JP2000253352A - Video tape copy preventing signal insertion releasing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a video tape copy prevention signal insertion release device by which a user can simply insert/release a copy guard. SOLUTION: A video signal enters a synchronizing separator circuit and a video switch circuit after passing through a buffer. The synchronizing separator circuit generates a vertical synchronizing signal and a horizontal synchronizing signal for the video signal. A control signal for the video switch is produced by counting and processing the obtained two kinds of the synchronizing signals. Furthermore, oscillators 1, 2 generate a guard signal to be inserted to the video signal. The video switch selects the video signal directly received and the guard signal on the basis of the control signal of the video switch and provides an output of the selected signal. The outputted signal is amplified by an amplifier circuit and outputted as the video signal to which the guard signal is inserted. In the case of releasing the insertion of the guard signal, the guard signal from the oscillators 1, 2 is replaced with a usual signal such as a composite signal or a DC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for releasing a duplication preventing signal from a videotape.

[0002]

There has been conventionally known an apparatus for applying a copy guard to a video tape in order to prohibit copying of the video tape. There is no device that can be easily personally guarded by a user. In the conventional device, only the guard is applied, and the guard cannot be released.
An object of the present invention is to solve the above-mentioned problems of the prior art.

[0003]

To achieve the above object, the present invention provides a means for inserting a guard signal into a vertical synchronizing signal and a horizontal synchronizing signal of an NTSC image signal, and detects a portion where the guard signal is inserted. Means, and means for replacing the detected portion with a normal signal.

[0004]

Embodiments of the present invention will be described below with reference to the drawings. The NTSC image signal used in Japan is divided into a luminance signal for expressing light and dark, a color signal for expressing color, and a synchronization signal for transmitting the position and timing of a screen. These three types of signals are combined so as not to affect each other. Therefore, for example, even if the synchronization signal is slightly different from the standard, it does not affect the brightness and color image information. Therefore, by inserting a guard signal into the synchronization signal, it is possible to record an image without duplication without changing the image.

Hereinafter, the synchronizing signal will be described. There are three types of synchronization signals: a horizontal synchronization signal, a vertical synchronization signal, and a color synchronization signal. Usually these are H SYNC, V SYNC
C, called a color burst, is added to a period that does not appear as an image on the screen. This period is called a blanking period. In the NTSC signal, one screen (frame) is constituted by two scans (fields), which is 30 frames per second. Since one frame is 525 fields, HSYNC = 2 × 30 = about 60 Hz VSYNC = 525 × 30 = about 15.75 KHz. That is, as shown in FIG. 1, the time required for the scanning line to go from the top to the bottom of the screen and return to the top is 1/60 second. Similarly, the left and right are 1 / 15.75 K seconds. Copy guard can be applied by superimposing a guard signal during this blanking period.

First, vertical blanking will be described with reference to FIG. By adding a pulse signal to the period after the equalization pulse after the vertical synchronization signal in FIG. 2A, the waveform becomes as shown in FIG. As the signal to be added, a sine curve, another DC signal, or the like can be used in addition to the pulse.

Next, as shown in FIG. 3A, a waveform shown in FIG. 3B is obtained by adding a DC signal to about half of the color burst signal after the horizontal synchronizing signal.

Next, a method of releasing the guard signal will be described. Basically, it can be released by replacing the part where the guard signal is inserted with a normal signal. That is, the part where the guard signal is inserted is detected, and a normal signal is
For example, it is replaced with a composite output signal. In FIG. 4, (A) shows a waveform in which a sine wave guard signal is inserted, and (B) shows a waveform in which that portion is detected.

[0009] Similarly, the horizontal synchronizing signal detects the inserted portion and replaces it with another signal. FIG. 5A shows a waveform obtained by detecting a horizontal synchronization signal near the vertical synchronization signal.

An embodiment of the apparatus will be described with reference to FIG.
After passing through the buffer, the video signal enters a sync separation circuit and a video switch circuit. The sync separation circuit generates a vertical sync signal and a horizontal sync signal of the video signal. The two obtained synchronizing signals are counted and calculated to be used as a video switch control signal. Further, guard signals to be inserted by the transmitters 1 and 2 are generated. The video switch selects and directly outputs a video signal and a guard signal that are directly input by a control signal of the video switch. The output signal is amplified by an amplifier circuit and output as a video signal including a guard signal.

At the time of release, the transmitters 1 and 2 are replaced with normal signals, for example, composite signals or direct current.

[0012]

As described above, according to the present invention, the insertion of the copy guard can be easily released.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of one embodiment of the present invention.

FIG. 3 is an explanatory diagram of one embodiment of the present invention.

FIG. 4 is an explanatory diagram of one embodiment of the present invention.

FIG. 5 is an explanatory diagram of one embodiment of the present invention.

FIG. 6 is a circuit diagram of a specific device according to an embodiment of the present invention.

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Claims (3)

[Claims] 1. A means for inserting a guard signal into a vertical synchronizing signal and a horizontal synchronizing signal of an NTSC image signal, a means for detecting a part where the guard signal is inserted, and a means for replacing the detected part with a normal signal A video tape duplication prevention signal insertion / release apparatus comprising: 2. The video tape duplication preventing signal insertion / release apparatus according to claim 1, wherein the guard signal is a sine curve. 3. The video tape duplication preventing signal insertion / release apparatus according to claim 1, wherein the guard signal is a pulse signal.