JPH04286278A - Device for removing noise - Google Patents

Abstract

PURPOSE:To obtain a reception picture with the excellent reproducibility of a minute part and with little sense of noise by adding a reverse polarity high band component to an input signal only during a period when the high band component being more than a specified level is detected. CONSTITUTION:Detecting means for the high band level of the input signal(a noise detecting circuit 4 and a Schmitt circuit 5) and control means which add the reverse polarity high band component to the input signal only during the period when the high band component being more than the specified level is detected by the detecting means 4 and 5(the Schmitt circuit 5 and a switch 10) are provided. Noise is removed by adding the reverse high band component to a video signal 200 only when the noise level of the inputted video signal is high. When the noise level is low, the addition of the reverse high band component is not executed at all. The removal of noise in the video signal is operated when the noise level with an adverse reception state is high.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removal device for removing noise from video signals obtained by receiving satellite broadcasting.

0002

2. Description of the Related Art Satellite broadcasting video signals are frequency modulated and transmitted. Here, if the diameter of the antenna that receives the satellite broadcasting is small, the C/N (carrier/noise) ratio of the input video signal may become low due to rain attenuation, etc.
In such a case, triangular noise, in which the noise spectrum is concentrated in a high frequency band peculiar to frequency modulation, occurs in the received video signal. For this reason, many recent BS tuners or devices with a built-in BS tuner include built-in noise removal devices for removing the triangular noise and the like from input video signals.

FIG. 4 is a block diagram showing an example of a conventional noise removal device of this type. When a video signal such as that shown in FIG. 5A is input from the input terminal 15, this video signal is input to a high-pass filter 16 and an adder 19. The high-pass filter 16 extracts a high frequency component containing noise as shown in FIG. 5(B) from the input video signal and outputs it to the limiter 17. The limiter 17 limits the amplitude component of the input signal as shown in FIG. 5(C),
This is output to the inverting amplifier 18. The inverting amplifier 18 inverts the polarity of the input signal as shown in FIG. 5(D),
This is output to the adder 19. Therefore, in the adder 19, the noise component of the opposite polarity shown in FIG. 5(D) is added to the input video signal shown in FIG. 5(A), so that the noise component is removed from the original video signal. A video signal as shown in (E) is output from this adder 19. Note that since the output signal of the high-pass filter 16 contains large amplitude components other than noise components at the steep rise and fall portions of the video signal input from the input terminal 15, it is necessary to limit the amplitude by the limiter 17. Become.

[0004] However, since the conventional noise removal device described above removes all high-frequency minute amplitude components in the video signal, when the reception condition is good and there are few noise components, the above-mentioned noise removal device cannot be used. If this signal is passed through, the minute amplitude components that reproduce the details of the video signal will be removed, resulting in the received image quality lacking any sense of detail.

[0005]

[Problem to be Solved by the Invention] The conventional noise removal device as described above has the principle of removing noise components by removing the high-frequency minute amplitude components of the video signal, so it is possible to eliminate noise components when the reception condition is good. If the amount of noise is small, the small amplitude component that reproduces the details of the video signal will be removed when the signal is passed through the noise removal device, resulting in a disadvantage that the image quality of the received image will lack a sense of detail.

Therefore, the present invention aims to eliminate the above-mentioned drawbacks, and when the reception condition is good, it is possible to provide a received image with excellent detail reproducibility, and when the reception condition is poor, it is possible to provide a received image with less noise. An object of the present invention is to provide a noise removal device that can provide a received image with a high quality. [Structure of the invention]

[0007]

[Means for Solving the Problems] The present invention provides a noise removal device that removes noise components from the input signal by adding opposite polarity high frequency components of the input signal to the input signal. and a control means that adds the opposite polarity high frequency component to the input signal only during a period when a high frequency component of a predetermined level or higher is detected by the detection means. .

[0008]

In the noise removing device of the present invention, the detection means detects the level of the high frequency component of the input signal. The control means adds the reverse polarity high frequency component to the input signal only during a period in which the high frequency component of a predetermined level or higher is detected by the detection means.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the noise removal device of the present invention. 1 is an input terminal into which a video signal/audio signal (hereinafter referred to as input signal 100) output from a second converter (not shown) is input; 2 is an amplifier that amplifies the input signal 100 input from input terminal 1; 3 is a video signal processing circuit that performs de-emphasis processing on the video signal in the input signal 100, removes the audio signal from the input signal 100, amplifies the de-emphasized video signal to a predetermined level, and outputs the amplified video signal; is a noise detection circuit that detects noise components included in the input signal 100, which includes a bandpass filter 41 that extracts high-frequency signal components that include noise components, and an amplifier 42 that amplifies the extracted noise components.
It also has a peak detector 43 that converts the level of the input noise component into a DC voltage 50 and outputs it. 5 is a Schmitt circuit that shapes the waveform of the DC voltage 50 output from the noise detection circuit 4 into a square wave control pulse 60; 6 is a high-pass filter that extracts high-frequency components from the de-emphasized video signal 200; 7; 8 is a limiter that limits the amplitude level of the high frequency component output from the high pass filter 6, 8 is an inverting amplifier that inverts the polarity of the high frequency component, that is, the noise component output from the limiter 7, and 9 is the output from the video signal processing circuit 3. An adder that adds a noise component of opposite polarity input from the switch 10 to the output video signal 200;
This is a switch that changes whether or not to input.

Here, the noise detection circuit 4 and the Schmitt circuit 5 constitute a detection means, and the Schmitt circuit 5 and the switch 10 constitute a control means. Further, the peak detector 43 constitutes a detection means, and the Schmitt circuit 5 constitutes a waveform shaping means.

Next, the operation of this embodiment will be explained. When input signal 100 is input from input terminal 1, amplifier 2
After being amplified, the signal is input to the video signal processing circuit 3 and noise detection circuit 4, and is also input to an audio signal processing system and a detection output system (not shown). Video signal processing circuit 3
performs de-emphasis processing on the input video signal 100 to amplify it, removes the audio signal, and outputs the de-emphasized video signal 200 to the adder 9 and the high-pass filter 6 .

On the other hand, in the noise detection circuit 4, the input signal 1
After extracting a high frequency signal component, that is, a noise component from 00 using a band pass filter 41 and amplifying it using an amplifier 42,
This noise component is input to the peak detector 43. The peak detector 43 converts the level of the noise component input from the amplifier 42 into a corresponding DC voltage and outputs it to the Schmitt circuit 5. FIG. 2(A) shows the peak detector 43.
When such a DC voltage 50 is input to the Schmitt circuit 5, the Schmitt circuit 5 changes the input DC voltage 50 from the rising edge to the falling edge or from the falling edge to the rising edge. A square wave control pulse voltage 60 as shown in FIG.
Output to. That is, when the DC voltage 50 input to the Schmitt circuit 5 reaches the level shown in A in FIG. 2, the control pulse 60 of the Schmitt circuit 5 becomes high level, and the switch 10 is turned on. Further, when the input voltage 50 becomes lower than the low level, the control pulse 60 outputted from the Schmitt circuit 5 becomes low level, and the switch 10
is turned off.

By the way, high-frequency signal components are extracted from the video signal 200 inputted to the high-pass filter 6, and the amplitude thereof is further limited by the limiter 7, so that only noise components are inputted to the inverting amplifier 8. The inverting amplifier 8 inverts the polarity of the input noise component and then outputs it to the terminal a of the switch 10. Therefore, Schmitt circuit 5
When the control pulse 60 output from the video signal 200 becomes high level, that is, when the level of the noise component included in the video signal 200 is high, the switch 10 is turned on. Therefore, the noise component 300 of the opposite polarity output from the inverting amplifier 8 is input to the adder 9, canceling the noise component on the video signal 200, and producing the video signal 201 from which the noise component has been removed. output in stages. However, when the level of the noise component detected by the noise detection circuit 4 is low, the control pulse 60 output from the Schmitt circuit 5 is at a low level, so the switch 10 is turned off, and the video signal processing circuit Video signal 2 output from 3
00 passes through the adder 9 as it is and is output as a video signal 201.

FIG. 3 is a diagram showing the relationship between the output voltage of the peak detector 43 shown in FIG. 1 and the C/N ratio. The closer the C/N ratio is to 0, the higher the output voltage becomes, and conversely, the larger the C/N ratio becomes, the lower the output voltage becomes. Therefore, in the apparatus shown in FIG. 1, the noise removal operation is performed when the output voltage of the peak detector 43 is high, that is, when the noise is large, and the noise removal operation is not performed when the noise is small.

According to this embodiment, noise removal is performed by adding an inverted high frequency component to the video signal 200 only when the noise level of the input video signal is high, and when the noise level is small, the inverted high frequency component is added to the video signal 200. Since high-frequency components are not added at all, high-frequency components in the video signal are not lost in good reception conditions with low noise levels, and a received image with excellent detail reproducibility can be provided. Furthermore, when the noise level is high in poor reception conditions, an operation is performed to remove the noise in the video signal, so it is possible to provide a received image with less noise. Therefore, in order to obtain the best received image depending on the reception condition, control is performed to perform or not perform the noise removal operation.
As a result, the quality of the received image can be improved. In the above embodiment, the output signal of the noise detection circuit 4 was waveform-shaped using the Schmitt circuit 5, but it is also possible to waveform-shape the output signal using a microcomputer.

[0016]

As described above, according to the noise removal device of the present invention, when the reception condition is good, a received image with excellent detail reproducibility can be provided, and when the reception condition is bad, the
A good received image with less noise can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a noise removal device of the present invention.

FIG. 2 is a diagram showing the relationship between the output voltage of the peak detector shown in FIG. 1 and the control pulse output from the Schmitt circuit.

[Figure 3] Output voltage and C/N of the peak detector shown in Figure 1
A diagram showing the relationship with the ratio.

FIG. 4 is a block diagram showing an example of a conventional noise removal device.

FIG. 5 is a waveform diagram illustrating the operation of the conventional device shown in FIG. 4;

[Explanation of symbols]

3...Video signal processing circuit, 4...Noise detection circuit, 5...Schmidt circuit, 6...High pass filter, 7...Limiter, 8...inverting amplifier, 9...adder, 10...Switch, 41...Band pass filter, 43...Peak detector

Claims (2)

[Claims] 1. A noise removal device that removes a noise component from the input signal by adding a reverse polarity high frequency component of an input signal to the input signal, wherein the detection means detects the level of the high frequency component of the input signal. and a control means for adding the reverse polarity high frequency component to the input signal only during a period in which a high frequency component of a predetermined level or higher is detected by the detection means. 2. A claim characterized in that the detection means comprises a detection means for peak-detecting a high-frequency component of the input signal, and a waveform shaping means for shaping the waveform of a detected output signal of the detection means. Item 1. The noise removal device according to item 1.