JPH02101886A - Noise reduction device for carrier chrominance signal - Google Patents

Abstract

PURPOSE:To reduce the noise of a carrier chrominance signal without causing the blurring of color by reducing noise after the carrier chrominance signal is demodulated by plural demodulators, modulating and synthesizing the resulting signal. CONSTITUTION:A carrier chrominance signal CCS including AM noise and PM noise is decomposed into demodulation signals Da, Db whose noise is comparatively easily reduced based on a subcarrier CS 3 and a carrier CS 4 whose phase differs from that of the CS 3 at angles other than 180 deg.. Then the AM noise in the signals Da, Db is eliminated by noise cancellers 9a, 9b, given to balanced modulators 10a, 10b under the same condition at demodulation, and synthesized by a synthesizer 11 again and the resulting signal is sent as a chrominance carrier signal CCS''.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention applies to televisions and video tape recorders (hereinafter referred to as rV
It's called TRJ. This paper relates to an m-sound reduction device for a carrier color signal containing noise such as ).

[Conventional technology]

FIG. 4 is a block diagram showing a conventional carrier color signal generation method. As shown in the figure, the balanced modulator 1a has a color a
I! The transmitted wave C81 is the color difference signal E, -E.

The balanced modulator 1b modulates the color subcarrier C32, which has a phase difference of 90° from the color subcarrier C81, into the color difference signal E.
-E, the balance is modulated. The color subcarrier C31 is generated by the color subcarrier oscillator 2, and the color subcarrier C32 is generated by shifting the phase of the color subcarrier C81 by 90'' by the phase shifter 3.

Modulation signal B-Y modulated by balanced modulators 1a and 1b
, RY are combined by an adder 4, and the output signal of this adder 4 becomes the carrier color signal CC8.

In this way, the carrier color signal CC8 is the color difference signal EBE,
It is obtained by quadrature modulating ER-E.

The carrier color signal CC8 of the VTR is affected by expansion and contraction of the videotape, jitter of the running system, noise of the videotape, etc. during playback of the VTR, and suffers from amplitude noise (hereinafter referred to as
This is called rAMAM noise. ) and phase noise (r
It is called PMPM noise.

) is included in the signal. Also, AM noise, P
M-type noise is also included in the carrier color signal received by a television receiver in a weak electric field.

From the above, AM noise included in the carrier color signal,
It is necessary to reduce PM noise.

FIG. 5 shows a conventional carrier color signal noise reduction device.
FIG. As shown in the figure, the 1 horizontal scanning period delay line 5 (hereinafter referred to as 11H delay line) delays the carrier color signal CC8 by 1 horizontal scanning period (1H) and outputs a signal CCS. . The subtracter 6 receives the signal C
C5o and the carrier color signal CC8 are input, and the carrier color signal CC
It outputs a signal ccs' obtained by subtracting the signal @ccso from 8.

The principle of the above-described noise reduction device will be explained below. The frequency f'cs of the color subcarrier C8I (C82) is NTS
For C method, #3.58 (MHz)
...(1) has been selected. Here, fH is the horizontal scanning frequency.

From equation (1), the carrier color signal ccs and the signal CCS.

can be said to have a phase difference of 180''.

Therefore, subtracting the signal CC8° from the carrier color signal 5ccs adds the signal C to the carrier signal component of the carrier color signal CC8.
This is equivalent to adding the carrier signal component of CS. As a result, the carrier signal component of the signal ccs' is the carrier color signal CC8
is twice the carrier signal component.

On the other hand, since the noise components of the carrier color signal CC8 and the noise components of the signal CC8 are uncorrelated in phase, the signal ccs'
The noise component of is four times the noise component of the carrier color signal CC8. As a result, signal CC8' carries color signal @ccs,
The carrier color signal is improved in S/N by 3 dB, and the noise of the carrier color signal CC8 can be reduced.

[Problem to be solved by the invention]

The conventional carrier color signal noise reduction device is constructed as described above, and requires one delay line 5. However, in order to accurately realize a delay of one horizontal scanning period (11-1), there is a problem in that an expensive glass delay line must be used as the one-day delay line.

In addition, since this device always subtracts the carrier color signal CCS from the original carrier color signal CcS, the signal ccs
If there is no correlation in the vertical color components between , ccs, and ccs, there is a problem in that color bleeding, called color blur, occurs in the image obtained by reproducing the noise-reduced carrier color signal ccs'. .

It is also possible to reduce noise in the carrier color signal using other methods, but the carrier color signal is a signal obtained by quadrature modulating a color difference signal, and includes AM noise and F'Mfi noise. Therefore, it is difficult to reduce the noise of this color signal carried within the film, and the reality is that other methods are not widely used.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a carrier color signal noise reduction device that is inexpensive and capable of reducing the noise of the carrier color signal without causing brown smudges. With the goal.

[Means to solve the problem]

A carrier color signal noise reduction device according to the present invention includes a first demodulator that demodulates a carrier color signal using a first reference subcarrier and outputs a first demodulated signal; 1
a second demodulator that outputs a second demodulated signal by demodulating with a second reference subcarrier having a phase different from the reference subcarrier of 180°, and an M sound of the first and second demodulated signals; first and second noise reducers each reducing the noise component;
a first modulator that modulates a reference subcarrier of with the output signal of the first noise reducer to output a first modulated signal; a second modulator that modulates with the output signal and outputs a second modulated signal;
and an adder that combines the first and second modulated signals and outputs the combined signal as a carrier color signal.

[Effect]

The first and second demodulators in this invention once demodulate using the first and second reference subcarriers and output the first and second demodulated signals, and the first and second noise reducers output the first and second demodulated signals. 1st and 2nd
The noise of the demodulated signal is reduced.

Since these first and second demodulated signals contain only amplitude noise, noise removal is relatively easy.

〔Example〕

FIG. 1 is a block diagram showing a carrier color signal noise reduction device according to an embodiment of the present invention. As shown in FIG. 1, the carrier color signal CC8 is demodulated into two demodulated signals L, D, by two demodulators 37a and 7b based on subcarriers C83 and C84, respectively. In addition, subcarrier C
83 is a signal having the same frequency as the subcarrier C81 when the carrier color signal CC8 is generated, and the subcarrier C84 is the same frequency as the subcarrier C81 when the carrier color signal CC8 is generated.
83 is shifted by an angle φ (≠180') by the phase shifter 8.

FIG. 2 is a vector diagram showing the relationship between the carrier color signal @ccs and the demodulated signal M8°M. As shown in the figure, the subcarrier C83 is on the X axis. In a coordinate system with subcarrier C84 as the y-axis, vector A of carrier color signal CC8 is
a, 7b, vector Δ8. of demodulated signal M32Mb.
It is decomposed into A. Note that ψ is a shift angle between the carrier color signal CC8 and the subcarrier C83 (x-axis).

Therefore, AM noise (appears in the change in the length of vector A) and PM noise (ψ
This is reflected in changes in ) are all AM noises of the demodulated signals M, , Mb (the demodulated signals D8, Db demodulated by the vector demodulators 7a, 7b are processed by noise reducers (hereinafter referred to as "noise cancellers") 9a, 9b, respectively). The signals D 1 and Db are converted into signals D 1 and Db 2 with reduced AM noise.

FIG. 3 is a block diagram showing an example of the noise canceller 9 (9a, 9b). As shown in the figure, the demodulated signal D (D) contains AM noise.

Db), only the high frequency components are extracted by the bypass filter 21, and the large amplitude components of the high frequency components are further removed by the limiter 22. Then, the output signal 822 of the limiter 22 and the original demodulated signal are taken into the subtracter 22. This subtracter 22 outputs a signal D'(D', D
fi') is output. Therefore, the signal D' becomes a signal with AM noise reduced from the demodulated signal.

The noise cancellers 9a and 9b generate demodulated signals and D
The DaDb' signals from which AM noise has been removed are taken into balanced modulators 10a and 10b, respectively. Balanced modulators 10a and 10b transmit subcarriers C83 and C84, respectively, to signals D8' and 0. ' to output modulated signals M and M. These modulated signals Ma2Mb are then input to the adder 11. The adder 11 combines the modulated signals M and M, and outputs this combined signal as a carrier color signal CC8''.

As described above, the carrier color signal noise reduction device according to this embodiment reduces the carrier color signal C including AM bamboo noise and PM noise.
C8 is first decomposed into two demodulated signals that contain only AM noise and whose noise is relatively easy to reduce, and after removing the AM noise from these two demodulated signals, they are modulated under the same conditions as during demodulation. , are combined again and output as a carrier color signal CC8''.

Therefore, the combined carrier color signal CC8'' is a signal with reliably reduced noise.

Further, since the carrier color signal before 111 is not subtracted, no color bleeding occurs. Furthermore, since there is no need to use a delay line (1), the structure can be constructed at low cost.

Note that the shift angle φ by the phase shifter 8 is 90″ in the −shell.
' or 270°, but it may be set arbitrarily other than 06.18° (vector A of carrier color signal CC8 cannot be separated into two vectors (see FIG. 2)).

Furthermore, the configuration of the noise canceller 9 is not limited to that shown in FIG. 3.

〔Effect of the invention〕

As explained above, according to the present invention, the carrier color signal is the first . Once demodulated by the second demodulator, the first .
A second demodulated signal is received 19. Then, noise reduction of the first and second demodulated signals is performed by the first and second noise reducers. Furthermore, this noise-reduced first . The second demodulated signal is converted into the first demodulated signal. A carrier color signal is generated by modulating using the second modulator under the same conditions as during demodulation and combining again using an adder. This ensures that the newly generated carrier color signal is noise-free and does not produce a brownish tint.

Furthermore, since expensive components are not used in each component, the structure can be constructed at low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a carrier color signal noise reduction device according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the relationship between the carrier color signal and demodulated signal in the circuit of FIG. 1, and FIG. Figure 3 is a block diagram showing an example of a noise canceller used in the circuit in Figure 1, Figure 4 is a block diagram showing a conventional carrier color signal generation method, and Figure 5 is a conventional carrier color signal noise reduction method. FIG. 2 is a block configuration diagram showing the device. In the figure, 7a and 7b are demodulators, 8 is a phase shifter, 9a,
9b is a noise canceller, 10a, 10b are balanced modulators, 11 is an adder, CC8, CC8 is a carrier color signal, C8
1, C82 is a color subcarrier, D and D are demodulated signals,
M, M are modulation signals ab
a Yes. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] (1) Demodulate the carrier color signal using the first reference subcarrier and
a first demodulator that outputs a demodulated signal; and a second demodulated signal by demodulating the carrier color signal with a second reference subcarrier having a phase other than 180° from the first reference subcarrier. a second demodulator for outputting; first and second noise reducers for reducing noise components of the first and second demodulated signals, respectively; modulated by the output signal of the
a first modulator that outputs a modulated signal; a second modulator that modulates the second reference subcarrier with the output signal of the second noise reducer and outputs a second modulated signal; A carrier color signal noise reduction device comprising: an adder that combines the first and second modulated signals and outputs the combined signal as a carrier color signal.