JPS6028382A - Control circuit for video camera - Google Patents

Abstract

PURPOSE:To suppress an abnormal phenomenon such as blooming or comet tail to a degree not remarkable by adding a voltage detecting a high light signal exceeding a prescribed level to a conventional control signal so as to apply the control also to a signal of an abnomal high light portion. CONSTITUTION:An output signal of a gate circuit 9 is detected by a peak detection circuit 10 and an average value detecting circuit 11, and an output signal of a high light signal detecting circuit 16 is detected by a peak detecting circuit 17 respectively and they are outputted to an output of an adder circuit 20 as a control voltage. In case of the content of image pickup where the contrast ratio among various objects in a pickup screen is almost uniform over the entire screen or a video signal is a prescribed high light detection level Vth or below, an iris circuit and an AGC circuit are controlled by a control voltage only obtained based on the video signal at the screen center portion extracted by a gate circuit 9. If an abnormal high light is generated at the surrounding of the screen, the circuits are controlled for a prescribe rate also with a voltage detecting the high light signal being the Vth or over, and an optimum picture is obtained by suppressing comet tail or blooming.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a signal processing circuit for a video camera, and particularly to a detection circuit that generates control voltages for an automatic iris circuit and an automatic gain control (AGC) circuit. .

[Background of the invention]

Conventionally, video cameras are generally equipped with an auto-iris circuit or an AGC circuit in order to optimize the amount of incident light or signal for the dynamic range of the circuit. The voltages that control each of the above circuits are obtained by detecting the video (luminance) signal and rectifying and smoothing (detecting) it, but if necessary, an average detected voltage can be obtained depending on the video content to improve the image quality. The brightness is controlled to an average brightness, the peak detection voltage corresponding to high brightness is obtained to optimize the high brightness area, or a mixed voltage is obtained for both.

FIG. 1 shows an example of a conventional G-circuit configuration, and the conventional example will be explained below using FIGS. 1 and 2. In FIG. 1, 1 is a lens device and 2 is an iris mechanism. Reference numeral 3 denotes an image pickup device that outputs a video signal, which is amplified by a preamplifier 4, and then subjected to various signal processing such as clamping, addition of a pedicle component, and blanking by a signal processing circuit 5. After that, the AGC circuit 6 optimizes the signal level and outputs it to the terminal 7. After that, although not shown,
Separately, various camera signal processing is performed. Of the video signals obtained at the terminal 7, a signal corresponding to approximately the center of the screen is extracted by a gate pulse applied to the terminal 8 of the gate circuit 9, and the extracted signal is sent to the peak value detection circuit 10. The average value detection circuit 11 detects each wave, and the addition circuit 12
The control voltages for the iris and AGC are obtained by adding them at a desired ratio. The control voltage obtained by the detection is amplified by the amplifier circuit 13 and applied to the AGC and iris switching circuit 14. When the amount of incident light is relatively small, this switching circuit 14 first applies a control voltage to the AGC circuit B such that the gain attenuates from the maximum gain state as the amount of incident light increases, and after completing the predetermined gain control, As the amount of light incident on the iris mechanism 2 increases, the iris mechanism 2
The amount of light incident on the image sensor 3 is controlled by applying a control voltage to the iris drive circuit 15 so as to gradually close the iris from an open state. As explained above, the level of the video signal obtained at the terminal 7 is controlled to a predetermined value over a wide range of the amount of incident light.

The role of the gate circuit 9 will be explained below. In general, video camera photographers position the subject they want to photograph in the center of the screen. For example, if they want to photograph a person, they position the person's face in the center of the screen as shown in Figure 2. When operating a camera, the contrast ratio between various objects within the imaging screen is often uniform, so there is nothing unnatural about detecting video signals over the entire area of the imaging screen and controlling the iris and AGCf. . However, as shown in Figure 2, when the background of a person, for example the sky is photographed in the upper part of the screen A, or in a backlit situation, or when a light source such as a lamp is photographed directly behind the person indoors, etc.
Photographing situations often occur in which the contrast ratio of the object to be photographed is relatively large. In such shooting situations,
In the conventional control method, the video signal level is controlled so as to optimize the amplitude corresponding to the background pattern (, 4) that is dominant at the video level, as shown in FIG. 3 (α).
As shown in part (B), the object that is originally intended to be photographed becomes dark and dull compared to the rated level, and the photographed image becomes extremely unnatural. Here, a gate circuit 9 is provided to provide a second gate circuit.
If the video signal in the center B of the screen is detected as shown by the broken line in the figure, the video signal will be optimized for the subject to be photographed even under the above situation, as shown in B' in Figure 3<h). Ru. In this case, the high brightness part (A') of the background that exceeds the rated level is processed by the white peak clipping process of the camera signal processing circuit provided nine times after terminal 7.
Clipped by about 50 inches. Clipping high-brightness areas is a normal signal processing method in video cameras.
Since the brightness is originally high (white image), the captured image does not seem very unnatural. Therefore, as described above, the gate circuit 9 is very effective for photographing purposes. However, as shown in section 0 of FIG. 3(C), when the contrast ratio with the subject to be photographed is abnormally large, a beam current shortage occurs in the highlight section of the image sensor, which is called a comet tail. This causes a white trailing phenomenon and a pluming phenomenon when the camera is panned, resulting in image deterioration.

The degree of this image quality deterioration increases as the image becomes brighter and brighter. As a countermeasure to this problem, the beam current automatically follows the highlighted area, and the ABO (Aatornatic
Although it is possible to solve this problem by using a circuit called a beam optimization circuit, it is not so easy to design a basic circuit, and a considerable amount of consideration and expense must be invested. Therefore, it cannot be used in inexpensive home video cameras. Further, even if an ABO circuit is adopted, it is impossible to completely suppress the above phenomenon considering the actually existing contrast ratio.

[Purpose of the invention]

The purpose of the present invention is to improve the above-mentioned drawbacks of the prior art, and furthermore, to reduce the occurrence of comet tails, blooming, etc.
It is an object of the present invention to provide a control device for iris control or AGC control.

[Summary of the invention]

In order to achieve the above object, the present invention provides a predetermined level (Fig. 3(C)
The iris AGC control voltage is obtained by detecting the value of the signal (Vth) that exceeds the above-mentioned conventional detection control voltage. In other words, even with abnormally large light signals around the screen (outside the broken line in Figure 2), the control operations of the iris and AGC are somewhat affected for pictures that exceed a predetermined level Vth. In this way, as shown in Fig. 3 @), the image area D' to be photographed is adjusted to the extent that an abnormally large comet table and blooming do not occur for the highlight area C, as shown in the 0 area and D' area processing. In contrast, the level of the video signal is appropriately controlled to the extent that the image does not become too black (dark), thereby obtaining a good photographed direct image. This predetermined level Vth is set to an appropriate value larger than the rated level, but it is convenient to select it to be about twice the rated level, for example.

[Embodiments of the invention]

An embodiment of the configuration of a detection circuit according to the present invention will be described below with reference to FIG.

In this figure, circuit blocks with the same symbols as in FIG. 1 indicate the same functions and operations. In FIG. 4, the video signal obtained at the AGC circuit power terminal 7 is sent to various camera signal processing circuits 19 such as a white peak clip circuit and an r correction circuit following the subsequent stage.
Detects the signal in the center of the screen,
(Alternatively, signals outside the center of the screen may be weighted by clipping them at a predetermined level.) The voltage is applied to the gate circuit 9 and the highlight signal detection circuit 16 that detects only signals exceeding the predetermined level. and the respective signals are detected. The output signal of the gate circuit 9 is sent to the peak detection circuit 10. The average value detection circuit 11 passes the output signal of the highlight signal detection circuit 16 to the peak detection circuit 17.
Peak detection and average value detection are performed, respectively, and addition circuit 12.
18, the signals are added and mixed at an appropriate ratio and output as a control voltage to the output of the adder circuit 20. According to this circuit configuration, when the contrast ratio between various objects in the shooting screen is almost uniform over the entire screen, or when the video signal is below a predetermined highlight detection level (Vth), The iris circuit and AGC circuit are controlled only by the control voltage obtained based on the video signal at the center of the screen extracted by the gate circuit 9, and the video signal level is optimized under most shooting conditions. Ru. Here, if abnormal highlights occur in the periphery of the screen as described above, set an appropriate value for Vth and detect all highlight signals with a level higher than twice the rated level. It is also controlled at a predetermined rate by the applied voltage.
Optimal images can be obtained by suppressing comettail and blooming mink. Although the above explanation deals with the case where the gate circuit 9 is provided, the effects of the present invention can be obtained to some extent even if the gate circuit 9 is omitted.

Next, a specific example of a circuit according to the present invention is shown in FIG. Blocks 9, 11, 20, 10, and 17°16 indicated by broken lines in this figure correspond to the parts indicated by the same reference numerals in FIG. Transistors Q1, Q2, Q3, Q4 Diode D
1. A gate circuit is constituted by resistors R1 and 'R2. A positive gate pulse is applied to the base of the transistor Q2, and the transistor Q2 is at a high (H) level for a period corresponding to the center of the screen. In other words, II>E with respect to the base bias voltage ER of the high-level transistor Q1, and the transistor Q2 is turned on, and as a result, the transistor Q3 is turned off.
F.

Therefore, during the I level period, the video signal input to the base of the transistor Q4 is directly applied to both ends of the resistor R2. Next, during a period corresponding to the outside of the center of the screen, a low (L) level is applied to the terminal 8, so that the transistor Q1 is turned on and the transistor Q2 is turned off. therefore,
The level is shifted by the level shift diode D1, and the voltage ER is applied to the base 9 of the transistor Q3. Here, the level of the video signal obtained at terminal 8 is E, I-
If the signal level is higher than EB (black level), transistor Q4 is turned off. In other words, arbitrary weighting can be performed by setting the level of ER.The video signal generated across the resistor R2 is applied to the base of the transistor Q5, and is smoothed by the transistor Q5, the resistors R5 and R7, and the capacitor C1. and an average detected voltage is generated across the resistor R.
The video signal generated at both ends of the transistor Q6 is also applied to the base of the transistor Q6, and the peak value detection voltage that follows the peak value of the signal applied to the base of the transistor Q6 is applied to both ends of the capacitor C2 by the transistor Q61 capacitor C2. Occur. On the other hand, the video signal obtained at terminal 7 is transmitted through resistor R5.
After being divided and set to a predetermined level by R6, it is also applied to the base of transistor Q7 and Q7. Similarly, peak detection is performed by C2. That is, depending on the division ratio of the resistors R5 and R6, a highlight signal higher than an arbitrarily determined level can be detected. By setting the resistor R4, each of the detected voltages described above can be added at an arbitrary ratio, and a control voltage having the characteristics of the present invention can be obtained at the terminal 21. As can be seen from this embodiment, the highlight signal detection section, which is the main part of the present invention, is the transistor Q7. Resistance R5, R
It can be realized with only 6 and is extremely simple. Of course, weighting may be performed by applying a parabolic waveform voltage to the gate voltage application terminal 8 of the gate circuit 9.

〔Effect of the invention〕

As explained above, according to the present invention, a highlight signal exceeding a predetermined level is detected even under relatively special shooting conditions where a large highlight signal is generated in the background, and the detected voltage is controlled using conventional control. By simply adding it to the signal, it is possible to control the signal in the highlighted area by an appropriate amount, suppressing abnormal phenomena such as pluming and comet tails to an unnoticeable level, and greatly improving the overall quality of the screen.

In addition, by adopting the present invention, there are economical effects such as eliminating the ABO circuit or reducing the capacity of the ABO circuit, and if the ABO circuit is used in combination, an even greater effect of improving image quality can be obtained. .

[Brief explanation of drawings]

Figure 1 shows the iris of a conventional video camera. A block diagram showing the AGC control system, FIG. 2 is an explanatory diagram showing an example of a photographed image, and FIG. 3 shows iris control. A waveform diagram for explaining the operation of AGC control, FIG. 4 is a block diagram showing an embodiment of the iris and AGC detection circuit according to the present invention, and FIG. 5 is a specific circuit of a main part of an embodiment of the present invention. FIG. 1: Lens system 2 Near iris mechanism 6: Imaging device 4: Preamplifier 5: Signal processing circuit 6: AGC circuit 8 Negative signal application terminal 9: Gate circuit 10: Peak value detection circuit 11: Average value detection circuit 12: Addition circuit 16: Amplification circuit 14: A'GC, iris control voltage switching circuit 15 near Iris drive circuit 16: Highlight signal detection circuit 17: Peak detection circuit 20: Addition circuit 19: Camera signal processing circuit Jbl Fig. 11 Fig. 2 Δ 3rd figure

Claims (1)

[Claims] 1. Depending on the size of the video signal, the iris of the optical system;
Alternatively, in a video camera having means for automatically controlling the gain of a video signal processing circuit, the first detection means detects the level of the video signal, and the first detection means detects a high brightness component exceeding a predetermined level of the video signal. The second detection means and the signals obtained by these two means are added to control at least one of the iris and the gain of the processing circuit. A control circuit for a video camera characterized by using C5. 2. In the video camera control circuit according to claim 1, the first detection means for detecting the level of the video signal detects the video signal at approximately the center of the imaging screen. Features a video camera control circuit.