JPH08321986A - Television camera - Google Patents

Abstract

PURPOSE: To acquire a video image stable at all times by adjusting a weighting coefficient based on decision of image pickup scene so as to conduct iris control for allowing main object ease to see in all scenes, thereby preventing a too blacky object due to deficient exposure or a too whity image due to excessive exposure. CONSTITUTION: After iris control, a mean luminance level in areas 5, 6 is compared with a prescribed threshold level. The threshold level is used to set luminance level data of major object desired to be observed. When the luminance level in the areas 5, 6 is lower than the threshold level, it is decided to be deficient exposure and the weighting coefficient is decreased. On the other hand, when the luminance level in the areas 5, 6 is higher than the threshold level, it is decided to be excessive exposure and the weighting coefficient is increased. Moreover, scanning is repeated to a control a lens aperture so as not to cause hunting. Through the constitution above, a picked-up image at a stable luminance level is obtained at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic iris control device for a television camera.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the structure of a conventional television camera. FIG. 2 is a control operation flowchart of the auto iris of the conventional television camera.

In FIG. 3, 1 is an auto iris lens, 2 is an image pickup element, 3 is a CDS (correlated double sampling) circuit and AGC (auto gain control).
Circuit 4, A / D converter, 5 DSP for video signal processing
(Digital signal processor), 6 is a D / A converter,
Reference numeral 7 is a Y / C mix circuit and an output amplifier, 8 is a microcomputer (microcomputer), and 9 is an iris drive circuit.

Next, the operation will be described. Light incident from the subject through the auto iris lens 1 is photoelectrically converted by the image pickup device 2, the CDS and AGC circuit 3 corrects sample hold, AGC, gamma, etc., and the A / D converter 4 converts it into a digital signal. . Video signal processing DSP 5 creates Y, R, G, and B signals from this signal, performs luminance processing and color signal processing, and adds necessary coefficients for the camera such as enhancer coefficient and gamma correction coefficient according to the program of microcomputer 8. , White balance processing is performed to produce Y and C digital signals. These digital signals are converted into analog signals by the D / A converter 6, and the Y / C mix and the output amplifier 7 superimpose the chrominance signal on the luminance signal and amplify it to a sufficient size for output to a monitor or the like. To do.

The iris control signal is a video signal processing D.
Microcomputer 8 based on iris data obtained from SP5
A scene such as back light / forward light is discriminated by, and a weighting coefficient determined for each scene is multiplied and output to the iris drive circuit 9 to drive the diaphragm of the auto iris lens 1. Next, the iris control data processing in the microcomputer 8 will be described. The iris data is the integrated value of the luminance signal divided into 6 areas as shown in FIG. It is assumed that the main subject is in the normal areas 5 and 6. First, in order to roughly classify the scenes, the area 1
The luminance level data of the + region 2 and the region 5 + region 6 are compared, and when the luminance level of the region 1 + region 2 is higher, it is "backlit", when it is smaller, it is "excessive forward illumination", and when there is not much difference, it is " Normal light ”. Next, for each of these scenes, the area 1 and the area 2 are compared, and it is determined which of the left and right is brighter. For example, in the case of backlight, when the brightness level of the area 1 is higher, "bright backlight on the left side", when it is small, "bright backlight on the right side" is determined, and when there is not much difference, it is determined that "backlight with equal brightness on the left and right". To do. It is divided into a total of 9 scenes in total, and a weighting coefficient determined in advance for each scene is multiplied for each area, and these are added to obtain iris control data for the entire screen. The smaller the weighting coefficient, the smaller the iris control data,
Since the lens diaphragm 1 becomes more open, it is set to a smaller value for the back light than for the normal light and set to a large value for the excessive normal light.

[0006]

Since only one weighting coefficient is set for each scene with the above-mentioned prior art alone, it is possible to make the subject easy to see when the main subject is in a backlit condition such that it is faint. When the weighting coefficient is set, underexposure occurs under a strong backlight condition in which the main subject is completely black and cannot be seen. On the contrary, if a weighting coefficient is set so that the subject can be easily seen under the strong backlight condition, there is a problem that the overexposure occurs under the weak backlight condition. Therefore, it is an object of the present invention to increase or decrease the weighting coefficient depending on the scene being imaged, and perform iris control so that a main subject can be easily seen in any scene.

[0007]

In order to achieve the object of the present invention, first, a weighting coefficient is set by scene determination as in the prior art, and the iris control luminance data is multiplied and output to an iris drive circuit. Control the aperture. At this time, it is determined whether the brightness level of the area including the main subject is higher or lower than a certain threshold value. If the brightness level is lower, the weighting coefficient is decreased until the brightness levels become equal, and if the brightness level is higher, the weighting coefficient is increased. is there.

[0008]

As a result, the brightness level of the area containing the main subject is kept constant in any shooting scene, so that the subject is not underexposed in black or overexposed and is not crushed in white, and is always stable. You can get the video.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the flow chart of FIG.

Since the overall structure is the same as that shown in FIG. 3, the description thereof will be omitted. In addition to the conventional scene determination method, the average brightness level of the area 5 + area 6 is compared with a predetermined threshold after iris control. As the threshold value, the brightness level data of the main subject to be viewed is set. If the brightness levels of the areas 5 and 6 are lower than the threshold value, it is determined that the exposure is insufficient, the currently set weighting coefficient is decreased, and if the brightness level is high, it is determined that the exposure is excessive and the weighting coefficient is increased. This is repeatedly controlled so that hunting of the lens diaphragm does not occur.

[0011]

According to the present invention, the brightness level of the area including the main subject is controlled to be constant under any image pickup condition, so that the subject is underexposed or blackened or exposed. An image with stable brightness can always be obtained without being overshadowed by whitening.

[Brief description of drawings]

FIG. 1 is a diagram showing a flow chart of an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional iris control flowchart.

FIG. 3 is a block diagram showing the overall configuration of a camera.

FIG. 4 is a screen division pattern.

[Explanation of symbols]

 1 Auto Iris Lens 2 Image Sensor 3 CDS, AGC Circuit 4 A / D Converter 5 Video Signal Processing DSP 6 D / A Converter 7 Y / C Mix, Output Amplifier 8 Microcomputer 9 Iris Drive Circuit

Claims (3)

[Claims] 1. In a television camera using an auto iris lens and controlling a lens diaphragm using a video signal obtained from an image pickup device, a screen dividing means for dividing a screen into a plurality of photometric areas, and an average luminance of each area. A means for comparing the levels and a means for multiplying this average brightness level by a weighting coefficient according to the result of the comparison and adding them are provided, and the lens diaphragm is adjusted so that the area including the main subject has a predetermined brightness level. A television camera characterized by being controlled. 2. The television camera according to claim 1, wherein a DSP (digital signal processor) for video signal processing is used as a means for dividing a screen into a plurality of areas. 3. A television camera according to claim 2, wherein a microcomputer is used as means for comparing the brightness levels.