JPH08205090A - Video signal reproducing device - Google Patents

Abstract

PURPOSE: To provide a video signal reproducing device with simple configuration without the generation of disturbance of a pattern in the video signal reproducing device provided with a video head exclusive for a long time mode. CONSTITUTION: The device is provided with a couple of long time mode exclusive video heads 3a, 3b fitted to a drum cylinder 1, an amplifier circuit 4 amplifying a read signal read by the video heads 3a, 3b and providing an output, a signal processing circuit 5 converting the amplified signal into a video signal and providing an output, a DC conversion circuit 6 converting the amplified signal into a DC voltage, an A/D converter circuit 7 sampling a DC voltage between a start edge and an end edge of a head switching signal for several number of times to convert the voltage into digital data, a waveform storage circuit 8 storing data at each sample point, and an arithmetic control section 9 comparing the data stored in the waveform storage circuit 8 with preset reference data, discriminating whether or not a pseudo vertical synchronizing signal is outputted and giving a control signal to the signal processing circuit 5. The signal processing circuit 5 superimposes the pseudo vertical synchronizing signal to the image signal reproduced when the control signal is received and provides the output of the result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal reproducing apparatus for reproducing a video signal recorded on a magnetic tape in a long time mode, and more particularly to a video signal reproducing apparatus having a video head dedicated to the long time mode.

[0002]

2. Description of the Related Art Household VTR (Video Tape Recorder)
In the standard mode of, the video head whose head width is almost equal to the video track width (58 μm) is used.
In the long time mode such as the triple mode, the head (20 to 30 μm) wider than the video track width (19 μm)
Is used. This is because it is shared by heads with an intermediate width (about 30 μm) in order to cover a reproduction tracking error and to avoid the complexity of the structure due to the increase in the number of video heads.

However, when recording is performed by a head having a width wider than the track width, an overlapping recording portion occurs, and a low-pass color signal remains unerased in a deep layer portion of the overlapping portion. As a result, this signal appears as flicker noise on the screen during playback, and the residual component of the luminance signal that remains in the color signal without being separated by YC separation and the low-frequency component of the low-frequency part of the FM luminance signal. The leak to the signal appears as crosstalk noise on the screen. Further, since the azimuth effect is weakened in the low frequency part of the FM luminance signal, the amount of crosstalk becomes relatively large and appears as edge noise or fine jitter.

Therefore, recently, in order to improve the image quality in the long-time mode, many devices use a video head having a width equal to the track width (19 μm) as a long-time mode dedicated head. However, when a magnetic tape recorded by an apparatus not equipped with such a dedicated head is reproduced by the dedicated head, the trace loci of the video head shown by the broken line and the video track shown by the solid line may not match as shown in FIG. Occurs.

As a result, as shown in FIG. 4, the reproduction signal becomes small at a point several hundreds of microseconds delayed from the edge of the head switching signal, and the vertical synchronizing signal VD becomes squeezed. Then, the vertical sync signal is not recognized well on the monitor screen, and jitter may occur in the vertical direction.

FIG. 5 is a block diagram of a conventional video signal reproducing apparatus in consideration of such inconvenience. In the figure, the drum cylinder 11 has video heads 13a and 13b dedicated to the long time mode having a head width equal to the video track width on the magnetic tape 12, and a width wider than the video track width (about 1.5 times). Video heads 14a, 14
b is attached.

At the time of reproduction in the long time mode, the video tracks of the magnetic tape 12 are traced by the video heads 13a and 13b to reproduce the recorded signal, and the reproduced signal is amplified by the amplifier circuit 15 to be converted into the signal processing circuit 16 and DC conversion. Circuit 1
Send to 7. The signal processing circuit 16 converts this reproduction signal into a video signal and outputs it.

The DC conversion circuit 17 performs DC conversion on the reproduction signal by peak detection or the like, and the DC signal is AD conversion circuit 18
To enter. The AD conversion circuit 18 samples the DC signal at a specific time interval from the start time to the end time of the head switching signal, converts the value at each sampling point into digital data, and inputs it to the waveform storage circuit 19.

The arithmetic control unit 20 reads the digital data of each sample point stored in the waveform storage circuit 19 and compares it with the reference level in the arithmetic unit 20a, and when the level of the data is lower than the reference level or the waveform balance. When the value is bad, the control unit 20b sends a switching signal to the amplifier circuit 15. The amplifier circuit 15 selects and outputs the reproduction signal from the video heads 14a and 14b instead of the reproduction signal from the video heads 13a and 13b by this switching signal.

In this way, when the video track of the magnetic tape 12 and the trace loci of the video heads 13a and 13b deviate from each other, the reproduction signals from the wide video heads 14a and 14b are switched to increase the reproduction output. There is. The video head may be switched by the manual switch SW.

FIG. 6 is a block diagram showing another conventional example. In this conventional example, the magnetic tape 1 is attached to the drum cylinder 11.
In this example, only the long-time mode dedicated video heads 13a and 13b having a head width equal to the video track width of 2 are attached, and a wide head is not attached.

In the figure, the video heads 13a, 13
In b, the reproduction signal obtained by tracing the video track of the magnetic tape 12 is input to the amplifier circuit 15. The amplifier circuit 15 amplifies this reproduction signal and sends it to the signal processing circuit 16. The signal processing circuit 16 converts the reproduced FM signal into a video signal and outputs it.

When the manual switch SW connected to the arithmetic unit 20a is pressed during reproduction, the arithmetic control unit 20
A control signal is sent from the control unit 20b to the signal processing circuit 16.
Upon receiving this instruction, the signal processing circuit 16 mixes the pseudo vertical synchronizing signal with the video signal and outputs it. As a result, even if the trace locus of the video head deviates from the video track and the vertical sync signal VD is unrecognizable, the vertical jitter can be suppressed by supplementing it with the pseudo vertical sync signal.

[0014]

By the way, in the conventional example shown in FIG. 5 described above, it is necessary to provide two pairs of video heads only for long-time mode reproduction, and accordingly, two pairs of inputs are also input to the amplifier circuit. It is necessary to provide a section. For this reason,
The disadvantage is that the device becomes very expensive. Also,
Switching noise always occurs on the TV monitor when the video head dedicated to the long-time mode is switched to the wide video head, or conversely, when the wide video head is switched to the video head dedicated to the long-time mode. There was an inconvenience.

Further, in the conventional example shown in FIG. 6, since the user manually commands the output of the pseudo vertical sync signal when the vertical sync of the reproduction signal is lost, the vertical sync is not always correctly applied. There was an inconvenience that it was not limited.

Therefore, it is an object of the present invention to provide a video signal reproducing apparatus having a simple structure and not generating switching noise when reproducing a magnetic tape recorded in a long time mode with a video head dedicated to the long time mode. And

[0017]

A video signal reproducing apparatus according to the present invention comprises a pair of long-time mode dedicated video heads mounted on a drum cylinder for reading signals recorded in a long-time mode on a magnetic tape, and a video head. An amplifier circuit that amplifies and outputs the signal read by, a signal processing circuit that converts the amplified signal into a video signal and outputs the signal, a DC conversion circuit that converts the amplified signal into a DC voltage, and a DC voltage head switching An AD conversion circuit that samples the signal from the start edge to the end edge several times to convert it into digital data, a waveform storage circuit that stores the digital data at each sample point, and the digital data stored in the waveform storage circuit in advance. The control signal is sent to the signal processing circuit by comparing with the set reference data to determine whether to output the pseudo vertical sync signal. That the arithmetic control unit is provided, the signal processing circuit outputs superimposes the pseudo vertical synchronizing signal to the image signal reproduced by receiving a control signal.

[0018]

In the structure of the present invention, the signal read from the magnetic tape by the pair of video heads is amplified by the amplifier circuit, converted into a video signal by the signal processing circuit and output to the outside.

Further, the signal amplified by the amplifier circuit is converted into a DC voltage by peak detection or the like by the DC converter circuit, and further A
From the start edge to the end edge of the head switching signal in the D conversion circuit, the data is converted into digital data at a predetermined sampling period and stored in the waveform storage circuit.

The stored data is compared with preset reference data in the arithmetic control unit and used as data for determining whether or not it is necessary to generate a pseudo vertical synchronizing signal. Specifically, if the average value of each sample point is smaller than a predetermined reference value, it is determined as a non-recording tape. Further, the data at the position of several hundreds of microseconds from the edge of the head switching signal corresponding to the position of the vertical synchronizing signal is intensively compared to determine whether or not the vertical synchronizing signal is crushed.

As a result, when it is determined that the pseudo vertical synchronizing signal needs to be output, the arithmetic control section sends a control signal to the signal processing circuit to instruct the generation of the pseudo vertical synchronizing signal. Upon receiving this command, the signal processing circuit superimposes the pseudo vertical synchronizing signal on the image signal and outputs it.

[0022]

1 is a block diagram showing an embodiment of a video signal reproducing apparatus according to the present invention. In the figure, the drum cylinder 1 is provided with video heads 3a and 3b having a head width equal to the video track width on the magnetic tape 2 and dedicated to the long-time mode.

During reproduction in the long time mode, the video heads 3a and 3b trace the video track of the magnetic tape 2 to reproduce the recorded signal, and the reproduced signal is amplified by the amplifier circuit 4 to be processed by the signal processing circuit 5. And DC conversion circuit 6
Send to The signal processing circuit 5 converts the reproduction signal into a video signal and outputs it.

The DC conversion circuit 6 performs DC conversion on the amplified reproduction signal by peak detection or the like, and inputs this DC signal to the AD conversion circuit 7. The AD conversion circuit 7 samples the DC signal at a specific time interval from the start time to the end time of the head switching signal, converts the value at each sampling point into digital data, and inputs it to the waveform storage circuit 8.

The arithmetic control unit 9 reads the data of each sample point stored in the waveform storage circuit 8, and the arithmetic unit 9a outputs the data of a specific position (for example, a position delayed by several 100 μsec from the edge of the head switching signal) to the reference level. When the level of the data is lower than the reference level, the control section 9b sends a control signal to the signal processing circuit 5.

This specific position is an important position because it corresponds to the position of the vertical synchronizing signal in the video signal. However, if only this position is judged, the control signal will be output to the non-recording tape. Therefore, the arithmetic unit 9a determines whether to output the control signal from the data of each sample point stored in the waveform storage circuit 8. Specifically, confirm that there is data above a predetermined value in other parts as well,
Finally, it is determined whether to output the pseudo vertical synchronizing signal.

FIG. 2 is a flow chart for explaining the operation of this embodiment. This operation is started under the condition where the servo is stabilized after the tape speed is determined. When starting, first, the DC-converted signal voltage value input to the AD conversion circuit 7 is sequentially sampled at a predetermined sampling period from the start point of the head switching signal (step S1).

The data value D _N (N
Is stored in the waveform storage circuit 8 (step S2). Then, by dividing the sum of the up data values D ₁ to D _N number of times N to determine the average input voltage value D _AVE, determines whether a predetermined average voltage value d _AVE above (step S
3).

As a result, if the average value D _AVE is less than the average value d _AVE (that is, if the determination is no), it is determined that the tape is a non-recording tape, and it is not necessary to generate a pseudo vertical synchronizing signal, and the processing is ended. To do. Further, in the case where the signal is too small, even if the pseudo vertical synchronizing signal is output, the entire screen becomes noisy, and the process is ended in this case also considering that it is meaningless.

In step S3, if it is determined that the average value D _AVE is greater than or equal to the average value d _AVE (that is, the determination is YES), then the data value D _{N at} each sample point is less than the predetermined voltage value d _N. It is determined whether or not (step S4). In this case, the comparison between the data value D _N and the voltage value d _N is set so that the position of several hundred μsec from the edge of the head switching signal (that is, the position of the vertical synchronizing signal VD) is mainly compared. As a result, if the data value D _N is equal to or higher than the voltage value d _N (that is, if the determination is NO), it is determined that the video head is tracing the video track normally, and it is necessary to output the pseudo vertical synchronization signal. Since there is not, the processing ends.

In step S4, if the data value D _N is less than the voltage value d _N (that is, if the determination is YES), the control unit 9b sends a control signal to the signal processing circuit 5 to generate a pseudo vertical synchronizing signal. Command (step S
5). Upon receiving this command, the signal processing circuit 5 superimposes the pseudo vertical synchronizing signal on the image signal and outputs it (step S6).

After that, it is judged whether or not the recalculation is necessary for the continuous output of the pseudo vertical synchronizing signal (step S
7) If necessary, the processing from step S1 is repeated. If it is not necessary, it is judged whether or not it is the stop condition of the pseudo vertical synchronizing signal (step S8), and if it is not the stop condition, the processes from step S6 are repeated, and if it is the stop condition, the process is ended.

[0033]

According to the present invention, by comparing the data value of the reproduction signal with a predetermined reference value, it is automatically determined whether or not the pseudo vertical synchronizing signal is required to be output. Therefore, it is possible to superimpose the vertical synchronization signal on the correct position, and since the video head can be configured only by the video head dedicated to the long-time mode, it is possible to construct an inexpensive system.

Further, since it is not necessary to switch between the dedicated video head and the wide video head as in the conventional case, there is an effect that the noise and the disturbance of the screen which occur at the time of switching do not occur.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a video signal reproducing device according to the present invention.

FIG. 2 is a flow chart for explaining the operation of the present invention.

FIG. 3 is an explanatory diagram showing a trace locus of a video head with respect to a video track.

FIG. 4 is an explanatory diagram showing a state in which both ends of a reproduced signal are crushed.

FIG. 5 is a block diagram of a conventional video signal reproducing device.

FIG. 6 is a block diagram showing another example of a conventional video signal reproducing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 drum cylinder 2 magnetic tape 3a, 3b video head 4 amplification circuit 5 signal processing circuit 6 DC conversion circuit 7 AD conversion circuit 8 waveform storage circuit 9 arithmetic control unit 9a arithmetic unit 9b control unit

Claims (1)

[Claims] 1. A pair of long-time mode dedicated video heads mounted on a drum cylinder for reading a signal recorded in a long-time mode on a magnetic tape, and an amplifier for amplifying and outputting the signal read by the video head. A circuit, a signal processing circuit for converting the amplified signal into a video signal and outputting the video signal, a DC conversion circuit for converting the amplified signal into a DC voltage, and a DC voltage from the start edge to the end edge of the head switching signal An AD conversion circuit for sampling the interval between several times to convert it to digital data, a waveform storage circuit for storing the digital data at each sample point, the digital data stored in the waveform storage circuit, and preset reference data. Computation of a control signal to the signal processing circuit by determining whether to output a pseudo vertical synchronizing signal A video signal reproducing device, wherein the signal processing circuit superimposes a pseudo vertical synchronizing signal on a video signal reproduced upon receiving the control signal and outputs the superimposed video signal.