JPH0420182A - Noise removing circuit - Google Patents

Abstract

PURPOSE:To prevent excessive removing at an edge part by subtracting an extracted noise component from an original signal and controlling the level of the noise component on executing the noise removing with detecting the edge part of the waveform of the original signal. CONSTITUTION:A chroma signal component is removed by a trap circuit 4 from a composite video signal, the high frequency component of the video signal with the chroma signal component removal is extracted by a high pass filter 5 and the high frequency component is subtracted from the original composite video signal by a subtracting circuit 2. Then, the edge part of the waveform of the video signal is detected from the video signal with the chroma signal component removed and the level of the high frequency component subtracted corresponding to the detected signal is controlled by an attenuator 7. Thus, excessive removing by the rectangular signal of the noise component of the edge part is prevented and the good noise removing without the degradation of the waveform characteristic can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise removal circuit that removes noise components in a composite video signal.

[Summary of the invention]

The present invention relates to a noise removal circuit that detects the edge portion of the waveform of the original signal and controls the level of the noise component when performing noise removal by subtracting the extracted noise component from the original signal. Preventing excessive removal at the edges,
This makes it possible to always perform good noise removal.

[Conventional technology]

For example, in optical video disc players, noise components from the reproduced signal are extracted to remove noise from the reproduced signal.

That is, FIG. 5 shows an example of a circuit for this purpose.

In this figure, (1) is an input terminal for a reproduced and demodulated composite video signal, and the signal from this input terminal (1) is taken out to an output terminal (3) through a subtraction circuit (2).

On the other hand, the signal from the input terminal (1) passes through the chroma signal trap circuit (4) to the bypass filter (5).
The high-frequency noise components in the signal are extracted. This noise component can be detected by the limiter amplifier (6) and attenuator (7).
) to the subtraction circuit (2), where it is subtracted from the original composite video signal.

As a result, noise components in the reproduced signal are removed.

[Problem to be solved by the invention]

However, when removing noise components from such a reproduced signal, if a composite video signal as shown in FIG. 6A is supplied to the input terminal (1), this signal is supplied to the trap circuit (4). The signal after the chroma signal component is removed is as shown in FIG. Here, if this waveform has an edge part due to a large amplitude change as shown in the figure, the noise component extracted from this signal through the bypass filter (5) and limiter amplifier (6) will be As shown in C, a rectangular signal is formed at the edge portion. Therefore, if such a signal is subtracted from the original signal, the removal will be excessive, and as shown in the figure, the waveform at the edge portion will be shaved off and the waveform characteristics will be deteriorated.

This application has been made in view of these points, and is intended to provide a simple structure that can perform good noise removal without causing deterioration of waveform characteristics even at edge portions.

[Means to solve the problem]

The present invention removes the chroma signal component from the composite video signal (trap circuit (4)) and extracts the high frequency component of the video signal from which the chroma signal component has been removed (bypass filter (5)).
) L, in a noise removal circuit that subtracts this high-frequency component from the original composite video signal (subtraction circuit (2)), the edge of the waveform of this video signal is extracted from the video signal from which the chroma signal component has been removed. This is a noise removal circuit that detects the part and controls the level of the high frequency component to be subtracted according to the detected signal (attenuator (7)).

[Operation] According to this, since the subtraction level is controlled according to the detection signal of the edge portion of the waveform of the video signal, excessive removal of the noise component of the edge portion by the rectangular signal is prevented, and the waveform characteristics are Good noise removal can be performed without any deterioration.

〔Example〕

In Figure 1, the signal from the bypass filter (5) is supplied to a double-wave rectifier circuit (11), which passes through the output signal amplifier (12) and a micro-level slicer (13) to a low pass for extending the trailing edge of the signal. The output signal of the low-pass filter (14) is supplied to the gain control terminal of the attenuator (7).

The rest is the same as the circuit described in the prior art.

As a result, in this circuit, when a composite video signal as shown in FIG. 2A is supplied to the input terminal (1), this signal is transmitted to the trap circuit (4), the bypass filter (5), (11) and the signal extracted through the amplifier (12) is as shown in FIG. Furthermore, this signal is removed at a minute level by a slicer (13),
By stretching the trailing edge with the low-pass filter (14), a filter output with a substantially triangular waveform is formed according to the height of the edge as shown in C in the same figure. Ru.

The gain of the attenuator (7) is controlled by this filter output, so that the attenuator (7)
A signal from which the rectangular signal of the edge portion has been removed as shown in the figure is extracted.

Therefore, in this circuit, the level of the noise component to be subtracted is lowered at the edge portion, thereby reducing the influence of the rectangular signal at the edge portion, and preventing deterioration of the waveform characteristics.

In this way, according to the above-mentioned device, the subtraction level is controlled in accordance with the detection signal of the edge portion of the waveform of the video signal, so that excessive removal of the noise component of the edge portion by the rectangular signal is prevented, and the waveform characteristics It is possible to perform good noise removal without deterioration.

By the way, in the above-mentioned apparatus, if the content of the image formed by the video signal is monotonous, the effect of noise is extremely noticeable.On the other hand, if the content of the image is complex, the effect of noise is very noticeable. is relatively inconspicuous, and on the contrary, the sharpness of the image may be deteriorated due to the effect of removing the above-mentioned noise components.

Therefore, in the above-described apparatus, it may be possible to further determine the content of the image and lower the subtraction level for noise removal if the content of the image is complex.

That is, in FIG. 3, the output of the low-pass filter (14) for extending the trailing edge of the signal is further passed through the low-pass filter (21) for detecting the DC level for each horizontal scanning line.
), and the DC level detected here and the output signal of the low-pass filter (14) are added in an adder circuit (22) and supplied to the gain control terminal of the attenuator (7).

Therefore, according to this circuit, when a composite video signal as shown in FIG. 4A is supplied, a signal as shown in FIG. 4B is extracted from the amplifier (12), and the low-pass filter (
14), a filter output as shown in C of the same figure is formed. Furthermore, this signal is supplied to the low-pass filter (21), which outputs a high level signal when the image content is monotonous, and a low level signal when the image content is complex, as shown in the figure. A signal is extracted. Note that in the figure, the change is made steep for the sake of explanation, but the actual waveform is extremely gradual. This signal and the signal from the low-pass filter (14) are then added together and supplied to the gain control terminal of the attenuator (7).
As shown in the figure, a noise component signal is extracted from the attenuator (7), which has a high level when the content of the image is monotonous, and a low level when the content of the image is complex.

As a result, the level of the noise component is controlled according to the content of the image, and it is possible to perform good noise removal without fear of deterioration of the sharpness of the image.

Note that this application is not limited to optical video disc players;
It can be applied to remove noise from general video signals.

〔Effect of the invention〕

According to this invention, since the subtraction level is controlled according to the detection signal of the edge portion of the waveform of the video signal,
Excessive removal of noise components in edge portions by the rectangular signal is prevented, and it is now possible to perform good noise removal without deteriorating waveform characteristics.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an example of a noise removal circuit according to the present invention, FIG. 2 is a waveform diagram for explaining the same, FIG. 3 is a configuration diagram of another example, and FIG. 4 is a waveform diagram for explaining the same. , FIG. 5 is a block diagram of a conventional noise removal circuit, and FIG. 6 is a waveform diagram for explaining the same. (1) is a composite video signal input terminal, (2) is a subtraction circuit,
(3) is an output terminal, (4) is a chroma signal trap circuit, (5) is a bypass filter, (6) is a limiter amplifier, (7) is an attenuator, (11) is a double wave rectifier circuit, (
12) is an amplifier, (13) is a minute level slicer, (
14) is a low-pass filter for extending the trailing edge of the signal. Agent Hidemori Matsukuma M! Example of #4

Claims (1)

[Claims] A method for removing a chroma signal component from a composite video signal, extracting a high frequency component of the video signal from which the chroma signal component has been removed, and subtracting this high frequency component from the original composite video signal. In the noise removal circuit, the edge portion of the waveform of the video signal is detected from the video signal from which the chroma signal component has been removed, and the level of the high frequency component to be subtracted is controlled according to this detection signal. noise reduction circuit.