a variable negative transition from the gray to the next dark area (fade level typically). The difference between the lines that end in black or gray in turn causes a horizontal shift in the image information, that is, a ripple, which slowly rises or falls in the image.

The tendency of the television receiver to return (perform the horizontal beam return in advance) is to take advantage of by arranging the transition from light to dark (the left edge of the black rectangle or the right edge of the gray rectangle) before the position in the video line of the genuine horizontal line sync signal. The anticipated return thus triggered causes the image information to advance in the successive line, that is, to move horizontally to the right by an amount equal to the distance between the negative transition and the position of the leading edge of the genuine synchronization signal. horizontal. This shift causes a "tearing" (horizontal relocation) of the image information.

A somewhat similar modification in the vertical image direction inserts alternating dark and white bands in place of active video in the last few lines of selected video fields in the lower overscan portion of the image just before the vertical decay interval, and / or extended to the first few lines of the vertical extinction interval.

This vertical frequency modification can be done in several ways. In one embodiment, several of the active video lines (about five), immediately prior to the vertical sync signal, are caused to alternate between the decay level and the gray level (typically, about 30% of the peak level of white) at a frequency of approximately 1 to 5 cycles per second (Hz). This can cause the head drum servo to unlock on the copy VTR, or the wrong vertical return on the television receiver, causing the image from the unauthorized copy to exhibit vertical instability (jump up and down) at that point. particular frequency, substantially degrading image quality. In another version, two to five alternating (modulated) white-black-white lines are inserted at the end of each or alternate video fields, with the same vertical latch loss result in a copying VCR or observation television receiver for interpretation of the inserted pattern as a vertical sync signal when the video signal amplitude has been reduced by the automatic gain control response to a signal copy protection.

These vertical modifications can extend to the first few lines of the subsequent vertical extinction interval.

Thus, the methods according to embodiments of the invention ensure optimal conditions in terms of image content to cause the maximum level of subjective degradation: (1) in the reproduced image quality of the unauthorized copy and (2) in the functions recording and playback of VTRs.

The television receiver, in response to horizontal and vertical modifications, erroneously performs horizontal and vertical return at an abnormal point. In the same way that a television receiver will misinterpret the signal, so can both the recording VTR when the dub is made and the playing VTR when the dubbing is played. In this case, it is the color circuitry of the VTR that is affected, with the resulting image degradation in addition to that caused by the basic anti-copy process. This is an additional effect to what has been described so far. This is due to the special way a VTR processes color information. Image distortions include inaccurate color rendering and intermittent or permanent loss of color. Thus, the modifications further destroy the entertainment value of the illegal copy, in addition to the degradation of image quality caused by the basic prior art copy protection process described above.

A third modification that can be made to the video signal involves narrowing the horizontal sync pulses. In combination with a copy-protected video signal that has reduced signal amplitude when re-recording (copying), this narrowing causes the detection of spurious vertical sync signals, by a VCR or television receiver, causing vertical return to occur in other than at the beginning of a field and thus further degrading the image quality. This modification narrows the width (duration) of the horizontal sync pulses on certain lines (such as lines 250-262) of the video field. These narrowed horizontal sync pulses, when combined with a video signal that is of reduced amplitude, trigger a spurious vertical return in many television receivers and VCRs, further degrading the displayed image. Narrowing the horizontal sync pulses where checkered patterns exist (lines 10-250) also increases the distortion of the checkered pattern when making an illegal copy.

Image quality degradation caused by methods of the invention has been found to be particularly useful where the basic prior art copy protection process provides relatively little image quality degradation or relatively little recording or playback degradation. of the VTR. Thus, combining the prior art process with the current process greatly reduces the entertainment value of illegal copying on a much larger combination of VCRs and television receivers than does the basic prior art process on its own.

Provision of the horizontal modification checkered pattern or vertical modification only in the overscan portion of the television picture ensures that when the original recording or signal is viewed there is no visibility of the vertical modification or checkered pattern, and actually its presence is not known to the viewer of the original recording.

In other embodiments, the user of the process could trade image area for effectiveness (the

ES 2 136 200 T5 user can choose to exchange visibility of the process when the “legal” recording is played to increase the anti-copy effectiveness of the process). Thus, the modifications can, by inflicting the broadcasting standards, extend to the visible portion of the video field but still be acceptable in many applications. Furthermore, in another embodiment, the process exchanges deviations from accepted signal standards to further increase anti-copy effectiveness.

In any case, the modified signal is normally displayed on any television receiver or monitor as long as the signal is of the correct amplitude. When the modified signal amplitude is reduced, as in illegal dubbing, conditions are optimized for the television receiver to visually present, or for a VTR to reproduce, a distorted image. This will occur in a copying situation between interconnected VTRs using two VTRs when the recording being copied (illegally) is provided with the basic anti-copy process, for example that of US Patent No. 4,631,603.

The above video signal modifications, in addition to causing horizontal or vertical lack of stability in a television receiver, also additionally have similar effects, as described above, on a typical VCR, both during recording and during playback. VTRs use the leading edge of the horizontal sync pulse to correctly position the color sync signal gate. If the color sync signal gate is positioned incorrectly, the color sync signal is not sampled properly and color loss or distorted color occurs. The horizontal modification causes misinterpretation of the position of the leading edge of the horizontal sync pulse. This will occur in VTRs involved in both recording and reproducing a copy (copy protected), resulting in color loss / distortion. This effect can also be caused independently on the television receiver. In the same way that a television receiver will tend to lose vertical interlock as a result of this process, so will a VTR. The result is a loss of lock of the head drum servo in the VTR.

The modifications described here ensure that the conditions required for maximum image breakdown are always present, rather than relying on the possibility (the particular image being displayed) that these conditions will occur. Thus, the above processes, which may include horizontal and / or vertical modifications and / or horizontal sync pulse narrowing, have substantial value in improving the basic prior art copy protection process, and more generally improve any copy protection process. copy protection that reduces the amplitude of the video signal that is recorded when an unauthorized copy is attempted.

Horizontal jitter with illegal video dubbing is to use post-horizontal pseudosync pulses of approximately -20 IRE (Institute of Radio Engineers) width (-40 IRE equals normal sync width) and width of approximately 1-2 ps varying in position approximately 1-2 ps after the color sync signal.

Although the embodiments are specifically described herein in the context of the NTSC television standard, they can be applied to the SECAM or PAL television standard with appropriate modification.

Embodiments of the present invention will be described hereinafter, by way of example, with reference to the accompanying drawings, in which:

Figures 1a and 1b respectively show a normal image and a modified image with a horizontal modification checkered pattern and the position of a vertical modification;

Figures 2a and 2b show an image resulting from a normal amplitude video signal, without and with a checkered pattern respectively;

Figures 3a, 3b and 3c show the image of Figures 2a and 2b respectively displayed on a television receiver with a video signal of reduced amplitude, without and with the checkered pattern and the vertical modification;

Figure 4 shows a portion of a video signal with a checkered pattern;

Figures 5a and 5b respectively show a portion of a video signal with a vertical modification not extended to the horizontal and vertical extinction range and with a vertical modification extended to the vertical extinction interval;

Figure 5c shows a further vertical modification extended to the horizontal extinction range;

Figures 6a, 6b and 6c show a circuit for modifying video signals according to an embodiment of the invention;

Figures 7a, 7b show waveforms illustrating the operation of the circuit of Figures 6a, 6b and 6c;

Figure 8 shows a detail of a flicker generator of the circuit of Figure 6b;

Figure 9 shows another embodiment of a circuit for modifying a video signal;

Figure 10 shows a prior art sync splitter circuit;

Figures 11a to 11o show waveforms illustrating horizontal sync pulse taper;

Figure 12a shows a block diagram of a horizontal sync pulse taper circuit;

Figure 12b shows waveforms illustrating the operation of the circuit of Figure 12a;

Figures 13a, 13b show an embodiment of a horizontal sync pulse taper circuit;

Figures 14a, 14b show block diagrams of an apparatus for combining sync pulse tapering with horizontal and vertical modifications of a video signal;

Figure 15 shows a circuit for improving a checkered pattern using post-sync pulses; and Figures 16a to 16e show waveforms illustrating the operation of the circuit of Figure 15.

Figure 1a shows a normal television picture 10 (without showing any real video information), that is, including the left and right overscan portions 14,16 and the overscan portions4.

ES 2 136 200 T5 upper and lower sweep 7.9. The part of the image within the dashed line 13 is the visible video 11.

The overscan portion of a television picture, as is well known, is the portion of the television picture not visible on a standard television receiver. Due to design limitations and aesthetic considerations, standard television receivers are adjusted by the manufacturer to display slightly less than 100% of the transmitted image area. The portions of the television image that are not normally visible are called the overscan area. These portions are viewable on a professional-grade video monitor with subscan capability. However, all standard television receivers operate in an overscan mode and therefore the added checkered pattern and the modified lines at the end of each field would not be visible on such standard television receivers as sold in the United States. and elsewhere.

Figure 1b shows a modified television picture 12 that also includes the overscan portions 14,16. In the right overscan portion 16, a checkered pattern 20 of alternating gray rectangles 24 and black rectangles 26 is arranged. This 24,26 checkered pattern information provides the copy protection enhancement as described later. In the display of image 12 on a standard television receiver, the checkered pattern 20 would not be seen since it is in the overscan area 16. The dumped signal modification is inserted into the lower overscan area 9 and is therefore also not visible.

Figure 2a shows a video field 30, including left and right overscan portions 32,34, with active video 36 including a vertical and horizontal picture element 38 (such as, for example, a cross). This field 30 is in accordance with the prior art and the checkered pattern and the vertical modification signal are not clearly included. This is also without any signal amplitude reduction, that is, without provision of the prior art copy protection process.

Figure 2b shows the field 30 with the addition of a checkered pattern 42 in the overscan area 34 outside the boundary 13, and with the addition of a vertical modification pattern 87 to the lower overscan portion 9. Since there is normal signal amplitude present, the frame pattern 42 and / or the vertical modification pattern 87 have no effect on the appearance of the cross 38 that is normally displayed. It is to be understood that Figure 2b is what would appear on a monitor showing the entire area and would not appear on a normal television receiver.

It is not possible to show a graphical representation of the effect of these signals on a VCR. A television receiver will visually exhibit effects due to abnormally low signal amplitude; VCRs used to record and reproduce the copy can also be affected. In this case, the VTR servo systems will be disturbed, producing images that are unstable in position.

Figure 3a shows an image produced by the reduced signal amplitude, that is, according to the prior art copy protection process, acting on a relatively insensitive VTR, but without the addition of the checkered pattern. This figure shows only the actual visible portion (within boundary 13 of Figures 2a, 2b) of the picture on a standard television receiver. As can be seen, the cross 38 is displayed normally because in this case the image content is such that there is no horizontal shift. This is a case where the prior art copy protection process provides inadequate copy protection because the image is visible.

Figure 3b shows the effect of the presence of the checkered pattern 42 of Figure 2b when the reduced signal amplitude is present, that is, when the prior art copy protection process is used in conjunction with the checkered pattern. Again, the overscan portion is not shown in Figure 3b. Here it can be seen that the cross 38 experiences multiple horizontal "tears" 43 that occur at the position of the transition from the gray rectangle 46 to the black rectangle 44 (and vice versa) of the checkered pattern 42 of Figure 2b. As shown in the enlarged view of Figure 3c, the portions 43 of the vertical portion of the cross 38 are displaced horizontally by an amount dependent on the distance between the left edge of the black portions 44 of the checkered pattern and the position of true horizontal sync signal on each line (not shown). Clearly, the image 50 of Figure 3b is substantially degraded. The effect is further increased (not shown) by raising or lowering the checkered pattern 42 slowly in the vertical direction so that the horizontal displacements are seen to move, ie, "ripple." This provides a virtually unobservable image correctly and therefore substantial copy protection.

The checkered pattern 42 of Figure 2b typically includes five black rectangles 44, each alternating with one of the medium gray rectangles 46 (fewer such rectangles are shown in Figure 2b for clarity). Maximum image degradation has been found to occur with five gray-to-black transitions and five black-to-gray transitions approximately per image height.

The signal level of the black rectangles 44 is adjusted to be between the decay level and the black level for NTSC signals (the black level and the decay level are the same for PAL or SECAM signals), and at the black for PAL and SECAM, and the width of the middle gray rectangles 46 is about 30% of the maximum white level. The checkered pattern 42 produces the zigzag pattern as shown in Figure 3b. In alternative embodiments, there could be only one black rectangle 44 or two, three, four, or more black rectangles 44 per field 30 of Figure 2b. Also, the sizes (heights and widths) of the black rectangles 44 need not be uniform.

The process causes anticipated horizontal return in an environment of reduced video signal amplitude by providing a variable transition in the negative direction, that is, from the instantaneous image level at the starting point of the black rectangles 44 to the black level before the signal signals. horizontal sync in at least certain lines of the image. The checkered pattern 42 shown in Figure 2b is such a pattern that causes the intended effect.

The typical duration (width) of the Checkered 42 is approximately 1.0 to 2.5 microseconds,

ES 2 136 200 T5 as determined by the requirement that the checkered pattern is not normally inserted into the displayed portion of a standard television picture, that is, it is limited to the overscan portion, and does not encroach on the extinction period normal horizontal.

In other embodiments, the horizontal sync pulse is narrowed allowing the checkered pattern to be wider. This would provide a greater horizontal shift when viewing the reduced amplitude video signal but produces an original non-standard video signal which is, however, acceptable for certain non-broadcast applications. Also, the particular amplitudes of the medium gray rectangles 46 and / or the black rectangles 44 need not be exactly as described above. Any effects produced by the changed relative position of the leading edge of the horizontal sync pulse and the color sync pulse can be corrected by a corresponding relocation and / or expansion of the color sync signal.

Figure 4 shows the horizontal decay interval 60 for a single video line, with a portion of the checkered pattern present. The horizontal sync pulse 62 conventionally begins 1.5 microseconds after the beginning of the horizontal decay interval 60. Active video 66, 68 occurs both before and after the horizontal decay interval 60. However, in accordance with the invention, a portion 70 of active video 66, just prior to the horizontal decay interval 60, has been replaced by a medium gray level signal 74 or by a black level signal 76 (the level 74 gray and 76 black level are both shown in Figure 4 for illustration purposes only). Losing portion 70 of active video 66 is not problematic since, as explained above, in a standard television receiver this active video portion is not visible anyway, being in the overscan portion of the picture.

The transition 80 from active video level 66 down to black level 76 appears to the television receiver as a horizontal sync signal. This effect (as explained above) only occurs when the video signal being displayed has been reduced in amplitude due to the copy protection process.

The presence of gray level 74 (the gray portions of the checkered pattern) further ensures that the entire image is not shifted to the right. This would be the case if, for example, there was a continuous black streak running down the right side of the image. The alternating levels of gray and black provide the zigzag effect shown in Figure 3b, which has been found to be intolerable to vision by virtually any individual. Also shown in Figure 4 is a conventional color sync signal 82 going over the back plateau 84 of the horizontal decay interval 60.

In Figure 4 it will be appreciated that the only modification to the video signal is the deletion of the small portion 70 of active video and the consequent replacement by the gray level 74 or the black level 76.

The increase in image waviness described above causes the checkered pattern to move slowly from the bottom to the bottom of the image or vice versa. It is found that if this requires about a second for a given transition to shift from the bottom of the image to the top of the image or vice versa, this causes an optimal reduction in the entertainment value of the image. This moving ripple effect is provided by using a rectangular wave frequency, which is generated by the checkered pattern, that is slightly off the fifth harmonic of the field frequency, that is between 295 Hz and 305 Hz, for NTSC television. The corresponding frequency for PAL or SECAM systems is 245 to 255 Hz. This out of sync provides the desired slow motion of the checkered pattern. As noted earlier, even though such a lack of synchronism is not present and the checkered pattern is static, there is still substantial benefit due to the present process. The frequency of the signal generated by the checkered pattern can be adjusted to maximize image quality degradation when the low-amplitude signal is reproduced and displayed. Frequencies between 180 and 360 Hz for NTSC and between 150 and 300 Hz for PAL (3 to 5 times the field frequency) typically produce an optimal effect. The frequency can be varied over time to ensure optimal effect on various viewing and playback equipment.

The checkered pattern does not need to be present in all fields.

The above description is directed to horizontal image information; the video signal modification and the consequent effect of this modification are in the horizontal image direction. Vertical information modification can also be provided and can take various forms. In one embodiment, groups of 1 to 4 lines in the lower overscan portion of a video field have their active video alternately substituted for black or white. In another embodiment, the last few lines of video immediately before the vertical sync pulse are extinguished, as are the first few lines of the next vertical decay interval, and the original video image and the vertical sync pulse in it are replaced by a high level signal (such as the middle gray level which is about 30% of the maximum white level, or the actual maximum white) or by a low level signal (in the range of the black level decreasing to the extinction level) as shown at 87 in Figures 1b, 2b and described above.

These vertical modifications are not normally visible to the viewer since the modified active video lines are restricted to the lines that fall in the overscan area 9 at the bottom of the image in Figure 1b (likewise, the modified lines will be in a position similar to the head switching point when considering video from the VTR, and the video on these lines is unusable in any case as a result of disturbances produced at, and after, the head switching point).

In a standard NTSC video signal (or other standards), as is well known, each of the first three lines of the vertical decay interval includes two equalization pulses, and each of the next three lines includes two “wide” pulses of Vertical Sync. Typically, the vertical return begins shortly after the first of these vertical sync pulses.

IS 2 136 200 T5

The first vertical modification embodiment is shown in Figure 5a (the line numbers here refer to the second field of an NTSC video frame). Lines 517,518,519 have their active video portions replaced by a maximum white level signal (1.0 volt nominal); the same is done on lines 523,524,525. On lines 520,521,522, the active video is replaced by a black signal (0 volts nominal). Instead of groups of three lines, the groups can be 0 to 5 or more lines, and the black and white signals can be amplitude modulated or switched. Thus, in the last several lines of each field, the pattern of the black and white signals dynamically changes between fields.

The second embodiment of vertical modification (Figure 5b) extinguishes the last two lines of active video (lines 524 and 525 for example) in a video field and the first three lines (lines 1,2,3 for example) of the interval of vertical extinction that follows immediately. These two active lines are in the lower overscan portion 9 (Figure 1b) of the television picture. Then, a mid-gray video signal 87 (30% of the maximum white level) is generated and inserted into these five suppressed lines on a periodic basis. When the mid-gray signal is not activated (indicated by vertical arrows on lines 524, ...., 3), these extinguished lines "trick" the vertical sync circuitry of most television receivers into performing the vertical return to the beginning of the first of these five lines, rather than five lines later usually to the beginning of the vertical sync pulses. Thus, the vertical return is advanced by five lines. When these five lines are in the middle gray, the vertical return is initiated in its proper position by the normal vertical sync. It is to be understood that the number of such quenched lines and the amplitude of the inserted waveform may vary in other embodiments.

As shown in Figure 5b, lines 4-6 (only lines 1-4 are shown) are as in a standard signal, as are lines 517 to 523. The modification is only in lines 524,525,1,2 and 3; the active video portions of lines 524,525 and the corresponding portions of lines 1-3 are either suppressed (to black) or have a mid-gray signal of about 0.3 volts inserted (it is to be understood that this amplitude is nominal, without consider the amplitude reduction effect of the associated prior art copy protection process). Figure 5b shows a portion of a field with the medium gray level. As stated above, the gray signal turns on and off ("wobbles") at a frequency between 1 Hz and 10 Hz typically. In the 1 Hz version, there are 30 consecutive video fields with five lines having active video at the blanking level, followed by 30 consecutive video fields with all five lines in the 30% gray in Figure 5b. As shown in Figure 5b, the color sync signal may (or may not) be extinguished at lines 524 to 3.

This oscillation causes the image to "jump" up and down in 5 lines, once per second (the frequency of oscillation), which has been found to be extremely irritating to the viewer as suggested by "x" in the picture. Figure 3b. That is, in the fields where the vertical modification of Figure 5b is present, the vertical return occurs early in five lines, followed by the fields where the vertical return normally occurs. The early vertical return occurs because the total video amplitude has been reduced for example, to a maximum (maximum white level at sync peak) of 0.4 volts from the 1.0 volts of the NTSC standard due to the presence of prior art copy protection signals. The vertical sync signal separator of the television receiver then senses that the first of the five extinguished lines is the first vertical sync pulse (wide) and thus returns vertically shortly thereafter.

In another version of the vertical modification (not shown), instead of the last two lines of a field and the first three lines of the next field being modified as in Figure 5b, the modification is entirely in the last five lines (lines 521,522,523,524,525 ) of active video from a field, this avoids producing an “illegal” (non-standard) video signal. A variation of this vertical modification is to relocate about three lines or more like lines 524,525, in Figure 5b, in lines after the vertical sync area (ie, lines 22-24). In some television receivers, this causes additional hopping because the television receiver "sees" two vertical sync pulses, one at the correct time, ie line 4, and one at line 23 approximately.

It is to be understood that the vertical shift need not span the entire active video portion of a horizontal line. It has been found that providing about 1/2 modification of the active video duration in one line is sufficient to generate the premature vertical return.

In yet another embodiment of the vertical modification (similar in many respects to that of Figure 5a) as shown in Figure 5c, the horizontal extinction interval is removed (suppressed) at lines 517, 518, 519, 523,524,525 where add the white impulses. Therefore (like the one in Figure 5b), this is also an “illegal” (non-standard) video signal, but it is acceptable for many non-broadcast applications. Eliminating horizontal decay in these lines increases the automatic gain control gain reduction (in VTR automatic gain control circuits). Target pulses on lines 517,518,519 and 523,524,525 can be present in each field or be amplitude modulated or switched. Furthermore, these target pulsed lines can change positions on a few lines from field to field or some multiple of field frequency to produce vertical blur effects when an illegal copy is made and viewed on a television receiver. Groups of target pulses can extend over zero to four lines.

Vertical modifications in the video signal have no effect when applied to a television monitor as part of an original (authorized) signal. However, if the video signal amplitude is sufficiently reduced, for example by an anti-copy process, the television monitor will tend to incorrectly detect the vertical sync information, resulting in vertical instability as described above.

Also, if the vertically shifted signal is applied to a VTR in conjunction with a pro7

ES 2 136 200 T5 anticopying process that produces a video signal of reduced amplitude inside the recording VTR, when a recording is made, the servo of the head drum of the VTR will tend to be disturbed. This is because VTRs typically require a "clean" vertical sync signal to maintain correct phase, and the presence of a fluctuating vertical sync signal causes the VTR to lose its target. When the recording is played back, the visible effect is vertical jitter in the picture plus intermittent noise bands that appear when the head drum servo loses lock (this is similar to a variable tracking error).

In other words, the vertical frequency waveform modifications work in a similar way as the horizontal frequency waveform modification described above, except that vertical rather than horizontal disturbances occur. The two techniques combined are more effective in terms of image quality degradation than either one by itself. Sweeping the pulse frequency of vertical waveforms increases the effectiveness of more television receivers, that is, the frequency is varied between 2 Hz and 10 Hz, for example, over a period of about 20 seconds. The sweep of the checkered pattern frequencies will also cause the horizontal tear to go up and down producing a more irritating image when making an illegal copy.

In Figure 6a the circuit for inserting the horizontal and vertical modifications described above is shown in block form.

The main video signal path includes an input level clamp amplifier A1, a sync pulse taper circuit 96, a mixer point 98 at which the waveform components of the horizontal modifying frame and waveform are added. vertical modification (which produce jitter) and a line-out drive amplifier A2. In this case, also the input video signal to the circuit of Figure 6a can have the last nine lines of each field extinguished to a reference level. US Patent No. 4,695,901 shows an extinguishing switch circuit.

The process control and signal generation path includes a synchronization signal separator 100, control circuit 102, circuitry (see Figure 6b) for generating the required signal voltages to be added to the main video signal, and a system 104 switch selection (Figure 6a) that applies the required signal voltages under the control of the control circuit 102 (note that in the drawings certain part designations, for example U1, R1, OS1, A1, they are repeated from time to time for certain components; these are not intended to represent identical components unless explicitly stated).

The input video is restored in direct current by the input video level clamping amplifier A1 (the amplifier A1 is a commercially available component, for example the Elantec EL2090). Amplifier A1 ensures that the video signal (on extinction) is at a known predetermined direct current level before adding any additional waveform components to that video signal.

The resulting level-locked video signal is applied to mixer point 98 with a source impedance Ro, typically greater than 1,000 ohms. The added pulse signals to be injected are applied to mixer point 98 with a source impedance of less than 50 ohms. When it is necessary to modify the input video signal, for example with a checkered pattern component, the appropriate signal is selected and applied to the mixer point with a low source impedance, which overlaps the input video signal from amplifier A1 and replaces effectively the input video signal by the required signal. When the input signal is to remain unchanged, all switch elements 104 are in the open state, with the result that the video signal passes unchanged to the output line drive amplifier A2. The resulting video signal at mixer point 98 is applied to line drive amplifier A2 to supply standard output signal level and output impedance. An output of the video signal level clamp amplifier A1 is applied to the sync signal splitter 100 (this is a commonly available component, for example the LM 1881 from National Semiconductor). The sync signal separator 100 supplies the composite sync pulses and the frame identification signal required by the process control circuit 102.

The process control circuit 102 generates the control signals to turn on the signal selection switches 104 at the precise point in time (and for the required time) that the various signals are to replace the input video signal.

All the various signals that are to replace the original video signal (input) consist of a high or low level of steady state direct current signal. For example, the checkered pattern "high" signal is a medium gray level, typically about 30% of the maximum white level; the checkered pattern “low” signal is the black level or extinction level. These various levels of signals are generated (see Figure 6b) from potentiometers VRi, VR₂, VR₃, VR₄ supplying adjustable levels of signals (or alternatively from voltage divider resistors for fixed preset signal levels) connected between appropriate supply voltage lines. This signal is applied to the appropriate selection switch elements, 104-1, 104-2, 104-3 and 104-4 respectively, via the unity gain operational amplifiers A5 to ensure the necessary low output impedance within the mixing point 98.

The control circuit 102 generates the appropriate switch select control pulses for the checkered pattern and the vertical shift signals (see Figure 6a). Checkered pattern pulses apply only to selected lines; An example is starting the checkered pattern on the 10th line that contains image information (that is, after the end of the vertical extinction) and ending it 10 lines before the last line that contains image information (that is, 10 lines before of the beginning of the successive interval of vertical extinction). Similarly, the jitter modification signals are to be applied only to selected lines, for example the last nine lines before the vertical decay interval. Therefore, both the checkered pattern and vertical modification signals re8

ES 2 136 200 T5 want control signals with both horizontal and vertical frequency components.

The input video signal "video input" (see Figure 6c showing the detail of Figure 6a) is separated by the amplifier A3 and coupled to the synchronization signal separator via the coupling capacitor C1 and a pass filter. low which includes resistor R1 and capacitor C2. The sync signal splitter 100 supplies composite sync pulses and frame identification square wave signals. The compound sync pulses are applied to a phase locked loop 110. The phase control (“phase adjustment”) of the phase lock loop 110, which uses the VR potentiometer₆, is set so that the horizontal frequency output pulse starts at the required starting point of the checkered pattern, typically 2 ps before the onset of horizontal decay (Figure 7a). The output signal of the phase locked loop 110 is used to derive the f component_H horizontal frequency of both checkered pattern and vertical shift signals. The color sync signal gate output signal from the sync signal splitter 100 is inverted by the inverter U5 which supplies a clamp pulse to the clamp amplifier A1 (component number EL2090).

The frame identification square wave output ("frame pulse") from the sync signal splitter 100 is applied to a one-shot circuit OS1 to supply a frame identification pulse of approximately 1 ps duration. This signal f_V Monostable circuit output is used to derive the vertical frequency component of both checkered pattern and vertical shift signals. The horizontal frequency phase locked loop component fH from phase locked loop 110 is applied to the clock input terminal of a memory address counter 114. The frame rate (vertical) monostable output signal fV is applied to the counter reset input RS terminal 114. The output signals from memory address counter 114 are applied to memory 116, typically an erasable programmable read only memory (EPROM) that is programmed such that one of its data line output terminals supplies a checkered pattern pulse enable CPE signal (CPE signal: Checker pulse enable signal = checker pulse enable signal) which is high during that portion of the picture period in which the checker signal is to be present. A second EPROM memory data line output terminal supplies an EFI signal: end-of-field identification signal that is high during lines at the end. of each field that will have to include vertical modification signs.

The horizontal frequency latching loop component fH is also applied to an OS2 monostable circuit that generates an end-of-line pulse (ELP: end-of-line pulse) of the required duration of checkered pattern pulses, typically 2 ps (see Figure 7a).

The horizontal frequency phase locked loop output signal fH is also applied to another OS3 monostable circuit, supplying an output pulse of approximately 13 ps duration. The output of the OS3 monostable circuit triggers another OS4 monostable circuit with an output VJP pulse (VJP pulse: vertical jitter position pulse = vertical jitter position pulse) of approximate duration of 52 ps. The timing and duration of the VJP pulse define the position of the signal that produces the vertical modification within the line time; that is, the VJP pulse is essentially active during the desired portion of the horizontal line active period.

The four signals ELP, VJP, CPE and EFI generate the control signals required for the signal selection switches 104-1, ...., 104-4 (see Figure 6b). The end-of-line pulse ELP is applied to a divider circuit 122 to derive the desired frequency to determine the frequency of the checkered pattern. The higher this frequency, the greater the number of dark-light-dark transitions of the checkered pattern per image height. This frequency can be chosen within a wide range; a 52 divisor relation (n = 52) provides a useful result. The output signal from divider 122 is applied directly to an input terminal of the 3-input AND-type logic gate U4. An inverted output signal from divider 122 is applied to the corresponding input terminal of the second 3-input AND-type logic gate U5. The output portion of divider 122 may be a sweep oscillator circuit comprised of a pair of NE566 integrated circuits. One NE566 circuit is nominally set to 300 Hz and the other is set to 1 Hz. The output of the 1 Hz NE566 circuit is fed to the frequency control input of the 300 Hz NE566 circuit. Both U4, U5 3-input AND type logic gates have the checkered pattern pulse enable CPE and end-of-line pulse ELP signals applied to their other two input terminals. The result is a high checker control signal (HVJ signal: high checker control signal) at the output terminal of the 3-input AND-type logic gate U4, and a signal LVJ low checker control signal (LVJ signal: low checker control signal) at the output of the 3-input AND-type logic gate U5.

A similar arrangement generates the signals required for the vertical modification control signals. An oscillator 126 (such as commercially available component number NE555 or NE566) is configured to operate at low frequencies, typically between direct current and 10 Hz. Oscillator 126 can be set to a high logic level output. Similarly, the 10 Hz DC signal output can be swept over a range of frequencies to disturb as many television receivers as possible during the reproduction of an illegal copy. This can be done as described above with a pair of NE566 ICs. The output signal of oscillator 126 is applied to an input of a 3-input AND-type logic gate U2. An inverted output signal from oscillator 126 is applied to the corresponding input terminal of a second 3-input AND-type logic gate U3. Also, each TV receiver can “resonate” or fluctuate more at unique frequencies by sweeping the frequencies of oscillator 126, ensuring wide reception coverage.

ES 2 136 200 T5 different television sets. The end of field identification EFI and vertical jitter position signals VJP (with the EFI signal modified by flicker generator 130, and thus designated EFI ') are applied to the other two input terminals of the logic gates U2, U3 type Y with 3 inputs. The result is a high vertical jitter control signal EFCH (EFCH signal: high vertical jitter control signal) at the output terminal of the 3-input AND-type logic gate U2, and an EFCL signal vertical jitter control signal (EFCL signal: low vertical jitter control signal) at the output of the 3-input AND-type logic gate U3.

It will be understood that, with suitable modifications, the above apparatus will produce the horizontal or vertical modifications added after the normal horizontal or vertical sync signals, for example for the vertical modifications added on lines 22-24 of an NTSC television signal, at in order to cause a video return.

The circuit of Figure 6b in conjunction with the flicker generator circuit 130 via the signal EFI 'produces multiple patterns of vertical modification signals.

Figure 6b shows the field or frame "flicker characteristic" generator 130 used in certain embodiments of the invention to modify horizontal and vertical modifications.

This flicker feature achieves the following:

1) Change the “polarity”, that is, invert the gray rectangles with respect to the black rectangles of the checkered pattern at some particular multiple of the field frequency; this will cause, for example, attenuated video from an unauthorized copy to be interspersed with the frame pattern shift, further degrading the correct viewability of the copy.

2) A field-by-field change in the position of the end-of-field pulses (vertical shift) causes the unauthorized copy to reproduce a fluctuating up / down blur on a television receiver because each field has a pulse position of pseudocritical timing timed differently. For example, this is achieved if:

the EFI boost is high on lines 255257, and the EFI1 boost is high on lines 258260, and the EFI2 boost is high on lines 261262 and 1, and the EFI3 boost is high on lines 21-23.

Figure 8 shows the flicker generator 130 circuit of Figure 6b and shows that these four pulses are multiplexed via multiplexer U10 (that is, a CD4052) with a field frequency by EPROM memory U8 (component number 27C16 or 2716). As a result, the pseudo-vertical sync pulses occur at different positions depending on the field. In a simple example, the EFI, EFI1, EFI2, EFI3 pulses are stepped once per field. As a result, during the reproduction of an unauthorized copy, the pseudo-vertical synchronization occurs on lines 256 or 259 or 262 or 22 in successive fields or frames. As a result, the image flickers due to field frequency vertical sync relocation on the TV or VCR. The EPROM U8 provides flexibility regarding where the various end-of-field pulses are to be located as a function of time.

Figure 8 also shows how the black rectangles relative to the gray rectangles of the checkered pattern are inverted at some particular multiple of the field frequency. The vertical sync pulses time on the 8-bit counter U7 (divide by 256, component number 74HC393). The outputs of the counter U7 drive the address lines of the EPROM U8. The data output signal DO of the EPROM U8 memory goes high to invert the checkered pattern via the switches SW1K, SW2K. The flexibility of the DO signal from the EPROM U8 memory allows reversal orders in the checkered pattern to occur pseudo-randomly or periodically, and also allows different blink rates (i.e. every 2 fields or every 5 fields, etc.) . Lines Di and D₂ The data streams in EPROM U8 also drive multiplexer-switch U10 (component number CD4052), similarly enhancing the flexibility to generate the output EFI 'signal.

In Figure 6b, the end-of-field and end-of-line pulses are connected to cancel the video driving resistor Ro. Unless these switches have fairly low "make" resistance, video from the input program source will always overlap on top of the end of field or end of line pulses. For example, a typical analog connection resistance is approximately 100 ohms. Typical resistance Ro is approximately 1,000 ohms. With these values, 10% of the video is superimposed on the end of line and end of field pulses. If the video goes to the maximum white level, the end of field and end of line pulses will have a minimum of about 10% of the maximum white level (100 IRE) or 10 IRE, thus rendering these added pulses useless.

To overcome these possible shortcomings, in another embodiment the added pulses are added together and then switched on via multipole switches which at the same time switch off the video source.

As shown in Figure 9, the end-of-field high and low states are generated by the AND-type logic gate U23 with input from the U22 oscillator (a 0.1 Hz to 10 Hz oscillator) and the VJP and EFI signals. input. The switch SW103 switches between the high and low states controlled by the variable resistors R_B and R_TO respectively. The A10A, A10B amplifiers are unity gain crossover amplifiers. To insure against checkered pattern and end-of-field EOF pulse low-state crosstalk, switch SW103A is connected between switch S103 and amplifier A100, and switch SW102A is connected between switch SW102 and amplifier A101. The U23A Y-type logic gate controls the SW103A switch to ground on all lines other than the EOF end-of-field line positions. Likewise, the logic gate U21A controls the

ES 2 136 200 T5 SW102A switch to ground at all times other than when the checkered pattern pulses are active. Otherwise, switches SW103 and SW102A are transparent to the EOF and checkered pattern end-of-field pulses from switches SW103 and SW102, respectively. The output of switch SW103 is separated by unity gain crossover amplifier A100 and summed in summing amplifier A102. Similarly, switch SW102 receives the high, low end-of-line states generated via the end-of-line pulse signal ELP, counter U20 (a divide-by-n counter), and the pulse enable signal CPE of checkered pattern.

Variable resistors R_C and R_D provide adjustment for the high and low end-of-line pulses respectively. Amplifier A101 separates the input of switch SW102 to summing amplifier A102 via resistor R2. Amplifier A102 powers summing amplifier A103. The post-pseudosync pulse PPS (PPS pulse: post pseudo-sync pulse = post-pseudo-sync pulse) is also summed in summing amplifier A103. Then, the output of the summing amplifier A103 is: end-of-line pulses, end-of-field pulses and post-pseudo-sync PPS pulse. The switch SW101 connects all these impulses via logic gate U10 type OR and inverter U11 during their coinciding moments, and connects the video at all other moments. Amplifier A104 separates the output of switch SW101 and supplies a video signal output "video output" containing video with the added pulses. The switch SW104A pre-extinguishes the video from the synchronization pulse narrowing circuit to a voltage extinction level VBLNK (that is, 0 IRE) for the last 9 active lines of each television field via logic gate type U104B Y. The logic gate U104B has the end-of-field output signal EFO (going high during the last 9 lines of the television field), the EPROM memory data output signal, and the VJP (horizontal line pulse active) signal at its two entrances.

A position modulation source for the post-pseudosync pulse PPS is controlled by the voltage source Vgen. The source Vgen feeds the resistor R20 with an inverted chromatic synchronization signal gate pulse into the resistor R10 and the capacitor C2 to form a variable delay into the monostable circuit U20. The monostable circuit U20 is approximately 1.5 ps of variable position after the color sync signal of the input video signal, and it is output controlled during the vertical extension interval by the CPE signal and the logic gate U21B type NO-Y . Resistor R6 determines the amplitude of the post-pseudosync pulse PPS. Resistor R6 is typically set from -10IRE to -20IRE. The other input (U22A) of the NO-AND type logic gate U21B is normally high so that the entire post-pseudosync PPS pulse is a constant amplitude pulse position sync. If U22A is pulsatile (i.e. 300 Hz), then the PPS pulse signal is turning on and off as well (at 300 Hz). Thus, the PPS pulse can be a position modulated pulse, and pulse width modulated sync pulse after the color sync signal.

A sync pulse taper circuit and method for enhancing copy protection of video signals is used by itself or in series (as shown at block 96 of Figure 6a) with any of the signal modification techniques described above. The reason for narrowing the video signal sync pulses (mainly horizontal sync pulses) is that, when illegal copying, attenuated video signal with reduced sync pulse width (duration) causes a reproducibility problem when viewed in a television receiver. This is because most television receiver sync pulse separators incorporate dc restoration of sync peaks. Since these television receiver sync pulse dividers are typically driven by medium impedances, the sync pulses are partially offset. By narrowing the sync pulses, these sync pulses are further lowered. When an unauthorized copy of the video signal is made, especially with the checkered pattern and / or end of field modification signal described above, the copy has a reduced amplitude video signal with reduced sync pulse width. As a result, the television sync signal splitter sees a strong loss of sync due to its own offset from the narrowed sync pulse width and attenuation of the video signal itself. Thus, the synchronization signal separator of the television receiver does not properly "extract" the synchronization signals and this causes the television picture to be seen even worse because the effects of horizontal and / or vertical modifications are more intense.

Figure 10 shows a typical prior art sync signal splitter as used in many television receivers. This circuit works when the inverted video signal is fed to the transmitter base Q1 via a coupling capacitor C. The peaks of sync pulses in the video signal charge capacitor C just enough so that only the same peak of the sync pulses turns on the transistor. The resistor R_b it biases the transistor so that the sync pulse peaks are "cut off." Voltage V_c between terminals of capacitor C is related to resistance Ro, the excitation resistance of the video signal. The higher the resistance Ro, the greater the amount of sync pulse descretion seen in Vb. If the resistance Ro is too large, the transistor Q1 will start clipping of sync pulses in the video region (decay level), because the value of Vc is not loaded to a medium level to allow a cutoff of the transistor current together below the level of sync pulse peaks of the inverted video signal.

The insufficient charge of the capacitor C allows the transistor Q1 to be activated even though it reaches the extinction level. The base-emitter impedance of transistor Q1 is low when transistor Q1 is on (this causes attenuation of the variable sync pulses in the positive direction). As the load of the

ES 2 136 200 T5 capacitor C is a function of the width of the sync pulses, the narrowing of the sync pulses causes the sync pulse separator to cut off a portion of the narrowed sync pulses more than a normal pulse width sync. This is equivalent to cutting the sync pulses closer to the video signal (ie, video signal decay level). At normal video signal levels, a narrowed sync pulse does not present reproducibility problems on a VCR or television. But when a narrowed sync pulse is recorded on an illegal copy of a copy-protected cassette, the video signal is attenuated. This attenuation with the narrowed sync pulses causes the television (during playback viewing) to not reliably extract the sync pulses and instead desynchronize parts of the video signal, i.e. level off.

Selectively narrow certain horizontal sync pulses to near-zero pulse widths (up to a duration less than 600 ns) so that the filter in a TV or VCR sync splitter is unresponsive or that the coupling capacitor of the tape cutter is unresponsive. sync signals to be loaded negligibly is equivalent to no sync pulse in that area. These selected narrowed horizontal sync pulses near the end of the field can create a situation such that the sync splitter will cut a dead video line as a new vertical (spurious) pulse during playback. With a video signal from an illegal copy with attenuated video supplied to the television, then this situation causes the VCR or television to see two vertical pulses in one field, which can cause vertical jitter.

In one embodiment, the pulse frequencies (modulation) of the video end-of-field lines (the end-of-field lines having an amplitude of 0 IRE to at least 10 IRE having narrowed horizontal sync pulses) are swept from 1 Hz at approximately 15 Hz. This conveniently has the desired effect on a wide variety of television receivers.

Figure 11a shows a video signal waveform (Vin); This is the inverse of the video that enters the TV sync separator circuit in Figure 10, and is coupled to resistor Ro (where Ro ~ 0) in Figure 10. Figure 11b shows the effect of capacitor C of coupling and resistor R_b. Note in Vb that the video signal ramps up towards the Crete level of sync pulses (this is a result of the RC time constant of resistor Rb and capacitor C since Rb >> Ro).

Figure 11c shows narrowed horizontal sync pulses. The action of resistor Ro (where Ro is now a medium resistance, that is, 200 to 1,500 ohms), capacitor C, resistor Rb, and transistor Q1 cause the clipping action of the narrowed peak of sync pulses. Since the sync pulse widths are smaller, capacitor C does not charge sufficiently and causes more sync pulse descress. Recall that the charge on capacitor C is related to both the sync pulse width and its pulse width, that is, Vc is proportional to the sync pulse width multiplied by the sync pulse width. The lower the voltage Vc, the greater the declining action of the synchronization pulses. Figure 11d shows this result at point Vb in Figure 10.

Figure 11e shows an attenuated source video signal from an illegal copy with narrowed sync pulses, where "A" indicates the presence of the checkered pattern pulses. The sync pulse separator responds by clipping the sync pulses completely and, as a result, parts of the video towards the end of the line are interpreted as new sync pulses. Figure 11f shows this. The sync pulse separator (inverter) transistor Q1 turns on during the clipped portion of the video signal.

Figure 11g shows that by cutting off parts of the video signal, the leading edge of the sync pulse becomes unstable. This instability on the leading edge of the sync splitter causes the television to display an unstable picture (that is, wobbling from side to side). As shown by the arrows, the resulting unstable horizontal sync pulses are caused by narrowing of sync pulses or by checkered pattern pulses.

Figure 11h shows what the television sync separator output would have been for Figure 11d, which is a full level television signal with narrowed sync pulses. Thus, the signal of Figure 11d does not pose reproducibility problems for a television receiver. Only when the signal of FIG. 11d is added to a copy protection signal and an illegal copy is made, reproducibility problems are evident in the television receiver because the illegal copy produces a attenuated signal.

Figure 11i shows, with an unattenuated full television signal, that if lines selected near the end of a video field or after vertical sync pulses (i.e. NTSC standard lines 256259, lines 10-12 ) are narrowed with variable amplitude (that is, switching from the extinction level approximately to 10-100 IRE approximately), the transistor Q1 of the synchronization signal separator will begin to ramp up until it cuts within the image area, that is, "ZZ" of Figure 11j. This causes a wider pulse in the “ZZ” area but not wide enough to cause a vertical sync pulse.

Figure 11k shows the output of the sync splitter of the waveform of Figure 11j. If this waveform is to be accompanied by copy protection signals, the illegal copy will supply an attenuated signal to the TV sync signal splitter as in Figure

11l. Figure 11l is a television signal attenuated due to illegal dubbing with narrowed sync pulses accompanying the end-of-field lines.

Figure 11m shows the ramping action at point Vb via resistor Rb and capacitor C. The corresponding output of the sync splitter shows at "y" a

ES 2 136 200 T5 new pulse (spurious) wide (vertical sync). This new pseudo-vertical sync pulse has been created when the narrowed horizontal sync pulses are with the end-of-field lines at the extinction level. When the narrowed horizontal sync pulses are accompanied by a level from 10 to 100 IRE, the television sync splitter produces only narrow horizontal frequency sync pulses, and no new wide pulses. This is because the 10 to 100 IRE levels are totally ignored by the sync splitter. By turning on and off signals of extinction and greater than 10 IRE units, the sync signal splitter sees normal vertical sync sometimes followed by an early or delayed spurious vertical sync pulse (see Figure 11n). These spurious early and / or delayed vertical sync pulses then cause the television picture to fluctuate up and down when an illegal copy is played.

In some cases, to obtain the same effect above, you can:

Narrowing the selected sync pulses to about zero, that is, eliminating the horizontal sync pulse in order to cause the television sync signal splitter to form a spurious vertical sync pulse.

Relocate a few sync pulses with periods greater than 63.5 ps to cause the sync splitter to malfunction and form a new spurious vertical sync pulse. This causes the ramping action of some sync splitters to produce spurious vertical pulses.

Figure 11 shows a video signal that is free of spurious vertical sync pulses because a video signal is above the extinction level, that is, greater than about 10 IRE units in the area of ​​the narrowed pulses. Thus, if the video signal level is high enough relative to the decay level, the presence of narrowed horizontal sync pulses fails to generate a spurious vertical sync pulse.

As shown in the sync pulse taper circuit of Figure 12a, the input video signal (possibly already carrying the basic copy protection pulses) is input to terminal 160 where it is supplied to sync signal splitter 162 and also to video adder 164. Sync signal separator 162 draws separate horizontal sync (H sync) and vertical sync (V sync) signals to electronic line selector gate 166 which selects, for example, lines 10 to 250 from each video field. The separate horizontal sync pulses are also supplied to an OS10 monostable circuit which, in response, draws a signal of approximately 2 ps duration to the Y-type logic gate U12, the input of which is a line select signal indicating the lines. selected 10 to 250 from electronic gate 166. In response, the AND-type logic gate U12 draws a signal representing a horizontal sync portion on each of these lines 10 to 250, which is scaled by the amplifier 174. The output of the scaling amplifier 174 becomes to be added to the original video signal at adder 164, the output of which is supplied to video output terminal 180.

Figure 12b shows a representation of the waveform at the Q point of Figure 12a (the conventional horizontal sync signal with color sync signal) and the signal at R that is the output of the scale-change amplifier 174. The summed result of Q and R ("video out" at the bottom of Figure 12b) is seen at the video output terminal 180, which is a shortened horizontal sync pulse with a color sync signal.

Hereinafter, another circuit for realizing the extended envelope sync pulse narrowing of the color sync signal is described (the extended color sync signal is necessary to ensure color fixation for television receivers if the narrowed horizontal sync pulses cause a color fixation problem). Figures 13a, 13b show a circuit for introducing narrowed horizontal sync pulses throughout the active video field. Within this active field, an EPROM memory data output determines which lines are further narrowed. For example, this EPROM memory output EPD1 can allow lines 20-250 to have a sync pulse width of 3.7 ps, while lines 251-262 have a sync pulse width of 2.0 . Other combinations are possible depending on the programming of the EPD1 output in the EPROM U9 memory. Likewise, another output from the EPROM U9 memory can cause synchronization suppression on the lines (that is, lines 255 and / or 257) or so, before the position of the end-of-field pulses (this is done via the logic gate U10 type AND and the output EPD2 of the EPROM memory U9). Repositioned horizontal sync narrowed timing is also possible after sync suppression is performed in the normal horizontal decay range.

The input video carrying any combinations of: the basic anti-copy process, end-of-field pulses and checkered pattern process, or normal RS170 type video, is restored in DC synchronization by video amplifier A1 to OV (equal to level of extinction). Amplifier A1 draws a signal to sync splitter circuit U2 which, in turn, draws compound sync and a vertical pulse between 1 ps and 20 ps. To generate a color sync signal gate to fix the input video color sync signal to the 2015 circuit, care must be taken not to generate a color sync gate pulse when pseudosync pulses are present (that is, if the video input has the basic anti-copy process). Thus, the monostable circuit U3 receives compound sync (and pseudo-sync) and produces a non-retriggerable pulse of about 45 ps, long enough to ignore vertical 2H pulses and equalizers in the vertical decay interval and also pseudo-sync pulses that may be present. present (usually in the first 32 ps of the 10-20 TV lines). The monostable circuit U10 delays the leading edge of the pulse by 5 ps.

ES 2 136 200 T5 input video sync and triggers monostable circuit U11, a 2 ps pulse to match the input video color sync signal.

Amplifier A1 drives a chroma band pass filter amplifier A91 for input to the color sync signal phase lock loop circuit 2105. The output of phase locked loop 2105 is now a continuous wave subcarrier locked in phase with the input video color sync signal. The phase locked loop 2011 circuit adjusts the regenerated subcarrier phase to be correct at the output of amplifier A5. The frame sync pulse from the sync signal splitter U2 resets the address counter U8 for the EPROM memory U9. Counter U8 is incremented by a horizontal frequency pulse from amplifier A3. The EPROM memory U9 extracts each data line that contains particular high or low television lines in the active field.

One of the advantages of the circuit of Figures 13a and 13b is that the regenerated narrow timing can be located anywhere in the horizontal extinction range. This is especially advantageous if the new narrow sync can start 1 ps earlier than the input video horizontal sync. With a 1 ps lead in the new narrowed horizontal sync and post-pseudosync boost (PPS), horizontal jitter with an illegal copy that the basic anti-copy process has produces 1 ps more in horizontal jitter. By advancing the tapered horizontal sync pulse, there is a greater time gap between the tapered horizontal sync pulse and the post-pseudo sync pulse, producing proportionally greater jitter when playing an illegal copy.

To generate a narrowed horizontal sync ahead of time, the output of the U2 monostable circuit is a 45 ps pulse coincident with the input sync leading edge, it is "squared" via the 32 ps monostable circuit U4. The filter, which includes components R1, L1 and C1, band-pass filters the output of the monostable circuit U4 forming a 15.734 kHz sine wave.

By adjusting inductor L1, a sine wave is produced in front of (or behind) the input video horizontal sync. The comparator A3 converts this sine wave into pulses whose edges are before or after the leading edge of the video input sync. The “tracking” ability of the filter R1, L1, C1 (with a Q of four) to generate waveforms synchronous with the input video is generally better than most horizontal phase-locked loops when the Video input comes from a VCR. Then the output of the amplifier A3 goes to the 14 ps monostable circuit U5 to generate a horizontal fading interval gate signal to replace the old (input) sync and sync signal with narrow sync and extended color sync signal. new.

The U6 monostable circuit regulates a nominal narrowed sync delay of 0.5 ps from the beginning of the input video horizontal decay interval (from the leading edge of U5 monostable) and the U7 monostable triggers a new narrowed sync pulse. . Components R2, R3 and Q1 form a switch to narrow the pulse further by short-circuiting transistor Q1 (emitter to collector) and by means of the EPD1 output command (that is, for lines 251262 each EPD1 field output is low , and high elsewhere). So, the output of the one-shot circuit U7 is 3.7 ps pulses from lines 20 to 250 and 2 ps pulses from lines 251 to 262. Triggering the trailing edge of monostable circuit U7 is monostable circuit U12, the output of which is the chromatic-sync extended signal gate (approximately 5.5 ps pulse width).

The output of monostable circuit U12 controls the output of a color sync signal from circuit 2011 via switch SW22, and the band-pass filter amplifier A4 (3.58 MHz) makes up the extended envelope of the color sync signal. from the output of the switch SW22 and couples it to the summing amplifier A5, via the chromatic synchronization extended signal amplitude adjusting resistor R10. The narrow horizontal sync from the monostable circuit U7 is "matched" by means of the AND-type logic gate U13 with the EPD2 signal which is generally high, except for the few lines where the narrow sync has to be suppressed, which increases the end-of-field pulses. The output of logic gate U13 is summed at amplifier A5 via narrowed sync amplitude control resistor R8. So the output of amplifier A5 is the narrow sync plus the extended color sync signal. The switch SW25 switches the output of the amplifier A5 through the logic gate U14 type AND through the logic gate U20 type OR, which switches the output of the amplifier A5 during the horizontal extinction interval via the output of the monostable circuit U5 and the EPD3 output (active field position pulses, that is, lines 20-262).

Then the A2 crossover amplifier extracts video from the input with new narrowed horizontal sync and extended color sync signal. To input a relocated sync pulse (EOFRSP: end of field repositioned sync pulse) into the end of field position, the U16 monostable circuit is 10 ps to 40 ps in duration from the leading edge of input video sync. Electronic gate U16 couples to electronic gate U17 a 2 ps to 4 ps wide pulse that is delayed by 10 ps to 40 ps from the input video sync leading edge. The output of the electronic gate U16 is enabled via the AND-type logic gate U18 and the EPD4 output of the EPROM memory U9. So the EPD4 signal is high on certain lines at the end of the field after sync suppression is activated by the EPD2 signal. Electronic gate U16 drives summing amplifier A5 via end of field relocated sync pulse width adjustment resistor R85 (EOFRSP). The electronic gate U16 also connects the switch SW25 during the activation of the EOFRSP pulse through the logic gate U20 type OR to insert the relocated synchronization pulse (EO27

IS 2 136 200 T5

FRSP). Thus the output of amplifier A2 has input video, narrowed sync, and possibly 1 or 2 suppressed sync lines (no sync) or / and a few relocated narrowed horizontal sync lines.

Sync pulse narrowing is effective even though not all horizontal sync pulses in a video signal are narrowed as well. Even a relatively small number of narrowed horizontal sync pulses have been determined to provide spurious vertical return. For example, three to six consecutive video lines with a narrowed horizontal sync pulse are suitable for this purpose. It is preferred to group the narrowed horizontal sync pulses together in consecutive lines (or at least relatively close to each other) to generate the spurious vertical return.

Other circuits for narrowing sync pulses, in the context of removing copy protection signals, are described in US Patent No. 5,157,510 and US Patent No. 5,194,965.

Figures 14a and 14b show block diagrams of two apparatuses for combining the above described sync pulse narrowing with the prior art copy protection process described above and horizontal and vertical signal modifications.

Figure 14a shows the first such apparatus, with program video signal supplied to circuit block 204, for adding prior art copy protection signals including added pseudo-sync and automatic gain control pulses. The next block 206 (shown in detail in Figure 6a) adds (1) the checkered pattern and (2) the vertical frequency signal modifications to the end of each of the selected fields. Then, sync pulse taper circuit block 208 (shown in varying detail in Figures 12a and Figures 13a and 13b) further modifies the video signal that is drawn at terminal 209, for example, to a master copying VCR in a video cassette dubbing equipment. It has also been observed that the basic prior art copying process was improved by adding just in conjunction with the sync pulse narrowing process.

Alternatively, in Figure 14b, the input program video signal is first subjected to block 208 of sync pulse taper circuitry, and blocks 204, 206 of checkerboard pattern and vertical frequency signal modification circuitry (shown here combined into one block) and from here it is supplied to the output terminal 210.

It is to be understood that other apparatuses may also provide the described video signal modifications, ie, checkered pattern, vertical end-of-field pattern, sync pulse taper, and their equivalents.

Figure 15 shows a circuit for adding post-pseudo-sync pulses to improve anti-copy effectiveness (i.e., further degrade correct image viewing ability) when illegal copying is made with the basic anti-copy process described above of US Pat. US No. 4,631,603.

The video with the basic anti-copy process and the improvements described above is input to resistor R9. The amplifier A1 separates the input video and couples it via capacitor C1 into the synchronization signal separator U6. The vertical sync output of sync splitter U6 resets a 12-bit counter U1. Counter U1 is clocked by horizontal sync to a phase locked loop circuit U2 that is locked to compound sync. The EPROM U3 memory selects in which lines the post-pseudosynchronization (PPS) can appear. A pseudo-random distribution of post-pseudosynchronization can be used, as selected by EPROM memory U3. The DO signal (an output from EPROM U3) inhibits the OS3 monostable circuit accordingly. The color sync gate signal from sync separator U6 is inverted and low pass filtered by capacitor C2 and resistor R2. The voltage Vgen is summed into a signal (ie, 300 Hz triangle waveform) at capacitor C2. This causes a time varying threshold difference in the OS3 monostable circuit and thus causes a position change. The output of the OS3 monostable circuit is a fixed pulse (that is, 1.5 ps in duration) with pulse position modulation of, for example, ± 1 ps. The output of the monostable circuit OS3 extinguishes any video to the extinction level via switch SW1 and adds a pulse through the variable resistor R7 to generate a post-pseudo sync pulse. The summing amplifier A3 reverses the output pulse of the OS3 monostable circuit to maintain the correct form of the added post-pseudosync pulse. Figures 16a to 16e show waveforms at various points in the Figure 15 circuit, as designated. The post-pseudosynchronization pulse width can be amplitude modulated via the generator Vgen2 and the voltage-controlled amplifier A41 which is a multiplier amplifier. The output of the amplifier A41 varies in amplitude according to the generator Vgen2, being OV when the post-pseudosynchronization pulse is null.