JPH053795B2 - - 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 a clock to the read line address counter 14 based on the external reference synchronization signal 12. horizontal synchronization signal F _H 15 included;
A vertical synchronization signal (VP signal) 16 is added. The write line address counter 9 and the read line address counter 14 count _H10 and _FH15 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 when the tape V signal is 5, loads it into the read line address counter 14 when the VP signal is 16, and reads the write line address when the tape V signal is 5 and the read line address when the VP signal is 16. Make them 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 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.
Scanning is performed in the order of 5 and 26. 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 horizontal synchronizing signal position shift a _H , as shown at 27 in FIG. Here, the explanation will be made assuming a _H =25H.

The number of horizontal scanning periods H included in line segment P-Q is
In the case of the NTSC system, it is 262.5H for one field. The above line segment P'-R is added by a _H ,
One field will consist 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 H of horizontal scanning periods 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 is clear from the position in the figure where point P'' precedes point P' by _aH minutes.After all, 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 one 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 the opposite direction. That is, during reverse playback, the V signal interval is a combination of 265H and 267.5H.

If such a reproduced vertical synchronizing signal is applied as it is to the latch circuit 7 of FIG. 1, the vertical synchronizing signal will be irregular and will be affected by dropout, causing vertical movement of the image on the monitor screen.

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 includes a memory that stores a reproduced video signal reproduced by a video tape recorder, a write/read address generation circuit that generates a write and read address for each line to this memory, and a reproduction horizontal synchronization signal. a V prediction circuit that counts a predetermined number of synchronized signals, predicts the position of a reproduction vertical synchronization signal (tape V signal) of the next field from the vertical reference of the previous field, and generates a predicted V signal;
A pseudo V signal is derived from the leading edge of the signal that occurs first, the tape V signal or the tape V signal, and the trailing edge of the pseudo V signal is used as a vertical reference, and the trailing edge of the tape V signal is lower than the trailing edge of the pseudo V signal. If the V prediction circuit occurs later, the V prediction circuit is provided with a vertical reference generation circuit that uses the trailing edge of the tape V signal as a vertical reference, and changes the predetermined number counted by the V prediction circuit based on playback track skip information during slow motion playback. , latches the write line address of the memory at the vertical reference position of the vertical reference generation circuit, and transmits the latched data to the write/read address generation circuit as a read line address at the vertical synchronization signal position of the external reference synchronization signal. This is a time axis correction device characterized in that it is loaded.

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 and is used as a gate pulse for the tape V
Only the V signal immediately after the head switch is extracted from signal 5. 40 is the tape V signal immediately after the head switch is turned on by the gate circuit 32; 33 is a multiplier circuit that receives a signal _2H with twice the frequency of the horizontal synchronization signal.
is generated and supplied to the V prediction circuit 34 as a clock. The V prediction circuit 34 is composed of a counter and outputs a predicted V signal after counting a predetermined number of clocks. The predetermined number counted by the V prediction circuit 34 is changed by a signal indicating reproduction track jump information in the jump signal. A vertical reference generating circuit 35 generates a stable vertical reference.

FIG. 6 is a circuit diagram showing a main part of the vertical reference generation circuit 35, and FIG. 7 is a timing chart explaining the operation of FIG. 6.

In FIG. 6, 40 and 41 are input terminals for the tape V40 and predicted V signal 41 in FIG.
5 is an AND gate, and 43 and 44 are pulse generation circuits that generate downward pulses of a constant width at the falling edge of the input signal, and are composed of, for example, a mono multivibrator. , equal to the vertical sync pulse width
A pulse of 3H width (H is one horizontal scanning period) is generated. The pulse generating circuit 43 generates pulses of about 10H or more. A vertical reference signal generation terminal 46 is connected to the output of the vertical reference generation circuit 35 shown in FIG.

Next, the operation will be explained using FIG. The numbers in the figure correspond to the signals of the circuits with the same numbers in FIG. In FIG. 7A, when the tape V signal 40A is lost due to dropout or the like, the pulse generation circuit 43 generates a pulse 43A at the leading edge of the predicted V signal 41A, and the pulse generation circuit 44 generates a pseudo V signal 44A. Since the tape V signal 40A is missing from the AND gate 45, a pseudo V signal is outputted to the output terminal 46, and the trailing edge of the pseudo V signal serves as a vertical reference.

By the way, since there is no pulse generation circuit 43, the output of the AND gate 42 is directly sent to the pulse generation circuit 44.
When supplied to the pulse generating circuit 4 as shown in FIG. 7B,
4 generates two spurious pulses at the leading edge of the tape V signal 40B and at the leading edge of the predicted V signal. For example, this signal is input to the V prediction circuit 34 in FIG.
When input to the RESET terminal or the latch circuit 7 in FIG. 4, these circuits regard the trailing edge of the pulse as the vertical reference, so the reset etc. are performed twice using the vertical reference 46B, and eventually the trailing edge of the predicted V signal This is equivalent to sending the information, resulting in discarding the information of the tape V signal 40B, which causes inconvenience. Therefore, a pulse circuit 43 is added, and the pulse width is the same as that of the tape V signal 40B.
It is set to be greater than the maximum deviation amount between the signal and the predicted V signal.

FIG. 7C shows a case where the tape V signal 40C precedes the predicted V signal 41C, a pseudo V signal 44C is output at the leading edge of the tape V signal, and a vertical reference 46C is output from the AND gate 45. Here, for example, even if the trailing edge of the tape V signal 40C is dropped due to dropout as shown in the figure, the vertical reference remains stable without changing.

FIG. 7D shows a case where the predicted V signal 41D precedes the tape V signal 40D, and a pseudo V signal is generated from the leading edge of the predicted V signal, but the tape V signal 40D is added by the AND gate 45, and the vertical reference 4
6D, the trailing edge of the tape V signal is valid.

Further, FIG. 7E shows a case where the tape V signal 40E deviates much later than the predicted V signal 41E,
In this case, two vertical references 46E are generated, but
As a result, the subsequent circuits are reset, etc. at the trailing edge of the tape V signal, so there is no problem at all.

Effects of the Invention The present invention generates a predicted V signal by predicting the reproduced vertical synchronizing signal position of the next field from the vertical reference of the previous field, and combines the predicted V signal with the tape V.
A pseudo-V signal is derived from the leading edge of the signal that occurs first, and the trailing edge of the pseudo-V signal is used as a vertical reference,
When the trailing edge of the tape V signal occurs after the trailing edge of the pseudo V signal, since the trailing edge of the tape V signal is used as the vertical reference, a stable vertical reference can be obtained even if dropout occurs; Furthermore, since both the leading edge information and trailing edge information of the tape V signal are used, an accurate vertical reference can be obtained.
A high-quality image with no vertical movement on the monitor screen can be obtained.

Further, as shown in the embodiment, stable images can be obtained even in slow motion reproduction by introducing track jump information into the V prediction circuit.

[Brief explanation of drawings]

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;
The figure is an explanatory diagram of the head trajectory during special playback, FIG. 4 is a block diagram of a time axis correction device according to an embodiment of the present invention, and FIGS. 5 and 6 are block diagrams showing the configuration of essential parts of the embodiment. 7 are timing charts showing the operation of FIG. 6. 3...Synchronization separation circuit, 7...Latch circuit, 8...
...Memory, 9...Write line address counter,
14...Read line address counter, 34...
V prediction circuit, 35... Vertical reference generation circuit.

Claims (1)

[Claims] 1 A memory that stores a playback video signal played back by a video tape recorder, a write/read address generation circuit that generates write and read addresses for each line to this memory, and a predetermined number of signals synchronized with a playback horizontal synchronization signal. a V prediction circuit that counts and generates a predicted V signal by predicting the position of a reproduction vertical synchronizing signal (tape V signal) of the next field from the vertical reference of the previous field; and either the predicted V signal or the tape V signal. A pseudo V signal is derived from the leading edge of the previously generated signal, and the trailing edge of the pseudo V signal is used as a vertical reference, and if the trailing edge of the tape V signal is generated after the trailing edge of the pseudo V signal, the tape V and a vertical reference generation circuit that uses the trailing edge of the signal as a vertical reference, and changes the predetermined number counted by the V prediction circuit based on playback track skip information during slow motion playback, and A write line address of the memory is latched at a reference position, and the latched data is loaded as a read line address into the write/read address generation circuit at a vertical synchronization signal position of an external reference synchronization signal. A time axis correction device.