JPH0581116B2 - - Google Patents

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 a television receiver.

[Prior Art] Conventionally, in television receivers, contour correction means has been proposed that emphasizes the color signal of the video signal and seemingly reduces color noise. This invention aims to remove color noise and transmit it, and this invention relates to color noise reduction at the color carrier signal stage before being demodulated into a color signal.

A conventional circuit of this type is shown in FIG. The signal is separated into a luminance signal and a color carrier signal from the video detection circuit (not shown) of the television receiver.
The latter is fed to the input of FIG. In the figure, the color carrier signal is supplied to a coefficient unit 7 and a subtracter 4, the signal level is multiplied by (1-K) in the coefficient unit 7, and the signal is supplied to an adder 3 which adds this output and the output of the coefficient unit 6. be done. Next, the delay element 1 which delays the output of the adder 3 by one horizontal scanning period (1H) and the subtracter 4 are further supplied to the adder 5. The output of the delay element 1 is supplied to a coefficient multiplier 6 having a coefficient of K smaller than 1, and the signal level is multiplied by K and supplied to an adder 3. The output of the subtracter 4 is applied to an adder 5 via a noise clipping circuit 2 that passes only the high signal level portion.

Next, the waveform diagram of each part of the block diagram in Figure 4 is shown in Figure 5.
This operation will be explained with reference to the figure. A waveform diagram of the input color carrier wave signal for one vertical scanning period (1V) is shown in FIG. 5, waveform A.

Here, the signal passed through the 1H delay element 1 and the coefficient multiplier 6 multiplied by K and the input color carrier signal are (1-
K) If the signal from the coefficient multiplier 7 is added in the adder 3, the output waveform diagram of the adder 3 becomes waveform B. In other words, the displayed image has a waveform that looks like it has been passed through a low-pass filter in the vertical direction. Therefore, the system consisting of the coefficient multiplier 7, the adder 3, the delay element 1 of 1H, and the coefficient multiplier 6 is called a cyclic filter system, and the input signal is input to the coefficient multiplier 7, and the output signal of the adder 3 is output. Then, the transfer function A(w) of this cyclic filter system generally becomes as shown in the following equation.

A(w)=(1-K)/[1-Kexp(-jwT)] In addition, T = 1H (63.5μs), K=0.3~0.7 w is the angular frequency of the color carrier signal, It is.

With this transfer function A(w), for example, this coefficient K
If the value of is 0.7, the vertical frequency component 2~
Color noise (also referred to as hue unevenness) of approximately 3 kHz [(525/15 to 525/10) CPh (cycles per height)] or higher is removed to obtain waveform B in FIG. 5. Furthermore, if the value of K is 0.3, the vertical contours of the rising and falling edges of this waveform B will be sharper. However, if only this recursive filter system is used, the rise and fall are slowed down, and the resolution in the vertical direction is degraded. Therefore, the following measures are taken.

That is, if the signal of waveform B is subtracted from the input color carrier signal of waveform A by the subtracter 4 as shown in FIG. 4, a signal of waveform C is obtained. The signal of waveform C is clipped to a clip level a by the noise clipping circuit 2.
If clipped at , the output becomes a signal shown in waveform D. If the signals of waveforms B and D are added by an adder 5, a signal shown by waveform E is obtained. Here time t ₁ ,
_t2 corresponds to the vertical contour part, and there is a time difference before and after clipping. By adding the noise clipping circuit 2 and the adder 5, when waveform E and waveform A are compared, it is possible to restore a color carrier signal having a certain degree of vertical contour from which noise has been removed.

However, as shown in waveform E, there are signal dropouts and trailing. In other words, this is the time shown in Figure 5.
This occurs based on the difference between t ₁ and t ₂ .

Note that when the video signal is of the NTSC system, the polarity of the color carrier signal is inverted every 1H, so the coefficient K becomes negative polarity every 1H.

[Problems to be Solved by the Invention] Since the conventional color noise reduction circuit is configured as described above, part of the contour component is also missing along with the noise component in the output of the noise clipping circuit 2.
This method has disadvantages in that colors become pale due to lack of color signals at the rising edge of a color in the vertical direction, and tails appear in the downward direction of the image at the falling edge.

Furthermore, when the noise clipping level of the noise clipping circuit is increased, there is a problem in that trailing occurs in the downward direction of the image at the falling edge of the color carrier signal.

[Means for Solving the Problems] The present invention was made in order to eliminate the above-mentioned conventional drawbacks.
Taking the difference between this input color carrier signal and the output of the adder 3 of the cyclic filter system including the delay element 1,
The difference output is passed through a noise clipping circuit and a coefficient multiplier having a coefficient of _K1 , and is added to the input color carrier signal and introduced into the cyclic filter system, and the output of the adder 3 and the output of the noise clipping circuit are added. By outputting a signal with reduced color noise, there is provided a color noise reduction circuit that does not cause missing color outlines or trailing, and also does not cause trailing in the downward direction of the image at the falling part of a color carrier signal. The purpose is to

[Example] Hereinafter, an example of the present invention will be described based on the drawings. In Fig. 1, 8 is a coefficient multiplier having a coefficient of _K1 , which is composed of an operational amplifier, etc., and 10 is an adder that adds the output of noise clipping circuit 2 and the output of adder 3, which is equivalent to Fig. 4. Parts are indicated by the same reference numerals, and explanations of overlapping parts will be omitted.

First, the signal flow will be explained. The input color carrier signal is supplied to an adder 5 and a subtracter 4. The other input of the adder 5 is the output signal of the subtracter 4, the noise component of which is removed by the noise clipping circuit 2, and the signal is multiplied by _K1 to a predetermined level by the coefficient multiplier 8. The output of the adder 5 is the same as in the conventional example shown in FIG. It is input to a cyclic filter system consisting of 6. The output of this cyclic filter system is extracted from the output of adder 3, subtracter 4 and adder 1.
0, and one input of the adder 10 is taken out from the output of the noise clip circuit 2.

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 waveform A, the output of the cyclic filter system will be a waveform B signal. Here, the transfer function A(w) of the cyclic filter system is A(w)=(1-K)/[1-Kexp(-jwT)] as described above.

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 passes through a noise clipping circuit 2 that passes signals of a predetermined level or higher, becomes a predetermined level at a K1 _times coefficient multiplier 8, and is supplied to an adder 5.

Here, the level of the signal input to the noise clip circuit 2 will be discussed. When the level of this signal is lower than the noise clip level, noise clip circuit 2 is off and adders 5 and 10
Since no signal is supplied to the filter, the transfer function A'(w) of this embodiment in this case is equal to the transfer function A(w) of the cyclic filter system.

However, if the signal level is higher than the noise clip level (which is often the case in the vertical contours of the color carrier signal), the noise clip circuit 2 is on;
The transfer function A'(w) in this case is A'(w)=1.

The results will be explained below using FIG. 3, which replaces FIG. 1. In FIG. 3, numeral 9 is the recursive filter system having the transfer function A(w), and since the noise clipping circuit 2 is on, it is passed through.
The two signal inputs and outputs to the subtracter 4 and the output of the adder 10 are V ₁ , V ₂ , V ₃ , respectively as shown in the figure.
If V ₀ , then V ₃ = V ₁ −V ₂ V ₂ = (V ₁ +K ₁・V ₃ )・A(w), and from these two equations, V ₂ = [V ₁ +K ₁・(V ₁ − V ₂ )]A(w), and therefore the output V ₂ becomes V ₂ ={(1+K ₁ )/[K ₁ +1/A(w)]}V ₁ .

On the other hand, since V ₃ =V ₁ −V ₂ V ₀ =V ₂ +V ₃ , V ₀ =V ₂ +V ₁ −V ₂ =V ₁ , the transfer function A′(w) is A′( w)=1.

As described above, the transfer functions A(w) and A′(w) of this example are
As can be seen from the above, when the noise grip circuit 2 with less noise is off, the time constant of the transfer function is made as small as possible by changing the coefficients of the coefficient unit of the cyclic filter system in the vertical contour part of the color carrier signal. The device is operated to transmit a color carrier signal that changes sharply. Further, if the noise exceeds the clip level of the noise clip circuit 2 and the noise clip circuit 2 is turned on, only the color carrier signal from which noise components have been removed can be obtained.

Note that waveform B in FIG. 2 is an output waveform diagram of the adder 3 when the noise clipping circuit 2 is off, and waveform C is an output waveform diagram of the adder 3 when the noise clipping circuit 2 is on.

As a result of the above, the actual output of the adder 10 is the waveform D
As shown in the figure, the waveform has a clear vertical contour with no signal loss or trailing.

Although the above embodiment describes the case of removing noise from a color carrier wave signal used in a television receiver, it may also be used in the case of a video tape recorder or a video disc player that handles a color carrier wave signal, and the above implementation may also be used. The same effective effect as in the example can be achieved.

Further, in the above embodiment, the case of a color carrier wave signal has been described, but it may also be a case of a luminance signal, and the same effect can be achieved in this case as well.

[Effects of the Invention] As described above, according to the present invention, the vertical contour components of the color carrier signal are returned to the first stage of the cyclic film system via the noise clipping circuit, added at a predetermined level, and added to the cyclic filter system. Since the configuration is such that it is added to the output of the color carrier signal and taken out, the noise contained in the color carrier signal can be removed not only when the noise is small, but also when the noise becomes large. In particular, even if you increase the noise clip level and reduce the number of times the noise clip circuit turns on,
It is possible to remove color dropouts and trailing in vertical contour areas, faithfully reproduce color contours, and reduce only color noise (hue unevenness/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. 3 is a block diagram of the color noise reduction circuit portion of Fig. 1. FIG. 4 is a block diagram of a conventional color noise reduction circuit, and FIG. 5 is a waveform diagram of the main part of the block diagram of FIG. 4. 1...Delay element, 2...Noise clip circuit,
3, 5, 10... adder, 6, 7, 8... coefficient unit.

Claims (1)

[Claims] 1 A cyclic filter system consists of a first coefficient unit that multiplies the input signal by (1-K), a first adder that adds the output of this coefficient unit and the output of the second coefficient unit, and a first adder that adds the output of this coefficient unit and the output of the second coefficient unit, and a delay element that delays the output by one horizontal scanning period; and a second delay element that multiplies the signal from this delay element by K.
a subtracter for subtracting the input signal from the output of the cyclic filter system; a noise clip circuit that clips the output; a third coefficient multiplier that sets the signal level from the noise clip circuit to a predetermined level and supplies it to one input of the second adder; The second adder adds the output of the coefficient multiplier and supplies the result to the input of the cyclic filter system, and adds the output of the noise clipping circuit and the output of the cyclic filter system to obtain an output signal. A color noise reduction circuit comprising an adder.