JPH09307852A - Video signal recorder and copy preventing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the video signal recorder by which a recording medium after video recording such as a software tape with a copy prevention signal added thereto is easily produced and disadvantages of the copy prevention signal are easily eliminated. SOLUTION: Processing of adding an additional signal SAD denoting a level LAD and a period TAD to a front porch of a horizontal synchronizing signal of a video signal is conducted over n-fields, and processing not adding the additional signal over succeeding m-fields is conducted repetitively. Then a dark clip level after pre-emphasis processing is changed from a conventional level DCLVL1 into a level DCLVL2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal recording apparatus and a copy protection method capable of preventing copying of a video signal recorded on a recording medium.

[0002]

2. Description of the Related Art As a copy protection method for a video soft tape on which a video signal such as a movie is recorded, a method in which an AGC (automatic gain control) circuit of a video tape recorder (hereinafter referred to as "VTR") malfunctions is conventionally used. It is more known (Japanese Patent Laid-Open No. 61-288582). The contents of this conventional method will be described below.

FIG. 10 is a diagram showing the configuration of an AGC circuit generally adopted in a VTR. This AGC circuit is
It comprises a voltage control amplifier circuit (VCA) 101, a sync tip voltage detection circuit 102, a pedestal voltage detection circuit 104, a differential circuit 104 and an LPF (low pass filter) 105. The sync chip voltage detection circuit 102 and the pedestal voltage detection circuit 103 detect the sync chip voltage Vs and the pedestal voltage Vp of the video signal shown in FIG. 11, and input them to the differential circuit 104. The differential circuit 104 is
The difference voltage Vx between the pedestal voltage Vp and the sync tip voltage Vs is input to the LPF 105, and the output voltage of the LPF 105 is supplied to the gain control input of the VCA 101. Then, the VCA 101 operates so that the sync signal level at its output becomes substantially constant.

Here, the LPF 105 comprises a resistor R1 and a capacitor C1, and the time constant determined by C1 × R1 is A
It becomes the time constant of GC. An AGC circuit similar to that shown in FIG. 10 is also provided on the television side for displaying a video signal, but FIG.
The capacitance of the capacitor corresponding to the capacitor C1 of 0 is C
When set to 1 ', C1' is generally set to a much larger value than C1. The above-mentioned conventional method pays attention to the difference in the time constant of the AGC circuit, and considers the fast time constant (C1 ×
R1) malfunctions, slow TV time constant (C1 '× R
In 1), a copy protection signal that does not cause a malfunction is added during recording.

As disclosed in Japanese Patent Laid-Open No. 63-107281, a copy protection signal is added to a video signal for recording, and the copy protection signal is detected when the recorded tape is reproduced by a VTR. In such a case, a method is also known in which the recording of the reproduced video signal is prohibited.

[0006]

However, according to the method described in the above-mentioned Japanese Patent Laid-Open No. 61-288582,
Since a pair of a pseudo sync pulse and a white pulse is used as the copy protection signal, there is a problem that a circuit for inserting the copy protection signal becomes complicated and expensive.

Further, since the time constant of the AGC circuit of the VTR used for copying can be easily changed by changing the capacitor C1 of FIG. 10, for example, the adverse effect of the copy protection signal can be eliminated without cost. it can. Therefore, it is difficult to commercialize a VTR that can be dubbed even if a copy protection signal is inserted, or to remodel an existing product, and it is difficult to achieve copy protection.

In the method disclosed in Japanese Patent Laid-Open No. 63-107281, it is necessary to provide a copy-prevention signal detection circuit and a video recording prohibition circuit in a VTR sold to consumers, so that the VTR as a commercial product can be used. There is a problem that not only the cost is increased, but also the existence of the VTR without these circuits makes it impossible to achieve the copy protection effect.

The present invention has been made in view of the above points, and it is possible to easily manufacture a recorded recording medium such as a soft tape to which a copy protection signal is added.
Moreover, it is an object of the present invention to provide a video signal recording apparatus and a copy protection method in which the harmful effect of the copy protection signal cannot be easily removed.

[0010]

In order to achieve the above object, the present invention is a video signal recording apparatus for recording a video signal on a recording medium, wherein the video signal is a copy protection signal whose waveform changes with time. Video signal transforming means for transforming the video signal by adding the pre-emphasis processing to the video signal transformed by the video signal transforming means, and dark clip processing of the signal after the pre-emphasis processing. Recording means for recording the modified video signal on the recording medium, and the dark clip level in the dark clip processing is changed to a direction in which the loss of the signal is further reduced. It was done like this.

Further, the video signal transforming means repeats the operation of adding the copy protection signal to the video signal in the first predetermined period and not adding the copy protection signal in the subsequent second predetermined period. It is desirable to modify the video signal by

Further, it is preferable that the copy protection signal is a signal added to the front porch of the horizontal synchronizing signal of the video signal.

Further, it is preferable that the waveform of the predetermined copy protection signal is determined according to the changed dark clip level.

It is desirable that the dark clip level be changed at least during the first predetermined period in which the copy protection signal is added.

It is desirable that the dark clip level be changed at least within the horizontal blanking period of the video signal.

To achieve the same object, the present invention provides a copy protection method for preventing copying of a video signal, wherein a copy protection signal whose waveform changes with time is added to the video signal. The step of transforming a video signal, the step of performing pre-emphasis processing of the transformed video signal, and the step of performing dark clip processing of the signal after the pre-emphasis processing are performed, and the dark clip level in the dark clip processing is set. The present invention provides a copy protection method characterized in that the loss of the signal is changed to a direction in which it is further reduced.

According to the present invention, the video signal is modified by adding a copy protection signal whose waveform changes with time to the video signal, and the dark clip after the pre-emphasis processing of the modified video signal. The dark clip level in the processing is changed so that the loss of the signal is further reduced.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a structure of a main part of a video tape recorder (VTR) according to an embodiment of the present invention. Before explaining this structure, referring to FIGS. 7 to 9, The recording signal processing of a general VTR will be described.

FIG. 7 is a block diagram showing a part of a general VTR recording signal processing system. In FIG. 7, the AGC circuit 1 is the AGC circuit as shown in FIG. Y with the video signal at a nearly constant level
Input to C separation circuit 2. The YC separation circuit separates the luminance signal (Y signal) and the color signal, supplies the color signal to the color signal processing system, and inputs the luminance signal to the LPF (low pass filter) 3. The LPF 3 limits the band of the luminance signal, and its output signal is supplied to the emphasis circuit 4. The emphasis circuit 4 performs a predetermined pre-emphasis process for emphasizing the high frequency component of the frequency, and supplies the processed signal to the W / C clip circuit 5. The W / D clip circuit 5 performs white clip processing and dark clip processing, which will be described later, and supplies the processed signal to the FM modulation circuit 6. The FM modulation circuit 6 FM-modulates a carrier wave with an input signal and outputs an FM-modulated signal. The FM modulation signal is added to the output signal of the color signal processing system, supplied to the magnetic head through a recording amplifier (not shown), and recorded on the magnetic tape (recording medium).

FIG. 8 is a diagram for explaining the white clip processing and the dark clip processing. FIG. 8A shows an input signal waveform of the emphasis circuit 4, and FIG. 8B shows a W / D clip. The output signal waveform of the circuit 5 is shown. Normally, for example, in a VHS standard VTR, the sync tip is used as a reference (0%) and the white peak level is 100%.
Then, 200% is the white clip level,
A portion exceeding the level is clipped (white clip processing), and a portion below the level is clipped (dark clip processing) with -40% as the dark clip level.

9A and 9B are views showing only the horizontal synchronizing signal of the video signal. FIG. 9A shows the input waveform of the emphasis circuit 4, and FIG. 9B shows the input waveform of the W / D clip circuit 5. , (C) is an output waveform of the W / D clip circuit 5. Since a part of the horizontal sync signal is lost due to the dark clip processing, the waveform of the VTR reproduction signal processing system after the pre-emphasis processing and the de-emphasis processing having the reverse characteristic is as shown in FIG. , The trailing edge is missing (however, this figure highlights the missing area for explanation). As described above, in the normal dark clip processing, a part of the signal component is lost at the trailing edge of the video signal, so the present invention pays attention to this point and adopts the configuration described below.

FIG. 1 shows a V according to an embodiment of the present invention.
FIG. 8 is a diagram showing a configuration of a main part of a TR recording signal processing system, in which the same components as those in FIG. 7 are denoted by the same reference numerals.
In the configuration of FIG. 1, a sync separation circuit 11, an additional signal generation circuit 12, a field counter 13, a switch 14 and an addition circuit 15 are added. Further, the W / D clip circuit 16 has a dark clip level which is not -40% of the normal level during a horizontal bun-ranking period (a period including a horizontal synchronizing signal, its front porch and a back porch), and a level at which signal loss is further reduced. (For example, −140%) is changed. Other configurations are the same as those in FIG. 7.

In FIG. 1, the sync separation circuit 11 separates the sync signal of the input video signal and supplies it to the additional signal generation circuit 12 and the field counter 13. As shown in FIG. 2A, the additional signal generation circuit 12 is a so-called front porch timing from the end point of the horizontal image effective period (the period displayed on the television screen) TDSP to the fall point of the horizontal synchronizing signal. Then, an additional signal (copy protection signal) SAD having a white peak level is generated and supplied to the terminal 14a of the switch 14. As shown in FIG. 2B, the additional signal SAD maintains a period TAD (for example, NTSC signal of 500 nsec, which corresponds to about 40% of the front porch period) and a level LAD (for example, white peak level). It is a signal.

The additional signal SAD is not limited to the one shown in the figure, but a normal dark clip level (-40
%), The signal loss is large, and the signal may be of a level and period that is hardly affected by the dark clip level (for example, −140%) in the present embodiment. That is, it is desirable to determine the level LAD and the period TAD of the additional signal SAD according to the dark clip level with which the loss of the signal is reduced. Further, in general, the longer the predetermined period TAD and the larger the predetermined level LAD, the larger the signal dropout at the normal dark clip level. Therefore, it is desirable to extend the period and increase the level as much as possible. Therefore, the period TAD is, for example, 30% or more (100% or less) of the front porch period.
It is preferable that the level LAD is 50% or more (100% or less) of the white peak level.

The change of the dark clip level described above may be made during the period when the additional signal SAD is added.

The field counter 13 counts the vertical synchronizing signal in the synchronizing signal and is at a high level for n fields (n is an integer of 1 or more (first predetermined number)) (first predetermined period), During the subsequent m fields (m is an integer of 1 or more (second predetermined number)) (second predetermined period), the switch switching signal SW of low level is output. First predetermined number n
The second predetermined number m is, for example, “2” (n = m = 2) so that the switch switching signal SW is a signal that repeats high level and low level for each frame.

The switch 14 is switched to the terminal 14a side as shown in the drawing when the switch switching signal SW is at the high level and to the terminal 14b side when it is at the low level. Since no signal is input to the terminal 14b, the additional signal SAD is input to the adder circuit 15 for n fields,
The process in which no signal is input during the subsequent m fields is repeated at (n + m) field periods. Therefore, the output signal of the adder circuit 15 is an n field to which the additional signal SAD shown by the solid line in FIG. 2A or 2B is added, and an additional signal SAD shown by the broken line in FIG. The field becomes a repeating signal.

At this time, the output waveform of the emphasis circuit 4 becomes as shown in FIG. Solid line is additional signal SA
The waveform of the field to which D is added, and the waveform of the field to which the broken line is not added. In addition, DCLVL
1 indicates a normal dark clip level, DCLVL2
Indicates the dark clip level in the present embodiment, and by setting it to DCLVL2, the signal loss is eliminated.

Next, the reproduced output signal waveform in the case where the video signal recorded by performing the above-described processing is dubbed will be described.

FIG. 3 is a block diagram showing a configuration of a main part of a reproduction signal processing system of a general VTR. The reproduced FM signal obtained by amplifying the magnetic head output signal is supplied to the HPF (high-pass filter) 21 and the LPF 25. LPF
A reference numeral 25 extracts a reproduction color signal contained in the reproduction FM signal and outputs it to the color signal processing system.

The HPF 21 removes the reproduced color signal from the reproduced FM signal and inputs it to the FM demodulation circuit 22. The FM demodulation circuit 22 demodulates the FM signal and supplies the demodulated signal to the de-emphasis circuit 23. De-emphasis circuit 23
Performs a process with the characteristics opposite to the pre-emphasis process,
The processed signal is input to the LPF 24. LPF24 is
Unnecessary high frequency components are removed and a reproduction luminance signal is output.

When the tape recorded by the VTR having the recording circuit shown in FIG. 1 is reproduced by the VTR having the circuit shown in FIG. 3, the signal components at the falling portion of the additional signal SAD and the falling portion of the horizontal synchronizing signal are lost. 2B, it is possible to obtain a reproduction signal (output of the LPF 24) having a waveform substantially similar to the waveform at the time of recording shown in FIG.

Next, when the reproduced signal is recorded (dubbed) again on the magnetic tape by the VTR of the normal dark clip level DCLVL1, the reproduction signal is clipped at the level of DCLVL1 shown in FIG. 2C. , The signal components of the trailing portion of the additional signal SAD and the trailing portion of the horizontal synchronizing signal are significantly lost and recorded. Therefore, when the recorded tape is reproduced,
As shown by the solid line in FIG.
Compared to the case where the falling waveform of D) is blunt and the additional signal SAD is not added (waveform of the broken line in the figure), time τ
However, the horizontal synchronization timing shifts to the previous position (position that is earlier in time). As a result, the image of the field to which the additional signal is added becomes as shown in FIG. 5A, and the image of the field to which the additional signal is not added becomes as shown in FIG. Above, the display is as shown in FIG. As a result, the output image when the dubbed tape is reproduced is visually disturbed, and copy protection can be performed.

As described above, according to the present embodiment, it is possible to prevent the copy of the soft tape with a simpler structure than the conventional system. Further, in order to eliminate the influence of the additional signal SAD, a synchronizing signal separation circuit, a waveform shaping circuit, etc. are required, and the adverse effect of the copy protection signal cannot be easily removed as in the conventional case, and therefore the copy protection effect is obtained. Can be improved. Furthermore, since the circuit configuration for inserting the additional signal SAD is simple, it can be easily integrated into an IC.

The present invention is not limited to the above-mentioned embodiment, but various modifications can be made. For example,
The additional signal SAD may be inserted anywhere between before the video signal input in FIG. 1 and the input to the emphasis circuit 4. Therefore, as shown in FIG. 6, a unit for performing a process of adding a copy protection signal (additional signal SAD) may be inserted between the software master VTR and the video software recording VTR.

Further, in the above-described embodiment, the period in which the additional signal SAD is added and the period in which the additional signal SAD is not added are set on a field-by-field basis. However, the present invention is not limited to this. For example, several tens of lines (tens of horizontal synchronization periods). ) May be set in units. Further, instead of repeating the process of adding the additional signal SAD and the process of not adding the additional signal SAD, for example, the additional signal SAD
AD level LAD and / or period TAD from 0% to 1
The process of gradually changing between 00% may be periodically performed.

The recording medium is not limited to a magnetic tape, but may be any medium having a storage function such as a magnetic disk, a magneto-optical disk, a semiconductor memory or the like.

The copy protection method of the present invention may be applied to the processing on the transmission side of communication (broadcast).

[0040]

As described above in detail, according to the present invention, a video signal is modified by adding a copy protection signal whose waveform changes with time to the video signal, and the modified video signal. Since the dark clip level in the dark clip processing after the pre-emphasis processing is changed so that the loss of the relevant signal is further reduced, it is easy to manufacture a recorded recording medium such as a soft tape to which a copy protection signal is added. can do. Moreover, since the harmful effect of the copy protection signal cannot be easily removed,
The effect of copy protection can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of a video signal recording device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a waveform of a copy protection signal.

FIG. 3 is a diagram showing a configuration of a reproduction signal processing system of a VTR.

FIG. 4 is a diagram for explaining a video signal waveform after dubbing.

FIG. 5 is a diagram for explaining a display image by a reproduced video signal after dubbing.

FIG. 6 is a diagram for explaining a location where processing for adding a copy protection signal is performed.

FIG. 7 is a diagram showing a configuration of a recording signal processing system of a general VTR.

FIG. 8 is a diagram for explaining a waveform after clip processing.

FIG. 9 is a diagram for explaining a modification of a horizontal synchronization signal due to dark clip processing.

FIG. 10 is a diagram showing a configuration of a general AGC circuit.

FIG. 11 is a diagram showing a waveform of a general video signal.

[Explanation of symbols]

 4 Emphasis Circuit 11 Sync Separation Circuit 12 Additional Signal Generation Circuit 13 Field Counter 14 Switch 15 Addition Circuit 16 W / D Clip Circuit

Claims (7)

[Claims] 1. A video signal recording apparatus for recording a video signal on a recording medium, wherein a video signal modification for modifying a video signal by adding a copy protection signal, the waveform of which changes with time, to the video signal. Means, a pre-emphasis means for performing pre-emphasis processing on the video signal transformed by the video signal transforming means, and a dark clip means for performing dark clip processing on the signal after the pre-emphasis processing, and the transformed video. A video signal recording apparatus, comprising: a recording unit for recording a signal on the recording medium, wherein the dark clip level in the dark clip processing is changed in a direction in which the loss of the signal is further reduced. 2. The video signal modifying means repeats an operation of adding a copy protection signal to the video signal in a first predetermined period and not adding the copy protection signal in a second predetermined period that follows. The video signal recording apparatus according to claim 1, wherein the video signal is modified by the following. 3. The video signal recording apparatus according to claim 1, wherein the copy protection signal is a signal added to a front porch of a horizontal synchronizing signal of the video signal. 4. The waveform of the predetermined copy protection signal is
The video signal recording apparatus according to claim 3, wherein the video signal recording apparatus is determined according to the changed dark clip level. 5. The dark clip level is changed at least during the first predetermined period in which the copy protection signal is added.
The video signal recording device according to any one of 1. 6. The video signal recording apparatus according to claim 2, wherein the dark clip level is changed at least within a horizontal blanking period of the video signal. 7. A copy protection method for preventing copying of a video signal, the step of modifying the video signal by adding a copy protection signal, the waveform of which changes with time, to the video signal. The step of performing pre-emphasis processing of the deformed video signal and the step of performing dark clip processing of the signal after the pre-emphasis processing are performed, and the dark clip level in the dark clip processing is further reduced in loss of the signal. A copy protection method characterized in that the direction is changed.