JPH03158078A - Noise elimination device - Google Patents

Abstract

PURPOSE:To prevent the reduction in the S/N due to production of smear at an edge of a luminance signal by the noise elimination processing by decreasing the amplitude level of an amplitude limit output subtracted from a luminance signal when the amplitude level of the output extracted from a noise signal extraction means exceeds a prescribed level. CONSTITUTION:An absolute value outputted from an absolute value circuit 28 is larger than a reference level VR when an output extracted from a high pass filter(HPF) 22 includes a high frequency component of a luminance signal with a large amplitude level. Thus, in this case, an output level of a comparator circuit 29 goes to a high level and a switch 25 is turned off. As a result, since an amplitude limit output is not fed to a subtraction circuit 26, the high frequency component with a large amplitude level included in the luminance signal is outputted as it is to an output terminal. Thus, the amplitude level of the high frequency component with a large amplitude level is unchanged even with the noise reduction processing. Thus, the reduction in the S/N due to the production of smear at the edge of the noise elimination output is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a noise removal device for removing a noise signal from a luminance signal in television video equipment.

(Prior Art) In recent years, various methods have been taken to improve the image quality of television video equipment such as television receivers and video tape recorders (hereinafter referred to as VTRs).

One of them is a method of removing a noise signal from a luminance signal using a noise removal device. According to this method, the S/N ratio of the luminance signal is improved, so the image quality can be improved.

FIG. 7 shows the configuration of a conventional noise removal device.

The illustrated device uses a bypass filter (hereinafter referred to as HPF) 12 to extract a noise signal from a luminance signal input from an input terminal 11, and subtracts it from the input luminance signal using a subtraction circuit 14, thereby outputting the noise signal to an output terminal 15. A luminance signal from which noise signals have been removed is obtained.

Note that the limiter 13 is provided to limit the amplitude level of the high frequency component of the luminance signal.

That is, the noise signal and the high-frequency components of the luminance signal exist in the same band. Therefore, the extraction output of HPF12 is:
In addition to the noise signal, high-frequency components of the luminance signal are also included. If this high frequency component is directly subtracted from the input luminance signal, the high frequency component of the luminance signal will be lost. Therefore, by providing a limiter 13 having input/output characteristics as shown in FIG. 8 and limiting the extracted output of the HPF 12 to the amplitude level of the noise signal, it is possible to prevent the high frequency components of the luminance signal from being lost due to the noise removal operation. That's what I'm doing.

As described above, the conventional noise removal apparatus removes the noise signal by extracting the noise signal from the input luminance signal, limiting the amplitude of the noise signal, and subtracting it from the input luminance signal.

However, the luminance signal does not always include a noise signal. For example, in a portion of a luminance signal where a high frequency component with a large amplitude level exists, there is often a small amount of noise signal.

Therefore, as in the past, the input luminance signal is always HP
In the configuration that reduces the extraction output of F13, the amplitude level of the luminance signal changes in a portion where a high frequency component with a large amplitude level exists. As a result, smear reduction occurs at the edge portions of the luminance signal, and the S/N ratio decreases.

This will be explained using FIG. 9.

FIG. 9(a) shows an input luminance signal Y including a noise signal N. In FIG. When the luminance signal Y is a rectangular wave as shown in the figure, the HPF 12 outputs a high-frequency component H located at the edge of the luminance signal Y in addition to the noise signal N, as shown in FIG. 9(b). is extracted.

The amplitude of this high frequency component H is limited by the limiter 13, as shown in Figure '1s9 (C). However, even with this amplitude limitation, a high frequency component H having an amplitude limitation level ±vL remains. This residual high frequency component H is subtracted from the input luminance signal Y. As a result, the waveform of the luminance signal Y is as shown in Fig. 9 (d
), and a smear phenomenon occurs at the edges. As a result, the S/N ratio of the luminance signal Y decreases.

(Problems to be Solved by the Invention) As described above, in conventional noise removal devices, the amplitude level of high-frequency components with large amplitude levels changes due to noise removal processing, so a smear phenomenon occurs at the edge portions of the luminance signal. There was a problem in that the S/N ratio was lowered.

SUMMARY OF THE INVENTION An object of the present invention is to provide a noise removal device that does not cause a smear phenomenon to occur at the edge portion of a luminance signal due to noise removal processing, thereby preventing the S/N ratio from decreasing.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention takes into account that when the amplitude level of the high frequency component of a luminance signal is large, there is less noise signal, and the input luminance is In a configuration in which a noise signal is extracted from a signal, its amplitude is limited, and subtracted from the input luminance signal, if the amplitude level of the noise signal extraction output exceeds a predetermined level, the amplitude level of the amplitude-limited output is subtracted from the input luminance signal. It is designed to reduce the

(Operation) If the extracted output of the noise signal does not include high-frequency components with large amplitude levels, the amplitude level of this extracted output does not exceed the predetermined level. Therefore, in this case, the amplitude limited output is directly subtracted from the input luminance signal. This removes the noise signal from the input luminance signal.

On the other hand, if the extracted output of the noise signal includes a high-frequency component of the luminance signal with a large amplitude level, the amplitude level of this extracted output exceeds the predetermined level. Therefore, in this case, the amplitude level of the amplitude-limited output subtracted from the input luminance signal is lowered. This suppresses changes in the amplitude level of high-frequency components with large amplitude levels included in the luminance signal.

As described above, it is possible to prevent the S/N ratio from decreasing due to the occurrence of a smear phenomenon at the edge portion of the noise-removed output.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

In the figure, the luminance signal input from the input terminal 21 is
The signal is supplied to the HPF 22 and also to the delay circuit 23 for time adjustment. The HPF 22 extracts the noise signal from the human signal. The amplitude of this extracted output is limited by the limiter 24 to the amplitude level of the noise signal. This amplitude limited output is supplied to a subtraction circuit 26 via a switch 25, the details of which will be described later. This subtraction circuit 26 subtracts the amplitude limited output from the input luminance signal time-adjusted by the delay circuit 23. As a result, a luminance signal from which noise signals have been removed is obtained at the output terminal 27.

The on/off state of the switch 26 is controlled as follows.

The extracted output of the HPF 24 is supplied to an absolute value circuit 28, and its absolute value is determined. This absolute value is supplied to the comparator circuit 29 and compared with the reference level VR.

The output of this comparison circuit 29 becomes a high level when the absolute value is greater than the reference level ■, and becomes a low level when it is smaller than the reference level v$l.

The switch 26 is turned off when the output of the comparator circuit 29 is at a high level, and turned on when the output is at a low level. As a result, the output level of the switch 26 is
As shown in the input/output characteristics of FIG. 2, the input level increases as the input level increases until it reaches a predetermined level, and when the human power level exceeds the predetermined level, it becomes 0 level.

The reference level V is set to a value slightly larger than the amplitude level of the noise signal. Therefore, if the extracted output of the HPF 22 does not include high-frequency components of a luminance signal with a large amplitude level, the absolute value output from the absolute value circuit 28 will be smaller than the reference level vR. As a result, in this case, the output level of the comparator circuit 29 becomes a low level, and the switch 25 is turned on. As a result, the amplitude limited output is provided via switch 25 to subtraction circuit 26 and subtracted from the input luminance signal. This results in the removal of noise signals.

On the other hand, when the extracted output of the HPF 22 includes a high frequency component of a luminance signal with a large amplitude level, the absolute value output from the absolute value circuit 28 becomes larger than the reference level vR.

As a result, in this case, the output level of the comparator circuit 29 becomes high level, and the switch 25 is turned off. As a result, the amplitude-limited output is not supplied to the subtraction circuit 26, so the high-frequency component with a large amplitude level included in the luminance signal is outputted to the output terminal as it is.

From the above, even if the noise removal process is performed, the amplitude level of the high frequency component with a large amplitude level does not change.

This makes it possible to prevent the S/N ratio from decreasing due to the occurrence of a smear phenomenon at the edge portion of the noise-removed output.

This situation will be explained using FIG. 3.

3(a) shows a rectangular waveform input luminance signal Y including a noise signal N, and FIG. 3(b) shows the extracted output of the HPF 22. When the absolute value of the amplitude level of the high-frequency component H extracted from the edge portion of the luminance signal Y is larger than the reference voltage vR, the output level of the switch 25 becomes 0 level at the edge portion, as shown in FIG. becomes. Accordingly, in such a case, the edge portion of the luminance signal Y is output from the subtraction circuit 26 as is.

As described above, according to this embodiment, it is possible to prevent a decrease in the S/N ratio and the occurrence of smear phenomenon at the edge portions caused by performing noise removal processing on high-frequency components of a luminance signal with a large amplitude level. There is something to do.

This means that when the amplitude level of the extracted output of the HPF 22 is higher than a predetermined level, by turning off the switch 25, the amplitude level of the amplitude limiting output given to the subtraction circuit 26 is set to 0 level, and the noise removal process is essentially performed. This is because it was prohibited.

Furthermore, since the configuration is suitable for analog circuits, it can be realized at low cost.

FIG. 4 is a circuit diagram showing the configuration of a second embodiment of the invention.

This FIG. 4 differs from the previous FIG. 1 in that a variable gain amplifier circuit 31 and a comparator circuit 32 are provided in place of the switch 25 and the comparator circuit 29, respectively, and the other parts are the same. Therefore, the same parts are given the same reference numerals and detailed explanations will be omitted.

In the previous embodiment, when the output level of the HPF 22 exceeds a predetermined level, the amplitude level of the amplitude limiting output supplied to the subtraction circuit 26 is set to 0 level.

In contrast, in this embodiment, the amplitude level of the amplitude-limited output is gradually lowered.

That is, in this embodiment, the amplitude limited output of the limiter 24 is supplied to the variable gain amplifier circuit 31.

Further, when the absolute value outputted from the absolute value circuit 28 exceeds the reference level 8, the comparison circuit 32 amplifies this absolute value. This amplified output is supplied to the variable gain amplifier circuit 31 as a control signal. This variable gain amplifier circuit 31 has a fifth
As shown in the figure, it is configured such that the gain decreases as the amplitude level of the amplified output of the comparator circuit 32 increases. Therefore, as the amplitude level of the amplified output of the comparison circuit 32 increases, the amplitude level of the amplitude limiting output supplied to the subtraction circuit 26 gradually decreases.

According to such a configuration, when the amplitude level of the extracted output of the HPF 22 exceeds a predetermined level, the amplitude level of the amplitude limiting output supplied to the subtraction circuit 26 is reduced.
Almost the same effects as in the previous embodiment can be obtained.

Further, according to this embodiment, although the amplitude level of the extracted output of the HPF 22 exceeds a predetermined level, noise exists in a portion where a noise signal is likely to be included, such as a portion having a value close to this level. The signal can be removed.

This is so that when the amplitude level of the extracted output of the HPF 22 exceeds a predetermined level, the amplitude level of the amplitude limiting output supplied to the subtraction circuit 26 is not immediately brought to the 0 level, but gradually approaches the 0 level. Therefore, a certain amount of noise removal processing is performed even in the above-mentioned portions.

FIG. 6 is a circuit diagram showing the configuration of a third embodiment of the invention.

The difference in FIG. 6 from the previous FIG. 1 is that a low-pass filter (hereinafter referred to as LPF) 41 is provided between the absolute value circuit 28 and the comparison circuit 29, and the other parts are the same. Therefore, the same parts are given the same reference numerals and detailed explanations will be omitted.

According to the above configuration, since the carrier component is removed by the LPF 41, the operation accuracy can be improved compared to the previous embodiment shown in FIG.

It goes without saying that such a configuration can also be implemented in the embodiment shown in FIG. 4 above.

Although several embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

For example, in the previous embodiment, the subtraction circuit 2 is provided after the limiter.
A case has been described in which the amplitude level of the amplitude limited output supplied to 6 is reduced. However, in the present invention, this control can be performed anywhere as long as it can reduce the amplitude level of the amplitude-limited output supplied to the subtraction circuit 26.

Furthermore, in the previous embodiment, a case has been described in which the absolute value of the amplitude level of the noise signal extraction output is determined, and when this absolute value exceeds a predetermined level, the amplitude level of the amplitude limited output is reduced. However, in this invention, since it is sufficient to perform the above control when the amplitude level of the extracted output exceeds a predetermined level, two reference levels, positive and negative, are set, and the amplitude level of the extracted output itself is set to the positive and negative levels. , the above control may be performed when the negative reference level is exceeded.

It goes without saying that the present invention can be modified in various other ways without departing from the spirit thereof.

[Effects of the Invention] As described above, according to the present invention, it is possible to prevent a decrease in the S/N ratio due to a smear phenomenon occurring at the edge portion of a luminance signal by noise removal processing.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a first embodiment of the present invention;
Fig. 2 is a characteristic diagram for explaining the operation of Fig. 1, Fig. 3 is a signal waveform diagram for explaining the operation of Fig. 1, and Fig. 4 shows the configuration of the second embodiment of the present invention. 5 is a characteristic diagram for explaining the operation of FIG. 4, FIG. 6 is a circuit diagram showing the configuration of a third embodiment of the present invention, and FIG. 7 is a diagram of a conventional noise removal device. FIG. 8 is a characteristic diagram for explaining the operation of FIG. 7, and FIG. 9 is a signal waveform diagram for explaining the operation of FIG. 7. 21...Input terminal, 22...HPF, 2B...Delay circuit, 24...Limiter, 25...Switch, 2
6... Subtraction circuit, 27... Output terminal, 28... Absolute value circuit, 29.32... Comparison circuit, 31... Variable gain amplifier circuit, 41... LPF.

Claims (3)

[Claims] (1) Noise signal extraction means for extracting a noise signal from the luminance signal; amplitude limiting means for limiting the amplitude of the extracted output of the noise signal extraction means to the amplitude level of the noise signal; and amplitude limiting means for extracting the noise signal from the luminance signal. The apparatus further comprises a subtracting means for reducing the limited output, and an amplitude reducing means for reducing the amplitude level of the amplitude limited output to be subtracted from the luminance signal when the amplitude level of the extracted output of the noise signal extracting means exceeds a predetermined level. A noise removal device characterized by: (2) The amplitude reducing means is configured to set the amplitude level of the amplitude limiting output to 0 level when the amplitude level of the extracted output of the noise signal extracting means exceeds a predetermined level. The noise removal device according to claim 1. (3) The amplitude reducing means is configured to reduce the amplitude level of the amplitude limiting output in accordance with the increase in the amplitude level of the extracted output when the amplitude level of the extracted output of the noise signal extracting means exceeds a predetermined level. The noise removal device according to claim 1, characterized in that: