JPH0479515B2 - - 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, for example, a television receiver.

[Prior Art] In conventional television receivers, a contour correction means has been proposed for emphasizing the color signal of the video signal and seemingly reducing color noise, one example of which 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 signal is supplied to the coefficient multiplier 7 and the subtractor 4, and the color carrier signal is converted to (1-K) by the coefficient multiplier 7.
It is supplied to an adder 3 which adds the multiplied output and the output of the K times coefficient unit 6. Next, the output signal of the adder 3 is supplied to a delay element 1 that delays the output signal by one horizontal scanning period (hereinafter referred to as 1H), the subtracter 4, and an adder 5. The output signal of the delay element 1 is multiplied by K by a coefficient multiplier 6 having a coefficient of K smaller than 1 and is supplied to an 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.
The waveform diagram of the input color carrier wave signal during one vertical scanning period (1V) is shown in FIG. 6A. Here, the signal passed through the 1H delay element 1 and the coefficient unit 6 which multiplies the supplied signal by K, and the input color carrier signal are expressed as (1-K).
The output waveform diagram of the adder 3 which adds the signal from the multiplier 7 becomes 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 input is a color carrier wave signal, and a coefficient unit 7 multiplies it by (1-K);
Adder 3, 1H delay element 1 and K times coefficient unit 6
Assuming that the connection and configuration consisting of is a cyclic filter system, and the output signal of the adder 3 of this cyclic filter system is the output, the transfer function A(w) of this system is generally expressed by 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 transmitted signal, It is.

Due to the transfer function A(w) of this cyclic filter system, for example, if the value of K is 0.7, the vertical direction is approximately 2 to 3 kHz [(525/15 to 525/10) CPh (cycles per height)]. A waveform B in FIG. 6 from which the above color noise (also referred to as hue unevenness) has been removed is obtained. Furthermore, when the value of K is set to 0.3, the vertical contour portion of waveform B becomes slightly less rounded. However, if this system is used alone, the resolution in the vertical direction deteriorates, so
The following measures will be taken.

That is, the subtracter 4 subtracts the signal of waveform B from the input color carrier signal of waveform A, resulting in a signal shown in waveform C. If the signal of waveform C is clipped by the noise clipping circuit 2 at clip level a, the output becomes a signal shown in waveform D. Here waveform C
The noise clipping circuit 2 is turned on when the clip level is larger than the clip level a, and turned off when it is smaller than the clip level a. 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, waveform A
Compared to this, 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. 6th
This is the difference between periods t ₁ and t ₂ shown in the figure.

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

[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 has resulted in disadvantages such as the color becoming lighter at the rising edge of the vertical color and the trailing downward of the image at the falling edge.

[Means for Solving the Problems] The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional art. cyclic filter type adder 3 including delay element 1
This difference output is passed through a noise clipping circuit and added together with the output of the adder 3 to an adder 5 provided between the adder 3 and the delay element, and the output signal of this adder 5 is obtained. By taking out as the output, the transfer function of the real noise reduction circuit when the noise clipping circuit is on can be set to 1, and when the noise clipping circuit is off, it can be made the same as the transfer function of the recursive filter. Therefore, it is an object of the present invention to provide a color noise reduction circuit in which the transfer function at the color contour portion becomes 1, thereby causing no dropout or tailing of the color carrier signal.

[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 cyclic filter system. The other input of the subtracter 4 is the cyclic filter system adder 3.
is supplied from the output of Next, the output signal of the subtracter 4 is added to the noise clipping circuit 2, and when this output signal is large, the noise clipping circuit 2 is turned on.
When the output signal is small, it is turned off and the noise component of this output signal is removed. Furthermore, an adder 5 is installed between the adder 3 of the cyclic filter system and the 1H delay element 1.
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 cyclic filter type adder 3 is a signal of waveform B.
When the noise clipping circuit 2 is off, the transfer function A(w) of the recursive filter system is A(w)=(1-K)/[1-Kexp(-jwT)], as described above. 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 via a noise clipping circuit 2 which passes signals above a predetermined level. 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 in a cut-off state, that is, it is turned off, so that the transfer function A'(w) of this embodiment in this case is
The transfer functions A(w) of the cyclic filter system become equal.

However, when the signal level is higher than the noise clip level (at the contour part of the color carrier signal), the noise clip circuit 2 is in a conductive state, and the transfer function A'(w) in this case is A' (w)=1. In addition, this formula is shown in Figure 4, which replaces Figure 1.
Explain using diagrams. Here, since the noise clip circuit 2 is on, the signal is passed through. If the input color carrier signal is V ₁ (t), the output of subtracter 4 is V ₂ (t), and the output of adder 5 is V ₃ (t), then V ₃ (t) = (1-K) V ₁ (t) +KV ₃ (t-T) +V ₂ (t) V ₂ (t) = V ₁ (t) - [(1-K)V ₁ (t) +KV ₃ (t-T)], and this From equation 2, V ₃ (t) = (1-K) V ₁ (t) + KV ₃ (t-T) + V ₁ (
t)-(1-K)V ₁ (t)-KV ₃ (t-T), so the output V ₃ (t) is V ₃ (t) = V ₁ (t), and the transfer function A '(w) becomes 1 as described above.

As described above, the present color noise reduction circuit works so as to continuously change the coefficient of K of the cyclic filter system in accordance with the contour signal in the vertical contour portion of the color carrier signal. Unlike methods that add part of the components, this method does not cause problems such as missing colors or trailing.

Furthermore, in the above embodiment, the recursive filter system has the same structure as the conventional example, but as shown in FIG.
The input color carrier signal is directly applied to the adder 3, the output of the adder 3 is supplied to the (1-K) times coefficient unit 7, this output is supplied to the subtracter 4, and also added to the adder 5. The output signal of K is set as the output of this circuit and added to delay element 1,
The configuration is such that the signal 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 2 is conducting and on, and A(w)=(1-K)/[1 when it is non-conducting and off. −Kexp(−jwT)].

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 1, so the waveform transmission of the vertical contour part of the color carrier signal is It will be the same as the input.

In each of the above embodiments, 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 disc player that handles color carrier wave signals, and the same effective effects as in the above embodiments can be obtained.

Further, in the above embodiment, the case where the 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 a subtracter that adds a color carrier signal to a cyclic filter system and takes the difference from the output of the cyclic filter system, a noise clipping circuit is provided for the output of the subtracter. Since the output is added to another adder between the cyclic filter type adder and the delay element, the transfer function when the noise clipping circuit is on is set to 1, so the vertical It is possible to remove color dropouts and trailing in the 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 a color noise reduction circuit according to another embodiment of the invention. 4 is a rewritten block diagram of the color noise reduction circuit shown in FIG. 1, FIG. 5 is a block diagram of a conventional color noise reduction circuit, and FIG. 6 is a summary of the block diagram of FIG. 5. FIG. 1...Delay element, 2...Noise clip circuit,
3, 5... Adder, 6, 7... Coefficient unit.

Claims (1)

[Claims] 1. A subtracter for extracting the difference between a color carrier wave signal separated from a color video signal and a signal obtained by passing this color carrier wave signal through a cyclic filter system, and an output signal of this subtracter at a predetermined level. It is equipped with a noise clipping circuit for clipping, 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 the coefficient, T is one horizontal scanning period, and w is the angular frequency of the transmitted signal. ) A color noise reduction circuit configured to have a cyclic filter characteristic.