JPS6337998B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video signal recording method, and when recording a video signal by frequency modulating it, the phase of the frequency modulated video signal in each horizontal retrace period is made to match relatively. It is an object of the present invention to provide a method for recording video signals so as to obtain stable and high-quality images.

Generally, a 2-head helical scan VTR
Crosstalk from adjacent tracks is one of the causes of deterioration in reproduced image quality. Conventionally, in order to prevent the deterioration of the reproduced image quality due to this crosstalk, recording was performed by making the gap angles of the rotating video heads that form adjacent tracks different from each other, and by making the magnetization directions of the adjacent tracks on the magnetic tape different from each other. It adopted an azimuth recording and playback method.

However, in order to record and reproduce video signals for as long as possible on a magnetic tape of limited length, as the magnetic tape running speed decreases, the track width actually decreases and the reproduction output level decreases. Therefore, there is a need for higher performance recording and reproducing characteristics than ever before. As a result of various experiments, the applicant found that
We discovered a phenomenon in which the reproduced image in parts where the video signal level changes sharply becomes unclear, especially during the long recording and playback described above. We found that this is caused by a difference in phase. Furthermore, even with the above-mentioned azimuth recording and playback method, during long-term recording and playback, there is a problem of deterioration of the reproduced image due to crosstalk, which particularly degrades the reproduced image in parts where the video signal level changes sharply as described above. I was letting it happen.

That is, if an image is to be recorded and played back, for example, as shown in FIG. 1A, the left side of the screen is a black area 1, the right side of the screen is a white area 2, and the boundary line between them is in the vertical direction of the screen. Black portion 1 to white portion 2 on the reproduced image in any horizontal scanning line during recording
The video signal in the vicinity of the transition position becomes as shown in FIG. 1B, and has a waveform portion 4 that rises steeply. This video signal is frequency-modulated and recorded on a magnetic tape, and the waveform of the video signal (hereinafter referred to as FM video signal), which is a frequency-modulated wave before demodulation and reproduced, is shown in Figure 1C during a certain horizontal scanning period. The horizontal scanning periods before and after _the horizontal scanning period are as shown in _FIG . In addition, the first
The same applies to the FM video signal of n fields in Figure C, and the FM video signal of (n±1) fields in Figure D.

When the FM video signal shown in FIG. 1C is demodulated, the video signal shown at 5 in E in the same figure is demodulated, and when the FM video signal shown in FIG. 1D is demodulated, the video signal shown at 6 in FIG. Different transient responses are shown depending on the phase difference between T ₁ and T ₂ , and △E,
Different unspecified fluctuations indicated by △E' appear randomly every horizontal scanning period, and on the screen, a noise-like flicker appears at the boundary line between white part 1 and black part 2, as shown by 3 in Figure 1A. It looks like 3. The more crosstalk there is, the more the image appears to be distorted.

The present invention eliminates the above-mentioned drawbacks, and embodiments thereof will be described below with reference to FIGS. 2 to 4.

FIG. 2 is a block system diagram of one embodiment of the video signal recording method according to the present invention, and FIGS.
A signal waveform diagram for explaining the operation of the figure is shown. In FIG. 2, the color video signal input to the input terminal 10 is
The signal is supplied to a band filter 11, a low-pass filter 12, and a horizontal synchronization signal separation circuit 13, respectively. The carrier color signal in the input color video signal whose frequency is selected and extracted by the band filter 11 is frequency-converted by the recording color circuit 14 to a frequency lower than the band of the frequency modulated luminance signal, which will be described later, and then sent to the mixer, which will be described later. supplied to

In FIG. 2, the luminance signal extracted from the low-pass filter 12 is sent to the pedestal clamp circuit 3
After the pedestal level is clamped to a constant value, it is supplied to the mixer 33. The output luminance signal of this pedestal clamp circuit 32 is
It becomes as shown by a in Figure A.

On the other hand, the horizontal synchronizing signal b, as shown in FIG.
3.7MHz, it is supplied to the reset terminal of the counter 35, and is reset at the leading edge of the horizontal synchronizing signal, and the time from that leading edge to the front end of the front porch during the horizontal retrace period of the luminance signal (Fig. 3A) , B to T
3.7MHz pulse c from the 235 multiplier 34 (shown in Figure 3C) until the count value corresponds to
have them counted. When the counter 35 finishes counting the set count value, it applies a pulse to the set input terminal of the flip-flop 36 to bring it into the set state. The flip-flop 36 in the set state supplies a high level signal to the mixer 33,
Here, the luminance signal a is superimposed on the front porch within the horizontal retrace period. This flip flop 3
It is desirable that the high level signal of 6 has a value corresponding to the white level. This means that the FM brightness signal obtained by frequency modulation by the recording brightness circuit 37, which will be described later, has the highest white level at the carrier wave frequency.
It is a frequency modulated wave with a frequency of 4.4MHz, and therefore, when it is set as a white level, the phase quickly matches the output pulse c of the 3.7MHz 235 multiplier 34 in the phase detection circuit 38, which will be described later, and is superimposed on the luminance signal a. This is because the output pulse width of the flip-flop 36 is shortened, and the luminance signal is not adversely affected.

The brightness signal with white level pulses superimposed on the front porch taken out from the mixer 33 is supplied to the recording brightness circuit 37, where the brightness signal is adjusted such that the carrier frequency is 4.4MHz at the white level and 3.7MHz at the pedestal level. After being made into a frequency modulated wave, the frequency component of the low-pass conversion carrier color signal band is removed by a high-pass filter. As a result, the FM luminance signal e shown in FIG.

The phase detection circuit 38 detects the phase of the FM luminance signal e.
The phase is compared with a constant frequency of 3.7MHz (frequency corresponding to the pedestal level) from the 235 multiplier 34,
When the phases match, a reset pulse is applied to the reset terminal of flip-flop 36 to reset it. As a result, the output of flip-flop 36 becomes low level. Therefore, the output of the flip-flop 36 contains a luminance signal a as shown in FIG. 3D.
A white level pulse d is generated for a period corresponding to the front porch of , and this is superimposed on the luminance signal a by the mixer 33 as a phase compensation pulse.
The output signal of the mixer 33 is as shown in FIG. 3F. It is desirable that this phase compensation pulse be inserted into the front porch within the horizontal retrace period so as not to adversely affect the horizontal synchronizing signal, color burst signal, and video signal (adjusted by the counter 35).

The reason why the signal frequency for phase detection with the FM luminance signal in the phase detection circuit 38 was set to 3.7MHz, which corresponds to the pedestal level, is that immediately after the phases of both coincide, the FM luminance signal frequency changes to 3.7MHz, which is the pedestal level. This is because the frequencies of both signals are equal to each other, which is preferable in terms of circuit operation.

According to this embodiment, one of the two input signals of the phase detection circuit 38 is a signal c having a frequency corresponding to the pedestal level and phase-synchronized with the horizontal synchronization signal.
The other input signal is the FM brightness signal e, and the frequency of the signal section modulated by the phase compensation pulse d of this FM brightness signal e increases sharply toward 4.4MHz, and the phase change accelerates. Because it is done,
The phase of signal c matches the phase of both input signals within the front porch.

Then, when the phases of both input signals match, the phase compensation pulse d falls, and the acceleration of the above-mentioned phase change is stopped. The pulse width of this phase compensation pulse d is determined by the frequency of the FM luminance signal e depending on the picture immediately before the rise of the pulse d.
Since the time point at which the luminance signal e and the signal c match in phase is different, it changes depending on the picture, but the falling point of the phase compensation pulse d is always within the front porch.
The phase of the horizontal retrace period of the FM luminance signal e after the falling point is the same for each horizontal scanning line.

Therefore, the phase of the final position of the back porch (the starting position of the video line period) of the FM luminance signal e is always the same in each horizontal scanning line, so that the phase is compensated.

This FM luminance signal e is supplied to the mixer 21,
Here, it is frequency-division multiplexed with the low-pass converted carrier color signal. The frequency division multiplexed signal taken out from the mixer 21 is amplified by a recording amplifier 22 and then passed through a rotary transformer 23 to a rotating video head 24.
is supplied to the magnetic tape (not shown).
It is recorded by forming a track that is inclined upward in the longitudinal direction. Therefore, the phases of the FM luminance signals during each horizontal retrace period on the magnetic tape are matched (particularly in the back porch, the phases are precisely matched) and recorded.

Therefore, when a magnetic tape recorded in the above manner is reproduced, an image with line correlation (with field correlation) is formed, for example, as shown in FIG. (Similarly in the case of images), when recording video signals, the waveform of the recorded video signal in a certain horizontal scanning period near the boundary line between black portion 1 and white portion 2 rises rapidly as shown in FIG. 4B. The waveform of the reproduced video signal (reproduced brightness signal) causes damped oscillation due to the transient response at the rising edge, but at least the phase of the start position of the video period of the recorded FM brightness signal is recorded in the same manner in each horizontal scanning period. Therefore, the reproduced FM luminance signal in a certain horizontal scanning period near the boundary line and the reproduced FM luminance signal in the adjacent horizontal scanning period have a relative phase difference as shown in FIGS. 4C and D, respectively. Therefore, the demodulated waveforms substantially match in adjacent horizontal scanning periods, as shown by solid lines and broken lines in FIG. Therefore, the reproduced image is reproduced as shown in FIG. 4A, and a static line 7 is reproduced without causing flickering noise at the boundary line as in the conventional case, so that an adverse visual effect can be prevented.

Furthermore, even if crosstalk occurs, the relative phase of the crosstalk signal is the same for each horizontal scanning period in the case of images like the one above, so it will not be reproduced as a flickering noise. Figure 4A
7 is reproduced as a stable image that is extremely easy to see.

In each of the above embodiments, a case has been described in which the luminance signal is frequency modulated, the carrier color signal is frequency-converted to a lower frequency band, and these two signals are frequency-division multiplexed and recorded on a magnetic tape. The method of the present invention can also be applied to a recording system in which the entire video signal is frequency-modulated and recorded.

As described above, the video signal recording method according to the present invention includes a means for superimposing a phase compensation pulse of a preset level in the horizontal retrace period of a video signal, and a means for superimposing a phase compensation pulse of a preset level on a carrier wave with the video signal superimposed with the phase compensation pulse. frequency modulation means for frequency modulating the signal to obtain a frequency modulated wave; signal generation means for generating a signal of a constant frequency that is phase synchronized with the horizontal synchronization signal in the video signal; means for detecting the phase of the frequency modulated wave and stopping the output of the phase compensation pulse when the phase of the constant frequency signal matches the phase of the phase compensation pulse signal section of the frequency modulated wave; Since the recording means records the output frequency modulated wave of the means on the recording medium, the flickering noise that conventionally occurs in the reproduced image at a sharp level change part of the video signal does not occur, and crosstalk does not occur. Even if damped oscillation occurs in the demodulated signal waveform, the relative phases of each horizontal retrace period after the trailing edge of the phase compensation pulse are the same, so that the relative phases of each horizontal scanning period and each field are the same. The phase of the sharp level change part of the video signal will match if there is line correlation or field correlation, so it will not be reproduced as a flickering noise, and a stable image that is extremely easy to see can be obtained. It is possible to record a frequency-modulated video signal to obtain a stable reproduced image without providing a special circuit, and furthermore, it is possible to generate the phase compensation pulse at a level corresponding to the white level of the video signal, thereby improving the quality of the video signal. Since it is arranged to overlap with the horizontal retrace period, it has the advantage that the time point at which phase coincidence is detected by the phase detection can be accelerated.

[Brief explanation of the drawing]

1A to 1E are diagrams showing reproduced images, recorded signal waveforms, and reproduced signal waveforms, respectively, according to the conventional method, and FIG. 2 is a block system diagram showing an embodiment of the present invention method.
3 is a signal waveform diagram for explaining the operation of FIG. 2, and FIG. 4 is a reproduced image and recording signal waveform according to the method of the present invention,
FIG. 3 is a diagram showing a reproduced signal waveform. 10...Color video signal input terminal, 11...Band filter for carrier color signal separation, 12...Low pass filter for luminance signal separation, 13...Horizontal synchronization signal separation circuit, 17...Frequency modulator, 19... Phase control circuit, 25... Reproduction brightness signal input terminal, 27...
Reproduction horizontal synchronization signal input terminal, 34...235 multiplier,
35...Counter, 36...Flip-flop,
37...recording brightness circuit, 38...phase detection circuit.

Claims (1)

[Claims] 1. Means for superimposing a phase compensation pulse of a preset level on the horizontal retrace period of a video signal, and a means for frequency modulating a carrier wave with the video signal on which the phase compensation pulse is superimposed. Frequency modulation means for obtaining a frequency modulated wave; Signal generation means for generating a constant frequency signal that is phase synchronized with a horizontal synchronization signal in the video signal; A constant frequency signal from the signal generation means and the frequency modulated wave. means for performing phase detection of the constant frequency signal and stopping the output of the phase compensation pulse at the time when the phase of the signal of the constant frequency matches the phase of the phase compensation pulse signal section of the frequency modulated wave; A video signal recording method comprising a recording means for recording a frequency modulated wave output from a frequency modulating means on a recording medium. 2. Claim 1, wherein the superimposing means generates the phase compensation pulse at a level corresponding to the white level of the video signal and superimposes it on the horizontal retrace period of the video signal. Video signal recording method described.