JPH04335776A - Television camera device - Google Patents

Abstract

PURPOSE:To obtain the television camera device in which the reproducibility of a white level is excellent even when an object having a large contrast difference is picked up in the monitor CCTV camera or the like. CONSTITUTION:A video signal is separated into a main signal and a sub signal, and the sub signal is given to a high level passing circuit 5, in which the signal with a prescribed level or over is passed and a low pass filter 6 passes only a low frequency component. The signal is subtracted from the main signal subject to phase adjustment by a subtractor 7 to obtain an excellent television signal without a white level distortion.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to signal processing of a television camera device used in a surveillance CCTV system or the like.

0002

2. Description of the Related Art In surveillance television cameras, the following methods are available for reproducing gradations with large contrast differences. (1) Increase the gain of the γ correction characteristic from the black level to the low level. (2) Provide a white level compression circuit with a high compression ratio. (3) The compression start level of the white level compression circuit is changed according to the APL (average value level) of the image signal.

On the other hand, these prerequisites are that the lens aperture value is automatically controlled by the average value of the image, the peak value, or a mixed value of these, or the light intensity vs. output characteristic of the image sensor itself is controlled. It has one of automatic sensitivity adjustment functions to control the sensitivity.

Next, the above (1) to (3) will be explained in detail. First, method (1) aims to improve the phenomenon of image blurring on the monitor screen by increasing the gain near the black level compared to the normal γ correction curve, and the gain of the γ curve is usually , about 2.5 to 3 times, but this is set to 4 to 8 times.

However, even at this magnification, the input contrast ratio is as high as 1000:5, so the effect is weak, and as the magnification increases, the S/N also deteriorates, so noise is generally noticeable in dark subjects, and is at the limit. There is.

[0006] Method (2) is based on the white level part, for example, 10
It lowers the gain to about 1/10 from around the 0% level output, and is often used in conjunction with the above item (1). However, even with this, the contrast ratio of 1000:5 is only reduced to 100:5, which is a weak effect, and increasing the gain compression ratio also compresses the contrast signals in the vicinity. The gradation becomes difficult to see on the monitor, in other words, it becomes close to the phenomenon of whitewashing.

Regarding method (3) described below, (
Rather than fixing the level at which gain compression starts at the white level in item 2), for example, at 100% level, if the screen APL is low, the white level part is considered as a spot light, and the starting level is lowered, for example, from 90% to 80%. %, the starting level is automatically controlled from the screen APL information, and the purpose is to prevent white collapse.

However, this method also changes the starting point of white compression, which is equivalently a means of changing the γ correction curve in item (1), and its effect is only doubling the effect in item (2). Almost no effect.

[0009]

The above-mentioned prior art contributes to some improvement in white and dark shadows, but has the drawback that no significant improvement effect can be obtained. It is an object of the present invention to eliminate these drawbacks and to realize reproduction of white level parts over a wide range on a monitor.

0010

[Means for Solving the Problems] In order to achieve the above object, the present invention branches a video signal into a main signal and a sub signal during signal processing, sets a predetermined threshold value, and sets the threshold value to This system allows only the sub-signals of the high-level parts exceeding the sub-signal to pass through, limits the band using a low-pass filter, changes the polarity of one of the branched main signals, and mixes them in a subtracted manner. .

FIG. 1 is a block diagram showing the entirety of the present invention. In the figure, 1 is a video signal input terminal, 2 is a signal branch point, 3 is an amplifier, 4 is a delay circuit, 5 is a high level pass circuit, 6 is a low pass filter, 7 is a subtracter, 8 is a signal processing circuit, 9 is a television camera signal output terminal.

0012

[Operation] To explain the operation of the present invention, a video signal is branched into a main signal and a sub signal at a signal branch point 2. The amplifier 3 in the main signal path passes signals from the black level to the maximum level, but the high level pass circuit 5 in the sub signal path has a so-called low-level clipping characteristic, allowing only signals above a predetermined level to pass through. Next, a low-pass filter 6 passes only the low-frequency components, and a subtracter 7 subtracts them from the main signal.

[0013] As a result, no processing is performed up to a predetermined level, and for signals above a predetermined level, the high-frequency components remain unchanged, but the low-frequency components are compressed, that is, a white level with a clear outline is created. A compressed signal is obtained.

[0014]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. 10 is an image sensor that converts an optical image into an electrical signal, 11
is a pre-amplifier, which includes a well-known correlated double sampling circuit and a signal amplification circuit.

A transistor 12 forms an emitter follower together with a resistor 13 and is connected to video amplification circuits 14 and 15. 16 is a capacitor, transistor 17,
A DC regenerative clamp circuit consisting of a resistor 20 is formed,
The emitter of transistor 17 is connected to voltage bias means 21 .

Reference numerals 18 and 19 denote transistors whose emitters are connected to each other, and the connection point thereof is connected to the power supply VSS via a resistor 22. Furthermore, the base of the transistor 18 is
Connect the aforementioned clamped signal and connect the transistor 19
The base of is connected to constant potential supply means 23. The emitters of transistors 18 and 19 are connected to a low pass filter 24.

On the other hand, the output of the video amplifier circuit 15 is connected to the positive input terminal of the differential amplifier 28 via the delay circuit 25, and the output of the low-pass filter 24 is connected to the negative input terminal of the differential amplifier 28 through a resistor. 26, and its output is connected through resistor 2
7 to connect to the negative polarity input terminal. 29 is a video signal processing circuit to which the output of the differential amplifier 28 is connected and used as an input. This output is connected to an output amplification circuit 30.

Next, this operation will be explained. A preamplifier 11 reduces noise in a relatively low frequency range of the entire frequency band of the video signal from the image sensor 10. This method includes well-known correlated double sampling and the like.

This output signal is applied to the base of the transistor 12, which operates as an emitter follower, and the output signal is taken out from the emitter at low impedance.

[0020] This signal is divided into a main signal path and a sub-signal path, and is added to the video amplifier 15 of the main signal path, and then to a delay circuit 25 that delays the signal by a predetermined time τD corresponding to the delay time in the sub-signal path. In addition, it is input to the differential amplifier 28.

On the other hand, as a sub signal path, the video amplifier 1
4 is amplified by capacitor 16 and transistor 1.
Consists of 7th magnitude. DC regeneration is performed using a DC clamp circuit. Next, in the emitter coupling circuit consisting of transistors 18 and 19, (E2
-EBE) A clip circuit is configured that does not pass signals at a lower level than that, but only passes signals higher than that level.

That is, only signals above a predetermined level of the video signal are passed through, and only signals in a low frequency band are passed through the low-pass filter 24, and this signal is passed through a resistor 26 to a differential amplifier 28. Add to the negative polarity input terminal of

Therefore, when the output of the differential amplifier 28 is below a predetermined level, it has the same conventional characteristics, but for signals above a predetermined level, the low frequency components are compressed and the high frequency components are compressed. A signal whose components are not compressed is obtained.

In other words, even if a signal with a large contrast ratio is input, the low-frequency white level part is properly compressed, but the high-frequency component contour signal remains as it is, so a reproduced video signal without white collapse can be obtained. .

[0025] Note that the present invention is not limited to this embodiment,
A low frequency pass filter 2 is installed after the video amplifier 14 in FIG.
4 may be arranged. Also, the differential amplifier 28
The same effect can be obtained by simply mixing the signals with a resistor, by making the sub signal path and the main signal path different in signal polarity.

Furthermore, by appropriately adjusting and setting the signal mixing amount of the sub signal path with respect to the signal of the main signal path, it is also possible to obtain compressed signal level gradations in the large level portion. Furthermore, the same effect can be obtained by providing a conventional white compression circuit in the main signal path or at a stage before branching into the main signal and sub signal paths.

Furthermore, the clip circuit (transistor 18
, 19) is not fixed, for example, the average value or peak detection value of the video signal is given to the base of the transistor 19, and it changes according to the situation of the subject scene. You can also change the transition point automatically.

[0028]

According to the present invention, it is possible to obtain a good television signal without blown-up whites for objects with a large contrast difference, so that the present invention can be applied to surveillance CCTV camera devices and the like with great effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the entirety of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

3 Amplifier 4 Delay circuit 5 High level passing circuit 6 Low pass filter 7 Subtractor 8 Signal processing circuit

Claims (3)

[Claims] 1. Means for branching a video signal obtained from an image sensor of a television camera device into a main signal and a sub-signal, and a first means for passing only a low frequency band component of the branched sub-signal. , a second means for passing only a signal having a predetermined signal level or higher of the branched sub-signal, and a third means for mixing the output signal of the second means with the branched main signal with a different polarity. A television camera device comprising: Claim 2: Claim 1, further comprising delay means for matching the phases of the main signal and the sub-signal.
The television camera device described. 3. The video signal has an average value or peak detection means, and the output thereof is used as a threshold value of the second means for passing only the signal whose level of the sub-signal is equal to or higher than a predetermined level. The television camera device according to claim 1 or claim 2, characterized in that: