JPH05292465A - Video tape reproducing device - Google Patents

Abstract

PURPOSE:To obtain reproduced pictures easy to see by inserting pseudo vertical synchronizing pulses into video signals at the time of special reproducing at the almost same timing as vertical synchronizing pulses at the time of normal reproducing. CONSTITUTION:The video signal obtained in a demodulation circuit 5 at the time of special reproducing contains noises generated every time video heads 3a and 3b cross video tracks 15.... In an inserting circuit 11, the pseudo vertical synchronizing pulse is inserted into the video signal and outputted to a monitor 13. A measuring circuit 7 does not measure time difference, and a storage circuit 8 holds time measured at the time of normal reproducing. Thus, since this VTR generates the pseudo vertical synchronizing pulses based on the time difference measured in the case of normal reproducing, the pseudo vertical synchronizing pulse can be obtained at the almost same timing as the timing of vertical synchronizing pulses obtained at the time of normal reproducing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video tape reproducing apparatus for inserting a pseudo vertical synchronizing pulse into a video signal during special reproduction such as slow reproduction and still reproduction.

[0002]

2. Description of the Related Art In a VTR (video tape recorder), a video head switching signal 5 shown in FIG.
According to 1, the two video heads are switched every field time. The switching timing is set to come before the vertical synchronizing pulse 53 ... Of the video signal (FIG. 3 (b)), whereby the switching noise of the video head is made inconspicuous on the reproduction screen.

By the way, when special reproduction such as still reproduction or fast-forward reproduction is carried out, the video head crosses the video track on the video tape at an angle, so that the video signal has a waveform as shown in FIG. , Noise 55 ... is generated every time the video track is crossed. When the noise 55 overlaps with the vertical sync pulse 53, the vertical sync is disturbed on the playback screen, making the screen hard to see.

Therefore, in order to prevent the disturbance in the vertical direction of the screen, a pseudo vertical synchronizing pulse 57 is generated and, as shown in FIG.
It is inserted at the same timing as or earlier than 3.

For example, in the VHS type VTR, the switching timing of the video head is determined by the vertical synchronizing pulse 53 ...
It is set to be 6.5 ± 1.5H before (1H indicates one horizontal scanning period), and the above-mentioned pseudo vertical synchronizing pulse 5
No. 7 is designed to be inserted within 5H after switching the video head.

[0006]

However, in the above-mentioned conventional configuration, there is a deviation of about 1.5H between the timing of the vertical synchronizing pulse 53 ... And the timing of the pseudo vertical synchronizing pulse 57. At the moment of switching, the whole screen moves up and down, which is unnatural and unsightly.

[0007]

In order to solve the above-mentioned problems, the video tape reproducing apparatus of the present invention is arranged such that two rotating video heads are alternately switched for each pulse of the switching signal, and the video signal is transferred from the video tape. In a video tape playback device that plays back video, a sync separation circuit that extracts the vertical sync pulse from the video signal, a measurement circuit that measures the time difference from the pulse of the switching signal to the vertical sync pulse during normal playback, and the time measured by the measurement circuit. , A pulse generation circuit that generates a pseudo vertical sync pulse at the timing of adding the time stored in the storage circuit to the timing of the pulse of the switching signal, and a pseudo vertical sync pulse is inserted into the video signal during special playback. It is characterized in that an insertion circuit for

[0008]

With the above structure, in the video tape reproducing apparatus for reproducing the video signal from the video tape by alternately switching the two rotating video heads for each pulse of the switching signal, the sync separation for extracting the vertical sync pulse from the video signal. Circuit, a measurement circuit that measures the time difference from the switching signal pulse to the vertical synchronization pulse during normal playback, a storage circuit that stores the time measured by the measurement circuit, and a storage circuit that stores the switching signal pulse timing. Since a pulse generation circuit that generates a pseudo vertical sync pulse at the timing with added time and an insertion circuit that inserts the pseudo vertical sync pulse into the video signal during special playback are provided, the vertical sync during normal playback during special playback is provided. The pseudo vertical sync pulse can be inserted into the video signal at substantially the same timing as the pulse. As a result, the entire screen does not move up and down at the moment when the normal reproduction is switched to the special reproduction, or at the moment when the special reproduction is switched to the normal reproduction, so that a reproduction screen that is easy to see can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 and 2.

The VTR of this embodiment is, as shown in FIG.
Drum 1 and drum motor 2 for rotating the drum 1
And a video head 3a arranged 180 degrees on the drum 1.
3b, a microcomputer 12 for controlling the system, a switch 4 for switching the video heads 3a and 3b for each field time according to a switching signal 21 from the microcomputer 12, and a video head 3a selected by the switch 4. Alternatively, a demodulation circuit 5 for demodulating a video signal from the reproduction signal from 3b is provided.

As shown in FIG. 2A, the level of the switching signal 21 of the video heads 3a and 3b is inverted every field time, and the switch 4 is switched each time the level is switched. ..

Further, the VTR of the present embodiment uses the sync separation circuit 6 for extracting the vertical sync pulse from the video signal and the control signal 28 from the microcomputer 12.
A measuring circuit 7 that measures the time difference from the pulse edge of the switching signal 21 to the pulse edge of the vertical synchronizing pulse, a storage circuit 8 that stores the time measured by the measuring circuit 7, and a pulse edge of the switching signal 21. A pulse generation circuit 9 for generating a pseudo vertical sync pulse at a predetermined time (described later) based on the time and the time stored in the storage circuit 8.
An insertion circuit 11 for inserting a pseudo vertical synchronizing pulse into the video signal from the demodulation circuit 5, and a microcomputer 1
The switch 10 is provided for inputting a pseudo vertical synchronizing pulse to the insertion circuit 11 based on the control signal 28 from 2.

The measurement of the time difference in the measuring circuit 7 is executed at the time of normal reproduction based on the control signal 28 from the microcomputer 12. Therefore, during special reproduction, the time measured during the immediately preceding normal reproduction is held in the storage circuit 8.

The pulse generation circuit 9 adds the time stored in the storage circuit 8 to the time of the pulse edge of the switching signal 21 from the microcomputer 12 so that the timing of the vertical synchronizing pulse obtained during normal reproduction is almost the same. Pseudo vertical sync pulses are generated at the same timing. The pseudo vertical sync pulse is input to the insertion circuit 11 via the switch 10 as described above.

The opening and closing of the switch 10 is controlled by a control signal 28 from the microcomputer 12, and the pseudo vertical synchronizing pulse is input to the inserting circuit 11 only during special reproduction. Therefore, the pseudo vertical sync pulse is inserted into the video signal only during special reproduction.

In the above structure, the rotary drum 1 is rotationally driven by the drum motor 2, and accordingly, the video heads 3a and 3b are rotated while alternately tracing the video tracks 15 on the video tape 14. The reproduced signals obtained by the video heads 3a and 3b are switched by the switch 4 for each field time and input to the demodulation circuit 5. The demodulation circuit 5 demodulates the video signal from the reproduced signal.

The video signal obtained by the demodulation circuit 5 during normal reproduction is shown in FIG. Since the pseudo vertical synchronizing pulse is not input to the inserting circuit 11, the video signal is not included in the inserting circuit 1.
1 is simply passed and output to the monitor 13. The sync separation circuit 6 extracts the vertical sync pulse 23 ... From the video signal, the measurement circuit 7 measures the time difference, and the storage circuit 8 stores the time measured by the measurement circuit 7.

FIG. 2C shows a video signal obtained by the demodulation circuit 5 during special reproduction. The video signal includes noise 25 ... Generated each time the video heads 3a and 3b cross the video tracks 15. In the insertion circuit 11, FIG.
As shown in (d), the pseudo vertical sync pulses 27 ... Are inserted in the video signal and output to the monitor 13. The measuring circuit 7 does not measure the time difference, and the storage circuit 8 holds the time measured during normal reproduction.

As described above, in the VTR of this embodiment, the pseudo vertical synchronizing pulses 27 ... Are generated based on the time difference measured during normal reproduction, so the timing of the vertical synchronizing pulses 23 ... Obtained during normal reproduction. The pseudo vertical synchronizing pulse 27 ... Has the almost same timing as the above. As a result, even if the normal reproduction is switched to the special reproduction or the special reproduction is switched to the normal reproduction, the entire screen does not move up and down, and a reproduced image that is natural and easy to see can be obtained.

[0020]

As described above, the video tape reproducing apparatus of the present invention measures the time difference between the sync separation circuit for extracting the vertical synchronizing pulse from the video signal and the pulse of the switching signal to the vertical synchronizing pulse during normal reproduction. Circuit, a storage circuit that stores the time measured by the measurement circuit, a pulse generation circuit that generates a pseudo vertical synchronization pulse at the timing of the switching signal pulse timing plus the time stored in the storage circuit, and special playback Since an insertion circuit that inserts a pseudo vertical sync pulse into the video signal is sometimes provided,
During special playback, a pseudo vertical sync pulse can be inserted into the video signal at almost the same timing as the vertical sync pulse during normal playback. As a result, the entire screen does not move up and down at the moment when the normal reproduction is switched to the special reproduction, or at the moment when the special reproduction is switched to the normal reproduction, so that an easy-to-see reproduction screen can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a VTR according to the present invention.

FIG. 2 is a waveform diagram for explaining a reproducing operation of the VTR shown in FIG.

FIG. 3 is a waveform diagram for explaining a reproducing operation of a conventional VTR.

[Explanation of symbols]

 1 Drum 3a Video Head 3b Video Head 5 Demodulation Circuit 6 Sync Separation Circuit 7 Measurement Circuit 8 Recording Circuit 9 Pulse Generation Circuit 11 Insertion Circuit 21 Switching Signal 23 Vertical Sync Pulse 27 Pseudo Vertical Sync Pulse

Claims (1)

[Claims] 1. A video tape reproducing apparatus for reproducing a video signal from a video tape by alternately switching two rotating video heads for each pulse of a switching signal, and a sync separation circuit for extracting a vertical sync pulse from the video signal. A measurement circuit that measures the time difference from the pulse of the switching signal to the vertical synchronization pulse during normal playback, a memory circuit that stores the time measured by the measurement circuit, and a time that is stored in the memory circuit at the timing of the pulse of the switching signal. A video tape reproducing apparatus characterized in that a pulse generating circuit for generating a pseudo vertical synchronizing pulse at an added timing and an inserting circuit for inserting the pseudo vertical synchronizing pulse into a video signal during special reproduction are provided.