JPS60167575A - Noise eliminating circuit of video signal - Google Patents

Abstract

PURPOSE:To eliminate only noise of a video signal without giving deformation to the sudden rise and fall parts and the detail part of the incoming video signal by having the subtraction and mixture of a high frequency component to the video signal as a subtracting signal only in a period when the high frequency component of the video signal is kept within a prescribed level range. CONSTITUTION:The video signals supplied to a terminal 1 are supplied to a mixer 2 and an HPF3. The HPF3 extracts the high band component of the video signal and supplies it to a wind comparator 6 and a switch circuit 7. The comparator 6 has the 1st and 2nd reference voltages V1 and V2 and delivers the control signals of H and L levels when the input voltage is lower than V1 and higher than V2 and set between V1 and V2 respectively. Both V1 and V2 are set at an approximately equal level to the limiter value of a conventional circuit. The circuit 7 delivers the signal given from the HPF3 as it is when the control signal is set at an L level and cuts the signal from the HPF3 when the control signal is set at an H level. Thus the subtracting signal is extracted out of the circuit 7 and supplied to the mixer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal noise removal circuit, and more particularly, to a video signal noise removal circuit that subtracts and mixes noise components of a video signal to obtain a noise-free video signal.

BACKGROUND OF THE INVENTION FIG. 1 shows a block diagram of an example of a conventional video signal noise removal circuit. In the figure, Figure 2 (
Noise component A+ as shown in A).

A2. The original video signal including A3 is supplied to a mixer 2 and a high-pass filter 3. The high-pass filter 3 extracts the high-frequency component of the video signal and generates a signal as shown in FIG. The mixer 2 subtracts and mixes the signal from the limiter 4 with the video signal to produce the result shown in FIG. 2(D).
A video signal from which noise has been removed is extracted and output as shown in FIG.

Problems to be Solved by the Invention The conventional circuit described above deforms the sharp rising portions B+, B2, Ba and the falling portions C+, C2, C3 of the original signal, as shown in FIG. 2(D).

In addition, the part with high frequency and small amplitude (larger amplitude than the noise component) in Figure 2 (A>), which corresponds to the details of the image (hereinafter referred to as "
D+ is part D in Figure 2 (D)
It is deformed as shown in 2. In this way, Figure 2 (A
), which causes problems such as the resulting image being distorted because part of the original signal is lost.

Means for Solving the Problems The present invention provides a filter circuit that extracts the high frequency components of an incoming video signal, a circuit that extracts the high frequency components as a subtraction signal only during a period when the level of the high frequency components is within a predetermined range, and a filter circuit that extracts the high frequency components of an incoming video signal. The above problem is solved by comprising a mixer that subtracts and mixes a subtraction signal with the signal and outputs a video signal from which noise components have been removed. I will explain about it.

Embodiment FIG. 3 does not show a block diagram of the first embodiment of the circuit of the present invention. In the figure, the same parts as in FIG. 1 are given the same reference numerals. In FIG. 3, a video signal as shown in FIG. 2(A) is input to a terminal 1, and this video signal is supplied to a mixer 2 and a high-pass filter 3.

The high-pass filter 3 extracts high-frequency components from the video signal to generate a signal as shown in FIG. 2(B), and supplies this signal to the window comparator 6 and the switch circuit 7.

The window comparator 6 has a first reference voltage V1 and a second reference voltage V2, and as shown in FIG. It outputs a control signal that becomes a torque level when the voltage is from the reference voltage 1 to V2. Each of the reference voltages V+ and V2 is set to approximately the same level as the limiter level in the limiter 4 of the conventional circuit.

Therefore, when the window comparator 6 is supplied with the signal shown in FIG. 2(B), it generates the control signal shown in FIG. 2(E), and supplies this to the switch circuit 7.

The switch circuit 7 is closed when the control signal is at a torque level and outputs the signal from the high-pass filter 3 as it is, and is opened when the control signal is at a torque level to cut off the signal from the high-pass filter 3. As a result, from the switch circuit 7, as shown in FIG.
A signal for subtraction as shown in FIG. The mixer 2 subtracts and mixes the video signal shown in FIG. 2(A) with the signal shown in FIG. 2(F) to produce the signal shown in FIG.
A video signal as shown in G) is output from the terminal 8.

In this way, the video signal of FIG. 2(G) output from the terminal 8 has noise components A+, A2, Aa, etc. removed. Also, the sharp rising and falling portions of the original signal B1-83. Each of C1 to C03 is not deformed, and the detail portion D+ is also hardly deformed. Therefore, an image without distortion can be obtained.

FIG. 5 shows a block diagram of a second embodiment of the circuit of the present invention. In the figure, the same parts as in FIG. 3 are given the same reference numerals, and their explanations will be omitted. In FIG. 5, the signal shown in FIG. 2(B) output from the high-pass filter 3 is supplied to a limiter 9 and a mixer 10 in addition to the switch circuit 7. limiter 9
band-limits the incoming signal to produce a signal as shown in FIG. 2(C) and supplies this to the mixer 10. The mixer 10 subtracts and mixes the signal from the limiter 9 with the signal from the high-pass filter 3, and outputs a signal as shown in FIG. 2(H). This signal is rectified by a rectifier 11 as shown in FIG. 2(1) and then supplied to a comparator 12, where it is compared with a predetermined reference level to obtain a control signal as shown in FIG. 2(E). It will be done.

5- As a result, the same video signal as shown in FIG. 2(G) is taken out from the mixer 2.

Limiter 9 in FIG. Mixer 10. The rectifier 11 and the comparator 12 constitute the same function as the window comparator 6 shown in the third figure. Therefore, similarly to the circuit shown in FIG. 3, it is possible to remove noise components and obtain a video signal in which the original signal is hardly modified, thereby obtaining a distortion-free image.

Effects As mentioned above, the video signal noise removal circuit according to the present invention has the following effects:
A filter circuit extracts the high frequency component of an incoming video signal, a circuit extracts the high frequency component as a subtraction signal only during a period when the level of the high frequency component is within a predetermined range, and a noise component is obtained by subtracting and mixing the subtraction signal with the video signal. Since it consists of a mixer that outputs a video signal that has been removed, it is possible to remove only the noise without distorting the sharp rises, falls, and detailed parts of the incoming video signal, thereby obtaining an image without distortion. 6- It has the following features:

[Brief explanation of the drawing]

Figure 1 is a block system diagram of an example of a conventional circuit, and Figure 2 (A
) to (I) are signal waveform diagrams of each part of the circuit shown in FIGS. 1, 3, and 5, respectively. FIGS. FIG. 4 is a characteristic diagram of a part of the circuit shown in FIG. 1.8...terminal, 2.10...mixer, 3...high-pass filter, 6...window comparator, 7...
Switch circuit, 9... limiter, 11... rectifier,
12...Comparator. 7- D Knee, I ν,.

Claims (1)

[Claims] a filter circuit that extracts a high frequency component of an incoming video signal; a circuit that extracts the high frequency component as a subtraction signal only during a period when the level of the high frequency component is within a predetermined range; and subtractive mixing of the subtraction signal to the video signal. 1. A video signal noise removal circuit comprising: a mixer for outputting a video signal from which noise components have been removed.