JPH04117874A - Video signal processing unit - Google Patents

Abstract

PURPOSE:To make the visual S/N compatible with the preservation of detailed video information with well balance for portions in which a high level of a video signal not relatively eminent in noise and a low level of the video signal eminent in noise by varying the level of a high frequency small amplitude component to be eliminated from an original signal in response to a level of a low frequency component of the video signal. CONSTITUTION:A high frequency component YH of a luminance signal being the output of a high pass filter 2 is multiplied with a coefficient at an analog multiplier 3, the amplitude is limited to a prescribed limit level or below thereby obtaining a luminance signal high frequency component small amplitude component YN including much noise component. Then the output signal of the limiter 4 is divided by a coefficient at an analog divider 5. Thus, an output signal from which noise is reduced is obtained. Since the noise reduction is varied by applying amplification and attenuation to a pre-stage and a post-stage of the limiter at a variable gain, the limit level of the noise reduction device is made variable without use of a complicated circuit configuration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal processing device used in equipment that handles video signals, such as video tape recorders and video discs.

[Conventional technology]

FIG. 3 is a block diagram of an example of a conventional noise reduction device used in a magnetic recording/reproducing device.

In the figure, 1 is an input terminal, 2 is a bypass filter, 30
3 is an amplifier, 4 is a limiter-1305 is a polarity inverter, 3
06 is an attenuator, and 9 is an adder.

A conventional noise reduction device is configured as shown in the figure, and is used, for example, in a reproduction signal processing circuit of a VTR.

Next, its operation will be explained.

The reproduced luminance signal input to the device is passed through a high-pass filter 2.
The high frequency components are separated. High pass filter 2
After the first high frequency component which is the output of is amplified by the amplifier 303, the signal amplitude is limited by the limiter 4 to below a predetermined limiting level.

Since the noise in the flat portion of the image that is visually noticeable is concentrated in the small amplitude component of the high frequency component, most of the output signal of the limiter 4 is a noise component.

The polarity of the output of the limiter 4 is inverted by a polarity inverter 305, the output signal is adjusted to an appropriate level by an attenuator 306, and the output noise/gancel signal is added to the video signal by an adder 9. Ru.

Here, since the polarity of the high-frequency minute amplitude component added to the video signal is inverted by the polarity inverter 305, the high-frequency minute amplitude component with many noise components is subtracted from the original video signal. This will reduce noise in the video signal.

Since the conventional noise reduction device is configured as described above, there is a problem in that a signal representing a minute part of an image included in a high-frequency minute amplitude signal is also removed at the same time as noise.

That is, is it desirable to limit the amount of noise reduction within a range where the noise is not visually noticeable?The amount of noise reduction in conventional noise reduction devices is determined by the setting of the limiting level of the limiter 4 or the amount of attenuation of the attenuator. Therefore, it was not possible to adaptively change the amount of noise reduction depending on the state of the video signal.

An example of a video signal processing device that solves the above-mentioned problems is a noise reduction circuit disclosed in Japanese Patent Laid-Open No. 1-204573 '4'Ei. Figure 4 is its configuration diagram,
The operation will be described below.

In this noise reduction circuit, a luminance signal forming a video signal supplied to an input terminal 401 is supplied to one input terminal of a subtraction unit 403 via a delay unit 402, and
High pass filter 404 and luminance signal level detection section 40
7 is also supplied.

The luminance signal level detection section 407 detects the average level of the luminance signal, and a level detection output signal representing this average level is supplied to the level control signal detection section 408. The level control signal detection unit 408 generates a limit level control signal C+ and a gain control signal C, according to the level detection output signal.
3 and sends them to the control end of the variable level limiter 405 and the control end of the level adjustment section 406 to adjust the limit level of the variable limiter 405 and the level adjustment section 40.
6 is changed in accordance with the level detection output signal.

A high-frequency component including a noise component is derived from the luminance signal supplied to the high-pass filter, and the high-frequency component is supplied to the variable limiter.

For example, as shown in FIG. 5, the variable level limiter connects a capacitor 5 to an input terminal 501 to which high-frequency components are supplied.
02. The output terminal is connected through a series connection of a resistor 503, and a diode 506 and a diode 5 whose cathodes are disposed on the output terminal side between the output terminal and the installation potential point.
A variable voltage source 508 that applies a negative bias voltage to the anode of 06 is connected in series, and a diode 507 whose anode is disposed on the output terminal side;
a variable voltage source 50 that provides a positive bias voltage to the cathode of
9 are connected in series. When a high frequency component is supplied to the input terminal 501, the variable voltage sources 508 and 509 limit the variable level limiter 405 by the negative and positive bias voltages supplied according to the limit level control signal CL from the level control signal detection section 408. The variable limiter 405 sets a level, and a high frequency component passes within a pass level width determined by the level, and a signal mainly consisting of a noise component whose relative level is relatively small among the high frequency components is output to the variable limiter 405.
This signal is used as a noise reduction signal. This noise reduction signal is supplied to the level adjustment section 406, and then in the subtraction section 403, the delay section 402
The noise reduction signal is subtracted from the time-aligned input luminance signal and output to the output terminal.

[Problem to be solved by the invention]

Conventional noise reduction circuits are configured as described above, and the limit level of the variable level limiter section and the gain of the level adjustment section can be changed according to the average level of the luminance signal, or the bias voltage can be changed by the level control signal. Therefore, it is difficult to appropriately adjust the limit width of the high frequency component, and the circuit configuration becomes complicated.

This invention was made to solve the above problems, and provides a video signal processing device that can adaptively change the amount of noise reduction depending on the state of the video signal with a simpler circuit configuration. The purpose is to

[Means to solve the problem]

A video signal processing device according to the present invention includes: a high-pass filter that extracts high-frequency components including noise components of a video signal; and variable gain amplification means that amplifies the output signal of the high-pass filter and whose amplification gain is variable. amplitude limiting means for limiting the amplification of the output signal of the variable gain amplifying means to a predetermined amplitude or less and outputting a minute amplitude component of the high frequency component containing many noise components; and attenuating the output of the amplitude limiting means. and a variable gain attenuation means whose attenuation gain is variable;
a calculation means for calculating the video signal and the output signal of the variable gain attenuation means to obtain a video signal with reduced noise; a low-pass filter for extracting a low frequency component of the video signal;
The structure includes gain control means for controlling the amplification gain of the variable gain amplification means and the attenuation gain of the variable gain attenuation means in accordance with the output signal of the low-pass filter.

[Effect]

The video signal processing device according to the present invention has a variable gain at the front and rear stages of the amplitude limiting means at a constant limiting level for extracting minute amplitude components containing a large amount of noise components from the high-frequency components including noise of the video signal extracted by the high-pass filter. Since the amplification means and the variable gain attenuation means are arranged, and the gain of each is controlled according to the reduction component of the signal extracted by the low-pass filter, it is possible to determine whether the level of the low-frequency component of the video signal is large (or small). When , the gain of the variable gain amplification means and the attenuation means becomes large (or small), and the larger (or smaller) this gain is, the smaller (or larger) the amplitude of the signal is subject to amplitude limitation. Therefore, the amount of noise reduction can be changed adaptively to the video signal level, and it is possible to maintain both the fine information of the video signal and the signal sequence noise ratio.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a video signal processing device according to an embodiment of the present invention, in which 1 indicates a luminance signal Y constituting the video signal;
2 is the input terminal to which the luminance signal is inputted, and 2 is the high frequency component Y of the luminance signal.
, 3 is an analog multiplier that multiplies the voltages of the signals applied to the two input terminals A and B, and outputs the resulting voltage signal to the output terminal C. The output signal of high-pass filter 2 is input. 4 is a limiter that limits the amplitude of the output signal of the analog multiplier 3 to below a predetermined limiting level; 5 is a limiter 2;
D is an analog divider that divides the voltage of the signal applied to the two input terminals and the two input terminals of E by the voltage applied to the input terminal E, and outputs the resulting voltage signal to F. The output signal of limiter 4 is also input. 6 is a low-pass filter that extracts the low-frequency component YL of the luminance signal; 7 is a gain control circuit for the input terminal B of the analog multiplier 3 and the input terminal E of the analog divider 5, respectively, according to the output signal of the low-pass filter 7; a gain control signal generator outputting signals K(YL') and 2(YL);
8 is a delay device that delays the luminance signal for a predetermined time; 9 is a subtracter that subtracts the output of the analog divider 5 from the output signal of the delay device 8 to obtain a noise-reduced luminance signal; 10 is a noise-reduced luminance signal; This is an output terminal that outputs a brightness signal.

Next, the operation of this embodiment will be explained.

The luminance signal input from input terminal 1 is passed through high-pass filter 2. The signals are supplied to a low-pass filter 6 and a delay device 8, respectively. The reduced component Y of the luminance signal, which is the output of the low-pass filter 6, represents the average level of the luminance signal. , , (YL) are output.

Figure 2 is an example of the relationship between YL, (Y,,), and K2 (YL), where K, (Y,), and 2 (YL) are linear functions, and for simplicity, (YL) The slope of 2 (Y,) is the same setting.

Furthermore, the high-frequency component Y of the luminance signal output from the high-pass filter 2 is applied to the gain control signal output from the gain control signal generator 7 by the analog multiplier 3 (YL
) is multiplied by Therefore, the output signal of the analog multiplier 3 becomes (YL).Yll, and the larger K and (Y,) are, the more the signal is expanded in the amplitude direction.

Next, the output signal of the analog multiplier 3 is amplitude-limited to a predetermined limiting level or less by a limiter 4 to obtain a luminance signal high frequency component minute amplitude component YN containing many noise components. Next, the output signal of the limiter 4 is divided by the gain control signal outputted from the gain control signal generator 7 by 2 (YL) by the analog divider 5, and the amplitude expanded by the analog multiplier 3 is compressed. Here,
(Yt) - 2 (YL), so analog multiplier 3
To the output signal of (Y,) ・Limiter 4 of Y8
The amplitude of the component whose amplitude is below the limiting level is the brightness signal high-frequency component Y11 extracted by the high-pass filter 2.
By subtracting this in the subtracter 9 from the luminance signal time-adjusted by the delay device 8, an output signal with reduced noise can be obtained.

Here, the limit ink level of the limiter 4 is fixed, so the larger the gain control signal ■<, (Y,) output from the gain control signal generator, the more
The high-frequency component of the luminance signal output from the high-pass filter 2 is subject to amplitude restriction by the transmitter 4 in large numbers. In other words, the higher the level of the low-frequency component YL of the luminance signal, the more the high-frequency component Y of the luminance signal is amplified, and the more parts are subject to amplitude restriction.In other words, only small amplitude signals pass through the limiter 4. , after being attenuated by the analog multiplier 5, it is subtracted and removed as noise from the original luminance signal. In other words, when the level of the average video signal is high and the signal-to-noise ratio is relatively high, the amplification gain of the variable gain amplification means becomes large, and therefore only a signal with a small amplitude is generated in terms of the high-frequency components. After being subject to amplitude limitation and attenuated at a large attenuation rate by the variable gain attenuation means, the high-frequency minute amplitude component subtracted from the original video signal becomes only a very minute amplitude component, and the minute information of the video signal is is well preserved.

On the other hand, when the level of the luminance signal low-frequency component Yt is low, the amplification amount of the luminance signal high-frequency component Yo is small, and there are few portions that are subject to amplitude limitations. Since the signal passes through the signal, even components with relatively large amplitudes among the high-frequency components of the original luminance signal are removed. In other words, when the average video signal level is small and the signal-to-noise ratio is relatively small, the amplification gain of the variable gain amplification means is small, and therefore the amplitude of the signal is small in terms of the high-frequency components. The high-frequency minute amplitude components that are subject to the restriction and are subtracted from the original video signal after being attenuated at a small attenuation rate by the variable gain attenuation means include those with relatively large amplitudes, and the noise reduction effect is large. Become.

As described above, in this embodiment, instead of sending a variable control signal to the limiter itself, the variable control signal is controlled by the low-frequency component before and after the limiter that limits the high-frequency component extracted from the luminance signal to a certain level. By amplifying and attenuating with gain,
Since the amount of noise reduction to be removed is changed, the limit amount of the noise reduction device can be made variable without using a complicated circuit configuration.

In the above embodiment, the amplification gain of the variable gain amplification means and the attenuation gain of the variable gain attenuation means have a linear relationship with respect to the level of the low frequency component of the video signal, but the present invention is not limited to this.

Furthermore, although the above embodiments are constructed using analog circuits, a part or all of them may be constructed using digital circuits.

〔Effect of the invention〕

As described above, according to the video signal processing device according to the present invention, the amplitude level of the high-frequency minute amplitude component to be removed from the original signal is made variable according to the level of the low-frequency component of the video signal. With this configuration, the amount of noise reduction can be effectively changed according to the level of the video signal, and the visual S/N ratio can be improved between high-level parts of the video signal where noise is relatively less noticeable and low-level parts where noise is more noticeable. The effect is that it is possible to achieve a good balance between image information and the retention of fine image information.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure is a diagram showing the input/output characteristics of the gain control signal generation circuit used in the embodiment shown in Fig. 1, Fig. 3 is a block diagram showing a conventional video signal processing device, and Fig. 4 is a conventional noise reduction method. FIG. 5, a block diagram showing a circuit, is a diagram showing a configuration example of a variable limiter ink level limiter of the conventional noise reduction circuit shown in FIG. 4. In the figure, ■ is an input terminal, 2 is a high-pass filter, and 3 is a high-pass filter.
4 is an analog multiplier, 4 is a limiter, 5 is an analog divider, 6 is a low-pass filter, 7 is a gain control signal generator, 8 is a delay device, 9 is a subtracter, and 10 is an output terminal. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A high-pass filter that extracts high-frequency components including noise components of a video signal, variable gain amplification means that amplifies the output signal of the high-pass filter and whose amplification gain is variable, and an output of the variable gain amplification means. amplitude limiting means for limiting the amplitude to a predetermined amplitude or less and outputting a minute amplitude component of the high frequency component containing many noise components; and an amplitude limiting means for attenuating the output signal of the amplitude limiting means and having a variable attenuation gain. a variable gain attenuation means;
a calculation means for calculating the video signal and the output signal of the variable gain attenuation means to obtain a video signal with reduced noise; a low-pass filter for extracting a low-frequency component of the video signal; A video signal processing device comprising gain control means for controlling the amplification gain of the variable gain amplification means and the attenuation gain of the variable gain attenuation means accordingly.