JPH053796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a time axis correction device in a video tape recorder (VTR) capable of slow motion playback.

Conventional configuration and its problems In broadcasting stations, etc., the time axis correction device shown in Figure 1 is indispensable because it is necessary to match the reproduced video signal from the VTR to the station's standard synchronization signal before sending it out. .

In FIG. 1, a reproduced video signal 1 from a VTR or the like is supplied to an analog-to-digital converter (A/D) 2 and a sync separation circuit 3. The synchronization separation circuit 3 supplies a horizontal synchronization signal 4 to a write clock generation circuit 6 and a vertical synchronization signal (tape V signal) 5 to a latch circuit 7. The write clock generation circuit 6 supplies a clock locked to the horizontal synchronization signal to the A/D 2 and the memory circuit 8, and also supplies the write line address counter 9 with a signal _H10 of the horizontal synchronization period. Further, the read clock generation circuit 11 applies a clock to the memory circuit 8 and the digital-to-analog converter (D/A) 13 based on the external reference synchronization signal 12, and applies the clock to the read line address counter 14 based on the external reference synchronization signal 12. The included horizontal synchronization signal F _H 15 and vertical synchronization signal (VP signal) 16 are added. The write line address counter 9 and the read line address counter 14 count _H 10 and F _H 15 respectively to create line addresses, and after these line addresses are mixed in the mixing circuit (MIX) 17, they are stored in the memory 8. has been added. The latch circuit 7 takes in the write line address at the tape V signal 5, and
Read line address counter 14 when VP signal 16
The write line address when the tape V signal is 5 and the read line address when the VP signal is 16 are made to match.

However, in the reproduced video signal 1 from the VTR, the tape V signal 5 may be missing due to dropout or the like. In this case, the operation performed by the latch circuit 7 is no longer performed stably, and as a result, the output video signal of the time axis corrector causes vertical fluctuations on the monitor. In addition, in a VTR equipped with a movable head for the purpose of noiseless slow motion playback, the tape V
Two signals of signal 5 appear in one field,
Sometimes it doesn't come out at all. Even in such a case, a stable image cannot be obtained.

In order to avoid malfunctions caused by missing tape V signals due to dropouts, etc., it is necessary to create a predicted V signal delayed by one field from the tape V signal of the previous field, and to replace it when the tape V signal is missing. It is. However, in VTRs that perform noiseless slow playback using a movable head, the time intervals between adjacent V signals are not constant, and in some cases, two V signals may appear in succession, resulting in very irregular playback. Generates a V signal. Next, the process of generating an irregular V signal will be explained using FIGS. 2 and 3.

FIG. 2 is a schematic diagram showing the running of the tape and video head of a two-head helical scan VTR. Two heads, an A head 18 and a B head 19, are mounted at 180° opposing positions on the circumference of a rotary cylinder 20 and rotate in the direction of an arrow 21. Further, the magnetic tape 22 is wrapped around the rotating cylinder 20 by more than 180 degrees, and the magnetic tape 22 is
Run in direction 3.

FIG. 3 shows the pattern recorded on the tape by the head of FIG. The magnetic tape 22 runs in the direction of the arrow 23, and the A head 18,
The B heads 19 alternately run in the direction of the arrow 21 and write recording tracks 24, 2 on the magnetic tape 22.
Write numbers 5 and 26 in that order. The areas 24', 25', 26', 24'', 25'', and 26'' indicated by broken lines in the figure are overlap recording areas. In order to eliminate video signal dropouts, the magnetic tape 22 is usually wound around the rotary cylinder 20 at an angle of 180° or more, so an overlap area occurs. It is.

During normal reproduction, the A head 18 scans the P-Q line segment. When the A head 18 reaches the Q point, the B head 19 is located at the P' point. Next, the B head 19 scans the P'-Q' line segment, and then the A head 18 scans the P'-Q' line segment. Scan the P″-Q″ line segment.

However, the situation is different during noiseless slow motion playback. For example, a case will be explained in which the tape is at rest.

In the stationary mode, the trajectories of the A head 18 and the B head 19 match, for example, the line segment P'-
It becomes a trajectory such as Q. However, since movement from recording track 25 to recording track 24 occurs during the trajectory, noise bands occur on the monitor screen.

For this purpose, heads movable perpendicularly to the track scanning are installed as the A head 18 and B head 19, and these movable heads are moved in a wedge shape. In the stationary mode, the head A1 is placed on the line segment P'-R.
8. Control so that the trajectory of head B19 follows. In this way, one recording track is always scanned within one field, and the generation of noise bands can be avoided.

Furthermore, in the recording track of a helical scan VTR, there is a shift (α _H ) in the horizontal synchronizing signal position, as shown at 27 in FIG. Here, the explanation will be made assuming α _H =25H.

In the case of NTSC system, the number of horizontal scanning periods (H) included in line segment P-Q is 262.5H for one field.
It is. The aforementioned line segment P'-R is added by _αH , so that one field is made up of 265H.

Two V signals appear within one field on the line segment P'-R in FIG. However, if you pay attention only to the original V signal shown by hatching at the bottom of the figure, after reproducing the V signal at the A head 18,
The number of horizontal scanning periods (H) included until the B head reproduces the same V signal is determined to be 265H.

Assuming slow motion playback at 1/2 speed, after the A head 18 and B head 19 scan the P'-R line segment, the A head 18 and B head 19
Scan the P″-R′ line segment. In this case, A head 18
from the time when the B head 19 reproduces the V signal on the same track until the B head 19 reproduces the V signal on the P'-R line segment.
265H exists, then the B head 19 reproduces the V signal on the P'-R line segment, and then the A head 18 reproduces the P''-
There are 262.5H until the V signal on the R' line segment is reproduced. This means that in the figure, point P″ is more α _H than point P′.
It is clear from the preceding position. In the end, the V signal interval during 1/2 slow motion playback is 265H.
It will appear alternately with 262.5H. In other slow motion playbacks from the static mode to the normal playback mode, the V signal interval is a combination of 262.5H and 265H. In other words, when playing the same track, 265H, when playing the next track,
It becomes 262.5H. Furthermore, from 1x speed to 2x speed, there is a combination of playing the next track as in normal driving and playing with a 1 track jump, and the V signal interval is:
It is a combination of 262.5H and 260H. Reverse 1
During slow motion playback up to double speed, the same track is played back, and the track jumps to a track in the opposite direction. That is, during reverse playback, the V signal interval is a combination of 265H and 267.5H.

In FIG. 3, the head switching positions P, P', and P'' are arranged in advance so that they are located just before the V signal.By doing this, even in the special playback mode mentioned above, The positional relationship between the V signal and the video signal that follows it becomes constant.For example,
When one field consists of 265H,
Before the head switching position, only 2.5H of data is reproduced in duplicate, and the positional relationship between the V signal and the subsequent video signal is constant. However, if the head switching position is set after the V signal, in the above special playback mode, the playback signal will expand or shrink by _αH units when switching the head, and the positional relationship between the V signal and the video signal will not be constant. do not. Therefore, if a V signal in which the positional relationship between the V signal and the video signal is not determined is used as tape V5 in FIG. 1, vertical movement of the image in units of α _H will occur on the monitor screen during special playback.

OBJECTS OF THE INVENTION In view of the above points, an object of the present invention is to provide a time axis correction device that does not cause vertical movement of an image on a monitor screen.

Structure of the Invention The present invention provides a memory that stores a reproduced video signal reproduced by a video tape recorder, a write/read address generation circuit that generates write and read addresses for each line to the memory, and a video head scanning A signal created based on a video head switch signal whose switching position is in the vertical blanking period before the vertical synchronization signal recorded near the start position is used as a gate pulse, and the video head is switched from the vertical synchronization signal of the reproduced video signal to the video head switch signal. A gate circuit derives the signal immediately after the switching position as the tape V signal, and a gate circuit that counts a predetermined number of signals synchronized with the reproduction horizontal synchronizing signal to predict the tape V position of the next field of the tape V signal to generate a predicted V signal. V that generates
It includes a prediction circuit and a V signal competition circuit which receives the tape V signal and the predicted V signal as input, normally outputs the tape V signal, and outputs the predicted V signal when the tape V signal is missing, and prevents playback track skipping during slow motion playback. The predetermined number counted by the V prediction circuit is changed based on the information, the write line address of the memory is latched at the output of the V signal competition circuit, and the latched address is latched at the vertical synchronization signal position of the external reference synchronization signal. The time axis correction device is characterized in that the read data is loaded into the write/read address generation circuit as a read line address.

DESCRIPTION OF EMBODIMENTS FIG. 4 shows a time axis correction device according to an embodiment of the present invention. In FIG. 4, the same components as in the conventional example are given the same numbers. In this embodiment, a reproduction vertical synchronization signal generation circuit 28 is added to the conventional configuration shown in FIG. The configuration of this reproduction vertical synchronization signal generation circuit 28 is shown in FIG.

In Figures 4 and 5, 29 is a terminal to which a video head switch signal (head SW signal) is applied. It has a switching position during the ranking period.
30 is a jump signal, which is a signal indicating playback track jump information. 31 is a monostable multivibrator (MM) which outputs a pulse triggered at the switching position of the head SW signal. This pulse is used as a gate pulse for the gate circuit 32. 33 is a multiplier circuit, which generates a signal with twice the frequency of the horizontal synchronization signal.
_2H is generated and supplied to the V prediction circuit 34 as a clock. The V prediction circuit 34 is composed of a counter, and after counting a predetermined number of clocks, calculates the predicted V
Output a signal. The predetermined number counted by the V prediction circuit 34 is changed by a signal indicating reproduction track jump information in the jump signal. 35 is a V signal competition circuit which inputs the tape V signal which is the output of the gate circuit 32 and the predicted V signal which is the output of the V prediction circuit 34, and normally outputs the tape V signal, but when the tape V signal is missing. At this time, a predicted V signal is output.

As shown in FIG. 6, it is assumed that 36 synchronization signals are obtained in the synchronization separation circuit 3 during special reproduction. 37 in the vertical synchronization extraction circuit (not shown) in the synchronization separation circuit 3.
A signal like this is obtained, and two V signals are generated across the head switching position 38.

However, according to the present invention, head switching position 38
Since V is located in the vertical blanking period before the vertical synchronization signal recorded near the scanning start position of the video head, the V before the head switching position 38
The signal is not important. In order to prevent malfunction, in this embodiment, M.M31 is
Thus, a gate pulse as shown in 39 is generated and used as a gate signal for the gate circuit 32. by the way,
The positional deviation between the head switching signal and the V signal must be planned for up to the correction range (correction window) of the time axis corrector, so the gate pulse 39
It is necessary to keep the width of the correction range larger than the correction range. By this gate pulse 39, unnecessary V signals are discarded from the tape V signal 5 (37) which is the output of the synchronization separation circuit 3, and a tape V signal such as 40 is obtained. By the way, 41, 42, and 43 are various predicted V signals derived based on track jump information from one field before, and in this example, the V signal interval is 262.5H.
A predicted V signal 41 has been derived. V prediction circuit 3
4 is reset by the tape V signal one field before or the predicted V signal, and the horizontal synchronization frequency _H
This is to predict V by counting the double clock _2H . During slow motion playback, as mentioned above, the V signal interval may _change due to track skipping.
There is an increase/decrease in units, and the position of the predicted V signal is shifted in units of α _H based on the track jump information.

The predicted V signal 41 obtained in this way and the tape V
Signal 40 is applied to the V signal contention circuit. Typically, the tape V signal 40 is located inside the predicted V signal 41. If the tape V signal 40 protrudes outside the predicted V signal 41, the V signal competition circuit 35 operates so that the tape V signal that protrudes takes priority.

Effects of the Invention As described above, even during irregular reproduction such as noiseless slow motion, it is possible to stably extract a vertical synchronization signal that always matches the reproduced video signal, and it is possible to reproduce a stable image without vertical movement on the monitor screen.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional time axis correction device.
Figure 2 is a plan view showing the running of the tape and video head of a two-head helical scan VTR;
4 is a block diagram of a time axis correction device according to an embodiment of the present invention. FIG. 5 is a block diagram showing the configuration of the main part of the embodiment. The figure is a waveform diagram for explaining the operation of the same embodiment. 3...Synchronization separation circuit, 7...Latch circuit, 8...
...Memory, 9...Write line address counter,
14...Read line address counter, 31...
Monostable multivibrator, 32...gate circuit, 33...multiplier circuit, 34...V prediction circuit, 3
5...V signal competition circuit.

Claims (1)

[Claims] 1 A memory that stores the reproduced video signal reproduced by the video tape recorder, a write/read address generation circuit that generates the write and read addresses for each line to this memory, and a memory that stores the reproduced video signal reproduced by the video tape recorder, and The gate pulse is a signal created based on a video head switch signal whose switching position is during the vertical blanking period before the vertical synchronizing signal, and the switching position immediately after the switching position of the video head from the vertical synchronizing signal of the reproduced video signal is used as a gate pulse. a gate circuit that derives the signal as a tape V signal;
A predetermined number of signals synchronized with the reproduction horizontal synchronization signal are counted and the tape V of the next field of the tape V signal is
A V prediction circuit that predicts the position and generates a predicted V signal, and a V signal competition circuit that receives the tape V signal and the predicted V signal as input, normally outputs the tape V signal, and outputs the predicted V signal when the tape V signal is missing. At the time of slow motion reproduction, the predetermined number counted by the V prediction circuit is changed based on reproduction track jump information, the write line address of the memory is latched by the output of the V signal competition circuit, and an external A time axis correction device characterized in that the latched data is loaded into the write/read address generation circuit as a read line address at a vertical synchronization signal position of a reference synchronization signal.