MXPA98009268A - Method and apparatus for modifications made to a video signal to inhibit the production of acceptable records of vibrates - Google Patents

Abstract

The present invention relates to a video signal being modified so that a receiver / television continues to produce a normal image from the modified signal, but where the recording of a video tape of this signal produces generally unacceptable images. Video tape recorders have an automatic gain control circuit (Fig. 2) that measures the level of the synchronization pulse in a video signal and develops a gain control correction signal to keep the video applied to a modulator FM in the video tape recording system, at a predetermined fixed level. A portion of the posterior plateau intervals, which follow the trailing edges of a substantial number of synchronization pulses, rise and fall significantly to improve the reproduction of the original signal without reducing the effectiveness of copy protection in the copied signal. This is achieved simply by adding pulses to the selected lines of the video signal during the interval of the posterior plateau, these pulses raise or decrease significantly the voltage amplitude during the extinction interval to provide a signal where the average value is approximately equal to the extinction interval. The level of synchronization and the duration of the synchronization in the selected lines are also reduced to improve the effectiveness of the process

Description

METHOD AND APPARATUS FOR MODIFICATIONS MADE TO A VIDEO SIGNAL TO INHIBIT THE PRODUCTION ACCEPTABLE RECORDINGS OF VIDEO TAPES CROSS REFERENCE WITH RELATED APPLICATIONS This application is related to Provisional Application Serial Number 60 / 017,859 filed on May 8, 1996, entitled METHOD FOR MODIFICATIONS TO A VIDEO SIGNAL TO INITIATE THE ACCEPTABLE RECORDING PRODUCTION OF VIDEO TAPE. This application is related to U.S. Pat. 5,583,936 ('936) entitled IMPROVEMENTS IN A VIDEO COPY PROTECTION PROCESS TO INTRODUCE HORIZONTAL AND VERTICAL IMAGE DISTORTIONS by Wondorf et al, filed December 10, 1996. This application is also related to US Pat. Number 4,819,098 ('098), filed on April 4, 1989 entitled METHOD AND APPARATUS FOR GROUPING MODIFICATIONS MADE TO A VIDEO SIGNAL TO INHIBIT THE PRODUCTION OF ACCEPTABLE RECORDS OF A VIDEO TAPE. Also, this application relates to U.S. Pat. Number 5,130, 810 ('810), filed on July 14, 1992, entitled METHOD AND APPARATUS FOR PROCESSING A VIDEO SIGNAL TO PROHIBIT THE PRCDUCTION OF AN ACCEPTABLE RECORDING OF VIDEO TAPE.

P1665 / 98MX BACKGROUND OF THE INVENTION The invention relates to a method and apparatus for modifying a video signal so that a video recording of a video signal generally produces unacceptable images while the television receiver / monitor produces an image generally normal from the modified signal. There is a need for a method and system for modifying a video signal that produces a normal color image on a television receiver, but video tape recording of the video signal is inhibited. Some of the previous work did not result in satisfactory methods. For example, U.S. Pat. No. 4,163,253 issued to Morio et al, in July 1979. This patent describes an arrangement in which a positive impulse is added to the posterior plateau portion of each horizontal extinction interval. This approach results in significant reproduction problems. In this connection, video cartridge recorders designed for the consumer market are invariably characterized by having some form of automatic gain control circuitry (AGC). The AGC circuit ensures that the level of video applied to the FM modulator in the engraving system remains at a fixed, predetermined value, even if the video level applied to the P1665 / 98MX input terminal of the machine varies widely over the nominal value. Without an AGC system, the high level signals are distorted and grouped and the low level signals will be erased by the noise and interference products generated by the recording process. If the input level drops to less than 1/3 of the normal value, the reproduced signal may not be strong enough to reliably synchronize the timbales of the receiver, thereby generating noisy, unstable images. This prior system, however, does not take into account the fact that many receivers / monitors use the region of the back portion of the video signal for a black level setting. The result is that while the approach described in the patent for Morio et al to confuse the AGC of a video cartridge recorder does not result in a copied tape generally not visible, the video signal also does not provide visible images on many receivers / monitors. of television when used directly. This converts the process with limited value. Another example of previous work in the art of protection against video copies is the work of Kagota in U.S. Pat. serial number 4,475,129. This work generates a first impulse in the posterior plateau of a horizontal extinction signal with a width P1665 / 98MX narrower than the posterior plateau and adds a second impulse essentially equal to the first impulse. These impulses are added to the posterior plateau at predetermined time intervals. The approach used by Kagota has problems similar to those of Morio. The effectiveness of copy protection does not result in non-visible copy tapes., but the video signal does not provide visible images on many television receivers / monitors when used directly. This makes the process of low commercial value. The inventor of the present is responsible for more recent and more successful approaches to avoid unauthorized recording of a video signal. Three of these approaches are described in U.S. Pat. Nos. 4,577,216; 4,621,603 and 4,819,098. Additionally, the inventor is co-owner of U.S. Pat. 5,583,986. US Patents 4,577,216; 4,631,603; 4,819,098; 5,130,810 and 5,333,986, are considered part of the present reference. The approach described and claimed in US Pat. No. 4,631,603 and the approach described and claiming er. Patent, 819, 093 (? 098; are similar to the arrangement of Mori; et al, in that they are based on confusing the AGC of a video cartridge recorder.) However, they are different from the arrangement of Morio et al. appearance P1665 / 98M.X important. As in Morio, they are based on the differences between a video cartridge recorder and a television receiver to ensure that while modifications made to a video signal prevent copying by a video cartridge recorder, they do not significantly affect the reproduction of the signal on a television receiver / monitor. The 098 patent uses a different approach to modify a composite video signal to confuse the AGC of a video cartridge recorder as described above, while not materially affecting the reproduction of the resulting signal. That is, it has been found that by "grouping" during a field the modifications of a composite video signal, responsible for confusing the AGC circuitry of a video cartridge recorder, the effect of the modification on the reproduction of the video signal in a television receiver / monitor is significantly attenuated. Desirably, modifications of the signal take place during the portion thereof which is responsible for vertical extinction, namely, the return of a beam change from the end of a frame scan field to the start. The video signal does not provide during that time a visible portion of a video image, with the result that any effect of the modifications to the video signal in the circuitry of P16S5 / 98MX a television receiver / monitor will not be presented during the visible interval. In this way, the detrimental effect on the ability to reproduce is virtually eliminated. While the? 098 patent provides a very useful means of copy protection, "clustering" can be done carefully to balance the effectiveness of copy protection and reproduction of the original signal. The '810 patent has one embodiment, as described in Figure 4 of the' 810 patent, where the video level of the posterior plateau area falls below the normal extinction level. This reduction affects increasing the gain of the AGC system to cause the recorded image to be brighter than normal and have a clear view. This reduction of the extinction level in the posterior plateau is not accompanied by the AGC impulse. There, the decrease in the level of extinction serves a purpose other than that desired in the present invention. One of the elements described in the 936 patent includes the concept of the horizontal synchronization narrowing so that when an illegal copy is made, the attenuated video with a reduced synchronization pulse width (duration) causes a reproduction problem when it is displayed in a TV set. While this P1665 / 98MX concept is useful for the present invention, as will be seen below, the reason for reducing the synchronization width in the present invention, goes beyond the improved effectiveness in protection against copying.

SUMMARY OF THE INVENTION Therefore, an object of the invention is to provide a method and apparatus for modifying a video signal for a conventional television receiver / monitor to produce a normal image from the modified signal, so that a recording Video tape made from the modified signal is unacceptable. A particular object of the invention is to provide a method and apparatus in which the voltage amplitudes of a portion of the intervals of the posterior plateau which follow the trailing edges of a substantial number of synchronization pulses, rise and fall in a manner significant to improve the reproduction of the original signal, without reducing the effectiveness of the protection against copies of a copied signal. This is easily achieved by adding pulses to the selected lines of the video signal during the interval of the back plateau; those pulses increase and decrease significantly the amplitude of the voltage during the extinction interval to provide a signal whose value Average P1S65 / 98MX is approximately equal to the extinction level. The level of synchronization and the duration of the synchronization in the selected lines is also reduced. Other objects and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS OR FIGURES With reference to the accompanying drawings: FIG. 1 is an illustration of the portion of the waveform of a typical video color signal, responsible for a horizontal trace and a protection segment. FIG. 2 is a block diagram of an automatic gain control circuit of a video tape recorder. FIG. 3 illustrates a portion of a waveform of a video composite signal as modified according to the invention; and FIG. 4 is a blosue diagram of a typical circuit that modifies a video signal waveform to produce the waveform of FIG. 3.

P1665 / 98MX DETAILED DESCRIPTION OF THE INVENTION It is known that by modifying certain characteristics of a video signal, the automatic gain control circuits in a video tape recorder can be forced to behave as if the video signal were longer than the video signal. what it really is. The result is that, when the signal is recorded on a tape, the recording is at such a low level that reproducing it on a television receiver / monitor produces noisy, unstable images. It has been found that by controlling the modifications to have an average value approximately equal to that of the extinction level while having both positive and negative peak levels of substantial values, the effect of the copy protection modifications on the control circuitry is minimized. Black level of a television receiver / monitor. By having these modifications inserted in a controlled manner during the horizontal extinction interval, from the observer's point of view, the condition is virtually eliminated. With reference to Fig. 1, the waveform of the portion of a typical video color signal responsible for a horizontal scanning trace and a protection segment is illustrated. The only 2 characteristics of this waveform portion that remain constant, a P1665 / 98MX despite the changes in the content of the image, are those that occur during the extinction intervals, mainly the synchronization pulses and the color burst. Because the level of the color burst is highly dependent on the response of the tuner, the level of the synchronization pulses (any of the pulses ranging from the extinction level to the synchronization tip level, which include the pulses equalizers and vertical sync pulses) are generally used at the reference level in the automatic gain control systems of video tape recorders. Synchronization pulses are often used as the reference level in the black level control systems of television receivers / monitors. With reference to FIG. 2, a typical automatic level or gain control system as used in video tape recorders is illustrated. In the typical system illustrated in FIG. 2, a Video Input signal in terminal 11 passes through an amplifier 12 and towards a synchronization tip level clamp or a DC restore circuit 13, which stabilizes the sync tip voltage to some value VI. A sampling circuit consisting of a transistor switch 14 and a positive peak detector, including diode 16, P1665 / 98MX capacitor 17 and resistor 18, measures the voltage of the video signal after the trailing edge of the synchronization pulse to produce a voltage V2. The voltage difference (V2 - VI) is a measure of the synchronization pulse level. A differential amplifier 19 compares the voltage of the synchronization pulse with the voltage V, eff, reference and generates in its output a gain or error correction signal which is coupled again in the amplifier 12. The negative feedback arrangement ensures that the level of the video signal applied to an input of the FM modulator in terminal 21 remains constant at the signal level value chosen by the circuit designer. Taking into consideration FIG. 3, a portion of the waveform of a modified video signal according to one embodiment of the present invention is illustrated. The portion of the waveform illustrated in FIG. 3 is a portion of a video signal during horizontal extinction. With reference to FIG. 3, it can be seen that a positive pulse 22 has been added to the video signal immediately after the trailing edge of the synchronization pulse 23. For a maximum effect, the amplitude of this pulse must be such that the voltage of the plateau posterior to the level of the white peak or more increases, as shown in FIG. 3. A typical value of P1665 / 98MX this positive impulse would be 127 IRÉ units in the NTSC format. The pulse width of the positive pulse must be wide enough to exceed the limited bandwidth of the video of the video cartridge recorder to be effective. This impulse should be at least 750 msecs, for greater effectiveness. This positive pulse causes the automatic gain control circuit in the video tape recorder to signal the level of the synchronization pulse to approximately 3 times its actual value. The feedback action of the automatic gain control circuit as discussed above in connection with FIG. 2, will reduce the signal at the FM modulator input to approximately 30% of the correct value in the ideal case. The signal reproduced as recorded on the videotape recorder will therefore be lower than the normal level and will have a poor signal / noise ratio. In many cases, the signal will not be strong enough to reproduce in order to properly synchronize the scan circuits of the television receivers / monitors. Immediately after and before the positive continuous impulse are negative continuous impulses in which the total area is approximately equal to the area below the next positive continuous impulse. The width of the synchronization has been reduced in order to P1S65 / 98MX provide a longer portion of the area to be used by the negative impulse, before the positive impulse. The narrowing of the synchronization is such that the narrow synchronization pulse is approximately 3.0 microseconds. The amplitude of the negative continuous pulse is less than half the burst amplitude to avoid placing the burst signal below the synchronization level. The level of this negative continuous pulse may be below the threshold of the synchronization separator of the VCR recorder. This threshold is described in detail in the patent number 5,194,965 for Quan, filed on May 16, 1993 (incorporated herein by reference). If this negative continuous pulse is greater than the threshold, it can improve the effectiveness of copy protection. This is because the VCR recorder can see this as a pseudo-pulse synchronization. The purpose of having a negative continuous impulse is to improve the reproduction of the original signal in a receiver, television monitor. As described above, a video cassette recorder detects the peak values of the synchronization and the pulse follows the synchronization signal. However, a receiver / monitor tends to detect an average value of the area following the synchronization pulse, called the P1665 / 98MX colloquial way back plateau. Since the area within the posterior plateau consists of positive and negative pulses where the area under the curves are approximately equal, the darkening effect caused by having only one positive continuous signal is significantly reduced in most recipients / television monitors. For greater effectiveness, the pulse pairs described above can be placed in horizontal extinction intervals different from those within the vertical synchronization area. However, it is desirable to determine the balance between effectiveness and reproduction by controlling the number of lines that have the modifications. One possibility is to place the lines containing the modification in groups of at least one line in various parts of the field. The above description has used the parameters for the NTSC / 60 field format. However, the principles of the invention can be applied equally to PAL, SECAM or other field formats 50. With reference to FIG. 4, there is shown a block diagram of a typical apparatus that can be used to practice the method of the present invention, as described above with reference to FIG. 3. It must be understood that different kinds of P166S / 98MX circuit arrangements to produce a modified signal, and the modality described in relation to the block diagram of FIG. 4 is only an example. With reference to FIG. 4, the video signal that enters the terminal 42 is applied to the Input Amplifier 42. The output of the Input Amplifier 42 is coupled to the Synchronization Separator 44 where the synchronization pulses are separated from the video signal. The output of the Synchronization Separator 44 is coupled to the Line Counter 46 which is pre-programmed to determine which lines in a field are to be modified. The output of the Line Counter 46 is coupled to the Synchronization Separator 58 and to the Monostable 52, 48 and 54. The Monostable 52, 48, and 50 determine the pulse width of the different portions of the modified signal including the width of the the timing, and the positions of the negative and positive pulses are shown in Figure 3. The outputs of the Monostable 52, 48, 50 and 54 are coupled to the Pulse Shaper 56 which produces an impulse described in Figure 3. These pulses they are coupled to the Pulse Summer 60 which receives the video signal that has been divided from the synchronization pulses in the selected lines. The burst of color in the original signal remains intact at the entrance of the Impulse Summer 60. The Pulse Adder adds P1665 / 98MX the pulses formed in the Impulse Trainer 56 for the video signal. In the area where a pulse of the Pulse Summer 56 and the Color Burst coexist, they are simply added as shown in Figure 3. The amplitudes of the positive pulse, the negative pulse and the synchronization of the selected lines are determined in the Puller, as shown. The modified signal is coupled to the Video Output Amplifier 62. What has been described is a method together with the sample apparatus for modifying a video signal for a television receiver to produce a normal image from the modified signal, where the recording of the tape of this signal produces images generally unacceptable Many different forms of the apparatus and circuits are possible to practice the method of this invention, and the particular circuitry illustrated in FIG. 4 is only as an example. The parameters described above are related to the NTSC television system. A person skilled in the art can easily apply the principles of the invention to the standards of PAL or SECAM. Various modifications are possible without departing from the spirit and scope of the present invention. For example, the duration of the added impulse can be adjusted within a broad duration limit (0.5 to 5).

P1665 / 98MX microseconds). The amplitude of this impulse can also vary or it can be different from the rectangular one, as a square sine.

P1S65 / 98MX

Claims (14)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. A method to process a video signal to inhibit the production of acceptable recordings of video tapes from them, while at the same time the video is able to produce an essentially normal image on a television receiver / monitor, where the video signal has synchronization pulses followed by back plateau intervals, which comprises the steps of: selecting one or more lines within the video signal; narrow the width of the synchronization pulses in the selected lines; significantly reducing the amplitude of the voltage of a first portion of an enlarged posterior plateau area in the selected lines; increase significantly the voltage amplitude of a second portion of the intervals of the posterior plateau in the selected lines; significantly decrease the voltage amplitude of a third portion of the portion interval Rear P16S5 / 98MX; retaining the normal position of a burst of color relative to the leading edge of the synchronization pulses; and where a sufficient number of lines are selected to inhibit the production of acceptable videotape recordings.
2. 2. The method of claim 1, wherein the positive portion is at least 750 ms wide.
3. 3. The method of claim 1, wherein the positive portion has an amplitude of approximately 127 IRÉ units. The method of claim 1 to 3, wherein the sum of the area under the second portion is approximately equal to the area under the first and second portions. The method of claim 1, wherein the selected lines consist of the lines containing a color burst signal. 6. The method of claim 1, wherein the selected lines consist of the last 6 lines preceding a vertical synchronization pulse in each field. The method of claim 1, wherein the color burst signal starts at about 5.6 P16S5 / 98MX microseconds after the leading edge of the horizontal synchronization pulse. 8. The method of claim 1, wherein the duration of the color burst signal is approximately 2.25 microseconds. 9. The method of claim 1, wherein the duration of the synchronization in the selected lines is approximately 3.0 microseconds. 10. The method of claim 1, wherein the synchronization amplitude is reduced to approximately -30 IRÉ units. 11. The method of claim 1, wherein the selected lines consist of a group of lines adjacent to a horizontal extinction range, which form the elements of the image that are not presented. 12. The method of claim 1, further comprising the step of reducing the level of each synchronization pulse. 13. The method of claim 1, wherein the selected lines are within a group thereof which is presented within no more than generally 20% of the video signal responsible for a field of a frame. 14. A device to process a video signal to prohibit the production of acceptable videotape recordings from it, while at the same time P1665 / 98MX time the video is capable of producing an essentially normal picture on a television receiver / monitor, where the video signal has synchronization pulses followed by back plateau intervals, comprising of the steps of: selecting one or more lines inside the video signal; narrow the width of the synchronization pulses in the selected lines; significantly reducing the voltage amplitude of a first portion of an enlarged posterior plateau area in the selected lines; increase significantly the voltage amplitude of a second portion of the intervals of the posterior plateau in the selected lines; significantly decrease the voltage amplitude of a third portion of the rear portion range; retain the normal position of a burst of color relative to the leading edge of the synchronization pulses. P166S / 98MX SUMMARY OF THE INVENTION A video signal is modified so that a receiver / television continues to produce a normal image from the modified signal, but where the recording of a video tape of this signal produces generally unacceptable images. Video tape recorders have an automatic gain control circuit (Fig. 2) that measures the level of the synchronization pulse in a video signal and develops a gain control correction signal to keep the video applied to a modulator FM in the video tape recording system, at a predetermined fixed level. A portion of the posterior plateau intervals, which follow the trailing edges of a substantial number of synchronization pulses, rise and fall significantly to improve the reproduction of the original signal without reducing the effectiveness of copy protection in the copied signal. This is achieved simply by adding pulses to the selected lines of the video signal during interval1 of the posterior plateau, these pulses raise or decrease significantly the voltage amplitude during the extinction interval ^ to provide a signal where the value average is approximately equal to the extinction interval. The synchronization level and the duration of the synchronization P1665 / 98 X in the selected lines are also reduced to improve the effectiveness of the process. P1665 / 98MX