JPH0523558B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an imaging apparatus that includes a zoom lens for varying an incident angle of view and that performs white balance adjustment of a video signal from an imaging means.

[Prior art]

To adjust the white balance on a TV camera, first change the color temperature (with or without inserting a color temperature conversion filter), then take an image of a white subject, such as a blank sheet of paper, or cover the lens with a milky white lens cap and use the indicator. While watching the video, adjust the white balance adjustment knob and adjust the gain so that the output signal of the color television camera is only the luminance signal.

Conventionally, the automatic white balance adjustment method that automatically performs this white balance is a setting type in which the color temperature is set to a desired setting value before shooting and the value is automatically maintained during shooting. There are two types: a tracking type that constantly follows changes in color temperature and maintains white balance when the color temperature changes.

By the way, with tracking type auto white balance, if the zoom angle changes and the angle of view changes, or if the color temperature differs between the actual scene being photographed and the location where the color temperature is being detected, the optimal Since white balance cannot be achieved, a method has been proposed in which changes in the zoom angle are detected and the incident light angle for color temperature detection is changed accordingly.

In this method, as shown in FIG. 1, a zoom angle is detected in a zoom angle detection circuit 1, and the angle of incident light incident on red and blue detection sensors 2 and 3 is changed depending on the imaging angle of view. And color temperature detection circuit 4
The color temperature at the angle of view that changes depending on the zoom angle is detected, and this information is input to gain control circuits 5 and 6, respectively, and the gains of the red component R and blue component B are controlled according to the respective color temperatures. It is something.

However, when the angle of view for detecting color temperature is changed according to the angle of view changed by the zoom lens as described above, when telephoto shooting is performed with the zoom lens, that is, when the incident angle of view is made small, There is a high possibility that a single object that has a large area and moves at high speed exists within that angle of view.
Therefore, due to the influence of the color of the subject, a white balance control signal that differs from the actual color temperature is generated, resulting in problems such as the white balance of the captured video signal shifting or the white balance control becoming unstable. will occur.

[Purpose of the invention]

The present invention has been made by focusing on the drawbacks of the above-mentioned conventional examples. Even when taking telephoto shots with a zoom lens, the present invention is not affected by the subject, is faithful to the color temperature of the shooting screen, and is always stable in white. It is an object of the present invention to provide an imaging device that can perform balance control.

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention will be described based on FIG. 2. In contrast to the conventional configuration shown in FIG. Variable time constant circuits 12 and 13 are provided as control signal forming means for outputting a white balance control signal, and a gain control circuit 5 as a white balance adjustment means is provided from the color temperature detection circuit 4.
6, respectively.

With the configuration described above, in a tracking auto white balance device that changes the incident light angle for color temperature detection according to the zoom angle, the zoom angle detection circuit 1 first detects the zoom angle and changes the incident light angle for color temperature detection. corner control, red and blue detection sensors 2 and 3
The color temperature is detected by the color temperature detection circuit 4.

On the other hand, the output value of the zoom angle detection circuit 1 is inputted to variable time constant circuits 12 and 13 via weighting means 11, respectively, and the time constant is changed according to the output value. The time constant thus controlled changes the gain in the gain control circuits 5 and 6 according to the output value of the color temperature detection circuit 4 to achieve white balance.

At this time, in the variable time constant circuits 12 and 13, when the zoom is set to the zoom telephoto side, the angle of view becomes narrower, so a deviation in color temperature occurs due to the influence of the color of the subject rather than the actual color temperature. By increasing the constant, the response to misaligned color temperatures is slowed down to obtain a natural screen, and conversely, when the zoom is set to the wide side, the angle of view is wide, so the color temperature detection information is Since it is accurate, it shortens the time constant and improves responsiveness.

Note that in the above embodiment, the variable time constant circuits 12, 1
3, the gain is controlled by a variable gain circuit 14 as a control signal forming means, as shown in FIG.
15, the same effect can be obtained by reducing the overall gain of the white balance control signal supplied to the gain control circuits 5 and 6 on the zoom telephoto side, and conversely increasing the gain on the zoom wide side.

〔Effect of the invention〕

As explained above, the present invention changes the incident angle of view using a zoom lens, and performs white balance control according to the output of the color temperature detection means that detects the color temperature within the angle of view corresponding to the incident angle of view. When forming the signal, by changing the responsiveness of this control signal to the output of the color temperature detection means and the gain of this control signal depending on the incident angle of view, it is possible to improve the white balance due to the influence of the color of the subject, especially during telephoto shooting. This has the effect of eliminating misalignment and instability, and allowing a natural image to be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional white balance device that changes the angle of incident light for color temperature detection according to the zoom angle, and Fig. 2 is a block diagram of an auto white balance device of the present invention that is equipped with a variable time constant circuit according to the zoom angle. 3 are block diagrams of an auto white balance device similarly equipped with a variable gain circuit depending on the zoom angle. 1...Zoom angle detection circuit, 4...Color temperature detection circuit, 5...Gain control circuit, 6...Gain control circuit,
12...Variable time constant circuit, 13...Variable time constant circuit.

Claims (1)

[Scope of Claims] 1. A zoom lens for varying an incident angle of view, an imaging means for forming a video signal from an optical image incident through the zoom lens, and an image within an angle of view corresponding to the incident angle of view. color temperature detection means for detecting the color temperature of the video signal; control signal formation means for receiving the output of the color temperature detection means and forming a control signal for controlling the white balance of the video signal; adjusting means for adjusting the white balance of the video signal, the control signal forming means slowing down the responsiveness of the control signal to the output of the color temperature detecting means when the incident angle of view is small; An imaging device characterized by increasing speed when an incident angle of view is large. 2. a zoom lens for varying an incident angle of view; an imaging means for forming a video signal from an optical image incident through the zoom lens; and a color temperature within an angle of view corresponding to the incident angle of view. color temperature detection means; control signal formation means for receiving the output of the color temperature detection means and forming a control signal for controlling the white balance of the video signal; and controlling the white balance of the video signal in accordance with the control signal. and adjustment means for adjusting the gain of the control signal with respect to the output of the color temperature detection means, when the incident angle of view is small, the gain of the control signal is small, and when the incident angle of view is large, the gain of the control signal is set to be small. An imaging device characterized by being enlarged.