JPH0560307B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal masking device suitable for use in after-recording.

Background technology and its problems A new type of compact helical VTR commonly known as 8mm video (hereinafter referred to as 8V type) has been proposed to the industry, and its standards have already been standardized.

First, an outline of the 8V system will be explained with reference to FIGS. 1 to 3.

As is clear from the frequency spectrum in Figure 1, in the 8V system, the FM-converted audio signal A _FM has a frequency domain set between the carrier luminance signal Y _FM and the low-frequency conversion chromaticity signal CL, and the video signal and frequency multiplexed recording. Furthermore, as an option, as shown in the format of FIG. 2, a two-channel PCM audio signal is divided into areas and recorded in an area on an extended track preceding the recording area of the video signal. It is designed so that only the audio signal can be recorded later (after recording, hereinafter simply referred to as recording). When recording and playing back PCM audio signals, the winding angle of the tape around the head drum is set to 221°, and the winding angles (recording areas) on the tape of PCM audio signals and video signals are 26.3° and 180°, respectively. It is. This PCM
A pilot signal recording and reproducing area is provided between each recording area for the converted audio signal and the video signal, in order to make the track pitch uniform during recording.

As mentioned above, in the 8V system, the audio signal is converted to FM and frequency multiplexed with the video signal, or
Since it is converted into PCM and recorded in area-divided areas on the extended track, the audio head used in conventional VTRs becomes unnecessary. Furthermore, since the pilot signal is frequency-multiplexed recorded on the track and used for tracking servo, a control signal head is not required, and therefore an audio/control erase head is also not required.

Therefore, an 8V erasing head for video is mounted on a rotating disk in the same way as the video head, making electronic editing possible. In addition, in the case of a rotating erase head (hereinafter referred to as an FE head), only a few tracks need to be erased at one time, so the erase power required is significantly reduced compared to the conventional fixed erase head that erases the full width of the tape. Ru. As the erasing signal, in order to avoid interference with the recording signal, the carrier luminance signal _YFM itself or a signal with a single frequency higher than the upper limit frequency of the carrier luminance signal is used.

When using FE head and video head together,
As conceptually shown in FIGS. 3A and 3B, there is a rotating body (not shown in the figure) on which two image heads 11A and 11B are installed, which are arranged at an angle of 180° in a head drum (rotating drum) HD. (omitted), the FE head 12 is usually mounted at an angle of 90° with respect to both the imaging heads 11A and 11B, maintaining an appropriate level difference. In this case, FE head 12
The erase width is set to approximately one or two times the track width.

When recording, first, as shown in Figure 3A,
The FE head 12 scans the PCM recording area on the extension track and if there is an already recorded audio signal,
Erase this. In its wake, a new audio signal is converted into PCM and recorded by one of the video heads, for example 11A, as shown in FIG. 3B. During this erasing and recording, the other video head, for example 11B, reproduces the video signal recorded on the track at a position parallel to the video head 11A at a wrap angle of 180 degrees. The reproduced video signal is supplied to a receiver and displayed as an image. However, compared to the level of the reproduced video signal, the levels of the erase signal and recorded video signal are significantly higher (about 100 dB), and the distance between each head is short, so the reproduced video signal is not transmitted to the FE head 12 and the video head. During a period of approximately 40 hours when 11A or 11B scans the PCM recording area, the horizontal synchronizing signal is substantially lost due to severe interference by the erasing signal and the recording signal. Therefore, corresponding to the disturbance period, disturbance regions 13E and 13R in which horizontal synchronization cannot be achieved appear at the center and lower part of the screen of the receiver, as shown in FIG. FE head 12 and video head 11A
Or after 11B finishes scanning the PCM recording area,
When the interference caused by the erase signal and the recording signal stops, a normal reproduced video signal is supplied to the receiver. However, since the horizontal oscillation circuit of the receiver is free-running oscillation during the duration of the disturbance, when the disturbance stops,
The lock phase of the receiver's horizontal AFC and the horizontal synchronization signal of the reproduced video signal are greatly deviated, and the above-mentioned interference appears on the receiver screen until the AFC circuit locks to the horizontal synchronization signal of the reproduced video signal. Regions 14E and 14R immediately below regions 13E and 13R
A so-called skew occurs.

The out-of-synchronization and skewed areas described above can make the receiver screen look extremely unsightly. Conventionally, therefore, a pseudo horizontal synchronization signal generated from the reproduced video signal before the disturbance period is supplied to the receiver instead of the reproduced video signal during the disturbance period to mask the video signal, and the disturbance areas 13E and 13R of the screen are masked. At the same time, the AFC lock phase at the time of interference stop is prevented from being largely deviated from the horizontal synchronization signal of the reproduced video signal.
I tried to reduce the unsightliness of the screen.

A conventional masking device will now be described with reference to FIGS. 5 and 6.

FIG. 5 shows an example of the configuration of a conventional masking device. In FIG. 5, a reproduced video signal as shown in FIG. 6A is supplied from an input terminal 21 to an electronic switch 22, and taken out to an output terminal 23 via one of the fixed contacts 22a and the movable contact 22c. Ru. 24 is a horizontal synchronizing signal separation circuit, and from the reproduced video signal supplied to this circuit, the signal shown in FIG.
A horizontal synchronizing signal as shown in FIG. 2 is separated and supplied to the counter 25. The counter 25 has one horizontal period H
For example, it is an m-sequence (longest linear code sequence) generator that can be rotated modulo an integer M, and counts the clock signal from the clock signal generator 26 and is reset by the horizontal synchronization signal from the separation circuit 24. Immediately after counting M, a pseudo horizontal synchronizing signal as shown in FIG. 6C is generated, and this signal is supplied to the other fixed contact 22b of the electronic switch 22. Note that the frequency of the clock signal must be several hundred times the horizontal frequency _fH , and in addition, it must be synchronized with the H or V of the television signal. used.

In the case of recording, as shown in FIG. 6D, a recording control signal is commonly supplied from the control terminal 27 to the electronic switch 22 and the counter 25, which lasts from the time _t1 when the recording disturbance occurs to the time _t2 when the disturbance stops. .
By this recording control signal, the movable contact 22c of the switch 22 is connected to the other fixed contact 22b, as shown in FIG.

During the disturbance period _t1 to _t2 , the synchronization separation circuit 24 is not supplied with a normal reproduced video signal as described above, so the counter 25 is switched to free running mode by the recording control signal. The counter 25 runs on its own at a precise period of the horizontal synchronization signal and generates a pseudo horizontal synchronization signal, and this pseudo horizontal synchronization signal is taken out to the output terminal 23 via the switch 22.

When the supply of the recording control signal is stopped at the disturbance stop time t ₂ , the switch 22 is connected in a state opposite to that shown in FIG. 5, and the reproduced video signal is supplied to the output terminal 23. On the other hand, counter 2
5 returns from the free running mode to the normal mode and is reset by a normal horizontal synchronizing signal from the separation circuit 24.

Therefore, during the disturbance period t ₁ to _{t 2} and before and after, the output terminal 23 has the following information as shown in FIG. 6E.
A reproduced video signal interpolated by the pseudo horizontal synchronization signal is extracted, and the horizontal synchronization signal does not disappear at all during the disturbance period. Additionally, while the control signal is being supplied, the DC level of the pseudo horizontal synchronization signal that interpolates the video signal is clamped to the black level or pedestal level, and during the disturbance period, the disturbed area on the receiver screen becomes dark. There is.

However, since the phase of the horizontal synchronization signal of the reproduced video signal fluctuates due to phase fluctuations of the rotating head servo, expansion and contraction of the magnetic tape, etc., the received image is locked to the correct phase of the quasi-similar horizontal synchronization signal at the time when the interference stops. There was a problem that there was a shift between the phase of the AFC of the aircraft, and skew occurred on the screen over 5 to 10 horizontal scans, impairing visibility.

Purpose of the Invention In view of the above, an object of the present invention is to mask the reproduced video signal not only during the disturbance period due to recording but also during the subsequent skew occurrence period, thereby preventing the visual appearance of the screen from being impaired. The object of the present invention is to provide a masking device for a video signal that does not contain any video signals.

SUMMARY OF THE INVENTION The present invention comprises a magnetic head which is equipped with a similar horizontal synchronizing signal generation means and a signal replacement means, and which records a video signal on a magnetic recording medium or erases a video signal recorded on the magnetic recording medium; The reproduction magnetic head of the magnetic recording and reproducing apparatus is configured to operate simultaneously with the reproduction magnetic head for reproducing the video signal recorded on the recording medium. In a video signal masking device that replaces the output of a similar horizontal synchronization signal generating means, a horizontal synchronization device operates to selectively pass a horizontal synchronization signal in a reproduced video signal by a reproduction magnetic head for a predetermined period of time following a simultaneous operation period. A signal selection passage means is provided, and a video signal conversion means is provided for converting a portion of the video signal reproduced by the reproduction magnetic head except for the substantially horizontal synchronization signal into a signal of a constant level for a predetermined time, and the horizontal synchronization signal selection passage means and the video A reproduced video signal is supplied to the signal conversion means, a horizontal synchronizing signal in the reproduced video signal is selectively passed through, and a portion of the reproduced video signal excluding the substantially horizontal synchronizing signal is converted to a constant level and outputted. It is something.

According to the present invention, there is provided a video signal masking device which masks the reproduced video signal not only during the period in which disturbance occurs due to recording but also during the subsequent period in which skew occurs, and does not impair the visibility of the screen. Obtainable.

Embodiment Hereinafter, an embodiment of the masking device according to the present invention will be described with reference to FIGS. 7 and 8.

FIG. 7 shows the configuration of an embodiment of the present invention. 7th
In the figure, parts corresponding to those in FIG. 5 are given the same reference numerals and redundant explanation will be omitted.

In FIG. 7, 31 and 32 are the second and third
The movable contact 31c of the switch 31 is connected to the movable contact 22c of the switch 22, and the movable contact 32c of the switch 32 is connected to the output terminal 23. One fixed contacts 31a and 32a of the switches 31 and 32 are directly connected, and the other contacts 31b and 32b are connected to the input side and output side of the waveform manipulation circuit 33, respectively. Reference numeral 34 denotes a delay pulse generation circuit, to which a recording control signal as shown in FIG. 8D is supplied from a control terminal 27. The output of the delayed pulse generating circuit 34 is commonly supplied to the switches 31 and 32 as a control signal. The rest of the structure is the same as that shown in FIG.

The operation of this embodiment is as follows.

When the recording control signal that has been connected since the disturbance occurrence time t ₁ is stopped at the disturbance stop time t ₂ ,
The switch 22 is in the connected state shown in FIG.
The delay pulse generation circuit 34 is, for example, a monostable multivibrator, and is triggered by the falling edge of the recording control signal, and generates a delay pulse that lasts for a time T _s from the disturbance stop time t ₂ as shown in FIG. 8F. Occur. This delayed pulse causes the switch 31
The movable contacts 31c and 32c of 32 are connected to the other fixed contacts 31b and 32b, respectively, as shown in FIG.

The waveform manipulation circuit 33 is composed of, for example, a clipper and a clamper, and during the duration of the delayed pulse, the waveform manipulation circuit 33 clips the reproduced video signal at the black level, as shown in FIG. Clamp at level.
As a result, the output of the waveform manipulation circuit 33 is only the reproduced horizontal synchronization signal.

When the delay pulse ends at time t ₃ , which is a time T _s after the disturbance stop time t ₂ , the switches 31 and 32 are connected in the opposite way to that shown, and the signals are transmitted via the three switches 22, 31 and 32 , input terminal 2
1 and an output terminal 23 are connected, and the reproduced video signal is output as is.

Therefore, the disturbance period and the delayed pulse generation period t ₁ ~
At t ₃ , as shown in FIG. 8H, a reproduced horizontal synchronizing signal appears at the output terminal 23 following the pseudo horizontal synchronizing signal. The AFC of the receiver, which had phase-locked to the pseudo-horizontal synchronization signal before time _t2 , will again phase-lock to the reproduced horizontal synchronization signal after time _t2 , but as mentioned above, there is a gap between the two synchronization signals. Because of the phase shift, it takes some time for the phase to lock again. During this period, the video signal level is clamped to the black level or pedestal level, so the screen of the receiver is dark. Here, the delay pulse generation period
By setting T _s equal to the above-mentioned skew occurrence period, skew can be masked.

Next, another embodiment of the masking device according to the present invention will be described with reference to FIGS. 9 and 10.

FIG. 9 shows the configuration of another embodiment of the present invention. In FIG. 9, parts corresponding to those in FIGS. 5 and 7 are given the same reference numerals, and redundant explanation will be omitted.

In FIG. 9, 41 and 42 are the second and third
The movable contact 41c of the switch 41 is connected to the movable contact 22c of the switch 22, and the movable contact 42c of the switch 42 is connected to the output terminal 23. One fixed contacts 41a and 42a of the switches 41 and 42 are directly connected, and the other contacts 41b and 42b are connected to the input side and output side of the masking circuit 43, respectively. The output of the delay pulse generator 34 is supplied to the masking circuit 43 . 44 is a drop pulse generation circuit, which includes the synchronous separation circuit 24 and the delay pulse generation circuit 3.
4 outputs are provided respectively. The output of drop pulse generating circuit 44 is commonly supplied to switches 41 and 42 as a control signal. The rest of the structure is the same as that shown in FIG.

The operation of this embodiment is as follows.

At the disturbance stop time _t2 , the switch 22
The connection state shown in the figure will be achieved. At the same time, a delayed pulse as shown in FIG. 10F is commonly supplied from the delayed pulse generating circuit 34 to the masking circuit 43 and the drop pulse generating circuit 44. The masking circuit 43 suppresses the positive polarity video signal supplied via the switch 41 to the black level or pedestal level while this delayed pulse is supplied. While the delay pulse is being supplied, the drop pulse generating circuit 44 generates a sync chip drop signal as shown in FIG.
Generates a timing pulse and uses it as a control signal,
Supplied to switches 41 and 42. When the timing pulse is at a low level, switches 41,4
2 is in the connected state shown in Fig. 9, and Fig. 10E
Only the horizontal synchronizing signal in the reproduced video signal as shown in FIG. 1 is led to the output terminal 23. During the period when the timing pulse is at a high level, the switches 41 and 42 are connected in the opposite way to that shown in the figure, and the reproduced video signal is supplied to the masking circuit 43. However, since the delayed pulse is also supplied at the same time, the switches 41 and 42 are connected to the masking circuit 43.
The output is either black level or pedestal level.

Therefore, in this embodiment as well, only the horizontal synchronizing signal in the reproduced video signal is taken out to the output terminal 23, as shown in FIG. 10H, during the delay pulse connection period _t2 to _t3 . , the same effects as the above-mentioned embodiment can be obtained.

Effects of the Invention As detailed above, according to the present invention, the reproduced video signal is masked not only during the period in which disturbance occurs due to recording, but also in the subsequent period when skew occurs, thereby impairing the visibility of the screen. It is possible to obtain a masking device for a video signal without any

[Brief explanation of the drawing]

Figures 1 and 2 show the spectrum and format of the 8V system, Figures 3 and 4 are schematic diagrams for explaining the present invention, and Figures 5 and 6 are the configuration of a conventional video signal masking device. FIGS. 7 and 8 are block diagrams and time charts showing one embodiment of a video signal masking device according to the present invention, and FIGS. 2 is a block diagram and a time chart thereof showing another embodiment. 11A and 11B are video heads, 12 is an erase head, 24 is a horizontal synchronization separation circuit, 25 is a counter, 33 is a waveform manipulation circuit, 34 is a delay pulse generation circuit, 43 is a masking circuit, and 44 is a drop pulse generation circuit.

Claims (1)

[Claims] 1. A magnetic head that is equipped with similar horizontal synchronization signal generation means and signal replacement means and records a video signal on a magnetic recording medium or erases a video signal recorded on the magnetic recording medium, and a magnetic head that records on the magnetic recording medium. During the simultaneous operation period, the signal replacement means converts the reproduced video signal by the reproduced magnetic head of the magnetic recording and reproducing apparatus configured to operate simultaneously with the reproduced magnetic head for reproducing the reproduced video signal. In a video signal masking device that replaces the output of a pseudo horizontal synchronization signal generating means,
A horizontal synchronizing signal selection and passing means is provided which operates to selectively pass a horizontal synchronizing signal in a video signal reproduced by the reproducing magnetic head for a predetermined period following the simultaneous operation period, and a video signal reproduced by the reproducing magnetic head for the predetermined period of time is provided. A video signal converting means for converting a portion excluding a substantially horizontal synchronizing signal into a signal of a constant level is provided, and the reproduced video signal is supplied to the horizontal synchronizing signal selection passing means and the video signal converting means for the predetermined period of time, and the reproduced video signal is reproduced. A masking device for a video signal, characterized in that a horizontal synchronization signal in the video signal is selectively passed through, and a portion of the reproduced video signal excluding the substantially horizontal synchronization signal is converted to a constant level and output.