JPH06253336A - Noise canceler circuit - Google Patents

Abstract

PURPOSE:To provide a noise canceler circuit which obtains an excellent reproduced image by varying the extent of noise removal following up variation of the reproduced image. CONSTITUTION:The noise canceler circuit which adjusts the level of a high frequency noise component after extracting the high frequency noise component by subtracting a high frequency component from a signal generate by limiting the high frequency component of a reproduced luminance signal extracted through a high-pass filter, and subtracts the noise component from the source reproduced luminance signal to output a reproduced luminance signal is equipped with a rectifying means 12 which performs the full-wave rectification of the high frequency component of the extracted reproduced luminance signal, a control signal generating means 13 which generates a control signal for noise level adjustment based on the rectified signal, and a noise level adjusting means 7 which adjusts the level of the extracted noise component according to the control signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise canceller circuit provided for improving the reproduced image quality of a VTR device.

[0002]

2. Description of the Related Art There are two signal systems handled by VTR devices, a video system and an audio system. Among them, the video input / output signal is a color video signal having a frequency band defined, and inside the device, the video signal is a luminance signal (referred to as Y signal) and a frequency band higher than the luminance signal. Is separated (Y / C separation) into a high color signal (referred to as a C signal) and a recording / reproducing process is performed.

Further, "resolution" and "S / N ratio" are basic items for evaluating the reproduced image quality of the VTR device. “Resolution” indicates the number of lines that can be visually recognized on the entire screen, and the horizontal resolution in the horizontal direction of the monitor screen,
There is vertical resolution in the vertical direction. In addition, "S / N
“Ratio” is the ratio of the magnitude of a significant signal S (signal) and the unwanted signal N (noise) that have meaning (the unit is dB).
There is an S / N ratio for a luminance signal and an S / N ratio for a color signal. In the home VTR device, the S / N ratio of the luminance signal usually becomes a problem.

Therefore, conventionally, the S / N ratio of the reproduced luminance signal after demodulation is improved by the "noise canceller circuit" before being superimposed on the reproduced color signal. FIG. 3 is a block diagram showing a configuration of a conventional noise canceller circuit for a reproduction luminance signal. 4A to 4D are schematic diagrams showing changes in the waveform of the reproduction luminance signal processed by the noise canceller circuit shown in FIG.

In FIG. 3, most of the noise components included in the reproduction luminance signal Y input from the input terminal 31 are high frequency components, and as shown in FIG. Of the reproduction luminance signal Y. However, in such a state, since the reproduction luminance signal Y also has a high frequency component, the noise component and the reproduction luminance signal Y cannot be clearly distinguished,
It is difficult to remove the noise component.

Therefore, in the noise canceller circuit, first, only the high frequency components of the input reproduction luminance signal Y are taken out by the high frequency filters (HPF) 32 and 33. Here, since the HPF is a differentiating circuit, as shown in (b) of FIG. 4, a waveform only at a changed portion of the signal (that is, corresponding to a high frequency component) can be obtained. And further,
It is amplified by the amplifier (AMP) 34 for the next processing.

On the other hand, a limiter (LI) is applied to the high-frequency component of the reproduced luminance signal Y extracted by the high-pass filter 33.
When M) 35 is applied, the waveform shown in FIG. 4C is obtained. Here, with respect to the extracted high frequency component of the reproduction luminance signal Y, by cutting out a portion protruding above a certain level, only a waveform below that level is extracted (note that the waveform was cut out). The rest is shown as a rectangle). As a result, the reproduction luminance signal Y (remaining after the limiter is applied) included in the high frequency component and the amplitude level of the noise component are approximately the same. Therefore, if the reproduction luminance signal Y is subtracted by the subtractor 36 from this state, only the noise component is eventually extracted.

Then, subsequently, the extracted noise component is attenuated by the attenuator (ATT) 37 and the level is adjusted, and the waveform shown in FIG. 4D is obtained. Therefore, the subtractor 39 causes the clamp circuit (CLAM
P) When the noise component is subtracted from the reproduced luminance signal Y that has passed through 38 (which is a circuit that suppresses the synchronizing signal portion to a constant DC voltage value), the noise component is removed from the reproduced luminance signal Y, and the reproduced luminance signal Y is output from the output terminal 40. It will be output.

[0009]

By the way, in order to adjust the effectiveness of the noise canceller circuit, the level of the noise component level adjustment in the attenuator 37 should be adjusted while actually watching the image displayed on the screen. It suffices to change the subtraction amount of noise from the reproduction luminance signal Y by changing it. In this case, when the effect of the noise canceller circuit is strengthened (that is, subtraction of the signal regarded as noise from the reproduction luminance signal Y). When the amount is increased), noise is naturally lowered and the S / N ratio is improved.

On the other hand, when the effect of the noise canceller circuit is weakened (that is, when the subtraction amount of the signal regarded as noise from the reproduction luminance signal Y is reduced), the noise does not decrease so much, but the reproduction luminance is reduced. Since many high frequency components of the signal Y remain, the resolution is increased. In this way, by changing the effectiveness of the noise canceller circuit, the effects of the S / N ratio and the resolution change in opposition to each other.

However, in order to improve the reproduced image quality of the VTR device, which of the S / N ratio and the resolution should be emphasized naturally depends on the content of the image to be reproduced. For example, when a flat image such as "sky" or "wall" is reproduced, the influence of the S / N ratio becomes large, and when reproducing an image with many vertical stripes, the resolution is reversed. Will have a greater impact.

In such a case, while actually looking at the screen,
The operation of changing the effectiveness of the noise canceller circuit according to the content of the image to be reproduced is actually
I have to say that it is impossible. Therefore, in the conventional noise canceller circuit, a method of selecting an intermediate effect that satisfies both the S / N ratio and the resolution to some extent is adopted, and a reproduced image that changes moment by moment is never satisfied. It has not yet been possible to obtain good image quality.

The present invention has been made in view of the above situation, and it is possible to obtain a good reproduced image quality by changing the degree of noise removal in accordance with the change of the reproduced image. It is intended to provide a noise canceling circuit.

[0014]

In order to achieve the above object, the present invention subtracts the high frequency component from the high frequency component of the reproduced luminance signal taken out through the high frequency filter and applied with a limiter. After extracting the high frequency noise component, the level is adjusted, the noise component is subtracted from the original reproduction luminance signal, and the reproduced luminance signal is output in the noise canceller circuit. Rectifying means for wave rectification, control signal generating means for generating a control signal for noise level adjustment based on the rectified signal, and noise level adjusting means for adjusting the level of the extracted noise component according to the control signal. It is characterized by having.

[0015]

According to the above construction, in the noise canceller circuit, only the high-frequency component is extracted from the reproduced luminance signal inputted by passing it through the high-pass filter. Then, a limiter is applied to the extracted high frequency component. Further, the high frequency component of the reproduced luminance signal is subtracted therefrom. As a result, the high frequency noise component included in the reproduction luminance signal is extracted. Then, the level of the extracted high frequency noise component is adjusted. Then, the noise component whose level is adjusted is subtracted from the original reproduction luminance signal to remove the noise.

On the other hand, the extracted high frequency component of the reproduced luminance signal is full-wave rectified by the rectifying means. Further, based on the rectified signal, by the control signal generating means,
A control signal for adjusting the level of the extracted high frequency noise component is generated. Therefore, according to the generated control signal, the noise level adjusting means adjusts the level of the extracted high frequency noise component.

As a result, the high-frequency noise component whose level is adjusted according to the state of the original reproduction luminance signal is subtracted from the original reproduction luminance signal, and then output from the noise canceller circuit.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a noise canceller circuit for a reproduction luminance signal according to the present invention. This noise canceller circuit uses the reproduction luminance signal Y
Input terminal 1 and an output terminal 10 for outputting a reproduction luminance signal Y after noise removal, and a high-pass filter (HPF)
2 and 3, an amplifier (AMP) 4, and a limiter (LI
M) 5, a subtractor 6, an attenuator (ATT) 7, a clamp circuit (CLAMP) 8 and a subtractor 9 as a main noise canceller circuit (same as the configuration of the conventional noise canceller circuit shown in FIG. 3). And the amplifier (AMP) 1 added to the main noise canceller circuit in order to detect the state of the input reproduction luminance signal Y.
1, a full-wave rectifier circuit 12, and a low pass filter (LPF) 1
3 and 3.

The waveform of the reproduced luminance signal Y input from the input terminal 1 is shown in FIG. 4 (a), the waveform of the high frequency component passing through the HPFs 2 and 3 is shown in FIG. The waveform of the signal obtained is shown in FIG. 4C, and the waveform of the signal passed through the subtractor 6 is shown in FIG. 4D. Also, H
The signal that has passed through the PF2 is input to the AMP11 and amplified, and then the full-wave rectifier circuit 12 and the low-pass filter (LPF).
It passes through 13 and is input to the attenuator 7. The full-wave rectification circuit 12 applies full-wave rectification in order to pulse the input signal to obtain a control signal (described later) for controlling the ATT 7.

Next, the signal waveform after passing through the full-wave rectifier circuit 12 is shown in FIG. As shown in the figure, if a waveform having many sharp peaks is obtained, it can be confirmed that the reproduction luminance signal Y contains many high frequency components. In such a case, increasing the resolution is more important than increasing the S / N ratio in order to improve the reproduced image quality. Therefore,
Control the level adjustment of the noise component in ATT7,
The original signal is faithfully reproduced by reducing the subtraction amount of the noise component from the original signal. On the other hand, when the reproduced luminance signal Y has no or a few high frequency components, it is more important to improve the S / N ratio than the resolution in order to improve the reproduced image quality. So A
The TT7 is controlled to increase the subtraction amount of the noise component from the original signal, thereby improving the S / N ratio.

Specifically, when the control signal is Low (that is, when the pulse does not rise), the level adjustment of the ATT 7 is controlled so that the S / N ratio is emphasized, and the control signal is High.
When h (that is, when a pulse rises), the level adjustment of the ATT 7 is controlled so that the resolution is emphasized. in this case,
As described above, since the signal waveform after passing through the full-wave rectifier circuit 12 has a fixed direction, it is easy to obtain (that is, pulse) such a control signal. And
It is assumed that a pulse is generated when the waveform has many high frequency components, and no pulse is generated when the waveform has no or few high frequency components.

Further, in order to improve the image quality by following the image which is changing every moment, the A based on the obtained control signal is used.
The control timing of TT7 becomes important. Therefore, in the present invention, first, by adjusting the gain of the AMP 11, the threshold level with respect to the input signal level is determined, and the LPF is passed through the full-wave rectification circuit 12.
13 is passed to delay the generation of the control signal.
In this way, based on the determined threshold level,
A decision is made as to whether or not to set a pulse as a control signal,
Further, the generation of the control signal is delayed so that the control signal can control the ATT 7 by following the image that changes every moment. As a result, the subtraction process is effectively executed by the subtractor 9, and the image quality of the flowing video is dramatically improved.

Since the LPF 13 does not need a high frequency when used as a control signal, a low frequency control signal is obtained, but the main purpose is the ATT7.
Since the timing of the control signal input to is delayed, another delay circuit may be used instead of the LPF 13.

[0024]

As described above, according to the present invention, the effectiveness of the noise canceller circuit can be automatically changed in a VTR device or the like in accordance with the content of an image to be reproduced. That is, depending on the content of the image to be reproduced,
It becomes possible to judge which of the S / N ratio and the resolution should be emphasized and automatically change the effectiveness of the noise canceller circuit so that each of them can effectively function. As a result, it becomes possible to dramatically improve the reproduced image quality as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a noise canceling circuit for a reproduction luminance signal according to the present invention.

FIG. 2 is a schematic diagram showing the level of a signal waveform after passing through a full-wave rectifier circuit in the noise canceling circuit shown in FIG.

FIG. 3 is a block diagram showing a configuration of a conventional noise canceling circuit for a reproduction luminance signal.

4 is a schematic diagram showing a level change of a waveform of a reproduction luminance signal processed by the conventional noise canceling circuit shown in FIG.

[Explanation of symbols]

 1 Input terminal 2, 3 High-pass filter 4, 11 Amplifier 5 Limiter 6, 9 Subtractor 8 Clamp circuit 10 Output terminal 12 Full-wave rectifier circuit 13 Low-pass filter Y Playback luminance signal

Claims (1)

[Claims] 1. A high-frequency component of a reproduced luminance signal extracted through a high-pass filter is subjected to a limiter, a high-frequency component is subtracted to extract a high-frequency noise component, and then its level is adjusted to obtain the original level. In a noise canceller circuit that outputs the reproduced luminance signal by subtracting the noise component from the reproduced luminance signal, rectifying means for full-wave rectifying the extracted high frequency component of the reproduced luminance signal, and noise based on the rectified signal A noise canceller circuit comprising: a control signal generating unit that generates a control signal for level adjustment; and a noise level adjusting unit that adjusts the level of the extracted noise component according to the control signal.