JPH04974A - Video signal noise reducing circuit - Google Patents

Abstract

PURPOSE:To reduce the change of the amplitude of a carrier chrominance signal of a video signal by eliminating a chrominance subcarrier component of the video signal from a first output of a distributor by a trap filter whose center frequency is the chrominance subcarrier frequency of the video signal and taking out only a high band component of the video signal by a high-pass filter. CONSTITUTION:The video signal inputted to a distributor 2 is divided into two, and the chrominance subcarrier component of the video signal in the first output 10 is attenuated by a trap filter 3. The high band component of the video signal is taken out by a high-pass filter 4, and the output of the high-pass filter 4 is amplified by an amplifier 5 and is inputted to a limiter 6 and the amplitude is limited to take out noise components other than the chrominance signal of the video signal. Taken-out noise components have the polarity inverted by a polarity inverter 7 and is superposed on a second output 11 of the distributor 2 by a superposing circuit 8, and thus, noise components of the video signal are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal noise reduction circuit that reduces noise components of a video signal used in video signal processing.

Conventional video signal reduction circuits are used in VTRs and the like to improve the signal-to-noise ratio of video signals during playback.

An example of the conventional video signal noise reduction circuit described above will be described below with reference to the drawings.

FIG. 5 is a block diagram showing the configuration of a conventional video signal noise reduction circuit. In the figure, 1 is an input terminal into which a video signal is input, 2 is a divider that divides the input signal into two parts, 4 is a high-pass filter (HPF) that extracts the high-frequency components of the video signal, and 5 is amplify the output of the high-pass filter 4. An amplifier, 6 a limiter that limits the amplitude and extracts noise components, 7 a polarity inverter that inverts the polarity of the signal, 8 superimposes two signals, the output of the polarity inverter 7 and the other output of the divider 2. superposition circuit, 9 is the output terminal, 10 is the first output of the distributor, 1
1 is the second output of the distributor.

The operation of the video signal noise reduction circuit configured as described above will be described below.

First, the video signal input from the input terminal 1 is divided into two parts by the distributor 2, and the first output 10 of the distributor 2 is sent to the high-pass filter 4.
The output of this high-pass filter 4 is amplified by an amplifier 5, and the output of this amplifier 5 is supplied to a limiter 6 that limits the amplitude to remove noise components from the high-frequency components of the video signal. The polarity of this signal is inverted by a polarity inverter 7, and the superimposition circuit 8 superimposes it on the second output If of the distributor to reduce the noise component of the video signal.

(References 2 Japan Broadcasting Corporation Akebono rNHK Home Video Technology J (1984.4.20), Japan Broadcasting Publishing Association, P2O3
) Problems to be Solved by the Invention However, in the above configuration, when the video signal includes a color subcarrier, the color subcarrier of the video signal other than the noise component is also reduced, so that the carrier color signal of the input video signal is reduced. When the amplitude of is small, the amount of reduction becomes relatively large, the degree of color saturation changes significantly, and there is a problem in that the color reproducibility in the output video signal deteriorates significantly.

In view of the above problems, the present invention provides a video signal noise reduction circuit that reduces changes in the amplitude of a carrier color signal of a video signal, that is, changes in color saturation, and improves color reproducibility in an output video signal during operation. This is what we are trying to provide.

Means for Solving the Problems In order to solve the above problems, the video signal noise reduction circuit of the present invention includes a divider that receives a video signal and divides it into two parts, and a divider that is connected to the first output end of the divider and divides the video signal into two parts. A trap filter that removes color subcarrier components, a high-pass filter that is connected to the trap filter and extracts the high-frequency components of the video signal, an amplifier that is connected to the high-pass filter and amplifies the output of the high-pass filter, and an amplifier that is connected to the amplifier that limits the amplitude. a limiter that extracts only the noise component; a polarity inverter connected to the output end of the limiter to invert the polarity; and a polarity inverter connected to the output end of the polarity inverter and the second output end of the distributor to superimpose the two signals. It is composed of a superposition circuit.

According to the above-described configuration, the present invention divides an input video signal into two parts using a divider, and converts the first output of the distributor into a color subcarrier component of the video signal using a trap filter whose center frequency is the color subcarrier of the video signal. A high-pass filter is used to extract only the high-frequency components of the video signal, an amplifier is used to amplify the signal, a limiter is used to limit the amplitude, only the noise component is extracted, the polarity is inverted using a polarity inverter, and then a superposition circuit is used to remove the high-frequency components of the video signal. Second
To improve image color reproducibility during operation by superimposing it on the output of the video signal, reducing noise components of the video signal, and reducing changes in the amplitude of the carrier color signal of the video signal, that is, changes in color saturation. I can do it.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a video signal noise reducer in one embodiment of the present invention.

In FIG. 1, 1 is an input terminal, 2 is a divider that divides the video signal into two parts, 5 is an amplifier, 6 is a limiter, 7 is a polarity inverter, 8 is a superimposition circuit that superimposes two signals, and 10
is the first output of the distributor, 11 is the second output of the distributor,
The above configuration is similar to the configuration shown in FIG.

A trap filter 3 is connected to the output terminal of the first output 10 of the distributor 2 and attenuates the color subcarrier component of the video signal, and a high-pass filter 4 is connected to the output terminal of the trap filter 3 and extracts high-frequency components of the signal. It's a filter.

The operation of the video signal noise reduction circuit configured as described above will be described below.

First, the video signal input to the distributor 2 is divided into two parts, and the first
The color subcarrier component of the video signal is attenuated from the output 10 by a trap filter 3. In the case of the NTSC system, the video signal consists of a luminance signal component and a carrier color signal component (center frequency is 3.579545 MHz), as shown in Figure 2.
3,579545Mff, which is the center frequency of the carrier color signal
The level near z is high. Therefore, it is desirable that the center frequency of the trap filter 3 is approximately 3.58 MHz in the case of the NTSC system. A high-pass filter 4 extracts high-frequency components of the video signal, and the output of the high-pass filter 4 is sent to an amplifier 5.
After amplifying it, input it to limiter 6 to limit the amplitude,
Noise components other than the carrier color signal of the video signal are extracted. The polarity of the extracted noise component is inverted by a polarity inverter 7, and then superimposed on the second output 11 of the distributor 2 by a superposition circuit 8, thereby reducing the noise component of the video signal.

As described above, according to the present embodiment, there is a divider 2 that receives a video signal and divides it into two parts, and a trap filter 3 that is connected to the first output terminal of the divider 2 and removes the color subcarrier component of the video signal. , 1 to a high-pass filter 4 connected to the ramp filter 3 and extracting high-frequency components of the video signal, an amplifier 5 connected to the high-pass filter 4 and amplifying the output of the high-pass filter 4, and an amplifier 5 connected to the amplifier 5 to amplify the amplitude of the output. Limiter 6 that limits and extracts only noise components;
A polarity inverter 7 connected to the output terminal of the polarity inverter 7 to invert the polarity, and a superposition circuit 8 connected to the output terminal of the polarity inverter 7 and the second output terminal of the distributor 2 to superimpose two signals. As a result, the carrier color signal component of the video signal input to the limiter 6 can be suppressed, reducing the noise component of the video signal and also reducing changes in the amplitude of the carrier color signal of the video signal, that is, changes in color saturation. , it is possible to improve the color reproducibility of images during operation.

The trap filter 3 can be realized using an inductor 20 and a capacitor 21 as shown in FIG.

The input/output characteristics of this filter are such that the value of the inductor 20 is L(
II), when the value of the capacitor 21 is C(F), the center frequency Fc is Fc=1/(2π(L) as shown in FIG.
C)-””), for example, L=0.1b+H, C=1
If it is 8pP, Fc=3.576MH2, and the color subcarrier component of the video signal can be attenuated.

Note that the trap filter 3 may be constructed of a circuit other than that shown in FIG. 3 as long as it has a trapping effect.

Effects of the Invention As described above, the present invention includes a divider that receives a video signal and divides it into two parts, a Trump filter that is connected to the first output terminal of the distributor and removes the color subcarrier component of the video signal, and a Trump filter that divides the video signal into two parts. a high-pass filter that is connected to the amplifier and extracts the high-frequency components of the video signal; an amplifier that is connected to the high-pass filter and amplifies the output of the high-pass filter; a limiter that is connected to the amplifier that limits the amplitude of the output and extracts only the noise component; a polarity inverter connected to the output terminal of the polarity inverter for inverting the polarity; and a polarity inverter connected to the output terminal of the polarity inverter and the second
By providing a superimposing circuit connected to the output terminal of the video signal without overlapping the two signals, changes in the amplitude of the carrier color signal of the video signal, that is, changes in color saturation, are reduced, and the color of the image during operation is reduced. Since the reproducibility of the image signal is improved, it is possible to more effectively reduce the noise component of the video signal, and the practical effects thereof are significant.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a video signal noise reduction circuit in an embodiment of the present invention, Fig. 2 is a spectrum diagram of a video signal, Fig. 3 is a circuit diagram showing an example of a trap filter, and Fig. 4 is its circuit diagram. The amplitude-frequency characteristic diagram of the trap filter, FIG. 5, is a diagram of a conventional video signal noise reduction circuit. 2...Distributor, 3...Trap filter, 4...High pass filter, 5...
Amplifier, 6...Limiter, 7...Polarity inverter, 8...Superposition circuit. Name of agent: Patent attorney Shigetaka Awano (1 person) Figure 35ri 9545 Shuzukesame (MHz) Figure

Claims (1)

[Scope of Claims] A divider that divides a video signal into two; a trap filter that removes a color subcarrier component of the video signal output from a first output end of the divider; a high-pass filter that extracts high-frequency components of a video signal; an amplifier that amplifies the output signal of the high-pass filter; a limiter that limits the amplitude of the output signal of the amplifier; and a polarity inverter that inverts the polarity of the output signal of the limiter. A video signal noise reduction circuit comprising: a superimposition circuit that superimposes the output signal of the polarity inverter and the output signal output from the second output terminal of the distributor.