JPH0767178B2 - Color noise reduction circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a circuit for reducing color noise included in a color signal at a color carrier signal stage in a television receiver.

BACKGROUND ART Conventionally, in a television receiver, a contour correction means has been proposed which emphasizes a color signal of a video signal to reduce the color noise, but the color noise is removed and transmitted without impairing the characteristics of the input color carrier signal itself. A color noise reduction circuit to be tried has already been devised.

Such a conventional color noise reduction circuit is shown in FIG. In the figure, a video detection circuit (not shown) of the television receiver
The chrominance carrier signal separated from the output of the above is supplied to the coefficient unit 7 and the subtractor 4. The color carrier signal supplied to the coefficient unit 7 is supplied to the adder 3 after the signal level is multiplied by (1-K). The output of the adder 3 is supplied to the 1H delay element 1, the subtractor 4 and the adder 5. The output of the adder 3 delayed by one horizontal scanning period (1H) by the 1H delay element 1 is supplied to a coefficient unit 6 having a coefficient K smaller than 1, and the signal level is multiplied by K. The output of this coefficient unit 6 is
It is supplied to the adder 3 and added to the output of the coefficient unit 7. The output of the subtractor 4 is supplied to the adder 5 via the noise clip circuit 2 which passes only a large signal level portion, and is added to the output of the 1H delay element 1.

In the above configuration, the waveform of the input color carrier wave signal a during one vertical scanning period (1V) is as shown in FIG. 6 (A).

Now, when the signal that has passed through the 1H delay element 1 and the coefficient unit 6 and the output of the coefficient unit 7 that multiplies the input color carrier signal a by (1-K) are added by the adder 3, the output b of the adder 3 Waveform is as shown in FIG. Output b of this adder 3
In the displayed image, the waveform of is a waveform that has been passed through a low-pass filter in the vertical direction. Therefore, a system composed of the coefficient unit 7, the adder 3, the 1H delay element 1 and the coefficient unit 6 is called a recursive filter system, which supplies an output signal to the coefficient unit 7 and cyclically outputs the output of the adder 3. If the output of the linear filter system is used, the transfer function A (ω) of this recursive filter system
Is generally expressed by the following equation.

A (ω) = (1−K) / [1−Ke × p (−jωT)] where T = 1H (= 63.5 μs), K = 0.3 to 0.7, and ω is the angular frequency of the color carrier.

With this transfer function A (ω), if the value of the coefficient K is 0.7, for example, the frequency component in the vertical direction is 2 to 3 kHz ((525
/ 15 ~ 525/10) CPh (cycle per height)] or more color noise (also called hue unevenness) is removed
A signal as shown in FIG. 3B is output from the adder 3. Further, if the value of K is 0.3, a signal having a steep rising and falling vertical contour portion than the signal shown in FIG. However, with only this recursive filter, the rise and fall are dull and the resolution in the vertical direction is deteriorated. Therefore, the following measures are taken.

That is, by subtracting the output b of the adder 3 shown in FIG. 6B from the input carrier signal a shown in FIG. 6A by the subtracter 4 as shown in FIG. The subtraction output c shown is obtained. When the subtraction output c is supplied to the noise clipping circuit 2 and clipped at the clipping level Lc, the output d as shown in FIG. When the addition output b and the output d are supplied to the adder 5 and are added, an addition output e as shown in FIG. Here, the times t ₁ and t ₂ correspond to the vertical contour portion, and there is a time difference before and after clipping. This noise clip circuit 2
By adding the adder 5 and the adder 5, it is possible to restore a chrominance carrier signal having a certain vertical contour portion from which noise is removed, as is clear from a comparison between FIGS.

However, as shown in (E) of the figure, there are missing signals and trailing. The missing or trailing of these signals is caused by the difference between times t ₁ and t ₂ shown in FIG.

If the video signal is NTSC, the polarity of the color carrier signal is
Since it is inverted every 1H, the coefficient K becomes negative every 1H.

As described above, in the conventional color noise reduction circuit, the output of the noise clip circuit 2 causes a part of the contour component as well as the noise component to be lost, and the color is light due to the loss of the color signal at the rising portion of the color in the vertical direction. There is a drawback in that there is an adverse effect such that the image becomes downward or a trailing part of the image is tailed at the trailing edge.

Further, when the noise clip level of the noise clip circuit is increased, there is an adverse effect that tailing occurs in the downward direction of the image at the trailing edge of the color carrier signal.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color noise reduction circuit capable of preventing a color signal dropout at a vertical color rising portion and a downward tailing of an image at a falling portion from occurring. That is.

The color noise reduction circuit according to the present invention is configured to superimpose a vertical decorrelation signal on a difference signal corresponding to a difference between a color carrier signal and a color carrier signal that has passed through a recursive filter and then clip the signal to obtain a signal for waveform correction. Has become.

EXAMPLES Examples of the present invention will be described below in detail with reference to FIGS. 1 to 4.

In FIG. 1, a delay element 1, a noise clip circuit 2,
The adders 3 and 5, the subtractor 4, and the coefficient units 6 and 7 are connected in the same manner as in the circuit of FIG. However, in this example, the input signal is supplied to the delay element 11 and the subtractor 12.
The delay element 11 is configured to delay the input by 1H with a frequency characteristic that the frequency band is narrow and only the color carrier component passes. The output of the delay element 11 is supplied to the subtractor 12. The output of the subtractor 12 is supplied to the subtractor 4 via a BPF (bandpass filter) 13, and the output of the subtractor 12 is subtracted from the output of the adder 3. Further, the delay element 1 has a wide frequency band and has frequency characteristics that allow not only the chrominance carrier signal but also the luminance signal to pass therethrough. The output of the adder 5 is supplied to the output terminal via the BPF 14.

In the above configuration, the delay element 11 and the subtractor 12 form a comb filter. When the composite video signal f as shown in FIG. 2 (A) is supplied to the comb type filter, the output g of the subtractor 12 as the output of the comb type filter is
A signal as shown in FIG. on the other hand,
In the recursive filter system including the coefficient units 6 and 7, the adder 3 and the delay element 1, the delay element 1 has a wide band and the coefficient unit 6
Since the count K becomes negative every 1H, it acts as a high-pass filter for the luminance signal and as a low-pass filter for the chrominance carrier signal. Therefore, the output b of the adder 3 as the output of the cyclic filter system is shown in FIG.
As shown in, the signal becomes a signal including a vertical decorrelation component corresponding to the difference between the luminance signal and the signal obtained by delaying the luminance signal by 1H. Since this vertical non-correlation component is circulated in the cyclic filter system, it becomes a signal that exists for a period corresponding to the value of K while gradually decreasing every 1H. The output b of the adder 3 is the subtractor 4
When the output c of the subtractor 4 is supplied to a signal obtained by superimposing a vertical decorrelation component on the difference between the color carrier signal and the color carrier signal that has passed through the cyclic filter system Become.

Therefore, since the level of the DC component of the vertical contour portion corresponding to the portion forming the vertical contour of the output c of the subtractor 4 becomes large, the clipping of the noise clip circuit 2 for clipping the output c of the subtractor 4 is performed. Even if the level Lc is increased to some extent, the color carrying component of the vertical contour portion in the output d of the noise clip circuit 2 is easily stored as shown in FIG. Since the output d of the noise clip circuit 2 is supplied to the adder 5 and added to the output of the adder 3, the noise component output from the adder 3 is reduced in waveform of the vertical contour portion of the color carrier signal. Good correction is performed. Therefore, when the luminance signal component is removed from the output of the adder 5 by the BPF 14, there is a signal dropout or a downward tailing of the image in the vertical color rising portion as shown in FIG. The color carrier signal h is obtained without noise and with reduced noise.

FIG. 3 is a block diagram showing another embodiment of the present invention, which includes a delay element 1, a noise clip circuit 2, an adder 3,
5, the subtractor 4, the counters 6 and 7, and the BPF 14 are connected in the same manner as in the circuit of FIG. However, in this example, the delay element 1 is configured to delay the input by 1H with a frequency characteristic that the frequency band is narrow and only the color carrier signal is passed. Further, the input signal is supplied to the delay element 11 and the subtractor 12. The delay element 11 is configured to delay the input by 1H with a frequency characteristic that the frequency band is wide and not only the chrominance carrier signal but also the luminance signal is passed. The output of the delay element 11 is supplied to the coefficient unit 7 and the subtracter 12 at the same time, and the output of the delay element 11 is subtracted from the input signal. The output of the subtracter 12 is supplied to the subtractor 4, and the output of the subtractor 12 is subtracted from the output of the adder 3.

In the above configuration, the delay element 11 is used in the same manner as the circuit of FIG.
And the subtractor 12 form a comb filter. When the composite video signal f as shown in FIG. 4 (A) is supplied to this comb-type filter, the delay element 11 has a wide band, so that the output g of the subtractor 12 as the output of the comb-type film is obtained.
Is a signal composed of a vertical decorrelation component and a color carrier signal component as shown in FIG. Output g of this subtractor 12
The vertical decorrelation component in the 1H exists only. On the other hand, in the recursive filter system, since a narrow band element is used as the delay element 1, the luminance signal component is not recursive, and the output b of the adder 3 as the output of the recursive filter system is The signal is as shown in (C). Then, adder 3
The output c of the subtractor 4 which subtracts the output g of the subtracter 12 from the output b of the above is present in the difference between the chrominance carrier signal and the chrominance carrier signal passing through the recursive filter system by 1H as shown in FIG. The signal is obtained by superimposing the non-correlation component.

Therefore, the level of the DC component of the vertical contour portion of the output c of the subtractor 4 is increased by 1H, and the clip level Lc of the noise clip circuit 2 for clipping the output c of the subtractor 4 is increased.
Even if the value is increased to some extent, the color carrier component of the vertical contour portion in the output d of the noise clip circuit 2 is easily stored by 1H as shown in FIG. Since the output d of the noise clip circuit 2 is supplied to the adder 5 and added to the output of the adder 3, the adder 3 is added in the same manner as the circuit of FIG.
The correction of the waveform of the vertical contour portion of the color carrier signal in which the noise component output from is reduced is performed satisfactorily with 1H, and the same effect as the circuit of FIG. 1 is obtained.

In the above embodiment, the signal delay time of the delay element 11 is
Although it is supposed to be 1H, the signal delay time of the delay element 11 is
It may be any value of N times N (N is a natural number),
The same effect can be obtained.

As described above in detail, the color noise reduction circuit according to the present invention superimposes the vertical decorrelation signal on the difference signal corresponding to the difference between the color carrier signal and the color carrier signal that has passed through the recursive filter, and then clips the signal. Since it is a signal for waveform correction,
Even if the clip level is increased, the instantaneous level of the vertical contour portion of the difference signal becomes large, the color carrier signal component is easily stored in the signal for waveform correction, and the vertical contour portion of the color is less likely to be damaged. The color carrier signal is obtained in which there is no signal loss or trailing and noise is removed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of each part of the circuit shown in FIG. 1, and FIG. 3 is a block showing another embodiment of the present invention. Figures and 4
FIG. 5 is a waveform diagram showing the operation of each part of the circuit in FIG. 3, FIG. 5 is a block diagram showing a conventional color noise reduction circuit, and FIG.
It is a wave form diagram which shows operation | movement of each part of the circuit of a figure. Explanation of symbols of main part 1,11 …… Delay element 2 …… Noise clip circuit 3, 5 …… Adder 4, 12 …… Subtractor 6, 7 …… Coefficient unit 13, 14 …… BPF

Claims (2)

[Claims] 1. A recursive filter for reducing a noise component of a color carrier signal in an input composite video signal, and a color carrier signal in the input composite video signal and a color carrier signal in which a noise component is reduced by the recursive filter. A difference signal generating means for generating a difference signal according to the difference between the difference signal and a clipping means for clipping and outputting a portion where the absolute value of the instantaneous level of the difference signal is a predetermined value or less. A chrominance noise reduction circuit adapted to correct the waveform of a chrominance carrier signal having a noise component reduced by mixing with the output of the recursive filter, wherein a luminance signal in the input composite video signal in one horizontal scanning period A delay unit for delaying by N (N is a natural number) times is provided, and a vertical decorrelation signal is generated in accordance with a difference between the luminance signal in the input composite video signal and the luminance signal delayed by the delay unit. Color noise reduction circuit being characterized in that so as to overlap to the difference signal. 2. The delay means comprises a delay element that delays the input by one horizontal scanning period with a frequency characteristic that allows the chrominance carrier signal and the luminance signal in the input composite video signal to pass through in the recursive filter. The color noise reduction circuit according to claim 1, wherein the output of the cyclic filter includes the vertical decorrelation signal.