JPS6382071A - Video recording and reproducing device - Google Patents

Abstract

PURPOSE:To minimize the width of a noise bar at the time of highspeed repro duction by switching magnetic heads automatically by a mode deciding means, measuring the time width of a part which is lower than the specific level in a signal obtained when an envelope detection signal is interpolated on the time base mutually between two fields, and optimizing the comparison potential of a comparator according to the measurement result. CONSTITUTION:The heads 2c and 2d, and 2e and 2f are switched according to the mode decision signal of a servo circuit 10. A microcomputer 20 and a comparator 6 constitute a measuring means which measures the time width of the part which is lower than the specific level in the signal obtained when the envelope signal is interpolated on the time basis mutually between two frames. Further, the microcomputer 20 and a D/A converter 30 constitute a means which varies the setting of the level of a comparison voltage to the comparator 6 and the microcomputer 20, a switch 13, and servo circuit 10 consti tute a mode switching means. Consequently, the optimum comparison voltage is supplied to the comparator 6 according to the time width obtained by said measuring means to adjust the range of writing to a memory 8 automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video recording and reproducing apparatus that uses field memory to reduce noise bars during high-speed reproduction.

[Prior Art] As a conventional example, a case will be described in which high-speed playback of a video tape recorder (hereinafter referred to as VTR) using a field memory is performed at an even multiple of 4 times the speed. Here, an odd numbered multiple speed is generally selected for high-speed playback, but this takes advantage of the property that the noise bar locks since the noise position is the same for each field. On the other hand, at even multiple speeds, the noise position and the signal position alternate for each field, and if a memory is used to take advantage of this property, the noise bar can be narrowed in some cases.

FIG. 4 is a block diagram showing a high-speed reproduction system of the conventional VTR. In the figure, (1) is a recorded video tape, and the playback signal is guided to the preamplifier (3) via the video heads (2a) and (2b), and then the playback signal is sent to the video signal processing circuit (4). ) will be sent to. (5) is an envelope detection circuit, which extracts the envelope of the reproduced signal from the output of the preamplifier (3), and the output is led to a comparator (6) for comparison with a certain level. (7) is a memory control circuit which receives the output of the comparator (6) and generates the timing and address for writing the output signal from the video signal processing circuit (4) into the field memory (8). Also.

A synchronization signal is sent from the video signal processing circuit (4) to the memory control circuit (7).

The field memory (8) is a dual port memory (not shown) and has a random output and a serial output as an output port, and if the serial port is used, writing and reading from the memory can be performed asynchronously. The operation here is to write the playback signal from the video signal processing circuit (4) to the field memory (8) and use the serial port to write the playback signal to the field memory (8).
8) performs an asynchronous operation to read the contents.

On the other hand, (8) is a control head, and based on this output, the servo circuit (10) controls the capstan motor (
11), the reel motor (12) is controlled to control the running of the tape in each mode.

Next, the operation of the above configuration will be explained.

Suppose that videotape (1) is being played back at 4x speed in the reverse direction. FIGS. 5 and 6 are diagrams for explaining the operation at this time. In Figure 5, (50)
is a video track, (A) and (B) represent azimuth recording, and for (A), the video head (
2a) and (B), the video head (2b) has the same azimuth.

Now, when one video head (2a) traces the broken line (d) in the figure, the output of the preamplifier (3) of the playback signal will be as shown in Figure 6 (a) due to the azimuth recording.
However, the video heads (2a) and (2b) used here are composed of two heads that also serve as video heads for the first mode and the second mode where the tape feed is slower than the first mode. The head width is narrower than the track pitch in the first mode.

Further, when the video head (2b) traces the trajectory indicated by the broken line (e) in the figure, the output shown in FIG. 6(b) is obtained. When the contents of these two fields shown in Fig. 6(a) and (b) are interpolated with each other on the time axis, one field image as shown in Fig. 6(C) is obtained, and this is stored in the field memory (8).
stored in the computer and displayed on the monitor. Here, the envelope waveforms shown in FIGS. 6(a), (b), and (c) represent only the upper side of the vertically symmetrical AC waveform.

The content of one field with almost no noise bars is the case without guard bands. However, when recording in the first mode with a two-head configuration that uses both the first mode and the second mode, where the head width is narrower than the track pitch in the first mode, the video track ( 50) A guard band is formed on top of the video track (51) as shown in Fig. 7.The video head (2a) runs over this video track (51).
2b) is traced along the loci of broken lines (f) and (g) in the figure, and the output of the preamplifier (3) obtained by this is shown in Figures 8(a) and (b). Figure 8 (C
)become that way.

By the way, when writing images interpolated on the time axis shown in FIGS. 6 and 8(c) to the field memory (8),
It is necessary to change the comparison potential of the comparator (8). That is, in FIG. 6(C), the comparator (
It is sufficient to keep the level indicated by the comparison potential (S) in 6). This means that if (Sl) is higher than (S), the image information in the part (J) disappears, and that part becomes a noise bar and is displayed. It's coming. Also, at (S2) lower than (S), (
Since the contents of the part J) are rewritten every time for each field, that part will appear blank.If you set the comparison potential (S) of the comparator (8), the above problem will not occur and the image will be Information is also connected smoothly.

However, in FIG. 8(C), if the potential phased out at (S) is applied to the comparator (8) in the same way as above, (K
), and in this case, for example, change the potential of the comparator (6) and apply a "0" (zero) potential to smoothly connect the interpolated image information. Even if the part indicated by (n) has almost no signal information, the S/N is poor and appears as a noise area with a predetermined noise width.This is because the playback head is Since it is also used as the second mode and has a narrow width, even if the potential of the comparator (6) is an appropriate potential, it cannot sufficiently pick up the envelope signal, so the S/N as shown in (n) is The bad parts are revealed.

Therefore, if the head width is set to be wide enough to obtain a sufficient signal, when speed search is performed in the second mode, the head width will be too wide and the adjacent signals will be spread, resulting in crosstalk. The noise caused by the noise appears on the screen.

[Problems to be Solved by the Invention] As described above, in a system that uses field memory to perform high-speed playback at an even multiple speed and interpolates the contents of each field to obtain signal information, the width of the noise bar is In order to narrow the time width, firstly, the time width differs in the part lower than a predetermined level of the signal obtained when the envelope signal is interpolated between two fields on the time axis. Depending on the difference, it is necessary to vary the comparison potential of the reproduced signal at the comparator and adjust the writing range to the memory.

Second, in a head configuration that uses both the first mode and the second mode, it is not possible to narrow the width of the noise bar for both modes.
mode and a multiple head configuration with separate heads for each mode.

This invention was made to solve the above-mentioned problems, and for both the first mode and the second mode, the envelope signals are interpolated between two fields on the time axis. Even if the time width of the portion of the obtained signal that is lower than a predetermined level differs from tape to tape, it is possible to minimize the width of the noise bar of the playback signal during high-speed playback and obtain a high-quality playback image. The purpose is to provide a video recording and playback device.

[Means for Solving the Problems] The video recording and reproducing apparatus according to the present invention includes a plurality of magnetic heads, which are automatically switched by a discrimination signal from a mode discrimination means, and uses a microcomputer or the like to x 7 <o-7' The time width of the portion lower than a predetermined level of the signal obtained when the detected signals are interpolated between two fields on the time axis is measured, and the comparator is compared based on this measurement result. It is characterized in that the potential is set to the optimum potential for signal reproduction.

[Operation] In the present invention, the time width of the portion lower than a predetermined level of the signal obtained when the envelope detection signal is interpolated between two fields on the time axis is automatically measured, and the first mode, In either of the second modes, it is possible to supply the comparator with the optimum potential corresponding to the measurement width. Therefore, it is not necessary to perform troublesome operations such as manually narrowing the width of the noise bar while viewing the reproduced image, and a reproduced image of high quality can be easily obtained.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of a video recording and reproducing apparatus according to an embodiment of the present invention. In the figure, the same parts as the conventional configuration shown in FIG. 4 are designated with the same reference numerals. , a detailed explanation thereof will be omitted.

In FIG. 1, (2c) and (2d) are heads for the first mode, (2e) and (2f) are heads for the second mode, and the control head (9)
Based on the output of the servo circuit, the head is switched by the switch (13) in accordance with the mode discrimination signal output from the servo circuit. In addition, (20) is a one-chip microcomputer (hereinafter simply referred to as microcomputer), which receives the synchronizing signal from the video signal processing circuit (4) and the comparator (
6), outputs the optimum potential to the comparator (8) via the D/A converter (30), and receives the mode discrimination signal output from the servo circuit (1o). A circuit (21), a data memory (23) that temporarily stores data, a timer (24) having a timer function and timer memory, a microprocessor (25) that performs calculations, and a program memory (22) that commands operations. It consists of

The microcomputer (20) and the comparator (6) provide a measuring means for measuring the time width of a portion of a signal whose level is lower than a predetermined level, which is obtained when the envelope signal is interpolated between two fields on the time axis. Level setting means for setting and changing the level of the comparison voltage supplied to the comparator (6) by the microcomputer (20) and the D/A converter (30).

Further, a microcomputer (20), a switch (work 3), and a servo circuit (lO) constitute switching means according to the first mode and the second mode.

Next, the operation of the above configuration will be explained.

Now, in the first mode, the control head (3
), a mode switching signal is output from the servo circuit (10) to switch the switch (13) towards the video heads (2c) and (2d) for the first mode. Assume that the video heads (2c) and (2d) reproduce the trajectories (h) and (i) of the video track (52) in FIG. 9 on the videotape (1) in the opposite direction at four times the speed. However, for (C), head (2
For C) and (D), the head (2d) has the same azimuth. The reproduced envelope signals obtained at this time are as shown in FIGS. 10(a) and 10(b).

Also, in Fig. 10 (C), the difference from Fig. 7 (C) in which the same Gartband-recorded video track is played back at high speed is that in Fig. 10 (C), the Since a head is used, there is no need to consider the influence on the second mode, and the head width can be increased.

Therefore, also in the part (thought) of the same figure, Figure 6 CC)
Unlike part (J), a sufficient S/N ratio can be obtained. Therefore, the output from the microcomputer (20) is set to the D/A so that the maximum potential 415 in this envelope signal is used as the reference potential for comparison of the comparator (8).
':17 /<- via the comparator (30)
6).

Note that the maximum potential here is almost determined by the preamplifier (3), and the potential of the above-mentioned 415 is known in advance. In addition, the "415 potential" here is a potential to be compared with the signal level obtained later when the envelope signal is interpolated between two fields on the time axis. It is necessary to select a potential such that the envelope signals do not always overlap, and this corresponds to the potential of 475.

When such a potential is supplied as the comparison potential of the comparator (8), the outputs of the two fields obtained from the comparator (6) become as shown in FIGS. 2(a) and (b), respectively. 2 The logic levels in Figures (a) and (b) are simply read mode (level “H”) and write mode (level “L”) for the field memory (8).
) is shown.

Note that the write and read modes here are for the random input and random output ports of the dual port memory used in the field memory (8) described above, and in the read mode, the memory contents are It does not mean that it is read and output, but rather that it is not written to memory.

That is, it is assumed that the output of the memory contents in the original read mode is performed using a serial port, and that the operation is asynchronous with random input.

In Figures 2(a) and (b), the time required for the logic level to invert the first and second times in the first field is [T1], (
T2), the time to similarly invert in the second field is (T3), (when 0 is 1〒3-Tll or
When IT2-41 is measured, the predetermined level of the signal obtained by interpolating between two fields, that is, the time width of the portion lower than the 415 potential is measured. When the period of l73-T11 or l72-T41 is long, the width of the low signal level portion is wide, and when it is short, the width is narrow.

Here, the reason for measuring not only l73-Tll but also l72-741 is that each field may be recorded with a different head width, and in this case, 1〒3-Tll.
This is to accommodate the case where the value of ll and the value of l72-741 are different.

From the values of 173-Tll and 172-741 obtained over two field periods as described above, the optimum reference voltage to the comparator (8) corresponding to various values of 173-Tll or 172-741 is determined in advance. Refer to a certain table and select each l73-Tll or l
An optimal potential corresponding to the value of 72-T41 is created via the D/A converter (30). The above table is written in advance in the program memory (22) in the microcomputer (20).

In this way, as for the comparison supply voltage to the comparator (6), what is recorded in the track (52) shown in FIG. 9 is determined by referring to the table and
), the potential at point (S3) of the waveform shown in
For the value of 73-Tll or l72-T41,
By referring to the table again and supplying the optimum potential in that case, a playback signal in which the envelopes of M length for each field are smoothly connected will be written to the field memory (8), and the maximum potential of the noise bar width will be written to the field memory (8). A narrow, high-quality playback image can be obtained.

Also, for the second mode, the same effect can be obtained by switching the switch (13) to the head (2e) or (2F) for the second mode and performing the same operation as above. It will be done.

The above will be explained with reference to the flowchart shown in FIG. Here, the vertical synchronization signal is used as a reference for one time axis, and the vertical blanking period is set to level "L".

In the flowchart of FIG. 3, first, the address of the data memory (23) in the microcomputer (20) is initialized and set to address 1 (step (100)).
.

Next, in order to supply potential 475, which is the maximum potential of the envelope signal, to the comparator (6), a potential code is output to the D/A converter (30) via the input/output circuit (21) (step (101)). ).

After performing the initial settings in this way, immediately after detecting the rising edge of the vertical synchronization signal obtained from the video signal processing circuit (4) (step (102)), the microcomputer (20)
The timer (24) inside is reset and started (step (1o3)).

Then, the logic level is inverted compared to the input logic at that time (steps (104), (105), (108))
If so, record the timer value of timer (20) in the microcomputer (20) in the memory area specified by the address of the data memory (23) (step (107)) L. Update the memory address by +1 (step (10B) ).

That is, here, after the timer value is written to address 1 specified in processing step (roo), the address becomes address 2.

It is determined whether the address value increased by 1 in the processing step (108) is equal to 3 or 5 (step (10
9) ), this means that in the waveforms (B) and (b) of Fig. 2, if the address value is 3, the measurement of the 1st field,
In other words, the measurements of (T1) and (T2) have been completed, and if it is 5, the measurement of the second field has also been completed.

Here, if the address value is 3 or 5, step (1
04) Return to continue measurement. If the address value is 3 or 5, the process moves to step (110) and it is determined whether the address value is 5 or not. If it is 5, it spans 2 fields (T1
) to (T4) have been measured. If it is not 5, return to step (102) and continue measurement.

5, then the mode determination signal obtained from the servo circuit (10) determines whether it is the first mode or not.

Determine whether it is the second mode (step (111)
), and here, if the first mode is determined, step (
112), from the contents obtained by the measurements up to now, that is, the contents of addresses 1 to 4 in the data memory (23), that is, the values corresponding to (TI) to (T4) l73
- Calculate Tll and l72-741, and use those values and the program memory (22) (741) in the microcomputer (20) in advance.
) area is compared with the table value for the first mode created in the area. The table here shows IT3-Tll and 17 in the first mode determined experimentally in advance.
The optimum comparison potential to the comparator (6) for the value 2-741 is recorded.

Therefore, from this table, the corresponding +73-
Select the optimum potential corresponding to the values of Tll and I 72-741 and output this potential code (step (113)
)) Here, the code refers to a BCD code expressed in binary. Also, when it is determined in step (111) that the mode is the second mode, the process moves to step (114) and the first mode is As in the case of mode, memory address 1~
From the contents of 4, find 173-Tll and l72-T41, and use those values and the second
It compares the table with the mode table and outputs the potential code for the corresponding table contents (step (115)
)).

In this embodiment, the time width of the portion whose level is lower than a predetermined level of the signal obtained when the envelope detection signal is interpolated between two fields on the time axis is detected, and the comparator (6) Since the comparison potential of the tape is determined, the width of the noise bar can always be minimized without manual 3I equalization for tapes recorded with any track width, and high-quality reproduced images can be obtained. Further, since the apparatus has a plurality of heads having separate heads for the first mode and the second mode, the same effect can be obtained for either mode.

In the above embodiment, a case of 4x speed playback was explained as high speed playback, but the present invention is not limited to 4x speed, and can be applied to any even numbered speed playback. The same effect can be obtained.

In addition, although the maximum potential of the envelope, 415, is output in step (101), the potential is not limited to 415; when the envelope signal is interpolated between two fields, adjacent signals do not always overlap. There is no problem as long as it is a potential, and by rewriting the contents of the table according to the potential, the same effect as in the above embodiment can be obtained.

Further, although the circuit configuration in which the switch (13) is provided after the magnetic head has been described, the same effect as in the above embodiment can be obtained even if a separate preamplifier is provided for each magnetic head and the switch (13) is provided after that. is obtained.

Further, although a microcomputer is used in the above embodiment, each control means may be configured by hardware, and the same effects as in the above embodiment can be obtained.

Furthermore, although the field memory used here is a dual-port memory or a multi-port memory, it may also be a general-purpose memory.

[Effects of the Invention] As described above, according to the present invention, a plurality of heads are provided, the heads are switched according to the mode discrimination signal, and the envelope signals of the reproduced signal are arranged by interpolating each other on the time axis between two fields. The time width of the portion of the signal being placed at a level lower than a predetermined level is detected, and the optimum comparison potential is supplied to the comparator based on the detected content, and the writing range to the memory is automatically adjusted. 1. In either of the second modes or on a tape recorded with any recording track width, it is possible to perform high-speed playback with good quality and minimize noise bars.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram showing the configuration of a video recording and reproducing device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of this device, and FIG. FIG. 4 is a block diagram showing the configuration of a conventional video recording and reproducing device, and FIG. 5 is a flowchart for explaining the operation of this device. FIG. 5 is a block diagram showing the configuration of a conventional video recording and reproducing device. Figure 6 shows the head trajectory when played back at high speed. Figure 6 shows the preamplifier output of the playback signal. Figure 7 shows the head trajectory when played back at high speed using a video recording and playback device with two heads. Figure 8 is a diagram showing the head trajectory; Figure 8 is a diagram showing the playback preamplifier output; Figure 9 is a diagram showing the head trajectory when a video track recorded with Gartband is played back at high speed by a four-head video recording/playback device; Figure 1O is a diagram showing the reproduction preamplifier output. (1)...magnetic tape, (2c), (2d)...
・Magnetic head for the first mode, (2e), (2
F)...Magnetic head for second mode, (5).
...Envelope detection! , (6)...Comparator, (7)...Memory control, (8)...Field memory, (13)...Switch, (20)...
...Microcomputer. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 1 Figure 4 Figure 5 - Forward direction ABABABABAB Figure 6 Figure 7 - Forward direction A BABABABA B Figure 8 Figure 10 Row-1 field period instrument procedure amendment (voluntary) 5゜1. Display of the incident Patent application No. 1983-228726
A.2. Title of the invention: “Video recording and reproducing device 3, person making corrections”
. Name (601) Mitsubishi Electric Corporation
B. In the "Detailed Description of the Invention" column for the fine teeth subject to correction and in the statement of contents for figure correction: Page 17, line 6; Add "ni" after "Address". Page 18, line 13; Correct the phrase ``if it's 5'' to ``any of 5.'' Drawing: In addition to writing the part corresponding to the number (100) in Figure 3, add the numbers (1, 11) to the figure and resubmit the same figure as attached. that's all

Claims (1)

[Claims] (1) When the playback signal level from the recorded magnetic tape during high-speed playback is equal to or higher than the first predetermined level by comparison with a preset first predetermined level, the playback signal is stored in the field memory. In a video recording and reproducing apparatus which stores the stored content and reads out the stored content asynchronously with the synchronization signal of the reproduction signal, the video recording and reproducing apparatus includes: a first head for a first mode; and a tape feed rate slower than that in the first mode. Second
A magnetic head having a second head for a mode of means for comparing the signal obtained when interpolating on the axis with a second predetermined level set in advance; means for measuring the time period during which the signal is below the second predetermined level; Level setting means capable of changing the first predetermined level to a level optimal for signal reproduction; means for determining whether the mode is the first mode or the second mode; and a signal from the mode determining means. A video recording and reproducing apparatus comprising: means for switching the magnetic head in response to a change in the magnetic head; and means for switching the setting program for the predetermined level.