JPH025354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a recording and reproducing apparatus that sequentially switches a plurality of rotary heads to record and reproduce video signals as intermittent recording trajectories on a recording medium, which eliminates head switching noise during reproduction. The purpose is to obtain a stable playback video signal.

Use 1/2 inch or 3/4 inch wide tape 2
In a head helical scan type VTR, the tape is wound around a rotating cylinder slightly more than 180 degrees, and each head records a signal of just over one field. During playback, the two heads are switched for each field to produce continuous video. I'm getting a signal. The head switching position on this reproduced video signal is usually set several lines (several horizontal scanning periods) before the vertical synchronizing signal. Since vertical blanking is performed from three lines before the vertical synchronization signal, if the head switching position is set three lines or more before the vertical synchronization signal, the switching noise will appear at the bottom of the screen. Also, if the head switching position is set within vertical blanking, the noise will not appear on the image, but will appear in the blanking area, and the time base collector (TBC) will
may cause malfunction. In addition, the head switching position is determined by controlling the rotational position of the rotary head and the phase of the vertical synchronization signal (during recording).
It fluctuates due to fluctuations in the rotational phase of the cylinder. This is particularly noticeable when the VTR is vibrated during recording, such as with a portable VTR, and the head switching position can vary over several lines. Further, when tapes are interchanged, the head switching position varies depending on the difference in the detection position (cylinder PG signal) of the rotational position of the cylinder in which the rotary head is installed in the recording VTR and the reproduction VTR.

A block diagram of one method for removing such head switching noise is shown in Fig. 1, and waveforms of each part are shown in Fig. 2.
It is shown and explained in the figure. In Figure 1, 1 and 1' are rotating video heads, 2 and 2' are head amplifiers, and 3
is a head switching circuit, 4 is a demodulation circuit, 5 is a dropout compensation circuit, 6 is a playback signal output terminal, 7 is a horizontal synchronizing signal separation circuit, 8 is a video head 1,
A cylinder that creates a signal according to the rotational phase of 1'
PG, 9 is a PG signal generation circuit, and 10 is a head switching signal and gate signal generation circuit. The modulated signals reproduced from the video heads 1 and 1' are amplified by the head amplifiers 2 and 2', and are switched at one field cycle by the head switching circuit 3, and then by the demodulation circuit 4.
, and the original continuous video signal is obtained as its output. Further, this signal passes through a dropout compensation circuit 5 and is outputted from an output terminal 6. The dropout compensation circuit 5 functions to replace the reproduced signal from the head with a signal from one line before when it is lost. On the other hand, the head switching signal 11 that controls the head switching circuit 3 is created as follows. A PG signal 12 as shown in FIG. 2 is generated by the PG signal generation circuit 9 based on the cylinder rotational position detection signal from the cylinder PG8. Further, a horizontal synchronizing signal 14 (FIG. 2 14) is separated from the demodulated video signal 13 (FIG. 2 13) by a horizontal synchronizing signal separation circuit 7.

From this PG signal 12 and horizontal synchronizing signal 14, a head switching signal and gate signal generating circuit 10 generates a head switching signal 11 (FIG. 2, 11) and a gate signal 15 (FIG. 2, 15). As an example of this generation circuit 10, a generation circuit for the head switching signal 11 uses the PG signal 12 as a data signal, and uses a signal delayed from the horizontal synchronization signal 14 by, for example, 1/4 line (time A in FIG. 2) as a clock signal. D
The circuit for generating the gate signal 15 uses the PG signal 12 as a data signal, and the circuit for generating the gate signal 15 uses the PG signal 12 as a data signal, and the circuit for generating the gate signal 15 has a signal with a delay slightly smaller than the delay A (1/4 line) of the head switching signal generating circuit from the horizontal synchronizing signal 14. It can be constructed from a D-type flip-flop which uses a signal (time (B) in FIG. 2) as a clock signal and a monostable multivibrator which delays its output by a time (C) in FIG. The head switching signal 11 created in this way is always a certain period of time (1/4 line in the above example) after the horizontal synchronizing signal.
The horizontal position on the screen is fixed, and it can be made so that it does not overlap with the horizontal synchronization signal or equalization pulse.
At the head switching position, noise occurs as shown in Fig. 2 13, but during the period C in Fig. 2 15 due to the gate signal 15, the dropout compensation circuit 5 replaces the signal with the previous line's signal, and this noise is removed. (Fig. 2, 16). The period C of the gate signal 15 is set to have enough width before and after the head switching position to include this noise. Here, the reason why the head switching position is synchronized with the horizontal synchronizing signal and not overlapping with the horizontal synchronizing signal and equalization pulse is to create a gate signal with a width before and after the head switching position, and to create a gate signal with width before and after the head switching position. Discontinuity (skew distortion) in the horizontal synchronizing signal occurs due to differences in cylinder diameter during expansion/contraction or compatibility, but even in this case, the dropout compensation circuit replaces the signal with the previous line, so that the horizontal synchronizing signal and equalization pulse are This is to prevent them from becoming unconnected or increasing by one.

However, the above method has the following drawbacks. As mentioned above, since the head switching position changes, when the above method is used, the head switching position moves line by line. Now, FIG. 3 shows the signals of the various parts in FIG. 1 when the head switching position is the first line after vertical blanking. 13-1, 15-1, 16
-1 corresponds to 13, 15, and 16 in FIG. 2, respectively. When the head switching noise is compensated for by the above method, a video signal appears at a place where blanking should normally be, as shown in FIG. 3, 16-1. This would violate broadcast standards. Alternatively, instead of replacing the head switching noise with the previous line signal as in the method shown in Figure 1, a method of blanking may be considered, but in this case, the head switching position is outside the vertical blanking. Sometimes, the video signal is blanked, resulting in that part turning black.

In view of the above, the present invention provides a method for performing head switching without head switching noise or video signals in vertical blanking, and without blanking certain portions of the video signal.

FIG. 4 shows a block diagram of an embodiment of the present invention.
FIG. 5 shows the signal waveforms of each part and will be explained. Fourth
In FIGS. 1 and 5, the same numbers as in FIGS. 1 and 2 represent the same elements and perform the same operations. 17 and 17' are blanking circuits, 18 is a vertical synchronization signal separation circuit, 19 is a blanking signal generation circuit, and 20, 21, and 21' are gate circuits.
Similarly to the case of FIG. 1, the head switching signal 11
and gate signal 15 are created. Further, from the reproduced video signal 13, the horizontal synchronization signal separation circuit 7 and the vertical synchronization signal separation circuit 18 generate the horizontal synchronization signal 14.
and the vertical synchronization signal 22 are separated and guided to the blanking signal generation circuit 19, as shown in FIGS. 23 and 24.
Blanking signals 23 and 24 shown in are created. The blanking signal generation circuit can be configured by a counter that is reset by the vertical synchronization signal and counts the horizontal synchronization signal. The blanking signal 23 is a low level signal during the vertical blanking period and one line after the end of vertical blanking and is high level during the other periods, and the blanking signal 24 is high level during the vertical blanking period excluding the vertical synchronization signal period. and other periods are low level signals. Blanking signal 23 is led together with gate signal 15 to gate circuit 20, and only when signal 23 is at a high level, gate signal 15 is transmitted to the dropout compensation circuit. That is, only when a head switch occurs while the signal 23 is at a high level, the previous stage of the head switch noise is replaced with the signal one line before. Therefore, no video signal enters the vertical blanking.
Further, the blanking signal 24 is the gate signal 15
Only when the signal 24 is at a high level, the gate signal 15 is transmitted to the blanking circuit and blanked to the vedestal potential. That is, if a head switching position exists during a period in which the signal 24 is at a high level, the period before and after the head switching position is blanked to the pedestal potential. Also,
The vertical synchronization signal 22 and the gate signal 15 are guided to a gate circuit 21', and the gate signal 15 is transmitted to a blanking circuit 17' only during the period of the vertical synchronization signal.
Blanking is performed to the level of the vertical synchronization signal. That is, if there is a head switching position during the vertical synchronizing signal period, the periods before and after the position are blanked to the vertical synchronizing signal level. In this way, even if the head switching position comes to any position other than the first line after vertical blanking, the noise is replaced with the signal from the previous line or blanked to the pedestal potential or vertical synchronization signal level. can be completely removed.

As mentioned above, the head switching position is usually set several lines before the vertical synchronization signal. Assuming that the head switching position is set 2.75 lines before the vertical synchronization signal within blanking, in most cases it will be between 6 lines before the vertical synchronization signal and the vertical synchronization signal even if the head switching position changes. Taking these points into consideration, the following modifications may be considered in order to simplify the circuit. The blanking signal 23 is a low level signal for a period including at least one line from the start of vertical blanking, the blanking signal 24 is a signal of opposite polarity to the signal 23, and the gate circuit 21'
and the blanking circuit 17' are omitted. In this way, during the period when the blanking signal 24 is at a high level, the areas before and after the head switching position are blanked to the pedestal potential, and one line at the beginning of vertical blanking is included within this period. No video signal is received. Furthermore, when the head switching position comes outside this period, the noise is replaced with the signal from one line before.

Further, the gate circuit 20 is omitted, and the dropout compensation circuit 5 is operated even when the head switching position is within vertical blanking, as in the case of FIG. The width is set slightly wider than the gate signal supplied to the dropout compensation circuit, and when the head switching position is on the first line at the start of vertical blanking and a video signal appears, the blanking circuit 17 transfers it to the pedestal potential. It may be configured so that blanking is performed.

Furthermore, in a device that does not have the dropout compensation circuit 5, during the vertical blanking period, the areas before and after the head switching position are blanked to the pedestal potential, and by not blanking during periods other than vertical blanking, the vertical blanking By removing the head switching noise in the video signal, the head switching noise in the video signal can be kept at a small point at a constant horizontal position without becoming black and wide due to blanking. At this time, it is better to blank the vertical synchronizing signal period to the vertical synchronizing signal level or not blanking.

Although the present invention has been described above with respect to a two-head helical scan type VTR, the present invention can be applied to any device that records and reproduces video signals by switching a plurality of heads.

As described above, according to the present invention, switching noise in vertical blanking is removed, video signals are prevented from entering the blanking, and further, when head switching occurs on a video line immediately after vertical blanking, blanking is performed. By leaving it as it is without performing ranking, etc., and performing dropout compensation when a head switch occurs on other video lines, you can obtain a perfect playback video signal without noise in the video and preventing TBC malfunctions. be able to.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a conventional head switching method, FIGS. 2 and 3 are diagrams showing signal waveforms at each part of FIG. 1, and FIG. 4 is an embodiment of the present invention. The block diagram of FIG. 5 is a diagram showing signal waveforms of each part of FIG. 4. 1, 1'...Video head, 3...Head switching circuit, 10...Head switching signal and gate signal generation circuit, 17...Blanking circuit, 19
...Blanking signal creation circuit, 21...Gate circuit.

Claims (1)

[Claims] 1. When recording and reproducing a video signal by sequentially switching a plurality of heads, a first method for setting the head switching position during reproduction to a location that does not overlap the composite synchronization signal.
means for creating a gate signal having a width sufficient to include head switching noise; a third means for creating a blanking signal; a fourth means for creating a second vertical blanking signal at a high level during a vertical blanking period excluding a vertical synchronization signal portion of the reproduced video signal; When the output gate signal of the second means is located within the vertical blanking period excluding the vertical synchronization signal section, the output gate signal of the second means is located within the vertical blanking period based on the output gate signal and the second vertical blanking signal. a fifth means for clamping to the pedestal potential; and when the output gate signal of the second means is located outside the period between the vertical blanking period and one line after the end of the vertical blanking period, the output gate signal and the first vertical blanking signal,
and a sixth means for replacing the reproduced video signal in the period of the output gate signal of the second means with the reproduced video signal from one horizontal scanning period earlier, wherein the output gate signal of the second means replaces the reproduced video signal in the period of the output gate signal of the reproduced video signal. A video signal recording and reproducing device characterized in that when the video signal is located on a line immediately after ranking, the reproduced video signal in the period of the output gate signal of the second means is not replaced with the reproduced video signal from one horizontal scan earlier.