JPS62144483A - Video recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a reproducing video of high quality having a minimum noise bar even if it is recorded in any track width by detecting the recording track width according to an envelope detecting signal and deciding a comparison potential of a comparator corresponding thereto. CONSTITUTION:When the locus of the video track on a video tape is reproduced at four times speed in an opposite direction by video heads 2a, 2b, reproducing envelopes are shown in Figs a, b. At this time, the output from a microcomputer 20 is supplied to a comparator 6 through a D/A converter so as to make 1/3 potential of the maximum potential of the envelope a comparing reference potential. Herein if the period T1-T4 of the level L of the envelopes (a), (b) is measured, the track width in which the signal is recorded is detected. The computer 20 refers to the table in which optimum reference voltage corresponding to the various track width in a program memory 22 is decided, supplies the optimum potential corresponding to the detected track width to the comparator 6 and adjusts a writing range to the memory.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a video recording and reproducing device, and particularly to a video recording and reproducing device that uses a field memory to obtain high-quality reproduced images with reduced noise bars during high-speed reproduction.

[Conventional technology]

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 this property is utilized and a memory is used, the noise bar can be narrowed in some cases.

FIG. 4 shows a high-speed playback system of the conventional VTR. In the figure, 1 is a recorded video tape, and the playback signal is guided to a preamplifier 3 via video tapes 2a and 2b.
Thereafter, the reproduced signal is sent to the video signal processing circuit 4.

On the other hand, 5 is an envelope detector that extracts the envelope of the reproduced signal from the output of the preamplifier 3, and its output is led to a comparator 6 that compares it with a certain level, and is sent from the video signal processing circuit 4 to the field memory 8. The output signal is sent to the memory control circuit 7 which generates the write timing and address of the output signal. Further, a synchronizing 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 an asynchronous operation in which the contents of the field memory 8 are read out using a serial port while writing the reproduced signal from the video signal processing circuit 4 into the field memory 8.

On the other hand, 9 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 tape running in each mode.

Next, the operation will be explained.

Suppose now that a video tape l 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 FIG. 5, 50 is a video track, and A and B represent azimuth recording, with the video head 2a for A and the video head 2b for B having the same azimuth.

Now, when the video head 2a traces the broken line d in the figure, the output of the preamplifier 3 of the reproduced signal will be as shown in FIG. 6(a) due to azimuth recording.
is the broken line in the figure (eJ traces the trajectory in Figure 6 (b)
) output is obtained. These figures 6(a), (bl
When the contents of the two fields are interpolated with each other on the time axis, one field image as shown in FIG. 6 fcl is obtained, which is stored in the field memory 8 and displayed on the monitor. Here, the envelope waveform shown by (bl, fcl) in FIG. 6(a) represents only the upper side of the vertically symmetrical AC waveform.

The content of the L field with almost no noise bars is obtained when the width of the video track is equal to or larger than the width of the magnetic head and there is no guard band. In fact, for example, popular machines that have a head configuration that uses both the standard mode and the 3x mode in the VHS system have head specifications that are mainly for the 3x mode.

When standard mode recording is performed with such a specification, 1/2 to 2/3 of the video track 50 becomes a guard band, resulting in a video track as shown at 51 in FIG. On this video track 51, the video heads 2a,'
The output of the preamplifier 3 obtained by lb tracing the trajectory of the broken lines f and g in the figure is shown in FIG. 8(a),
The image of one field obtained by interpolating these images mutually on the time axis becomes as shown in FIG. 8 (C1).

By the way, when writing an image 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 6. That is, in FIG. 8 (C1), the comparison potential of the comparator 6 is set to aO''
(zero) level, almost all of the envelope is written to the field memory 8. however,
In the area indicated by l, almost no signal information is obtained, so the S/N ratio is poor, and the area appears as a noise area with a certain noise width, but the interpolated image information continues smoothly.

However, in FIG. 6(C), if a "0" (zero) potential is applied to the comparator 6 in the same manner as above, the area indicated by J will appear blank because the contents are rewritten every time in each field. Noise appears at both ends m and n. That is, what would normally be one very small noise bar (about one horizontal period) now appears every time two noise bars with a certain noise width appear.

(Problem 3 to be Solved by the Invention As mentioned above, in the 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, It is not possible to reduce the number of noise bars or narrow the width of the noise bars unless the comparison potential of the playback signal at the comparator is varied depending on the recording track width and the writing range to the memory is adjusted.

This invention has been made in view of the above problems, and even if the recording track width on the tape differs from tape to tape, it is possible to produce high-quality video by minimizing the width of the noise bar of the playback signal from the field memory during high-speed playback. The object of the present invention is to obtain a video recording and reproducing device that can obtain the following information.

[Means for solving problems]

In this invention, the recording track width on the tape is detected from the envelope detection signal using a microcomputer or the like, and based on the detection result, the optimum potential is supplied to the comparator as a comparison potential.

[Effect]

In this invention, since the track width recorded on the tape is automatically detected and the Rik suitable potential is supplied to the comparator, it is possible to manually narrow the width of the noise bar while directly viewing the reproduced image from the memory. There is no need for any operations, and unnecessary noise bars are no longer displayed, making it easy to obtain high-quality playback images.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, 20 is a one-chip microcomputer (hereinafter simply referred to as a microcomputer), which receives the synchronizing signal from the video signal processing circuit 4 and the output from the comparator 6, and controls the optimum potential to the comparator 6. /
Input/output circuit 2 that outputs via the A converter 30
1, a data memory 23 for temporarily storing data, a timer 24 having a timer function and a timer memory, a microprocessor 25 for performing calculations, and a program memory 22 for controlling operation instructions. The microcomputer 20 and the comparator 6 serve as means for detecting the recording l-rank width on the video tape 1, and the microcomputer 20 and the D/A converter 30 serve as a level setting means for setting the level of the comparison voltage supplied to the comparator 6. It is configured. The rest of the structure is similar to the conventional structure, and the same reference numerals as in FIG. 4 represent the same components.

Next, the operation will be explained.

Now, video tape 1 is loaded by video heads 2a and 2b.
f of video track 51 of FIG. 7 above.

Suppose that the trajectory of g is played back in the opposite direction at 4x speed. The reproduction envelope obtained at this time is as shown in Figures 8(a) and (b), and is 1/3 of the maximum potential of this envelope.
The output from the microcomputer 20 is supplied to the comparator 6 via the D/A converter 30 in order to use the potential as the comparison base f$ potential of the comparator 6.

Note that the maximum potential here is almost determined by the preamplifier 3, and the above-mentioned ⅓ potential is known in advance.

Furthermore, the reason why "l/3 potential" was selected as the reference voltage for comparison was in consideration of the noise margin of the reproduced signal, the superposition of DC components by the envelope detection circuit 5, and the like.

When such a potential is supplied as a comparison potential to the comparator 6, the outputs of the two fields obtained from the comparator 6 become as shown in FIGS. 2(a) and 2(b), respectively.

Here, the logic levels in FIGS. 2(a) and 2(b) simply refer to the read mode (level "
?H"), indicates the input mode (level "L").

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 explained previously, and the read mode is for reading out the memory contents. It does not mean that it is 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.

Here, by measuring the time from T1 to T4 between the levels "L" in FIG. 2 (al, fb), it is possible to know with what track width the signal is recorded on the tape.

For example, if the period of level "L" from T1 to T4 is short, the recording track width is narrow. In particular, if the level "H" is longer, it means that a guard band is present. Similarly, the 6th
The outputs of the comparator 6 obtained from (al, bl, tc+, fd in Figure 2) have a long period of level "L". Therefore, the recording track width is wide. The measurement is carried out over two fields.This is because the head width may be recorded with a different head width for each field. Based on the time of the level "L" obtained over the period, assuming that recording has already been done with various track widths, refer to a table in which one reference voltage to the comparator 6 is determined, and find the optimum value corresponding to each track width. A potential is created via the D/A converter 30. The above table is written in the program memory 22 in the microcomputer 20 in advance.

In this way, as the comparison supply voltage to the comparator 6, the potentials at eight points of the waveform shown in FIG. 6(C) are applied to the voltage recorded on the track 50 shown in FIG. By supplying almost "0" (zero) potential to what is recorded on track 51 shown in Figure 7, the playback signal in which the envelope interpolated for each field is smoothly connected will be stored in the field memory. 8, it is possible to obtain a high-quality reproduced image in which the width of the noise bar is narrow and the noise bar is not displayed in unnecessary areas.

The above will be explained with reference to the flowchart shown in FIG. Here, the vertical synchronization signal is used as the 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 the comparator 6 with a potential that is 1/3 of the maximum potential of the envelope signal, the input/output circuit 2 of the D/A converter 30
1 to output a potential code (step 101).

After performing the initial settings in this way, when the rising edge of the vertical synchronizing signal obtained from the video signal processing circuit 4 is detected (step 102), the falling edge of the output from the comparator 6 is detected for writing to the field memory 8. (Step 103). When this is detected, the timer 24 in the microcomputer 20 is initialized and started (step 1).
04). If the rising edge of the vertical synchronizing signal is not detected, wait until it is detected. Furthermore, when the falling edge of the output signal from the comparator 6 is not detected, the falling edge of the vertical synchronizing signal is detected (step 105), and it is determined whether the transition to the next field has occurred.

As a result, when the falling edge of the vertical synchronizing signal is detected, the process returns to the beginning and prepares for processing in the next field from the rising edge of the vertical syncing signal. If not, wait until the logic of the output signal from the comparator 6 falls.

Next, after the timer is started, it is determined whether the logic of the output from the comparator 6 has been inverted (step 106). If it is reversed here, the timer value of the timer 24 in the microcomputer 20 is recorded in the addressed memory area of the data memory 23 (step 107), and then the timer 24 is reset (step 108). Then, the memory address is updated by +1 (step 109). That is, here, after the timer value is written to address 1 specified in □ processing step 100, the address becomes address 2.

Then, the address value +1 in processing step 109 is “
7” (step 110).
). This means that in the waveforms (al, (b) in Figure 2),
This is because there are 6 L/“L” periods (including T1 to T4) and the corresponding memory addresses are 1 to 6. Therefore, the memory address being 7 means that the measurement has ended. become.

If not, preparations for the next measurement begin. On the other hand, if they are equal, it means that the measurement of the envelope part over two fields has been completed, so next we will compare the contents obtained by the measurements up to now, that is, the contents of addresses 1 to 6 in the data memory 23. , and a table value previously created in an area of the program memory 22 in the microcomputer 20 (step 111). The table here has
The optimum comparison potential for the comparator 6 for the recording track width on the tape, which has been determined experimentally in advance, is recorded. Therefore, the optimal potential corresponding to the corresponding recording track width is selected from this table, and this potential code is output (step 112).

Here, the code refers to a BCD code expressed in binary.

In this embodiment, the recording track width is detected from the envelope detection signal and the comparison potential of the comparator 6 is determined accordingly, so manual adjustment is possible no matter what track width the tape is recorded on. The width of the noise par can always be minimized without causing any distortion, and high-quality playback images can be obtained.

In addition, although the case of 4x speed playback was explained as high-speed playback in the embodiment, the present invention is not limited to this 4x speed, and can be applied to any high-speed playback as long as it is an even numbered speed.
The same effects as in the above embodiment can be 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 multi-port memory), it may also be a general-purpose memory.

〔Effect of the invention〕

As described above, according to the present invention, the recording track width on the tape is detected from the envelope signal of the playback signal, and the optimum comparison potential is supplied to the comparator based on the detected content, and the writing range to the memory is automatically determined. This adjustment has the effect of enabling high-speed playback with high quality and minimizing noise bars, regardless of the tape recorded with any recording track width.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram of a video recording and reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the apparatus, and FIG. 3 is a diagram for explaining the operation of the apparatus. Flowchart diagram, Figure 4 is a block diagram of a conventional video recording/playback i2 device, Figure 5 is a diagram showing the head trajectory when a video track recorded without guard panning is played back at high speed, and Figure 6 is a diagram showing the playback. Diagram showing the preamplifier output of the signal,
FIG. 7 is a diagram showing the head trajectory when a video track recorded with guard hand is played back at high speed, and FIG. 8 is a diagram showing the playback preamplifier output. 1... Magnetic tape, 2a, 2b... Magnetic head, 5
...Envelope detector, 6...Comparator, 7
. . . Memory controller l-roll, 8 . . Field memory, 20 . . . Microcomputer. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Haya 'M! Constitution - Figure 1 Figure 2; Te's JL Gihe Figure 4 1, Figure 5 ← Gehikari ABABABABAB Figure 6 Figure 7 Figure 8 Procedural amendment (self-motivated) Patented on March 12, 1988 Director General
−°】■、Indication of incident
os-52, Title of the invention Video recording and reproducing device 3, Person making the amendment 5, Detailed description of the invention in the statement of subject matter of the amendment and drawings (Figure 3) 6. Contents of the amendment (1) Specification In the first line of page 6, "almost all of the envelope" is corrected to "almost all of the signal represented by the envelope". (2) Correct Figure 3 as shown in the attached sheet. That's it for A-, e'H1'.

Claims (1)

[Claims] (1) During high-speed playback, when the playback signal level from the recorded magnetic tape is higher than a preset level, the playback signal is stored in the field memory, and this stored content is used as the synchronization signal of the playback signal. In a video recording and reproducing apparatus that reads data asynchronously, the recording track width detection means measures the recording track width based on an envelope detection signal of a reproduction signal obtained when a magnetic head crosses the recording track on the magnetic tape; 1. A video recording and reproducing apparatus comprising: level setting means for setting the predetermined level to an optimal level for signal reproduction based on the result.