JPS63120576A - Video signal processing circuit for video camera or the like - Google Patents

Abstract

PURPOSE:To prevent degrading of S/N because of mixing noise from a chrominance signal system into the illuminance signal of a composite color television signal by adding a base noise clipping circuit to eliminate low-level chrominance signals to the circuit of the chrominance signal system. CONSTITUTION:In the base noise clipping circuit 7, a carrier chrominance signal is amplitude-amplified by an amplifier 9a, and by a limiter circuit 9 in the following stage, only such signal components, for instance, as equal to or lower than a slicing level Th are extracted. In thus extracted low level signals, noise components are included together with chrominance signal components. These low-level components are phase-inverted by an inverter circuit 9c in the following stage, then attenuated to a suitable level by an attenuator R2, and supplied to an adding circuit 9d. In such a manner, the low-level components are eliminated from the carrier chrominance signal supplied to the adding circuit 9d and a new carrier chrominance signal is thus formed. Accordingly, this signal is synthesized with the illuminance signal components by an adding circuit 10. As a result, the S/N of an illuminance signal can be upgraded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a video signal processing circuit for forming a composite color television signal output from a video camera, etc. The present invention relates to a video signal processing circuit in a video camera or the like that can reduce the influence of noise.

[Summary of the invention]

The video signal processing circuit in the video camera, etc. of the present invention includes:
When combining the luminance signal obtained from the imaging means and the color signal to form a composite color television signal, the color signal is converted into, for example, a carrier color signal and then passed through a small signal limiter circuit and an inverter circuit. The configuration is such that minute level noise components are removed and combined with the luminance signal. Therefore, the image quality is improved by preventing the noise components mixed in the color signal from being mixed in as high-frequency noise in the luminance signal.

[Conventional technology]

FIG. 4 is a block diagram showing an outline of a general video camera, in which 10 is an imaging means consisting of an optical system 10A, an exposure device 10B, an imaging device 10C, etc., and 11 is a color image of a subject obtained from the imaging means 1O. Increase signal (R-G-B) 4
12 is a Y process circuit that extracts a luminance signal from the signal component obtained from the matrix circuit and performs various signal processing; 13 is a Y process circuit that adds a synchronization signal etc. to the luminance signal and generates a predetermined signal. 14 is a chroma process circuit that modulates the color signal component output from the matrix circuit 11 with a color subcarrier frequency to form a carrier color signal; 15 is a chroma process circuit that modulates the color signal component output from the matrix circuit 11 with a color subcarrier frequency; This figure shows a chroma encoder that sets and outputs a frequency band and level, and by adding the Y encoder output and the chroma encoder output in a synthesis circuit 16, a composite color television signal can be obtained.

In a composite color television signal (hereinafter simply referred to as a color video signal) output from a video camera, noise mixed in the luminance system is important in evaluating the image quality of the color television signal, especially in low luminance parts. There is a need to suppress noise components present in

Therefore, as a method to improve the minimum subject illuminance, a complementary color filter is adopted, and a method of improving the S/N ratio of the luminance signal (the S/N of chroma decreases) is used.
As shown in the figure, the luminance signal component is passed through the bypass filter 21.
A noise component (leakage carrier component) of a high signal component is extracted via an amplifier 22, and this extracted noise component is passed through a limiter circuit 23 as a noise component below a predetermined level, and then inverted by an inverter circuit 24. and,
After returning this noise component to its original level, the adder circuit 2
5, and the noise on the high frequency side of the luminance signal component is canceled and output. (Jikko Sho 47
-1063 Publication) [Problems to be Solved by the Invention] Such a maze canceller is well known in video signal processing devices of playback devices, and is effective in improving the S/N ratio of luminance signals. In the case of a video camera, there is a particular problem in that noise contained in the color signal component degrades the S/N ratio of the luminance signal.

In other words, the frequency distribution characteristics of a color video signal output from a video camera etc. are determined by the luminance signal Y as shown in FIG.
On the other hand, a carrier color signal C modulated at a color subcarrier frequency of 3.58M H7 is superimposed on the high frequency side.
When this carrier color signal C contains noise N, the S/N ratio of the signal component on the high frequency side of the luminance signal deteriorates. This is because the noise components generated in the color signal system have no interleaving relationship with the luminance signal.

Therefore, it is necessary to suppress the chroma-based noise component by a color signal-based circuit, and it is also necessary to provide a noise canceler in the chroma-based signal circuit. However, the carrier color signal is at most 0.5M centered around 3.58MH7.
Since the noise is within the H2 band, it becomes difficult to extract and suppress only the noise components consisting of high frequency components using the noise canceller method shown in FIG.

In addition, by utilizing the line correlation of color signals, for example, a comb-shaped filter consisting of an IH delay line, etc., can be used to
A method to improve the /N ratio can be considered, but in this case, a phase lag of IH (one horizontal period) will occur in the color signal component, so it is necessary to provide an IH delay circuit in the luminance signal system, and the circuit design will be difficult. There are problems in that it becomes difficult and increases costs.

[Means for solving problems]

The present invention has been made in view of these problems.
A base noise clipping circuit that removes low-level color signals is added to the color signal system circuit, and color signal noise is mixed into the luminance signal of the composite color television signal, causing S
/N is easily prevented from deteriorating.

[Effect]

If a base noise clipping circuit that removes minute level color signal components is installed in the color signal system circuit, especially on the output side of the carrier color signal encoder, the noise components generated in the color signal system circuit will be removed from the color video signal. The S/N ratio of the luminance signal can be prevented from deteriorating.

In this case, minute level color signal components are also removed, causing the problem of color fading; however, in low illuminance, actively achromatic can improve image quality. Therefore, there is no problem in this respect.

〔Example〕

FIG. 1 shows an embodiment of a video signal processing circuit in a video camera or the like according to the present invention, in which 1 is an imaging means consisting of an optical system LA, an exposure device (Iris) IB, an image sensor IC, etc., and 2 is a matrix. circuit, 3 is AGC amplifier, 4 is A
5 is a detection unit that outputs a GC voltage; 5 is a Y signal processing block that sets the level in order to generate a luminance signal; 9 is a Y signal processing block that performs frequency characteristics, addition of a synchronization signal, etc.; 6 is a Y signal processing block for forming a carrier color signal. This is the chroma signal processing block.

7 shows a base noise clipping circuit for chroma signals, which is a feature of the signal processing circuit of the present invention.As will be described later, this base noise clipping circuit 7 removes the noise generated in the chroma signal circuit, and the color TV. The S/N ratio of the signal, especially the luminance system, is improved.

FIG. 2 shows a specific example of the base noise clipping circuit 7, in which 9a is an amplifier, 9b is a limiter, 9c is an inverter circuit for phase inversion, and 9d is an adder circuit. Note that R1 represents a clip level adjustment resistor, and R2 represents an attenuator.

Next, the two base noise clipping circuits 7 will be explained.

The amplitude of the carrier color signal as shown in FIG. 3A is increased by the amplifier 9a, and then in the next limiter circuit 9c.
For example, only signal components below the slice level T h are extracted as shown in waveform B.

This extracted minute level signal contains a noise component as well as a color signal component. Therefore, this minute level signal waveform B is phase-inverted in the next inverter circuit 9C, returned to an appropriate level in the attenuator R2, and then supplied to the adder circuit 9d. A carrier color signal from which the minute level portion has been removed is formed as shown in waveform C.

Therefore, the adder circuit 9d removes the noise component mixed in the minute level portion of the color signal component and outputs a carrier color signal, and this signal is combined with the luminance signal component in the adder circuit 10 of FIG. Become.

As described in Part 2 below, the video signal processing circuit in the video camera, etc. of the present invention is equipped with the base noise clipping circuit 7 that removes the noise component of the color signal, so the composite color television signal that is output is not the color signal. The noise mixed in from the components is reduced. As a result, the S/N ratio of the luminance signal is improved, so it is possible to improve the image quality.

In this case, the minute level color signal will also disappear, but the S/N ratio has already deteriorated in the image part of the low-light object, and by adding the color signal to this part, the S/N ratio will be further reduced. Degrading the ratio does not necessarily improve the image quality.

Therefore, when the low-level color signal is removed as seen in the present invention, the noise component from the color signal system is reduced, and this noise component is no longer mixed into the high frequency side of the luminance signal, so the luminance signal S /N is higher than that of the conventional method, and the image quality can be improved on the contrary.

Generally speaking, the deterioration of the S/N ratio becomes more noticeable in subjects with low illumination, and noise is relatively inconspicuous in high brightness, so the clip level of the base noise clipping circuit 7 decreases when the brightness is high. It is more preferable to make it small.

Therefore, in the present invention, as a second embodiment, it is recommended to add a clip level control circuit as shown by the dotted line in FIG.

That is, the detector 4 that sets the gain of the AGC amplifier 3
The control voltage e1 of the detector 8 and the control voltage e2 of the detector 8 which sets the aperture of the exposure device IB of the imaging means 1 are input to the level control circuit 9, and the clip level of the base noise clipping circuit 7 is determined by referring to these control voltages. It is configured to supply a signal S for setting .

When such a control means is added, for example, when the aperture of the exposure device IB is narrowed down using a variable resistor r to produce a low luminance signal, the clip level of the color signal is deepened, noise components are sufficiently suppressed, and the low luminance is produced. This prevents noise from the color signal system mixed in. At the same time, by automatically adjusting achromatization in minute level areas, S/N
You will be able to improve your performance.

〔Effect of the invention〕

As explained below, the video signal processing circuit in a video camera, etc. of the present invention provides a base noise clipping circuit in the color signal system circuit to adjust the minute color signal level when forming a composite color television signal. Since the included noise components are removed and then superimposed on the luminance signal, the S/N ratio, which is a problem especially in low-light subject images, can be improved with a simple circuit configuration. effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a video signal processing circuit in a video camera or the like of the present invention, FIG. 2 is a circuit diagram showing a specific example of a base noise clipping circuit, and FIG. 3 is a waveform diagram illustrating FIG. 2.
Figure 4 is a signal processing block diagram of a general video camera.
FIG. 5 is a circuit diagram of a noise canceller, and FIG. 6 is a frequency characteristic diagram of a color television signal. In the figure, 1 is an imaging means, 2 is a matrix circuit, and 3 is an AG
C amplifier, 5 is a Y signal processing block, 6 is a chroma signal processing block, 7 is a base noise clip circuit, and 10 is an adder circuit. Biku ○ 2nd eye / V theory @ Oigatame Ichibyo U Pite "Okame 7f) Faith 4" β-if 7th eye 4th eye

Claims (2)

[Claims] (1) A video camera that separates a video signal obtained from an imaging means into a brightness signal and a color signal, converts the brightness signal into a carrier color signal, and combines the color signals to form a composite color television signal. In the video signal processing circuit, the carrier color signal is passed through a base noise clipping circuit consisting of an inverter circuit, a small signal limiter circuit, and an adder circuit to remove color signal components below a predetermined limiter level and synthesized with the luminance signal. A video signal processing circuit for a video camera or the like, characterized in that the circuit outputs a composite color television signal. (2) A video signal processing circuit for a video camera or the like according to claim (1), wherein the limiter level is controlled to change in accordance with the level of the luminance signal.