JPH02249369A - signal processing circuit - Google Patents

Abstract

PURPOSE:To reduce undesired noise component of a luminance signal and to prevent deterioration in the transient response at a signal change part by outputting a signal change part as it is with a detection signal of the signal change part in which a level change of a luminance signal is large and reducing high frequency noise component in the part other than the signal change part. CONSTITUTION:A 1st means 1 detecting a signal change part in which a level change of a luminance signal and a 2nd means 2 controlled with a detection output of the means 1, outputting the luminance signal of the signal change part as it is and outputting the luminance signal at the part except the signal change part through noise reduction processing are provided to the circuit. The 2nd means 2 reduces the undesired noise component of the input luminance signal normally and when the means 1 detects the signal conversion part of the luminance signal, the noise reduction is stopped to output the signal change part as it is. Thus, the S/N of the luminance signal is improved and the deterioration in the transient response in the signal change part is prevented to improve the picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use] The present invention relates to a video signal processing circuit, and particularly to a signal processing circuit that removes noise components contained in a luminance signal.

[Prior Art] Television equipment such as television receivers is equipped with a noise reduction circuit in order to remove noise components mixed into video signals and reproduce images with a good S/N ratio. There is.

As an example of this, the video noise reduction circuit described in "Television Technology" September 1987 Special Issue All Manufacturers Service Book Denshi Gijutsu Shuppan ■ is configured to be able to control the amount of noise reduction. .

[Problems to be Solved by the Invention] Incidentally, although noise reduction circuits reduce noise components, they also have the property of deteriorating their response characteristics in transient parts where the level of the video signal changes, and the amount of noise reduction If an attempt is made to further improve the S/N by increasing the S/N ratio, the transient response of the video signal will deteriorate more and more.

Conventionally, in noise reduction circuits, the amount of noise reduction can be controlled and the amount of noise reduction is adjusted taking the above points into consideration. However, once the amount of noise reduction is adjusted, it is fixed at that adjustment amount. A noise reduction circuit is used.

For this reason, deterioration of the transient response of the video signal is unavoidable.
Particularly in areas where the level of the video signal changes significantly, such as the contour area of an image (hereinafter referred to as a signal change area), the deterioration of this transient response is significant, resulting in a significant deterioration of image quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal processing circuit that eliminates such problems, effectively reduces unnecessary noise components of m-degree signals, and prevents deterioration of transient response in signal change sections. It's about doing.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a first means for detecting a signal change portion where a change in the level of a luminance signal is large, and a control method based on a detection output of the first means. The signal changing section outputs the luminance signal as it is, and a section other than the signal changing section performs noise reduction processing on the luminance signal and outputs the luminance signal.

[Operation] The second means usually reduces unnecessary noise components of the input luminance signal, but when the first means detects a signal change part of the luminance signal, the noise reduction action stops and the signal Output the changing part as is.

This improves the S/N ratio of the luminance signal and prevents deterioration of the transient response in the seven signal changing sections, thereby significantly improving the image quality.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a signal processing circuit according to the present invention, in which 1 is a differentiation circuit, 2 is a control signal generation circuit, 3 is a waveform shaping circuit, 4 to 6 are resistors, 7 is a diode, 8 is a capacitor, 9 is a control terminal, 10 is a voltage source, and 11 is a noise reduction processing circuit.

Further, FIG. 2 is a waveform diagram showing signals of each part in FIG. 1, and signals corresponding to those in FIG. 1 are given the same symbols.

In FIGS. 1 and 2, the input luminance signal A is supplied to a noise reduction processing circuit 11-, and undesired noise components are removed.

This luminance signal A is also supplied to a differentiating circuit 1, which detects high-frequency noise components and parts where the level changes sharply such as the contour part of the luminance signal A (signal changing part), and detects the noise component and this signal. A signal B consisting of a changing part signal representing a changing part is output.

The level of this changing part signal is sufficiently higher than that of the noise component.

Furthermore, the polarity of the changing part signal included in the signal B is different depending on whether the signal changing part is rising or falling.

The signal B is supplied to the control signal generation circuit 2. In the control signal generation circuit 2, it is amplified by a waveform shaping port N3 consisting of a transistor, a resistor, a capacitor, and a diode, and the signal B is amplified so that all the changing part signals have the same polarity. The waveform is shaped. The output signal C of this waveform shaping circuit 3 is transmitted through resistors 4 to 6. It is supplied to a clip circuit consisting of a diode 7 and a capacitor 8. In this clip circuit,
A voltage from a voltage source 10 is applied to the cathode of the diode 7 after being divided by resistors 4 and 5, so that the portion of the signal C at a level higher than this divided voltage V is applied to the divided voltage ■, clipped to.

Further, the resistor 6 and the capacitor 8 constitute a low-pass filter, which removes unnecessary high-frequency noise components mixed into the signal C.

In this way, a signal is obtained in which the noise component is removed and the reference level is set to v2 and the changing part signal is set to level v4, and this signal is sent as a control signal to the controller of the noise reduction processing circuit 11. - supplied to the roll terminal 9; The noise reduction processing circuit 11 normally performs noise reduction processing on the luminance signal A when the level of the control signal is lower than V, and stops the noise reduction processing when the level of the control signal is higher than V1. luminance signal A
pass through as is.

Therefore, in the luminance signal E output from the noise reduction processing circuit 11, unnecessary noise is sufficiently reduced.
In addition, there is no deterioration in transient response in the signal changing section where the level changes sharply.

Figure 3 shows the noise reduction processing circuit 1 in Figure 1.
1 is a block diagram showing a specific example of No. 1, in which 12 and 13 are switches, and 14 is a noise reduction circuit.

In the same figure, the switches 1, 2, and 13 are controlled by the control signal supplied from the input terminal 9, and close to the b side when the control signal is lower than the level v4 shown in FIG. When , the switches 12 and 13 close to the a side.6 Therefore, as explained earlier, the control signal is lower than the level (1) except for the part where the signal changes to the luminance signal, so the switches 12 and 13 close to the b side. As a result, the luminance signal A is supplied to the noise reduction circuit 14 through the switch 12, the noise is reduced, and the signal is output through the switch 13. Further, in the signal changing portion of the luminance signal A, the control signal 1 has a level equal to or higher than V0, so the switches 12 and 13 are closed to the a side. This results in
The signal changing portion of the luminance signal A is output as is through the switch 1.2.13.

The noise reduction circuit 14 may be of any type. An example of such a circuit is a dynamic noise reduction circuit disclosed in Japanese Patent Application No. 84186/1986, previously filed by the applicant of the present invention. This reduces unnecessary high-frequency noise components by passing the input luminance signal through a low-pass filter, and at the same time passes this input luminance signal through a bypass filter, and processes the output signal with a coring circuit to eliminate this noise component. This method extracts the high-frequency component of a high-level luminance signal and adds this high-frequency component to the luminance signal processed by the low-pass filter, thereby compensating for the high-frequency component of the luminance signal that is lost by the low-pass filter. However, by adjusting the amount of coring according to the level of the luminance signal and reducing the amount of noise reduction in bright areas such as white spots, the luminance signal can be made more noticeable than the S/N deterioration caused by noise components. This improves the deterioration of the frequency characteristics.

According to such a dynamic noise reduction circuit,
In signal changing areas where the luminance signal changes from a low level to a high level, or vice versa, such as the contour area of an image, the degree of improvement in frequency characteristics differs depending on the level, and the transient response is It will deteriorate.

On the other hand, in FIG. 3, such a dynamic noise reduction circuit is connected to the noise reduction circuit 14.
Even when used in the signal changing section, the luminance signal A is output as is through the switches 12 and 13, so the waveform does not change in the signal changing section, and there is no deterioration in transient response.

Note that the switch 12 may be omitted in FIG. 3.

[Effects of the Invention] As explained above, according to the present invention, noise can be sufficiently suppressed, and deterioration of the transient response can be prevented in areas where the level change is large, and the S/N ratio is good and the transient response can be suppressed. A luminance signal without deterioration can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the signal processing circuit according to the present invention, FIG. 2 is a waveform diagram showing signals of each part in FIG. 1, and FIG. 3 is an example of the noise reduction processing circuit in FIG. 1. FIG. 2 is a block diagram illustrating an example. 1...Differential circuit, 2...Control signal generation circuit, 9...Control terminal, 11
...Noise reduction processing circuit.

Claims (1)

[Claims] 1. A signal processing circuit for removing high-frequency noise components contained in a luminance signal, and a first means for detecting a signal change portion in which the input luminance signal has a large level change. and a second means, which is controlled by the detection output signal of the first means, outputs the luminance signal as it is in the signal changing section, and reduces the high frequency noise component contained in the luminance signal outside the signal changing section. A signal processing circuit comprising means. 2. In claim 1, the first means comprises means for extracting a high-frequency component of the luminance signal, and means for detecting a component of the high-frequency component at a higher level than the high-frequency noise component. A signal processing circuit featuring: