JPH0479514B2 - - 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 the color noise. This invention is intended to be transmitted 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. Ru. 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 multiplied in signal level by K by a coefficient multiplier 6 having a coefficient of K smaller than 1, and then supplied to an adder 3. The output of the subtracter 4 is applied to an adder 5 via a noise clipping circuit 5 that passes only the high signal level portion.

Next, the operation will be explained based on the waveform diagram of each part of the block diagram of FIG. 4 shown in FIG. The waveform diagram of the input color carrier wave signal during one vertical scanning period (1V) is shown in FIG. 5A. Here, 1H delay element 1
The output waveform diagram of the adder 3 which adds the signal passed through the coefficient unit 6 which is multiplied by K and the signal from the coefficient unit 7 which multiplies the input color carrier signal by (1-K) becomes the B waveform, which is vertically The waveform looks like it has been passed through a low-pass filter. Let this input be a color carrier wave signal, (1-
K) Multiplier coefficient unit 7, adder 3, 1H delay element 1
When the output signal of the adder 3 of the cyclic filter system consisting of the coefficient multiplier 6 and the coefficient multiplier 6 is taken as the output, the transfer function A(W) of the cyclic filter system is generally expressed as shown in the following equation.

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

With this transfer function A(W), for example, this K
If the value of is 0.7, the vertical direction is 2 to 3 kHz
15~525/10) CPh (Cycle Per Height)]
A waveform B in FIG. 5 is obtained in which more than a certain amount of color noise (also referred to as hue unevenness) has been removed. Also, the value of K is
When it is set to 0.3, the contour part becomes sharper than this waveform B. However, since the resolution in the vertical direction deteriorates if only this recursive filter system is used, 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, a signal shown in waveform C is obtained. If the signal of waveform C is clipped by the noise clipping circuit 2 at clip level a, we get
This 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. As a result, compared to waveform A, it is possible to restore a certain degree of contour with noise removed.

However, as shown in waveform E, there are signal dropouts and trailing. That is, this is t ₁ shown in FIG.
It is generated based on the difference between 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 it causes problems such as the color becoming lighter at the rising edge of the color in the vertical direction and the trailing downward of the image at the falling edge.

[Means for Solving the Problems] The present invention was made in order to eliminate the above-mentioned conventional drawbacks. The difference output is passed through a noise clipping circuit and a coefficient multiplier having a coefficient of _K1 , and is added to the original color carrier signal and introduced into the system including the delay element 1, and the output of the adder 3 is converted into color noise. The object of the present invention is to provide a color noise reduction circuit that does not cause missing or trailing color outlines by outputting a signal with reduced color noise.

[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 K ₁ , and parts equivalent to those in FIG. 3 are designated by the same reference numerals.

Explain the flow of signals. 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, which removes the noise component in the noise clipping circuit 2 and sends it to the coefficient unit 8.
It is introduced as a signal multiplied by _K1 , which reaches a predetermined level at . The output of the adder 5 is multiplied by (1-K) as in the case shown in FIG. 4 of the conventional example.
The delay time of the adder 3 and 1H is inputted to a cyclic filter system consisting of a delay element 1 that delays the delay time and a K times coefficient unit 6. The output of this cyclic filter system is sent to the adder 3.
It is extracted from the output of , and is further input to the subtracter 4.

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, the noise clip circuit 2 is off, and in this case, the transfer function A'(W) of this embodiment is equal to the transfer function A(W) of the cyclic filter system. Become.

However, if the signal level is greater than the noise clip level (which is the vertical contour part of the color carrier signal), the noise clip circuit 2 is on;
The transfer function A'(W) in this case is A'(W)=(1+K ₁ )/[K ₁ +1/A(W)]. In addition, this formula is shown in Figure 3, which replaces Figure 1.
Explain using diagrams. Here, 9 is the transfer function A(W)
Since the noise clipping circuit 2 is on, the signal is passed through. Assuming that the two signal inputs and outputs to the subtracter 4 are V ₁ , V ₂ , and V ₃ respectively as shown in the figure, 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 is V ₂ = {(1+K ₁ )/[ K ₁ +1/A(W)]}V ₁ , and therefore the transfer function A'(W) is as shown above.

From the above, as can be seen from the transfer function A'(W) of this embodiment, the coefficients of the recursive filter system are changed in the vertical contour portion of the color carrier signal to reduce the time constant of the transfer function. Note that when the noise clipping circuit 2 is off, the waveform B in FIG. 2 is the same as the waveform C.
is adder 3 when noise clip circuit 2 is on.
FIG.

As a result of the above, the actual output of the adder 3 becomes a waveform with a clear vertical contour as shown in waveform D.

In the above embodiment, the case of a television receiver has been described, but the present invention may also be applied to a video tape recorder or a video disk player that handles color carrier wave signals, and the same effective effects as in the above embodiment can be obtained.

[Effects of the Invention] As described above, according to the present invention, the vertical contour component of the color carrier signal is returned to the first stage of the recursive filter,
Since it is configured to add at a predetermined level, it is possible to remove color dropouts and trailing at vertical contours, reproduce color contours faithfully, and reduce only color noise (hue unevenness/color noise). can do.

[Brief explanation of the drawing]

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... Adder, 6, 7, 8... Coefficient unit.

Claims (1)

[Claims] 1 The input signal to the cyclic filter system is (1-
K) a first multiplier that multiplies and a first adder that adds the output of the multiplier and the output of the second multiplier;
a delay element that delays the output of the adder by one horizontal scanning period; and a second delay element that delays the output of the adder by one horizontal scanning period;
The input color carrier signal is supplied to a subtracter and a second adder, and the other of the subtracters receives the cyclic coefficient. A noise clipping circuit to which the output of the filter system is supplied and connected to the output of the subtracter and clips the output; and a noise clipping circuit that sets the signal level from the noise clipping circuit to a predetermined level and sends a signal to the second adder. 3, and a color noise reduction circuit configured to supply the signal output of the second adder to the input of the cyclic filter system, and output the output signal of the cyclic filter system.