JPS60219888A - Processor of chrominance signal - Google Patents

Abstract

PURPOSE:To improve S/N of a low-frequency conversion carrier chrominance signal and to reduce the delay in the vertical direction by using a decoder and a comb-shaped filter whose frequency characteristic varies in accordance with the vertical correlation of the amplitude of decoded color difference signals to process said carrier chrominance signal. CONSTITUTION:A reproduced low-frequency conversion carrier chrominance signal is inputted to an input terminal 31, then enters a decoder 20, decoded into two color difference signals, then inputted to respective comb-shaped filters 24 and 25. The color difference signals passing through said filters 24 and 25 are rectangular-two-phase-modulated by a modulator 30, and carrier chrominance signals are obtained, then outputted to an output terminal 32. In the comb-shaped filter 24, the demodulated color difference signal passes through an one-hour delay line 21 and is added to a non-delayed signal in an adder 26. For this signal, the prescribed arithmetic processing is carried out by an one-hour delay line 22, an adder 27 and a subtractor 28. Finally, an output twice of the output of adder 26 can be obtained when the vertical correlation of the color difference signal is low and the output of the adder 27 when it is strong, respectively.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a video tape recorder (hereinafter referred to as VTR).
The present invention relates to a color signal processing device that processes a low-pass conversion carrier color signal used in the present invention.

Conventional configuration and its problems Color signal processing circuits commonly used in consumer VTRs are:
The sub-carrier color signal is frequency-converted to a low-band carrier color signal and recorded, and during playback, the frequency is converted back to the sub-carrier color signal, and at that time, the jitter of the color signal caused by the jitter of the rotating cylinder is removed. This is how it is called.

FIG. 1 shows an example of a reproduction system using a conventional analog circuit of color under type. In the figure, the reproduced low-pass converted color signal passes through a balanced modulator 1 and is frequency-converted into a subcarrier color signal, and a bandpass filter 2 removes unnecessary components generated during balanced modulation.

It is input to a comb filter 3.

On the other hand, a burst is extracted from the output by a burst gate 4, and its phase is compared by a reference oscillator 11 and a phase comparator 6. The phase error passes through a low-pass filter 6 to control a voltage controlled oscillator (hereinafter referred to as vCO). The output of vCO7 is added to the frequency multiplied by 40 by horizontal synchronization signal (fH) rough-used locked loop (pLL) 1o in balanced modulator 8, and passed through bandpass filter 9 to obtain the carrier of balanced modulator 1.

In this way, the circuit operates so that the output is always synchronized in phase with the reference oscillator 11. At this time, comb filter 3
extracts the vertical correlation component of the signal.

It serves to improve the SN ratio and to remove crosstalk components from adjacent tracks, if any. Therefore, in order to improve the S/N ratio, the characteristics of the comb-shaped filter 3 should be made such that many vertical correlation components of one color value are extracted.

This will be explained with reference to FIG. FIG. 2 shows, as an example, the amplitude frequency characteristics of two types of comb filters, with the horizontal axis representing the frequency and the vertical axis representing the output amplitude. The color signal has a spectrum peak at a frequency that is an integral multiple of the horizontal frequency (H), and the spectrum is concentrated near that frequency.

Therefore, the SN ratio of the color signal is improved by using the comb filter having the characteristic b shown by the dotted line rather than the comb filter having the characteristic a shown by the solid line.

However, the filter with the characteristic b has a longer delay time than the filter with the characteristic a, and the luminance signal does not change in areas where the hue or saturation changes rapidly on the playback screen, that is, in areas where there is no vertical correlation. On the other hand, there was a drawback in that the color signal dropped in the vertical direction of the screen. In order to prevent this, there is a method of detecting the vertical correlation of the luminance signals, and only when there is no correlation, switching the characteristic of the comb filter 3 from, for example, the characteristic b to the characteristic a in FIG. 2. However, with this method even if there is a vertical change in hue or saturation.

There is a drawback that the characteristics cannot be switched if there is no change in the luminance signal. In addition, since two color difference signals are quadrature modulated using color subcarriers, it is necessary to detect changes in the phase of the carrier color signal in order to know the vertical correlation of one hue. High accuracy is required for the delay time of the delay line used.

Furthermore, vertical correlation information has conventionally been obtained over one horizontal cycle period (hereinafter referred to as
However, if the reproduced low frequency conversion carrier color signal has a part due to crosstalk from the adjacent track, the crosstalk can be obtained by taking the difference from the signal 1H before. This method had the disadvantage that a component had to be extracted and a correlation signal could not be obtained.

Object of the Invention The object of the present invention is to process a low-pass conversion carrier color signal by using a demodulator and a comb filter whose amplitude frequency characteristics change according to the vertical correlation of the amplitudes of the color difference signals demodulated by the demodulator. This aims to improve the SN ratio of one color signal and reduce the vertical delay of the color signal in areas where the hue and saturation change.

Another object of the present invention is to provide a low-pass conversion carrier color signal even when there is crosstalk from adjacent tracks.

An object of the present invention is to provide a color signal processing device that can accurately control the characteristics of a comb filter.

Yet another object of the present invention is to use a feedback comb filter as the comb filter.

The object of the present invention is to obtain a color signal processing device with a better signal-to-noise ratio than when a non-feedback comb filter is used.

Configuration of the Invention The color signal processing device of the present invention includes a demodulator that demodulates a low-pass conversion carrier color signal into two color difference signals, and a nonlinear response that allows each of the two color difference signals demodulated by the demodulator to pass through. The device includes first and second comb filters.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention. In this embodiment, a case will be described in which two delay lines are used. The reproduced low-frequency conversion carrier color signal is input to the input terminal 31, enters the demodulator 2o, and is demodulated into two color difference signals.

The signals are input to comb filters 24 and 26, respectively.

The color difference signal passed through the comb filters 24 and 26 is sent to the modulator 3.
0, it is quadrature two-phase modulated and becomes a carrier color signal.

It is output to the output terminal 32. The comb filter 26 has the same configuration as the comb filter 24.

Next, the configuration of the comb filter 24 will be explained. One of the color difference signals demodulated by the demodulator 2o is 1
The signal that passes through the H delay line 21 and does not pass through the delay 1lJ21 is added by the adder 26. The output of the adder 26 is input to the 1H delay line 22.

The adder 27 adds the output of the adder 26 and the output of the 1H delay line 22, and the subtracter 28 subtracts the output of the 1H delay line 22 from the output of the adder 26.

Next, the output of the subtracter 28 passes through the slicer 23 to the adder 29.
It is added to the output of the adder 27 and sent to the modulator 3o. The slicer 23 is, for example, shown in FIG.
) has the input characteristics shown below.

When the amplitude of the input signal is constant and exceeds a bell T, an output appears.

Next, the characteristics of the comb filter 24 will be explained.

FIG. 6(a) shows the frequency characteristics of the output amplitude of the subtracter 28. VTRs that record color signals by converting them to low frequencies use methods such as inverting the low frequency carrier wave for each field, or changing the phase by 900 for each line in one field and delaying it by M2O3 in the next field. When demodulating such a signal into a color difference signal, the two color difference signals are JH
, (n is an integer), and the spectrum of the crosstalk component is (n-1-4)fH, (n is an integer). Also, the color difference signal is nfH
The sum of components far from the frequency of is information with low correlation. Therefore, the output of the subtracter 28 having the characteristics shown in FIG. 6(,) provides information indicating the low vertical correlation of the color difference signals. In other words, the output of the subtractor 28 has a lower vertical correlation in the color difference signal.
Large output can be obtained. Moreover, at this time, no crosstalk component appears. This is clear from the characteristics shown in Figure 5 (,).

This is because the (n++)fH component does not appear in the output of the subtracter 28. Next, the output of this subtracter 28 is input to the slicer 23. For example, if the characteristics of the slicer 23 are
As shown in FIG. 2B, a signal appears in the output of the slicer 23 only when the vertical correlation of the color difference signals is low. Therefore, when the vertical correlation of the nine color difference signals is low, the output of the adder 29 is twice the output of the adder 26, and when the vertical correlation is high, the output of the adder 26 and the output of the adder 26 are
The 11th signal delayed by H, ie, the output of the adder 27, appears. Therefore, the characteristics of the comb filter 24 have the characteristics shown by the solid line in FIG. 6 fb) when the vertical correlation of the two color difference signals is low. This is a characteristic of a conventional 1H type comb filter. In addition, when the vertical correlation is high, Figure 5 (
It has the characteristics shown by the dotted line in b). Therefore, S
The N ratio is improved, and the delay in the vertical direction of the color signal in the portion with low vertical correlation is reduced.

When the slicer 23 has the characteristics shown in FIG. 4 (ta), it performs the same operation as in (b) K, except that the DC level of the output of the comb filters 24 and 25 changes.

Note that if there is no crosstalk component in the reproduced low-frequency conversion color signal, the IH delay line 21 and the adder 26 can be omitted.

At this time, the characteristic of the subtractor 28 exhibits the fifth p(c) characteristic, and a signal corresponding to the vertical correlation is obtained as described above. In this case, the characteristics of the comb filters 24 and 26 are such that when the vertical correlation of one color difference signal is low, the input appears as is, and when it is high, it has the characteristics shown by the solid line in FIG. 5 (bl).

In addition, in this embodiment, there are two delay lines (delay lines 21° and 22).
However, the same effect can be obtained by using a configuration that obtains the characteristics shown in FIG. 6(a) even if three or more delay lines are used.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram showing the configuration of another embodiment of the present invention. In this embodiment, a case will be described in which two delay lines are used. The reproduced low-pass conversion carrier color signal is inputted to the input terminal 62 and input to the demodulator 4o, where it is demodulated into two color difference signals, and the comb-shaped filters 46 and 4, respectively.
7 is input. The color difference signal that has passed through the comb filters 46 and 47 is subjected to quadrature two-phase modulation by a modulator 45 to become a carrier color signal, which is output to an output terminal 53. The comb filter 47 has the same configuration as the comb filter 46. Next, the configuration of the comb filter 46 will be explained. One of the color difference signals demodulated by the demodulator 40 passes through the 1H delay line 41, and the signal that does not pass through the delay line 41 and the adder 4
8 is added. The output of adder 48 passes through adder 49 and enters 1H delay line 42 . The output of the adder 49 is subtracted from the signal obtained by delaying the output of the adder 49 by 1H. The output of the 51 adder 49 and the signal obtained by delaying the output of the adder 49 by 1H are added.

The output of the subtracter 60 passes through the limiter 44, is amplified by the amplifier 43, and is fed back to the adder 49. limiter 44it
For example, it has the characteristics shown in FIGS. 7(a) and (b), and when the input level exceeds a certain value T, the output becomes constant (zero in (b)). Further, the amplifier 43 may have an amplification factor of 1 or less. In other words, it may be an attenuator.Next, the characteristics of the comb filter 46 will be described in the case where the gain of the amplifier 43 is 1. The frequency characteristic of the output amplitude of the subtracter 50 shows the characteristic shown in FIG. 8(f). Follow-)
As explained in the previous example.

The output of the subtracter 50 appears larger when the vertical correlation of the color difference signals input to the comb filter 46 is lower. Further, no crosstalk component appears. This reduction 3')
The output of the -box 60 is fed back to the adder 49 through the limiter 44 and the amplifier 43?1:.

The characteristics of the comb filter 46 exhibit the characteristics of a non-feedback filter when the vertical correlation of the input signal is low [FIG.
) is high, it becomes a feedback type filter and has the characteristic shown by the dotted line in FIG. 8(b). Note that if there is no crosstalk component in the reproduced low-frequency conversion color signal, the 1H delay line 41 and the adder 48 can be omitted.

At this time, the characteristics of the subtracter 60 exhibit the characteristics shown in FIG. 8(C), and a signal corresponding to the vertical correlation is obtained as described above. In this case, the comb filters 46 and 47 exhibit the characteristics shown by the solid line in FIG. 8(d) when the vertical correlation of the two color difference signals is low, and the dotted line in FIG. 8(fd) when it is high. Indicates the characteristic it represents. Also, in this embodiment, by increasing the gain of the amplifier 43.

The characteristics of the comb filter can be made more rapid.

An example of the characteristics is shown by the dashed line in FIG. 8(b).

This is a characteristic when the 1H delay line 41 and the adder 48 are used.

In this embodiment, the comb filter is of the feedback type.

A higher SN ratio improvement effect can be obtained, and the characteristics can be changed by changing the amount of feedback.

In this example, there are two delay lines (41°42 delay lines).
However, even if three or more delay lines are used, similar effects can be obtained using a configuration that obtains the characteristics shown in FIG. 6(a).

Effects of the InventionAs is clear from the above explanation, the present invention can improve the output signal-to-noise ratio compared to conventional color signal processing devices, and can also reduce the vertical delay of the color signal. . In addition, by demodulating the low-pass conversion carrier color signal into two color difference signals and controlling the characteristics of the comb filter according to the vertical correlation of the amplitude of each color difference signal, the vertical correlation between the saturation level and hue of the nine color signals can be achieved. It becomes possible to control according to the Therefore, it is sufficient to use only an amplitude slicer or a limiter as a nonlinear element, and there is no need to detect the phase while processing the carrier color signal. Furthermore, even if there is crosstalk from adjacent tracks in the reproduced low-frequency conversion color signal, the comb filter can be controlled in accordance with the vertical correlation without malfunction.

Further, when the comb filter is configured as a feedback type filter, it has a feature that the SN ratio is improved more effectively than a non-feedback type filter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional example, FIG. 2 is a characteristic diagram of a comb filter, FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 4(a). (b) is a characteristic diagram showing the input/output characteristics of the slicer used in one embodiment of the present invention, and FIGS. 6(a), (b), (c
) are characteristic diagrams showing the input/output characteristics of the limiter used in the embodiment, which are similar in frequency to each part of the comb filter used in the embodiment of the present invention; FIGS. 8(a), (b), (C),
(d) is a frequency characteristic diagram of each part of a comb filter used in another embodiment of the present invention. 20.40... Demodulator, 23... Slicer, 24.25, 46.47... Comb filter, 30.45... Modulator, 43...
・Amplifier, 44...Limiter. Fig. 4, Fig. 5, 72- Seishi

Claims (1)

[Scope of Claims] (1) A demodulator that demodulates a low-frequency conversion carrier color signal into two color difference signals, and a demodulator that has a nonlinear response that passes each of the two color difference signals demodulated by the demodulator. 1. A color signal processing device comprising first and second comb filters. (2) The first and second comb-shaped filters include a plurality of delay circuits that pass the color difference signal, and have frequency characteristics such that a valley frequency is obtained at the position of the spectrum of the color difference signal and the spectrum of the crosstalk component. an arithmetic circuit that multiplies the input and the output of each of the delay circuits by a certain coefficient and adds them together;
an amplitude control circuit for controlling the amplitude of the output of the arithmetic circuit, and an output obtained by multiplying the output of the amplitude control circuit and each output of the delay circuit by a constant coefficient different from the coefficient; Claim 1 (1) is characterized in that the output of the first and second comb filters is obtained by adding the power
) The color signal processing device described in item 2. (3) The first and second comb filters are delay circuits that pass the color difference signal, and the frequency characteristics are such that a valley frequency is obtained at the position of the spectrum of the color difference signal. an arithmetic circuit that multiplies and adds an input and each output of the delay circuit by a certain coefficient; and an amplitude control circuit that controls the amplitude of the output of the arithmetic circuit, the output of the amplitude control circuit and the delay circuit. The outputs of the first and second comb filters are obtained by multiplying each output by a constant coefficient different from the coefficient and adding the summed outputs. 1) The color signal processing device described in item 1). (4) The first and second comb filters include a plurality of delay circuits that pass the color difference signal, and the input frequency characteristics are such that a valley frequency is obtained at the position of the spectrum of the color difference signal and the spectrum of the crosstalk component. and an arithmetic circuit that multiplies the outputs of each of the delay circuits by a certain coefficient and adds them together, and an amplitude control circuit that controls the amplitude of the output of the arithmetic circuit, and outputs the output of the amplitude control circuit to the delay circuit. Claims characterized in that the outputs of the first and second comb filters are obtained by multiplying the input and the output of the delay circuit by a constant coefficient different from the coefficient and adding them together. The color signal processing device according to item (1). (6) The first and second comb filters are delay circuits that pass the color difference signal, and have frequency characteristics such that a valley frequency is obtained at the position of the spectrum of the color difference signal. an arithmetic circuit that multiplies an input and each output of the delay circuit by a certain coefficient, and an amplitude control circuit that controls the amplitude of the output of the arithmetic circuit; and the outputs of the first and second comb filters are obtained by multiplying the input and the output of the delay circuit by a constant coefficient different from the coefficient and adding them together. The color signal processing device according to item (1).