JPS60126989A - Chrominance signal processing method - Google Patents

Abstract

PURPOSE:To omit an LPF or a BPF having sudden cut-off characteristics by eliminating the undesired side band wave component produced in a demodulation mode to a baseband through a comb-line filter of the base band and a holding circuit in case a carrier color signal of low band is converted into a chrominance signal of the base band or into a prescribed carrier chrominance signal. CONSTITUTION:A carrier chrominance signal CL of low band conversion which is recorded and reproduced by a color-under system is applied to a balanced modulators B5 and R6. The outputs of modulators B5 and R6 are converted into base band chrominance signals B-Y and R-Y through comb-line filters B9 and R10 and then sample holding circuits B11 and R12 respectively. The signal of a subcarrier frequency fL of a low band conversion carrier chrominance signal CL is applied to both modulators B5 and R6 respectively with a 90 deg. phase difference produced by a phase shifter 7. There a color demodulator 8 is formed with both modulators B5 and R6, the shifter 7 and the conversion carrier fL.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for processing a low frequency conversion carrier color signal used in a video tape recorder (VTR).
Particularly when converting a low-pass converted carrier color signal reproduced from a VTR back to a baseband color signal, or when converting a predetermined color subcarrier frequency (N
The present invention relates to an example of a processing method when converting into a carrier color signal having a frequency of approximately 358 MHz in the case of TSC.

Conventional configuration and its problems In most cases, the color signal recording method of recent consumer VTRs converts the carrier color signal to a low band and records it under the frequency-modulated luminance signal band by frequency multiplexing. This is a method called color under. This method has many advantages, such as being resistant to jitter caused by rotating cylinders, etc., and having good linearity due to the fact that the F and M luminance signals act as high-frequency biases, but it also has the following drawbacks. There is.

Figure 1 shows the central part of the color signal reproduction system in conventional color under recording (parts other than those related to this invention have been deleted), and each frequency shown in the figure is a typical example of N.
The figure shows VH8 using the TSC system. CL in FIG. 1 is the low-pass conversion carrier color signal reproduced from the VTR, which is transmitted by the main balanced modulator 1 and the bandpass filter (
C, which is the carrier color signal of the NTSC system, by BPF) 4.
The frequency is converted to SO. In this case, the main balanced modulator 1
The conversion carrier added to the sub-balanced modulator 3 is the subcarrier frequency of 6.29 kHz, which is the subcarrier frequency of the low-pass conversion carrier color signal CL, and the subcarrier frequency of 3.58 MHz, which is the subcarrier frequency of the carrier color signal ESC.
In addition to 1, there is a frequency of 4.2 MHz (fo
) k-band pass filter (BPF) 2. Here, 629I52 applied to the sub-balanced modulator 3 is V
``The horizontal synchronization signal of the IR reproduction signal is 3.58 MFI.
As is well known, z is configured to be locked to the burst signal S of the carrier color signal C8O. Na〉、
In vIIS, the subcarrier frequency of the low-pass conversion carrier color signal is 629I (Hz +
:τfI(.

Figure 2 is a spectrum representation of the frequency conversion, and ta) in the same figure shows the spectrum of the low-frequency conversion carrier color signal CL. It is a signal that has FIG. 6(b) shows the spectrum appearing at the output of the main balanced modulator 1, which is the converted carrier f. The frequency components of the difference and sum of (4,2M(z)) and the low-pass conversion carrier color signal CL are output (C
8o and C5a2), out of which only the necessary C8o is extracted by a bandpass filter 4 having characteristics as shown in FIG. 4(0). In this case, the upper sideband C3(1
12 becomes an interference, so the bandpass filter 4 requires steep cutoff characteristics on the high frequency side. In addition, the main balance modulator 1
Because carrier leakage occurs depending on the characteristics of the converted carrier f. It is necessary to have a blocking characteristic that sufficiently attenuates the components. In this way, the band pass filter (BPF
) Since the cut-off characteristic of band pass filter 4 is required to be steep, the pass band of band pass filter 4 tends to be narrow. Come. Furthermore, large group delay distortion occurs within the passband of the bandpass filter 4, which also causes deterioration in image quality.

As described above, in the conventional color under color signal recording method shown in FIG. This was one of the major causes of deterioration.

Furthermore, when it is necessary to output the reproduced color signal in the base band, the conversion carrier f is used. 6291G (z), but in this case too, the upper side wave component of the conversion carrier f. appears in addition to the baseband color signal, so a steep low-pass filter is required to remove it, which also causes image quality deterioration. There was a problem that occurred.

Purpose of the Invention It is an object of the present invention to reduce the need for a filter or relax the design conditions for a filter that should be used when converting a low-pass conversion carrier color signal into a base band or a predetermined carrier color signal, and to The objective is to improve group delay characteristics and improve image quality.

Structure of the Invention The color signal processing method according to the present invention demodulates the low-pass converted carrier color signal when converting the low-pass converted carrier color signal into a baseband color signal or into a carrier color signal having a predetermined subcarrier frequency. By configuring the baseband signal to pass through a hold circuit and a comb filter, unnecessary sideband components and cross-overs of adjacent tracks that occur during demodulation are removed, and sidebands generated due to conversion are removed. The low-pass Mataha band-pass filter can be removed and the characteristics can be reduced.

DESCRIPTION OF THE EMBODIMENTS FIG. 3 is a block diagram of a main part of an embodiment of a color signal processing method for realizing the color signal processing method of the present invention. The low frequency converted carrier color signal CL recorded and reproduced in the color under one-way system is sent to a balanced modulator (B) 5 and a balanced modulator (R).
) 6 and their outputs are respectively applied to comb filters (
After passing through B) 9 and a comb filter (R) 10, the signal passes through sample and hold circuits (B) 11 and (R) 12 and is converted into baseband color signals B-Y and R-Y. A signal of the subcarrier frequency fL of the low-pass converted carrier color signal CL is applied to the balanced modulators (B) 5 and (R) 6 with a phase thick 7 and a phase difference of 90 degrees. Here, the balanced modulators (B) 5 and (R) 6, the phase shifter 7 and the conversion carrier fL form a color demodulator 8.

4 to 7 are diagrams for explaining the operation of the configuration shown in FIG. 3. FIG. When the baseband color signal, which is the original signal, is expressed on the axis, the low-frequency conversion carrier color signal CL//i is shown in Fig. 4 (
As shown in a), the subcarrier frequency fL (6 for VH8
It consists of fL-fBH component and fL+fB component centered around 29KHz+f). Here, f indicated by the broken line
L:l:fo acid component Due to crosstalk between adjacent tracks of the color signal reproduced from the VTR, in the case of long-time mode,
Since the reproduction head width is wider than the recording track width on the tape, the color signal appears at a level of about -6 to -10 dB compared to the main track color signal level. The spectrum then has an interleaved relationship with the low-band converted carrier color signal of the main track. Since the subcarrier frequency fL is added to the balanced modulator (B) 5 along with this low-frequency converted carrier color signal CL, the phase of fL is 90 degrees in the balanced modulator CB) 5 (balanced modulator (R) 6). As shown in FIG. 4(b), the sum and difference frequency components of the low-pass conversion carrier color signal CL and the subcarrier frequency fL are output as shown in FIG. 4(b). fB, which is the baseband color signal, and 2fL-fB, 2fL, which is the upper side wave component of the subcarrier frequency fL.
f caused by the +fB component and crosstalk. ,2
fL−f, zfL+fo components appear. If you want to extract fB, which is the baseband color signal, and output the B-Y signal, then
It is possible to pass the signal through a bass filter and a baseband comb filter, but since the upper side wave component of the crosstalk, which is an unnecessary spectrum, remains, a filter with a steep cutoff characteristic is required, which results in deterioration of image quality.

Therefore, in the present invention, a comb filter 9 and a sample hold circuit (B) 11 are connected to the output of the balanced modulator (B) 5.
The above problem is solved by passing.

FIG. 5 shows an example of the configuration of the comb filters (B) 9 and (R) 10 in FIG. 3, which are composed of a COD delay circuit 14 driven by a clock generator 15 and an adder 1.3. There is. The CCU delay circuit 14 delays the signal by a time corresponding to one horizontal scanning period of the video signal by appropriately selecting the frequency and the number of transfer stages of the four-wave generator 15. Therefore, the output of the adder 13 includes the input signal and the input signal I
A summation output with the H-delayed signal appears, and its frequency characteristic is fH (horizontal scanning frequency) as shown in Figure 6.
This is a so-called Y-shaped comb filter characteristic in which the gain shows a peak at each time.

Now, it has been explained that a signal having a spectrum as shown in FIG. 4(b) is obtained at the output of the balanced modulator (B) 5 in FIG. 3, but let's take a closer look at the spectral distribution.

In the color under recording method, the subcarrier frequency fL of the low-pass conversion carrier color signal to be recorded is substantially selected to be an odd multiple of τI'8 (with the VI-L'3 method and Beta method, the processing is slightly (The relationship in which the four-stoke components increment to the main track color signal is the same). Therefore, the frequency fL of the conversion carrier applied to the balanced modulator (B) 5 is given by equation (1).

fn, = −i fH(2n−1) =−・−・−(1
) fH: horizontal scanning frequency n: integer Therefore, the demodulated baseband color signal is expressed by equation (2), and has a spectral distribution with a peak for each fH. On the other hand, since the crosstalk components of the adjacent tracks are in an interleaving relationship with the signal of the main track, they can be expressed as shown in equation (3).

fB=mfH River...(2) 1 fo-■-(2m'-1)...Song(3)m, +7
1': Integer Therefore, the baseband color signals are fB and f in FIG. 6(b). It will be shown as follows.

The upper side wave 2fL-fB and 2fL+fB components of fL are:
By substituting equations (1) and (2), the spectrum is obtained as expressed by equations (4) and (5).

2fL+fB= if yo (2M-1)...Song (5)
N, M: Integer In addition, crosstalk components of adjacent tracks also appear in the upper side wave, and these are equal to the 2fLlthfB component.

There is an interleap relationship, resulting in spectra shown by equations (6) and (7).

-2fL−fo=qfH−=・(6)2fL−f. =
pfH...river (7) q, p: integers These spectra q are as shown by 2fL-fB and 2fL-fo in Figure 6(b), and 2fIJ-fB
There is an interleaving relationship with the spectrum of the acid component fB, but there is no interleaving relationship with the 2fL-fo acid component fB, resulting in a spectrum that is an integral multiple of fH. In other words, among the outputs of the balanced modulator (B) 5, f is the baseband color signal.
f of the four Stokes component for B. and 2 which is the upper side wave.
Regarding fL-fB acid component interleap relationship? ! lIru.

However, the upper side wave component 2fL-fo of the crosstalk
is not in an interleaving relationship with fBK. Therefore, as is clear from FIG. 6, by passing through the Y-shaped comb filter 9 already explained, the base band color signal fB is output as is, and the unnecessary components 2fL-fB, 2fL
TenfB and f. Since the component has a spectrum in the stopband of the comb filter 9, it is greatly attenuated, and in the end, the unnecessary components are 2fL:I:fo acid component residue, 41st ffl(d
) will appear at the output of the comb filter 9. This signal is further processed by the next sample and hold circuit 11, which is an unnecessary component 2.
fL:E:fo is attenuated. As shown in diagram M7, the sample and hold circuit 11 basically consists of a gate element 1.
6. A circuit consisting of a capacitor 17 and a buffer amplifier 18 opens and closes the gate element 16 at a frequency of 2fL, and samples and holds the input signal at 2fL. Generally, the frequency response of a sample-and-hold circuit in the case of zero-order hold has a characteristic that has a zero point at the sample frequency, as shown in FIG. 4(e). As is clear from this, the sample and hold circuit 11 is effective in attenuating the 2fLf:fo acid component, which is a sideband wave of adjacent crosstalk that remains as an unnecessary component. Moreover, 2f has the largest amplitude.
The attenuation is largest in L, so p1 unnecessary part 2fL:l
: This is an extremely effective characteristic for removing fo. As a result, unnecessary components due to crosstalk can be attenuated without passing through a low-pass filter, and the output has a spectral distribution as shown in Figure 4(f) in which almost no unnecessary components exist, and only tB remains, so the The signal may be taken out through a loose low-pass filter as shown in FIG. 4(g), or it may be taken out directly as a BY signal without passing through the low-pass filter. In this way, by passing the demodulated baseband color signal through the comb filter 9 and the sample-hold circuit 10 to obtain the baseband color signal B-Y, unnecessary components can be removed to a greater extent than with the low-pass filter. Since it is possible to get away with unnecessary or loose characteristics, it is possible to reproduce a color signal with a wide pass band and small group delay distortion.

Although the above description has been made regarding the conversion to B--Y, the conversion to K--Y can be performed in exactly the same manner using the balanced modulator (R) 6 and the comb filter (R) 10.

Note that the sample frequency 2f of the sample hold circuit 11
Since L satisfies the sampling theorem with respect to the baseband color signal fBK, there is no loss of output signal B-YiC information.

Next, another embodiment will be described in which a reproduced carrier color signal is converted into a predetermined carrier color signal such as NTSC and is processed using a digital signal.

Fig. M8 is a configuration diagram showing this embodiment. The reproduced low-frequency conversion carrier color signal CL is converted into a digital signal by the AD converter 9, and the color demodulator 20 converts the digital signal into two baseband color signals. is demodulated. Here, if the AD converter 90 pull frequency is 4f, color demodulation can be performed by separating the sample values into two sample values every 2fL and alternately inverting the sign of each sample value. Since demodulation is performed by processing sampled digital values, a sample-and-hold circuit is not necessary, and all have a zero-order hold effect. The demodulated digitized baseband color signal is applied to comb filters 21 and 22 for removing unnecessary sidebands, which is similar to the embodiment shown in FIG. is a digital type using a memory), the outputs of <1-type filters 21 and 22 are applied to a modulator 23, and the subcarrier frequency 's of the carrier color signal is
Quadrature two-phase modulation by a is performed in digital form. The output of the modulator 23 is converted to analog by the DA converter 24, and in the case of NTSC, f8o = 3.58 MHz
By doing so, a carrier color signal Csa of 3.58 MHz±500 KHz is obtained.

FIG. 9 shows the conversion to a carrier color signal as a spectral distribution expressed in analog form. FIG. 4(a) shows the spectrum of the input low-pass converted carrier color signal CL, which is distributed around the subcarrier frequency axis. Figure (b) shows the spectrum after being converted to a baseband color signal and passed through the comb filter 21, with only a small amount of unnecessary sideband components that could not be removed by the baseband color signal fB and the comb filter 21 and the hold effect. remains.

Figure (c) shows the spectrum converted to the subcarrier frequency 'sa by the modulator 23, where most of the carrier color signal is centered at fBo, with only a few sidebands above and below it. . Therefore, it can be taken out as it is as a carrier color signal, or it can be taken out through a loose bandpass filter as shown in FIG. If we compare this with the conventional examples explained in Figures 2(b) and (C), it is clear that there is a significant difference in the spectral distribution after conversion to a single carrier color signal, and a filter to remove unnecessary spectra is required. The carrier color signal extracted is in the signal band, as it may be unnecessary, or even if necessary, have extremely loose characteristics.

A high-quality carrier color signal can be obtained without suffering image quality deterioration such as group delay distortion.

In the embodiments of the present invention according to FIGS. 3 to 9, the low-pass converted carrier color signal is converted to the base band and then passed through a hold circuit and a comb filter to remove unnecessary sideband components generated during demodulation. However, this comb filter is also used as a comb filter, which is necessary for removing crosstalk between adjacent tracks, in VTRs that use azimuthal high-density recording such as the Vl (S method or Beta method). In the conventional example shown in FIG. 1, crosstalk components of adjacent tracks are mixed into the output of the main balanced modulator 1 while maintaining an interleaved relationship with the main signal.
After conversion to a carrier color signal, a glass delay line is used to form a comb filter to remove crosstalk components of adjacent tracks. On the other hand, when this invention is applied to the above-mentioned azimuth type high-density recording, the balanced modulator (B) shown in FIG.
5, the output of (R) 6 and the color demodulator 1 of FIG.
At the output of No. 4, adjacent crosstalk components appear in an interleaved relationship with the baseband main signal component. That is, since the crosstalk components of adjacent tracks are on the same spectrum as the sideband components generated during conversion to the baseband color signal, they are simultaneously removed by the comb filters 9.10° 15 and 16. . Moreover, these comb filters 9, 10, 15° 16 can be used for baseband color signals as shown in FIG. The feasibility of expanding the bandwidth of the delay line is extremely high.This is also one of the major features of this invention.

Further, in the above-described embodiments, the explanation has mainly been given for NTSC, but the present invention is also sufficiently effective for, for example, a PAL system VTR. In a PAL system VTR, the subcarrier frequency of the low frequency conversion carrier signal is selected to be an odd multiple of Tf, as shown in equation (5), as opposed to equation (1) in the case of NTSC.

1 fL-TfH (2n-1) (5) Therefore,
The upper side waves 2fL'-fB and 2fL'+fB generated after conversion to the baseband are expressed by equation (6).

2fL'±fB= +fH(2N-1)...(6) Equation (6) shows that the unnecessary sideband component is relative to the baseband color signal,
↓ This shows that it is a line offset relationship, which means that a delay circuit with a delay time of 2H can be removed by a needle-comb filter. That is, by replacing the NTSC '74 IH comb filter with a 2H comb filter f, it can be easily applied to the PAL system.

Effects of the Invention According to the present invention, when converting a low-band conversion carrier color signal to a baseband color signal or converting it to a predetermined carrier color signal, 1.
This method uses a baseband comb filter and hold circuit to remove unnecessary sideband components that occur during demodulation to the baseband, and does not require a low-pass filter or bandpass filter that has a steep g property. In addition, the bandwidth of the color signal can be kept wide, and group delay distortion can be kept small, so that the image quality of the reproduced color signal can be extremely high.

Furthermore, when converting to a predetermined carrier color signal, the carrier frequency can be directly used without requiring a conversion carrier generation band-pass filter (indicated by 2 in Figure 1), which was conventionally required. It also has the effect of being simplified.

In addition, since the comb filter used can be of the base band, a digital delay circuit using a CCD delay circuit or a memory element is suitable9. Lowering prices is also effective.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main parts of the reproduction system for converting carrier color signals in conventional low-pass conversion carrier color signal recording, Fig. 2 is a characteristic diagram for explaining the frequency conversion, and Fig. 3 is a diagram of the present invention. 4 is a spectral distribution diagram for explaining its operation, and FIG. 5 is a block diagram showing an example of the configuration of a comb filter used in this embodiment. Fig. 6 is a characteristic diagram showing the relationship between the comb filter characteristics and the spectrum to explain the operation, Fig. 7 is a circuit diagram of a hold circuit, and Fig. 8 is a main part block diagram showing another embodiment of the present invention. , FIG. 9 is a spectrum distribution diagram for explaining the operation. 5... Balanced modulator (B), 6... Balanced modulator (R)
, 7... Phase shifter, 8... Color demodulator, 9... Comb filter (R), 11.12... Sample hold circuit, 14... CCD delay circuit, 15... Clock generator , 13... Adder, 20... Color demodulator, 21.
22...Comb filter, 23...Modulator, 19...
・AD converter, 24... DA converter ^ to... , Ω

Claims (6)

[Claims] (1) When converting a low-pass conversion carrier color signal to a baseband color signal, the low-pass conversion carrier color signal is demodulated by a demodulation circuit, and a hold circuit and a comb filter are applied to the baseband color signal obtained by demodulation. A color signal processing method characterized by passing through. (2) The hold circuit samples and holds the baseband color signal at a frequency of 2fL (fL is the low-frequency conversion carrier frequency), thereby suppressing sidebands that occur during demodulation due to crosstalk between adjacent tracks in an azimuthal video tape recorder. The color signal processing method according to claim 1, wherein the color signal processing method is a sample hold circuit that attenuates wave components. (3) The color signal processing method according to claim (1), wherein the low-pass conversion carrier color signal is converted into a digital signal, and the demodulation circuit, the hold circuit, and the comb filter perform digital operation. (4) When converting a low-pass conversion carrier color signal into a carrier color signal having a predetermined color subcarrier, the low-pass conversion carrier color signal is demodulated by a demodulation circuit, and the baseband color signal obtained by demodulation is A color signal processing method characterized in that the color signal is converted into a predetermined carrier color signal after passing through a hold circuit and a comb filter. (5) The hold circuit sample-holds the baseband color signal at a frequency of 2fL (fL is the low-frequency conversion carrier frequency), thereby preventing demodulation from occurring due to crosstalk between adjacent tracks in an azimuthal video tape recorder. The color signal processing method according to claim 4, wherein the color signal processing method is a sample and hold circuit that attenuates the generated sideband components. (6) The color signal processing method according to claim (4), wherein the low-pass conversion carrier color signal is converted into a digital signal, and the demodulation circuit, the hold circuit, and the comb filter perform digital operation.