JPS628074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color video signal recording and reproducing device,
In particular, it greatly improves the S/N of the carrier color signal, thereby enabling high-density recording of narrow tracks and short wavelengths.

Generally, in a magnetic recording and reproducing apparatus (VTR), modulation noise occurs during reproduction, and the narrower the track and shorter the wavelength recording, the worse the S/N of the luminance signal and carrier color signal.

A comb-shaped filter as shown in FIG. 1 is a conventional technique used to improve the S/N ratio. This FIG. 1 is an example of a C-shaped comb filter. 1 is the color video signal input terminal, 2
is a delay circuit whose delay time is 1 horizontal period _TH , 3
4 is a subtraction circuit, and 4 is an output terminal for a carrier color signal.
If the input and output signals are Ei and Eo, and the angular frequency of the input signal is ω (=2π), then the frequency versus amplitude characteristic in FIG. 1 is expressed by equation (1).

G=|2sinωT _H /2| (1) Therefore, the amplitude versus frequency characteristic of this comb filter is as shown by curve a in FIG. 4. When n is a positive integer and the horizontal frequency is _H (=1/T _H ), when =n _H , G=0...(2) When =2n+1/2 _H , G=2...(3). Since the subcarrier frequency of the NTSC color television signal is selected to be _S = 455/2 _H , the output of this comb filter has a carrier color signal output from equation (3), which has spectral components at intervals of _H. The luminance signal is removed. In this case, the carrier color signal amplitude is 2, and assuming that the noise reproduced from a VTR or the like is random, the comb filter output is √2, and the S/N is improved by 3 dB. This C-shaped comb filter not only improves the S/N ratio as described above, but also removes the luminance component, so it can also reduce cross color. Moreover, recent household use
In VTR systems, the carrier chrominance signal is converted into a reduced signal, and there is no guard band (non-recording band) between adjacent tracks, and the carrier chrominance signal is frequency-interleaved between adjacent tracks for recording. It is also possible to eliminate the crosstalk of the carrier color signal from the adjacent track, and it is widely used in color video signal recording and reproducing devices. However, in order to further reduce the tape consumption of these recording and reproducing apparatuses and to make them smaller and lighter, high-density recording technology with narrow tracks and short wavelengths is required. When performing narrow track/short wavelength recording (for example, a track width of 10 μm and a wavelength of 0.5 μm), the read head output decreases and modulation noise increases, causing problems with the S/N of the reproduced luminance signal and carrier color signal. come. The present invention focuses on this problem and significantly improves the S/N of the carrier color signal.
As a means for this purpose, for example, a circulating C-shaped comb filter as shown in FIG. 2 can be considered.

That is, a feedback circuit 5 and an adder 6 are provided from the output terminal 4, and the output signal of the feedback circuit 5 is fed back to its input side. In this case, the amplitude versus frequency characteristic of the comb filter when the feedback factor is K is expressed by equation (4).

Equation (4) is illustrated as the curve b in Figure 4, and when = n _H, G = 0, and when = 2n + 1/2 _H , G = 2/1 - K...Equation (6) is obtained. When K=0 in equation (4) is shown in FIG. 1, the characteristic is curve a in FIG. 4. Therefore, as K increases, the carrier color signal amplitude increases compared to the a-curve, and the relative valley portion (ratio of the same portion of the a-curve excluding the shaded area up to the maximum amplitude 2/1-K) increases, noise suppression increases, and the S/N ratio improves accordingly. However, since the carrier color signal circulates through the delay device 2, the vertical resolution decreases in proportion to K, resulting in an increase in color fringing in the vertical direction, resulting in a problem of deterioration of image quality. Therefore, it is not used in home VCRs at all. This will be briefly explained using FIG. A shows the input carrier color signal, and the burst signal is omitted. In other words, the diagram shows a case where the carrier color signal exists only during the period from _H1 to _H7 , and does not exist after _H8 .

B shows the output of the comb filter in Fig. 2.The envelope has become dull, and especially after H ₈ when the carrier color signal disappears, the amplitude gradually decreases over several H, for example, but the carrier color The signal is present, resulting in vertical color fringing.

The present invention eliminates these drawbacks, significantly improves the S/N ratio, reduces cross color and crosstalk, and reduces vertical color bleeding.

The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a basic block diagram of the present invention.

The same numbers as in FIGS. 1 and 2 indicate the same operations.

The amplitude versus frequency characteristic in this case is expressed by equation (7).

When = n _H , G = 0...Equation (8) =2n+1/2 When _H , G = 2...Equation (9) (7) becomes the c curve in Figure 4. In the present invention, we focus on the fact that line correlation is relatively strong in carrier color signals, and when line correlation is strong, K is increased (for example, K = 0.5), and when there is no line correlation, K is decreased ( For example, K=0), this method makes good use of human vision and keeps the vertical resolution within an acceptable range. In other words, the first step is to make K variable.
It has the characteristics of

In the figure, 7 shows that even if K is changed using the gain adjuster,
This is to ensure that the carrier color signal outputs have the same amplitude, and to obtain the signal for changing K.
This is a non-correlation detector 8, and a desired control signal is obtained from the output of this non-correlation detector 8 by a controller 9. The non-correlation detector 8 detects the absence of line correlation, and its configuration is as shown in FIG. becomes. That is, it is assumed that a carrier color signal as shown in FIG. 6A is input as the input signal. B is the output of the one horizontal period delay device 2. When these two signals A and B are added, a C signal corresponding to a period with no correlation is obtained for the carrier color signal. This is the output of the non-correlation detector 8, and this signal is converted into a signal as shown in FIG. 6D by the controller 9 and an envelope detector (amplitude detector). With this signal D, for example, at high level, K=0, and at low level, K=0.5. When configuring the decorrelation detector 8, 1
It is also possible to share the horizontal period delay device 2 and use a signal obtained by adding the output of the delay device 2 shown in FIG. 3 and the input carrier color signal Ei in an adder as the output of the non-correlation detector 8.
A signal as shown in FIG. 6 (E) is obtained at the carrier color signal output terminal 4 in FIG. 3.

This signal is obtained as follows. Figure 6 is Figure 3 where a certain value of K≠0 is fixed.
Showing Eo. Then, for example, if K=0 using the control signal in _FIG .
Therefore, the envelope amplitude changes during the first two to three horizontal periods. Furthermore, if K=0 during the _H8 period, the output of the adder 6 will be 0 since Ei=0 during that period, and therefore the output will be 0 after the _H9 period. Also, since the gain adjuster 7 has a gain of 1 during the _H8 period, the amplitude increases. As a result, the color fringing in the vertical direction becomes one horizontal period per Ei, which is sufficient for practical use in the NTSC system. Further, in a normal color television signal, it is unlikely that there is a long period without line correlation, so the gain adjuster 7 may not necessarily be provided. In this way, the problem of vertical color bleeding can be solved. As described above, when the non-correlation detector 8 selects a carrier chrominance signal as an input signal and uses a Y-shaped comb filter, the control signal can be easily obtained by envelope detection means, but the high frequency component of the luminance signal There are disadvantages that include. However, this problem does not arise when the present invention is applied to a color video signal recording and reproducing apparatus described below. Furthermore, it is also possible to detect the non-correlation detector 8 from the luminance signal, since the luminance signal and the carrier color signal are closely related.

Basically, it is sufficient to use the configuration shown in FIG. 1 and input a luminance signal as an input signal. In that case, the band may be limited to about 2 MHz so as not to include the carrier color signal component. This is the basic principle, and when a one horizontal period delay device is used as an ultrasonic delay line, it is necessary to modulate the luminance signal, pass it through the delay device, and then demodulate it. However, in the case of a recording/playback device, the luminance signal is FM
Since it is modulated, it can be passed through the delay device as is. Since the signal obtained by detecting non-correlation from the luminance signal in this way is a positive and negative control signal,
If the output is x, then 5 and 7 may be controlled using a signal |x|. By performing non-correlation detection from the luminance signal or carrier color signal in this way and controlling K proportionally or non-linearly using this amplitude, the S/N ratio can be significantly improved and color blurring in the vertical direction can be eliminated. It is. However, when handling something that has a lot of noise during playback, the noise can cause
In that case, the output of the non-correlation detector 8, for example, when detected from the luminance signal, is as shown in Figure 7 A, and it is |
The signal obtained by x| is shown in FIG. 7(b). A certain threshold value S is set for this signal B, and a binary pulse of 1 and 0 is created. Alternatively, when detecting from a carrier color signal, set the threshold value S in the envelope detector output (D in Figure 7), create a binary pulse (E) in Figure 7 in the same way, and change K by this (C) or (E). let
That is, at level 1, K=0, and at level 0, K=Q. In this way, the influence of noise will be reduced.

An embodiment in which the present invention is applied to a color video signal recording and reproducing device will be described below.

Figure 8 shows the configuration of a recording/reproducing device, in which two heads H _A and H _B are arranged on a rotating cylinder 1.
The cylinders are installed at intervals of 180°, and the tape 2 is wrapped over the cylinder over 180°. The rotating cylinder rotates at a rate of 30 times per second, and the heads H _A and H _B sequentially form tracks T _A and T _B as shown in FIG. 9, for example without a guard band. In this case, the gap directions of the H _A and H _B heads are different from each other, and an azimuth angle of, for example, ±6° is provided. FIG. 11 shows an embodiment of signal processing to which the present invention is applied. Input end 10
An NTSC color television signal is connected to the
Low pass filter 11, band pass filter 1
2, the luminance signal Ey and carrier color signal Es (s=
3.58MHz) is separated. Separated luminance signal Ey
is subjected to FM modulation by an FM modulator 13, and is input to an adder 17 after suppressing unnecessary components of a low-pass conversion carrier color signal band, which will be described later, by a high-pass filter 14. The separated carrier color signal Es is converted to a frequency converter 15 using a continuous wave having a frequency of s+c, which will be described later.
The signal is frequency-converted by a low-pass filter 16, and a low-pass converted carrier color signal Ec having a frequency c is obtained. The signal is mixed with the FM luminance signal by an adder 17, and recorded on a recording medium by a video head 9 via a switch circuit 18. Ru. The spectrum arrangement at that time is shown in FIG. When creating a continuous wave, a horizontal synchronizing signal from the horizontal synchronizing signal input terminal 28 and a variable oscillation frequency having, for example, c = 40 _H ( _H : horizontal synchronizing frequency, c: low frequency conversion carrier color signal frequency) are used. Frequency oscillator 31 output to frequency divider 3
The phase of the signal which is 1/40, for example, 0 is compared with the phase comparator 29, and the error signal is used as the variable frequency oscillator 31.
control. That is, a so-called AFC circuit is configured that creates a first continuous wave of frequency c that is phase-locked with the horizontal synchronization signal. This first continuous wave and switch circuit 36 are open during recording,
The variable frequency oscillator/fixed oscillator 35 works as a fixed oscillator during recording, converts the second continuous wave of frequency s (3.58 MHz) by the frequency converter 33, and converts the second continuous wave of frequency s (3.58 MHz) to frequency s+ by the bandpass filter 34.
A continuous wave of c is created and this continuous wave is input to the frequency converter. In the frequency interleap signal generator 32, the phase of c= _40H is advanced by 90 degrees line by line in the T _A track, and delayed by 90 degrees line by line in the T _B track. The low-pass conversion carrier color signal spectra thus recorded are shown in FIG. 12 A and B, respectively. In other words, the carrier color signals of the T _A track and the T _B track are frequency interleaved. For reproduction, the switch circuit 18 is set to the reproduction mode, and the signal from the video head 9 is separated by the high-pass filter 18 and the low-pass filter 19 into a reproduced EM luminance signal and a reproduced low-frequency conversion carrier color signal. The separated FM luminance signal has amplitude fluctuations removed by a limiter 20, is FM demodulated by an FM demodulator 21, passes through a low-pass filter 22, is added to a reproduced carrier color signal, which will be described later, by a mixer 49, and is output to an output terminal 50. Obtain a reproduced color video signal. During playback, crosstalk from adjacent tracks is also played back, but since FM modulation is performed at a high frequency, azimuth loss is large and does not pose a problem.

Now, the separated reproduced low-pass conversion carrier color signal contains unnecessary carrier color signals from the track with less azimuth loss because the recording wavelength is long. This low-pass conversion carrier color signal has a frequency of c+s
The continuous wave is frequency-converted by a frequency converter 23, and then converted by a bandpass filter 24 into a carrier color signal of the original frequency s. As shown in FIG. 12C, the output of this bandpass filter 24 consists of the necessary carrier color signal component whose spectrum exists at intervals of _H , centering on the frequency s, and the carrier color signal component and luminance signal component ( Contains unnecessary components (broken line). This carried color signal is processed by the C-type comb filter 25 =n _H component (dashed line)
is removed. The C-shaped comb filter 25 is the first
The configuration is similar to that shown in the figure, with reference numeral 26 a one-horizontal period delayer, and numeral 27 a subtracter. This comb-shaped filter 2
A burst signal is extracted from the 5 output by the burst gate circuit 39, and the phase of this burst signal and the output of the stable frequency fixed oscillator 37 is compared by the phase comparator 38, and the error signal is passed through the switch circuit 36 (during playback; mode) The so-called APC circuit output (second continuous wave of frequency s) that controls the variable frequency oscillator 35 and the variable frequency oscillator 31 with a frequency c that is phase synchronized with the horizontal synchronization signal mentioned at the time of recording.
The output is sent to the frequency interleave circuit 32,
During playback, the signal whose phase is advanced by 90° for each line on the T _A track and delayed by 90° for each line on the T _B track is sent to the frequency converter 33.
The bandpass filter 24 generates a continuous wave of frequency s+c, which is input to the frequency converter 23, where it is converted into the original carrier color signal and time axis fluctuations are removed. The output of the C-shaped comb filter 25 is input to the main section 40 of the present invention. 4
1 is an adder, 42 is a 1-horizontal period delay device, and 43 is a subtracter, which includes means for configuring a C-shaped cyclic comb filter and a C-shaped comb filter from which crosstalk and luminance components from adjacent tracks are removed. filter 25
1 horizontal period delayer 45 and adder 46 from the output of
Construct a decorrelation detector consisting of . In this case, as described above, crosstalk and luminance components are considerably reduced, and non-correlation detection can be performed relatively stably. The output of this non-correlation detector is amplitude-detected by an envelope detector 47 and converted into a signal without subcarrier, which is converted into a binary pulse of 1 and 0 by 48 circuits according to a certain threshold value S. is switched to the feedback rate K=Q (for example, 0.5), and to K=0 when there is no correlation. As a result, the carrier color signal S/N is significantly improved, adjacent crosstalk is further reduced, the luminance component is also further reduced, cross color can be removed, and the problem of color fringing due to a decrease in vertical resolution can also be removed. .
The output of the subtracter 43 is added to the reproduced luminance signal in a mixer 49 and outputted to an output terminal 50 as a reproduced color video signal. Furthermore, in VTRs and the like, dropout (signal loss) occurs due to dust, etc., and in that case, the color does not appear for a period of time, but according to the present invention, the dropout compensation is effective because it passes through the 1 horizontal period delay device several times. be. Also, the 11th
Although the gain adjuster is omitted in the figure, as mentioned above, there are few cases in which uncorrelated signals continue for a long period of time, and these are omitted. Furthermore, since the waveform tends to be rounded as shown in FIG. 6E, it goes without saying that the luminance signal may be delayed by an appropriate amount (for example, one horizontal period) to correct this.

Furthermore, in applying the present invention to a recording/reproducing device,
Another feature is that the APC circuit is composed of between 25 and 40. If there is a time axis variation Δ in the reproduced carrier color signal, this time axis variation changes instantaneously. However, especially in the case of a circulating comb filter, etc., the above-mentioned △ differs like △' because the time axis fluctuation components are averaged in the vertical direction. Therefore, when the APC is constructed from the output of the circulating comb filter, the frequency converter 23 receives the instantaneously changing Δ carrier color signal and the averaged Δ'. Therefore △′−△
A residual amount corresponding to the amount of noise is generated, causing hue unevenness on the screen, and at the same time, the degree of improvement in S/N by the circulating comb filter decreases. Therefore, the main APC
may be constructed from the output of the bandpass filter 24, but in the VHS system described in FIG. 11, etc., the APC malfunctions because adjacent crosstalk is included. Therefore, APC from between 25 and 40
It is most effective to configure

Next, the non-correlation detection by the present invention section may be performed as shown in FIG. When performing narrow track and short wavelength, S/
As the N deteriorates and the azimuth loss decreases, the influence of crosstalk may also become a problem for the luminance signal.Therefore, in order to remove the S/N and the crosstalk from adjacent tracks, as shown in FIG. Such circuits have been used recently. The input terminal 51 receives a luminance signal output from the low-pass filter 22 shown in FIG. 11, for example, in a band of 2.5 to 3.0 MHz. When this signal and the output of the one horizontal period delay device 53 are subtracted by the subtracter 54, only the area where the correlation of the luminance signals is broken is output as shown in FIG. 7A. This signal also contains noise, but if this signal is amplitude limited by the limiter 55, it can be reduced to almost only noise.If this noise and the reproduced luminance signal are subtracted by the subtracter 56, the output of the signal 56 is about as small as a small signal. A non-linear comb characteristic is obtained, and as a result, S/
Techniques are being used to improve N. Furthermore, if the FM carrier waves are made to differ by 2n+1/2 _H between the T _A and T _B tracks during recording, crosstalk from adjacent tracks can be eliminated as it becomes the valley of the comb characteristic.
A circuit 52 for improving the luminance signal S/N
The output of the subtracter 54 is shown in Fig. 7A, and if this signal is also used as the decorrelation detector of the present invention, a
There is no need to use a horizontal period delay device, and costs can be reduced. For the output of the subtracter 54, a |x| signal is generated by the control signal generator 57, and K of the feedback circuit 44 in FIG. Decide, 1,
K may also be switched using a binary pulse of 0.

Furthermore, the present invention can be made more effective as follows. In Fig. 14, A is the envelope-detected signal of the non-correlation detector or |x
｜The signal is shown by differentiating the A signal by an appropriate constant to obtain B, and extracting only the falling edge of this B signal and inverting the phase is C. The higher the level of the C signal, the higher the figure. input signal Ei or output signal of
By increasing the gain of either Eo or the subtracter 3, the blunting of the rise (the beginning of the correlation) as shown in FIG. 6E can be corrected. The falling edge (the end of the correlation) is unaffected because there is no output even if the gain is increased, and the effect is even greater. This is because the non-correlation is large in the first non-correlation part in FIG. 14C, so the amplitude becomes large and then gradually becomes small. In other words, if the decorrelation is large, the convergence time of the cyclic comb filter would be long, but by changing the gain, convergence can be made faster. Further, in the second case in FIG. 14C, since the non-correlation is small, the convergence is quick, so the gain is changed slightly to make the convergence even faster.

Even in the case where K is switched using a binary pulse of 1 and 0, improvements can be made using the same idea by differentiating the binary pulse.

As described above, according to the present invention, it is possible to significantly improve the S/N of the carrier color signal, reduce cross color, reduce crosstalk from adjacent tracks,
Since color fringing in the vertical direction can be removed, narrower track/shorter wavelength recording is also possible.

In the present invention, the VHS system has been explained as an example, but it is not limited to this system, and any system that separates the luminance signal and carrier color signal and performs signal processing suitable for recording can be included in the reproduction system. This allows the S/N ratio to be significantly improved. As a means of time axis correction, not only a combination of APC and AFC but also only APC or AFC may be used.

Further, although the present invention has been explained by taking as an example a circulating C-shaped comb filter as shown in FIG. 2, it can be implemented in any C-shaped comb filter in which looping is performed from the output to the input.

Furthermore, the present invention can be easily applied to PAL color TV signals by changing one horizontal period to a two-horizontal period delay device.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example of a C-shaped comb filter, Fig. 2 is a block diagram showing a conventional example of a circulating type C-comb filter, and Fig. 3 is a block diagram showing the basic configuration of the present invention. Figure 4 is a frequency characteristic diagram for explaining the operation of Figure 2, Figure 5 is a diagram explaining the operation of Figure 2, Figure 6 is a diagram explaining the basic operation of the present invention, and Figure 7 is a diagram for explaining the operation of Figure 2. Figure 8 is a plan view showing an outline of the main parts of the VTR, Figure 9 is a recording pattern diagram of the VTR, Figure 10 is a spectrum diagram of the recording signal, and Figure 11 is a diagram for explaining the creation of the control signal of the invention. A block diagram showing a basic embodiment of a recording and reproducing system to which the invention is applied. Fig. 12 is a diagram explaining the principle of carrier chrominance signal crosstalk removal method for guard bandless recording. Fig. 13 is an S/N diagram of a luminance signal. FIG. 14 is a diagram illustrating the operation of a circuit which serves both as an improvement circuit and a non-correlation detection circuit, making the present invention more effective. 1...Input terminal, 2...1 horizontal period delay circuit,
3... Subtraction circuit, 4... Output terminal, 5... Feedback circuit, 7... Gain adjuster, 8... Non-correlation detector,
9...Controller.

Claims (1)

[Scope of Claims] 1. In a reproduction system of a color video signal recording and reproducing device, a frequency conversion means removes a time axis variation component of a reproduced carrier color signal, and the reproduced carrier color signal from which the time axis variation component has been removed is used as a first reproduction carrier color signal. A continuous wave is generated from the burst signal output from the C-shaped comb filter to remove time axis fluctuation components and is supplied to the frequency converting means. The output of the C-shaped comb filter is connected to a second C-shaped comb filter which is equipped with at least an n horizontal period delay device (n=1, 2, . . . ) and a feedback circuit with a feedback rate K from its output side to its input side. The output of the second C-shaped comb filter and the reproduced luminance signal are mixed to form a reproduced color video signal, and the difference between the carrier color signal or luminance signal delayed by n horizontal periods and the non-delayed signal is A color video signal recording and reproducing apparatus characterized in that the line decorrelation is detected by calculating the sum, and the feedback rate K of the feedback circuit is changed according to the detected output. 2. The sum or difference of the reproduced carrier color signal from which the time axis fluctuation component has been removed is delayed by n horizontal periods and the non-delayed signal is created, and the sum or difference signal is returned to the feedback circuit according to the envelope-detected signal. Rate K
2. The color video signal recording and reproducing apparatus according to claim 1, wherein the color video signal recording and reproducing apparatus changes the color video signal. 3 The envelope detection output is set to 2 at a predetermined threshold.
3. The color video signal recording and reproducing apparatus according to claim 2, wherein the color video signal is converted into a value pulse and the feedback rate K is switched using the binary pulse. 4. The feedback rate K of the feedback circuit is controlled according to the absolute value of the difference signal between the luminance signal delayed by n horizontal periods and the non-delayed luminance signal. Recording and reproducing device for color video signals. 5. Recording of a color video signal according to claim 4, characterized in that the absolute value of the difference signal is converted into a binary pulse at a predetermined threshold value, and the feedback rate K is switched by the binary pulse. playback device.