JPS59210779A - Still picture reproducing device of video tape recorder - Google Patents

Abstract

PURPOSE:To obtain the best still picture without noise bar on screen by sampling an envelope signal of a reproduced FM video signal in each field and moving minutely a magnetic tape so that sample values of adjacent sampling points are equal. CONSTITUTION:When video heads A, B make scanning in the locus as shown in hatched lines 4, an output signal level of a hold circuit 20 is larger than an output signal of a hold circuit 21 and an output of an OR circuit 25 remains H level. Then, a Q output of a counter 27 goes to H level, an NAND circuit 26 remains L level to trigger a monostable multivibrator 28, a capstan motor 30 is turned by a minute angle by an H level output of the monostable multivibrator 28 and the magnetic tape is moved by a minute interval so as to allow the video heads A, B to scan the hatched lines 2. Thus, even if a control pulse is not recorded on the magnetic tape, the magnetic tape running is stopped so that the best still picture is obtained because noise bars exist in the vertical blanking period.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a still image reproducing device for a video tape recorder, in which an envelope signal of a reproduced FM video signal is sampled within each field, and a magnetic field is applied so that the sample values of adjacent sampling points are roughly equal. To provide a still image reproducing device for a video tape recorder which can obtain the best still image without noise bars on the screen even when no control pulse is recorded by moving the tape a minute distance. purpose.

Generally, when playing back still images in a helical scan type rotary head video tape recorder, as shown in FIG. 1, the running of the magnetic tape 1 on which video tracks Tl + T2 + .
3.13) 4 is scanned by two rotating video heads along the locus shown in the shaded area 2. In this case, track T
8 is recorded by the rotating video head Wf, t (hereinafter referred to as ``video head A''), and track T4 fi''
When the rotation detection signal of the rotating cylinder shown in FIG. When recording and playback is performed by video head B, the envelope waveform of the FM video signal played back by video heads A and B is as shown in Figure 2), where the θ level of the envelope waveform is small. In other words, the dog portion of the noise is concentrated near the vertical retrace period LbJ, and a high-quality still image can be reproduced.

In a conventional video tape recorder, the control pulse 3 shown in Fig. 1 is recorded in one frame (6 steps). Set the pulse width of the output pulse of the monomulti to an appropriate value, drive the capstan motor with this output pulse, and set the magnetic chip so that the video heads A and B scan the shaded area 2 in Figure 1. 1 had stopped running.

However, in so-called 8mm video that uses a magnetic tape with a tape width of 8mm, for which a standard has recently been decided, control pulses are not recorded, so the magnetic tape 11 is adjusted so that the shaded area 2 in Figure 1 is played back when still images are played back. /, 1 If the magnetic tape 1 cannot be stopped and the shaded area 4 of the first diagram is played back after the magnetic tape 1 has stopped, the envelope waveform will be as shown in Figure 2 (Q), and the noise generated at the minimum part of the envelope will be reflected on the playback screen. It appears near the center of the screen, which has the disadvantage of deteriorating the quality of still images.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described with reference to FIG. 3 and subsequent figures.

FIG. 3 shows a circuit configuration diagram of an embodiment of a still image reproducing apparatus for a video tape recorder according to the present invention.

In the figure, 10 is an input terminal to which an FM video signal reproduced by a rotating video head is input, 11 is an input terminal to which a still start pulse is input when the still button is pressed to enter still image playback mode, and 12 is obtained by detecting the rotation of the rotary cylinder, and indicates that recording/reproduction is performed by video heads A and I when the level is H, and video head B when the level is 30 Hz as shown in Figure 4 (g). This is the input terminal into which the drum pulse a comes.

The drum pulse a that enters through the input terminal 12 is a monostable multivibrator (hereinafter referred to as "monomulti") 13.1
4. The monomulti 13 generates a pulse whose pulse width is greater than the pulse width of the drum pulse a when the drum pulse a rises, and supplies it to the sampling pulse generator 15. Sampling pulse generator 1
5 detects the falling edge of the supplied pulse and generates a sampling pulse b that goes to L level at each field point of the FM video signal to be reproduced to the video head as shown in FIG. 4(C) for sampling. Supplied to gate 16.

Furthermore, the monomulti 14 generates a pulse whose pulse width is twice the pulse width of the drum pulse a (which rises at the falling edge of the drum pulse a). This pulse is supplied to the sampling pulse generator 17, where the falling edge of the pulse is detected and the pulse is L at the midpoint of each field of the F'M video signal reproduced by the video head B as shown in FIG. 4 (Q). A sampling pulse C serving as a level is generated and supplied to the sampling gate 18.

The FM video signal from the input terminal 10 is supplied to an envelope detection circuit 19 for envelope detection, and the extracted envelope signal is branched into two and supplied to a sampling game (16.18). sampling gate 16
.
Supply on 20.21. The hold circuits 20 and 21 hold the sample values supplied thereto until the next sample value is supplied, and supply them to the non-inverting input terminal 1 and the inverting input terminal of the differential amplifier 22. The differential amplifier 22 is simultaneously supplied with sample values from a large number of adjacent sampling points. The differential amplifier 22 is as shown by the solid line I in FIG.
When the potential of the input terminal V becomes higher than the potential of the inverting input terminal, the output voltage approaches Vcc according to the potential difference.
When the voltage decreases to (1) 1M, the output voltage approaches zero depending on the potential difference. The output voltage of the differential amplifier 22 is between the non-inverting input terminal of the comparator 23 and the inverting input terminal of the comparator 24, which constitute a window comparator.
C is supplied. The inverting input terminal of the comparator 23 has a voltage indicated by the broken line (2) in FIG. Therefore, when the potential difference between the sampled values of the hold circuits 20 and 21 is approximately zero, the OR circuit 25 generates a level error fraction 1 and supplies it to the NAND circuit 26 when the L level potential difference becomes thick (2).

Further, the drum pulse a that enters the input terminal is differentiated by a differentiating circuit consisting of a capacitor C1 and a resistor 1,
Furthermore, only the positive polarity portion is taken out by a diode Dl, and is made into a divisor pulse d as shown in FIG.
is supplied to the counting terminal of

The counter 27 is, for example, a quaternary counter whose count value is [o
When J, [j, the Q output goes to L level, and the counting point goes to r2J.
, r3J, the Q output is set to H level, and the Q output is supplied to the NAND circuit 26.

The output signal of the NAND circuit 26 is supplied to the mono 3 multi 28. The monomulti 28 is triggered by the fall of the output signal of the NAND circuit 26, generates a signal that remains at H level for a predetermined period of time, and supplies the signal to the drive circuit 29 and the reset terminal of the counter 27. The drive circuit 29 rotates the capstan motor 30 by a minute angle during still image playback to move the magnetic tape a minute distance, and this output drive voltage is used for normal recording and F! ) Drive 11i supplied to the capstan motor 30 at low power 444. 'The pressure has been lowered. The drive circuit 29 applies an open drive voltage supplied with an H level signal to the capstan motor 30 to rotate the cap.

Still start pulse coming from input terminal 11.

The output signals of the monomulti 28 are supplied to the set terminal and reset terminal of the counter 27, respectively. When a pulse is supplied to the set terminal, the counter 27 sets the count value to "3" and sets the Q output to H level, and while a signal of 1 level is supplied to the reset terminal, the counter 27 sets the /7Kl value to "0". Set Q output to L level.

Here, at time to, the methyl button is pressed and the still image is played back.
When the magnetic tape is turned on, the magnetic tape starts to stop running.

Time after this 1. During the sampling at time 1, the video head BVJ was not scanning tracks '2+'4+'6, etc. shown in the 1st to 1st position normally because the magnetic tape stopped running. The resample value is time 1- before time 1o.
OR circuit 25 to decrease the sample value at +
U) The output signal becomes H level as shown in FIG. 4G).

However, the Q output of the counter 27 is set to H level as shown in Fig. 4 due to the still start pulse that comes in at time to, so the output from the NAND circuit 26 (ff1 is 0 in Fig. 4). As shown in Figure 4, it becomes L level at time 1. As a result, the monomulti 28 is triggered and generates a signal at level 1 for a predetermined period of time as shown in Figure 4. This signal causes the capstan motor 30 to rotate by a minute angle. At the same time, the counter 27 is reset. This monomulti 28 output signal becomes L level at time t2, and the running drive of the magnetic tape is stopped. Here, time t
When the sampling values of 3 + '4 are approximately equal,
At time t4, the output signal of the OR circuit 25 reaches the L level.

At this time t4, the running of the magnetic tape has already been stopped. In addition, the counter 27 counts the count pulses d after time t2 when the monomulti 28 (7,1 output signal becomes L level), and the count value changes to "2" by the second count pulse that arrives at time t6. Then, the Q output is set to II level.

a time t4 when the running of the magnetic tape is completely stopped;
At subsequent time t5, sampling pulses b,
Then, at time t6, an H-level Q output is supplied to the NAND circuit 26. Comparators 23 and 24 compare sample values after the running of the magnetic tape has completely stopped. As a result, when the sample values at time t4 + t5 are approximately equal, that is, video heads A and B move the magnetic tape to the shaded area 2 in the first diagram.
When scanning with the trajectory shown in
ij [FIG. 4 O), 0, etc., the capstan motor 30 is not triggered and continues to reproduce the best still image.

If the sample values of the output of the mono multi 28 at the above times t and '-t2 and the sample values at the time "4h" 5 are different, the video heads A and B will move along the trajectories shown in the shaded area 4 in the first diagram. When scanning is performed with , the envelope signal output from the envelope detection circuit 19 becomes as shown in FIG. The output of the counter 27 remains at H level.Then, the Q output of the counter 27 at time t6 becomes H level, and the NAND circuit 26 becomes L level as at time t1, triggering the monomulti 28, and the resulting mono The capstan motor 30 is rotated by a small angle by the H level output of the multi 28, and the magnetic tape is moved a small distance so that the video heads A and B scan the shaded area 2.The operation during this time is at times 1-14. Almost the same.

In this way, when the sample values of the hold circuits 20 and 21 do not match with the H level output of the mono multi 28, the mono multi 28 repeatedly outputs an H level signal to move the magnetic tape a small distance, and the diagonal line fi 2 is scanned.

In this way, even if no control pulses are recorded on the magnetic tape, the running of the magnetic tape can be stopped so that the noise bar is in the vertical retrace period and the best still image is obtained. Even when applied to a conventional video tape recorder that records control pulses that have been truncated, the user has to adjust the pulse width of the monomulti output pulse that is supplied with the control pulse detection signal. Easy to operate.

In the above embodiment, the sampling position of the envelope waveform was set at the midpoint between the rising edge of drum pulse a and the falling edge of drum pulse a at 9, that is, the middle point of one vertical scanning period. Sampling may be performed at a symmetrical time point after [)1[, and the present invention is not limited to the above embodiment. However, if sampling is performed at the midpoint of one vertical scan period as in the above embodiment, the monomulti 13.1
4 time constants can be made the same and adjustment is easy.

As described above, the still image reproducing device for a video tape recorder according to the present invention detects the envelope of the reproduced video signal reproduced from the recorded tracks of the magnetic tape by each of a plurality of rotating video heads, extracts the envelope signal, and detects the envelope. sampling the envelope signal within each field and comparing sandal values of adjacent sampling sparks with each other;
If the sandal values of the sampling sparks after the magnetic tape stops running, the magnetic tape is moved a small distance and a specific recorded track on the stopped magnetic tape is repeatedly played back using a number of rotating video heads to produce a still image. In order to obtain the best still image without noise bars on the visible screen, the control pulses are concentrated on the magnetic tape during the vertical retrace period +M, and
When applied to a conventional tape recorder that records control pulses, the detection of control pulses eliminates the need to adjust the monomulti to make magnetic tape B run for a fixed time and stop this magnetic tape in the optimal state for still image playback. It has the following features.

[Brief explanation of the drawing]

Figure 1 schematically shows the tracks on the magnetic tape and the scanning locus during still image playback, and Figures 2 (5) to (C) are still images. ii ("+ A diagram showing the envelope waveforms of the drum pulse and the FM video signal at a small time. FIG. 3 is a block diagram of an embodiment of the device of the present invention. FIG. 4 (5) to Figure 5 is a characteristic diagram of an example of the differential amplifier shown in Figure 3. 1...Magnetic tape, 13, 14. Monomulti), 15.17... Sampling pulse generator, 16, 1.8... Sampling gate, 19... Envelope detection circuit, 20,
21... Hold circuit, 22... Differential amplifier, 23
, 24... Comparator 1/-ta.

Claims (1)

[Claims] Envelope detection is performed on the reproduced video signal reproduced from the recorded track of the magnetic tape by each of the plurality of rotating video heads to extract the envelope signal, and the envelope signal is sampled within each field and the adjacent sampling points are The sample values are compared with each other, and if the sample values at the sampling points after the magnetic tape has stopped running are different, the nuclear magnetic tape is moved a small distance and a specific recorded track of the stopped magnetic tape is recorded on the plurality of rotating videos. A still image playback device for a video tape recorder, characterized in that a still image is obtained by repeatedly playing back each head.