JPS62209989A - Color noise reduction circuit - Google Patents

Abstract

PURPOSE:To eliminate missing or after effect of a color at the vertical profile by designing the transfer function when a noise clip circuit is turned on as the unity. CONSTITUTION:A chrominance carrier signal is inputted to a cyclic filter system, the chrominance carrier signal and an output of an adder 3 of the cyclic filter system incoding a delay element 1 are subject to difference, the difference output is supplied to a noise clip circuit, the output is added to the output of the adder 3 by an adder 5 provided between the adder 3 and the delay element and the output signal of the adder 5 is extracted as the output. Thus, the transfer function of the color noise reduction circuit when the noise clip circuit is turned on is brought into the unity and the transfer function is made equal to the transfer function of the cyclic filter when the noise clip circuit is turned off, then the transfer function of the color of the profile is brought into the unity so as to obtain the color noise reduction circuit without missing or after effect of the chrominance carrier signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for reducing color noise superimposed on a color signal at the color carrier signal stage in, for example, a television receiver.

[Prior Art] In conventional television receivers, contour correction means has been proposed for emphasizing color signals of video signals to seemingly reduce color noise, and an example thereof is shown in FIG. A video detection circuit (not shown) of a color television receiver separates the signal into a luminance signal and a color carrier signal, and the latter is supplied to the input shown in FIG.

In the figure, the color carrier wave signal is supplied to the coefficient unit 7 and the subtracter 4, and the color carrier wave signal is multiplied by (1-K) by the coefficient unit 7, and the output is added to the output of the multiplication coefficient 46 to the adder 3. Supplied. Next, a delay element 1 which delays the output signal of the adder 3 by one horizontal scanning period (hereinafter referred to as lH) and the subtracter 4 are added to the adder 5.
L IJh 1 Coefficient unit 6 having h coefficients
The signal is multiplied by and supplied to the adder 3. When the output signal of the subtracter 4 is large, the noise clipping circuit 2 is turned on (conducting state), and when the signal is small, it is turned off (non-conducting state). is added as the other input.

Next, the operation will be explained based on the waveform diagram of each part of the block diagram of FIG. 5 shown in FIG. 6.

A waveform diagram of the input color carrier wave signal during one vertical scanning period (IV) is shown in FIG. 6A. Here, the signal passed through the IH delay element l and the coefficient multiplier 6 which multiplies the supplied signal is added to the signal from the coefficient multiplier 7 which multiplies the human color carrier signal by (1-K). The output waveform diagram of the device 3 is a B waveform, which is a waveform that looks like it has been passed through a low-pass filter in the vertical direction. Here, the human power is taken as a color carrier wave signal, and the coefficient unit 7 multiplies it by (1-K).
, an adder 3, an IH delay element l, and a double coefficient unit 6 are connected and configured as a cyclic filter system, and if the output signal of the adder 3 of this cyclic filter system is the output, then the transmission of this system is The function A (w) generally looks like the following equation.

A(W)=(1-K)/ [1-Kcxp (-jwT)] In addition, T-IH (63.5 us).

K=0.3~0.7 W is the angular frequency of the transmitted signal, It is.

For example, if the value of K is 0.7, the transfer function A (w) of this recursive filter system is 2 to 3 in the vertical direction.
kHz [(525/15~525/10)CPh(
A waveform B in FIG. 6 is obtained in which a moderate amount of color noise (also referred to as hue unevenness) has been removed.

Further, when the value of K is set to 0.3, the vertical contour portion of waveform B becomes slightly less rounded.

However, since this system alone degrades the resolution in the vertical direction, the following measures are taken.

That is, the signal of waveform B is subtracted from the input color carrier signal of waveform A by subtraction "js4, and the signal shown in waveform C is obtained. If the signal of waveform C is clipped at clip level a by the noise clipping circuit 2, this output is a signal shown in the waveform.Here, the noise clipping circuit 2 is turned on when the clipping level a of the waveform C is higher than the clipping level a, and is turned off when it is lower than the clipping level a of the waveform C.

If the signals of waveforms B and D are added by an adder 5, a signal shown by waveform E is obtained. As a result, compared to waveform A, it is possible to restore a certain degree of vertical contour with noise removed. However, as shown in waveform E, there are signal dropouts and trailing. This is the difference between periods 1+ and 11 shown in FIG.

Note that when the video signal is of the NTSC system, the polarity of the color carrier wave signal is inverted for each IH, so the coefficient has a negative polarity for each IH.

[Problems to be Solved by the Invention] Since the conventional color noise reduction circuit is configured as described above, a part of the vertical contour component as well as the noise component of the color carrier signal is omitted in the output of the noise clipping circuit 2. This results in problems such as the color becoming lighter in the rising part of the vertical color and trailing downward in the image in the falling part.

[Means for Solving the Problems] The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and it inputs a color carrier wave signal to a recursive filter system, and combines the color carrier wave signal and the aforementioned The difference between the output of the adder 3 of the cyclic filter system including the delay element I is taken, and the difference output is passed through a noise clipping circuit to the adder i5 provided between the adder 3 and the delay element. By adding the output signal together with the output and taking out the output signal of this adder 5 as an output, the transfer function of the true noise reduction circuit when the noise clipping circuit is on can be set to 1, and when the noise clipping circuit is off. In some cases, the transfer function can be the same as that of the recursive filter, so the transfer function at the color contour portion becomes l, thereby providing a color noise reduction circuit without missing or trailing color carrier signals. The purpose is to

[Example] Hereinafter, an example of the present invention will be described based on the drawings. 1 differs from the block diagram in FIG. 5 in the arrangement and connection of each part. Parts equivalent to those in FIG. 5 are designated by the same reference numerals, and explanations of overlapping parts will be omitted.

Explain the signal flow. The input color carrier signal is supplied to a (1-K) times coefficient multiplier 7 and a subtracter 4, which are input to a recursive filter system. The other input of the subtracter 4 is supplied from the output of the adder 3 of the cyclic filter system. Next, the output signal of the subtracter 4 is added to the noise clipping circuit 2,
When this output signal is large, the noise clipping circuit 2 is turned on, and when the output signal is small, it is turned off to remove the noise component of this output signal. Furthermore, an adder 5 is provided between the adder 3 of the cyclic filter system and the delay element l of the IH, and the output of the adder 3 and the output of the noise clipping circuit 2 are input to the adder 5. Therefore, the output of the main color noise reduction circuit is taken as the signal output of the adder 5.

Next, the operation of the present invention will be explained with reference to the waveform diagram of each part in FIG. 2. If the input color carrier wave signal is a waveform A containing noise, the output of the adder 3 of the recursive filter system is a signal of waveform B.

Here, when the noise clipping circuit 2 is off, the transfer function A (w) of the recursive filter system is like a multiplication, A (W) = (1-K) / [1-Kcxp (jwT)]. be.

The output waveform B signal of the adder 3 is supplied to a subtracter 4, and the difference between it and the input color carrier signal is taken. This difference signal is supplied to an adder 5 through a noise clipping circuit 2 that passes signals above a predetermined level.

Here, the level of the signal input to the noise clipping circuit 2 will be discussed. When the level of this signal is lower than the noise clipping level, the noise clipping circuit 2 is in a cutoff state, that is, it is turned off. Therefore, the transfer function A' (w) of this embodiment in this case is the transfer function A of the recursive filter system. (w).

However, when the signal level is higher than the noise clipping level (at the contour part of the color carrier signal), the noise clipping circuit 2 is in a conductive state, and the transfer function A'(w) in this case is A' (w)=1. This formula will be explained using FIG. 4, which replaces FIG. 1. Here, since the noise clipping circuit 2 is on, the signal is passed through. The input color carrier signal is V, (mu)
, the output of subtractor 4 is Vs(t), and the output of adder 5 is V3
(t), then V3(t) = (1-K) V, (t)
+ K V 5(t-T)+ ve(t)V *(t
)=Vt(t)−[(IK)V,(t)
+KV3(t-T)], and from these two equations, Vs(t)=(l K) ■+(t)+KVs(L
−T)+ V r (t) (I K ) V +
(t)-KV3(t-T) v3(t)=v,(t) Therefore, the transfer function A'(w) becomes 1 as described above.

As described above, this color noise reduction circuit uses K of the recursive filter system according to the contour signal in the vertical contour portion of the color carrier signal.
Since it works by continuously changing the coefficient of
No harmful effects such as color loss or trailing occur.

Further, in the above embodiment, the recursive filter system has the same configuration as the conventional example, but as shown in FIG. K)
In the multiplier 7, this output is supplied to the subtracter 4 and also added to the adder 5, and the output signal of the adder 5 is used as the output of this circuit and added to the delay element I. The output is added to the adder 3 through a multiplier 6.

In this case, the transfer function of this circuit is A'(w)-1 when the noise clipping circuit 9 is conductive and on, and A (w) = (,1-K) / [ when it is non-conductive and off. 1-Kexp(-jw, T)].

Therefore, in this case as well, the transfer function when the noise clipping circuit 2 is off is different from the above embodiment, but when it is on, it is l, so the waveform transmission of the vertical contour part of the color carrier signal is input. becomes the same as

In each of the above embodiments, the case of a television receiver has been described, but the case may also be applied to a video tape recorder or a video disc player that handles color carrier wave signals, and the same effective effects as in the above embodiments can be obtained. In the above embodiment, the case where the human input signal is a color carrier signal has been described, but the same effect can be obtained by using this circuit also for a luminance signal separated from a video detection circuit.

[Effects of the Invention] As described above, according to the present invention, in addition to adding the color carrier signal to the recursive filter system and adding a subtracter to take the difference from the output of the recursive filter system, a noise clipping circuit is added to the output of the subtracter. Since the configuration was such that this output was added to another adder between the adder of the cyclic filter system and the delay element, the transfer function when the noise clipping circuit was on was set to 1, so the vertical It is possible to remove color loss and trailing in the outline area, reproduce color outlines faithfully, and eliminate color noise (
It is possible to reduce only hue unevenness and color noise).

[Brief explanation of drawings]

FIG. 1 is a block diagram of a color noise reduction circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram of the main part of FIG. 1, and FIG.
Figure 4 is a block diagram of a color noise reduction circuit according to another embodiment of the present invention, Figure 4 is a block diagram of the color noise reduction circuit shown in Figure 1, and Figure 5 is a block diagram of a conventional color noise reduction circuit. The block diagram, FIG. 6 is a waveform diagram of the main part of the block diagram of FIG. 5. ! --Delay element, 2--Noise clip circuit

Claims (1)

[Scope of Claims] A subtracter for extracting the difference between a color carrier signal separated from a color video signal and a signal obtained by passing this color carrier signal through a cyclic filter system, and clipping the output signal of this subtracter at a predetermined level. and an adder that adds the output of the noise clipping circuit to the cyclic filter system, and when the noise clipping circuit clips the output signal, the transfer function of the entire system is 1. , when the output signal is not clipped, the transfer function is (1-
K)/[1-Kexp(-jwT)] (where K is a coefficient, T is one horizontal scanning period, and w is the angular frequency of a transmission signal). .