JPS62130075A - Noise cancel circuit for video signal - Google Patents

Abstract

PURPOSE:To improve the S/N of a video signal deteriorated due to the decrease of the quantity of light in photographing by varying the quantity of noise cancel by a variable attenuator in which the frequency characteristic of the quantity of attenuation is controlled in accordance with the quantity of light in an image picking-up of an input video signal. CONSTITUTION:The video signal Y is supplied from an input terminal 10A to a delay circuit 11 and the first and the second signal subtractors 12, 15. A limiter 13 forms a noise cancel signal only by a noise component. The variable attenuator 14 controls the signal level of the noise cancel signal and changes the quantity of the noise cancel. Namely, by the detecting output of the signal level according to the quantity of light in the image picking-up supplied from a detecting circuit 7 to a control input terminal 10B, the frequency characteristic of the quantity of attenuation is controlled. The attenuator 14 has a switching transistor and is switching controlled by the detecting output from the detecting circuit 7. The attenuator 14 is turned on by the detecting output of the video signal to an object of a prescribed quantity of light in the image picking-up and turned off by the detecting output of the video signal of the object below the prescribed quantity of light in the image picking-up.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise canceling circuit for a video signal obtained as an imaging output of a video camera, for example, and in particular to a noise canceling circuit for a video signal that deteriorates due to a decrease in the amount of shooting light. This invention relates to an improved noise canceling circuit.

(Summary of the Invention) The present invention provides a noise canceling circuit for a video signal obtained as an imaging output of a video camera, in which the amount of noise cancellation is controlled by a variable attenuator whose frequency characteristics of the amount of attenuation are controlled according to the amount of imaging light of the input video signal. By varying the S of the video signal, which deteriorates due to a decrease in the amount of shooting light
/ I am trying to improve N.

[Conventional technology]

Conventionally, in video cameras, video tape recorders, etc., image quality has been improved by so-called aperture correction, and noise canceling circuits using so-called C-type filters that utilize the vertical correlation of images have been used to superimpose noise on video signals. The noise component level was suppressed and the S/N ratio was improved to provide a video signal with good image quality.

Furthermore, it is generally known that the signal level of a video signal obtained by photographing a subject with a video camera decreases when the amount of imaging light, that is, the illuminance of the subject decreases, and the S/N deteriorates.

[Problem that the invention attempts to solve]

By the way, with conventional video cameras, if aperture correction is performed during low-light shooting, noise components that increase relative to the video signal will be emphasized, so the amount of aperture correction may be reduced to maintain a certain level of Although we tried to suppress only frequency noise components, there was no countermeasure against low frequency noise, and especially when a vertical aperture correction function was installed, uncorrelated horizontal noise could be suppressed. The problem was that it was emphasized.

In addition, conventional noise canceling circuits that utilize the vertical correlation of images are effective only for video signals of image parts that have vertical correlation, and cancel noise for image parts that do not have vertical correlation. There is a problem in that the processing reduces the vertical (W) image resolution.

Therefore, in view of the above-mentioned conventional problems, the present invention has been developed to perform low-light photography without reducing the vertical resolution by noise canceling processing for image quality obtained by photographing a subject with an appropriate amount of imaging light. An object of the present invention is to provide a noise canceling circuit for a video signal having a novel configuration that can reliably improve the S/N ratio of the video signal, which sometimes deteriorates due to a decrease in the amount of photographing light.

[Means for solving problems]

In order to solve the above-mentioned problems, the noise canceling circuit according to the present invention includes a delay means for giving a delay amount corresponding to one horizontal line to a human-powered video signal, and a noise canceling circuit that provides a delay between the input video signal and the delay means. a first signal subtracter to which the video signal is supplied; a limiter to which the subtracted output signal from the first signal subtracter is supplied; A controlled variable attenuator is supplied with the human video signal, and a subtracted output signal from the first signal subtracter is supplied through the limiter and the attenuator, and the respective signals are subtracted and synthesized. and a second signal subtracter that outputs a video signal with noise components canceled.

[Effect]

The image signal noise canceling circuit according to the present invention performs noise cancellation with a large amount of noise cancellation over the entire frequency band when imaging an object with a small amount of imaging light, and cancels the noise with a large amount of noise cancellation over the entire frequency band, During imaging, noise cancellation is performed by suppressing the amount of noise cancellation for high frequency bands.

[Example] Hereinafter, an example of the present invention will be described in detail according to the drawings.
I will explain to you.

The embodiment shown in the block diagram of FIG. 1 is an example in which the present invention is applied to a camera-integrated video tape recorder such as a so-called 8 mm video tape recorder.

In this embodiment, imaging light from a subject (not shown) passes through an aperture 2 from an imaging lens 1 and is irradiated onto a solid-state image sensor 3 such as a CCD.
A subject image is formed on the imaging surface of the camera.

The solid-state image sensor 3 converts the subject image into a video signal with a signal level corresponding to the amount of imaging light and transmits the signal to a preamplifier 4.
Output via.

The output of the two-leg preamplifier 4 and the video signal 2 obtained by the solid-state image sensor 3 are supplied to first and second detection circuits 5 and 7 and a first AGC amplifier 8. ing.

The first detection circuit 5 detects the video signal to form a detection output with a signal level corresponding to the amount of imaging light, and supplies this detection output to the aperture drive unit 6. and,
The diaphragm driving section 6 drives the diaphragm 3 to open and close in accordance with the detection output of the first detection circuit 5, ie, the amount of imaging light. Thereby, the aperture 2 is automatically controlled to an appropriate aperture amount according to the amount of imaging light.

Further, the second detection circuit 7 detects the video signal to form a detection output having a signal level corresponding to the amount of imaging light, and converts this detection output into a variable attenuator constituting a noise canceling circuit 10, which will be described later. 14 control input terminals 10B.

Further, the first AGC amplifier 8 amplifies the video signal supplied from the solid-state image sensor 3 via the preamplifier 4 to an appropriate signal level and supplies it to an electronic viewfinder (EVF) 19. , second AGC
The signal is supplied to an input terminal 10A of a noise canceling circuit 10 via an amplifier 9. Note that the second AGC amplification'
59 is the television channel 1 from an external input terminal (not shown).
-Various video signals such as output signals are supplied, and it is provided to amplify these video signals to an appropriate signal level.

The noise canceling circuit 10 includes a delay circuit I
L first and second signal subtractor 12゜15, limiter 1
3 and a variable attenuator 14, and the video signal is supplied from the input terminal 10A to the delay circuit 11 and the first and second signal subtracters 12 and 15.

The delay circuit 11 operates during the scanning period I 11 of one horizontal line.
, and gives a delay amount of IH to the input video signal Y supplied from the input terminal 10A. Then, the first signal subtracter 12 inputs the input video signal Y supplied to the input terminal 10A and the input terminal ! Each time the video signal Yo of one horizontal line before is subtracted and synthesized from the OA via the delay circuit 11, a signal component having no vertical correlation is extracted as the subtraction output. Here, the subtracted output signal from the first signal synthesizer 12 is obtained by extracting uncorrelated noise components for each IH, if there is vertical correlation in the image shown by the input video signal Y. becomes.

The subtracted output signal of the first signal subtractor 12 is supplied to the second signal subtractor 15 as a noise cancellation signal via the limiter 13 and the variable attenuator 14. The limiter 13 transmits a predetermined signal so that noise components below a predetermined signal level pass through as is, and noise cancellation is not performed on a portion of the image shown by the input video signal Y that has no vertical correlation. By suppressing the subtracted output signal above the level, a noise cancellation signal is formed using only noise components. Further, the variable attenuator 14 is for controlling the signal level of the noise canceling signal to change the amount of noise canceling, and has a control input terminal 10B connected to the second detection circuit 7.
The frequency characteristics of the attenuation amount are controlled by the detection output of the signal level corresponding to the amount of imaging light supplied from the sensor.

For example, as shown in FIG. 2, the variable attenuator 14 may include first and second resistors Ra and Rh connected in series between the input terminal and the ground, and an output terminal provided at the midpoint A of the connection. In addition, a circuit configuration in which a switching transistor Q, a third resistor Re, and a capacitor C are connected in series between the connection midpoint A and the ground is used.

Here, the switching transistor Q is switching-controlled by the detection output from the second detection circuit 7, and is turned on by the detection output of the video signal for a subject with a predetermined amount of imaging light, and is turned on by the detection output of a video signal for a subject with a predetermined amount of imaging light. It is turned off by the detection output of the video signal 3.

The variable attenuator 10 shown in FIG. 2 has Ka = determined by the ratio of the first and second resistors Ra and Rb when the switching transistor Q is off.
Attenuation ratio Ka that is constant over the entire frequency band of Ra /Rb
is applied to the noise cancellation signal supplied to the input terminal. 1. The damping ratio Ka is set to, for example, 0.5 of Ra-=Rb. Furthermore, when the switching transistor Q is on, a series circuit of the third resistor Rc and the capacitor C is connected in parallel to the second resistor Rh.
Attenuation JKb expressed by the ratio Rb // (Rh -1-1/jωC) is applied to the noise canceling signal supplied to the input terminal. The attenuation ratio Kb of the variable attenuator 10 is equal to the attenuation ratio Ka when the switching transistor Q is off in a low frequency band, and exhibits a frequency characteristic of about 0.13 in a high frequency band of, for example, 500 KTTz or more. , the values of the resistors Ra, Rh, Rc and the capacitor C are set.

In this way, the second signal subtracter 15 to which the noise canceling signal K (Y-Yo) is supplied via the variable attenuator 14 whose frequency characteristic of the attenuation ratio is controlled according to the amount of imaging light is The noise cancellation signal K (Y-Y
A video signal 'y'out of Yout=Y-K (Y-Yo), in which the noise component is canceled by subtracting 0), is output from the output terminal 10C.

Then, the output terminal 1 of the noise cancellation circuit 10 is
The video signal YouL output from 0C is supplied to the FM modulation circuit 16 and is sent to the magnetic tape 18 by the recording head 17.
recorded in

In the embodiment with the above-described configuration, when the solid-state image sensor 3 is irradiated with imaging light of a predetermined amount or more and a good image quality with a good S/N ratio is obtained, as shown by the solid line in FIG. By performing noise cancellation that suppresses the amount of noise cancellation in the high frequency band, a decrease in vertical resolution is prevented and a high quality video signal Yout is obtained, and the magnetic tape 1 is
8 can be recorded. In addition, when the amount of imaging light irradiated to the solid-state image sensor 3 is small and it is not possible to obtain an imaging output with a good S/N ratio, the amount of noise cancellation is large over the entire frequency band, as shown by the broken line in FIG. By performing noise cancellation that suppresses the vertical correlation, it is possible to cancel noise components having no vertical correlation, obtain a video signal Yout with good image quality, and record it on the magnetic tape 18.

Note that the video signal supplied to the electronic viewfinder 19 does not pass through the noise canceling circuit 10, so there is no deterioration in frequency characteristics due to noise canceling processing, so the electronic viewfinder 19 can focus the image signal. Convenient for making adjustments.

〔Effect of the invention〕

” As is clear from the description of the two series of embodiments, the video signal noise canceling circuit according to the present invention cancels noise with a large noise canceling amount over the entire frequency band when imaging a subject with a small amount of imaging light. When an object is imaged with an appropriate amount of imaging light, noise cancellation is performed by suppressing the amount of noise cancellation for high frequency bands. On the other hand, the noise canceling process reduces the vertical (1" image resolution), and it is possible to reliably improve the S/N of the video signal, which deteriorates due to the decrease in the amount of photographing light during low-light photography.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of a video signal noise canceling circuit according to the present invention, FIG. 2 is a circuit diagram showing a specific configuration example of the variable attenuator in the above embodiment, and FIG. The figure is an operational characteristic diagram showing the operation of the above embodiment. 3...Solid image sensor 7...Detection circuit 10...Noise cancellation circuit 11...l H delay circuit 12.15...Signal subtractor 13...Limiter 14...Variable attenuator

Claims (1)

[Scope of Claims] Delay means for giving an input video signal a delay amount corresponding to one horizontal line; and a first signal subtracter to which the input video signal and the video signal delayed by the delay means are supplied. , a limiter to which the subtraction output signal from the first signal subtracter is supplied; a variable attenuator to which the frequency characteristic of attenuation is controlled according to the imaging light amount of the input video signal; and a variable attenuator to which the input video signal is supplied. At the same time, the subtracted output signal from the first signal subtracter is supplied through the limiter and the attenuator, and the second signal subtractor outputs a video signal with noise components canceled by subtracting and synthesizing the respective signals. A noise canceling circuit for a video signal, comprising a signal subtracter.