JPS60218993A - White balance device - Google Patents

Abstract

PURPOSE:To correct the white balance shifting caused by that of color temperature at the side of a telescope in terms of a color television camera by constituting in such a way that a variable time constant circuit of a white balance control for varying time constants in accordance with an output of a zoom angle detection circuit is provided. CONSTITUTION:By detecting a zoom angle with the aid of a zoom angle detection circuit 1, an incident angle of the color temperature detection is controlled and made incident on red and blue detection sensors 2 and 3, while the color temperature is detected by a 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 through a weighting means 11, and time constants are changed in accordance with the output value. Thus the controlled time constants change gains in gain control circuits 5 and 6 in accordance with the output value of the color temperature detection circuit 4, thereby taking a white balance. At this time, since a picture angle is narrowed in the variable time constant circuits 12 and 13 when a zoom is shifted to the side of a zoomer, the color temperature is shifted. Accordingly the shifting is canceled out by making the time constant longer, and a natural screen can be obtained by lowering the response at the shifted color temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a white balance device for a color television camera that controls the angle of incident light according to the zoom angle and detects the color temperature.

[Prior art]

To adjust the white balance on a TV camera, first,
After switching the color temperature (with or without inserting a color temperature conversion filter), take an image of a white subject, such as a blank sheet of paper, or
Put a milky-white lens cap on the lens, adjust the white balance adjustment knob while watching the indicator, 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 is a tracking type process that constantly follows the change in color temperature and maintains the white balance.

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.
The zoom angle is detected at , and the angle of the incident light incident on the red and blue detection sensors 2 and 3 is changed depending on the imaging angle of view. Then, the color temperature detection circuit 4 detects the color temperature at the angle of view that changes depending on the zoom angle, and inputs this information to the gain control circuits 5 and 6, respectively. It performs gain control with component B.

However, this method has the disadvantage that the angle of view becomes narrower at the telephoto end, resulting in a slight deviation in the actual color temperature due to the influence of the color of the subject.

[Purpose of the invention]

The present invention has been made by focusing on the drawbacks of the above-mentioned conventional example, and solves this problem by providing a configuration including a variable time constant circuit for white balance control that changes according to the output value of the zoom angle detection circuit. The purpose is to resolve the issue.

[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 between the ζ color temperature detection circuit 4 and the gain control circuits 5 and 6, respectively.

In a tracking auto white balance device that changes the incident light angle for color temperature detection depending on the zoom angle, the zoom angle detection circuit 1 first detects the zoom angle and changes the incident light angle for color temperature detection. The angle of the light is controlled, the light enters the red and blue detection sensors 2 and 3, and the color temperature detection circuit 4 detects the color temperature.

On the other hand, the means 11 weights the output value of the zoom angle detection circuit 1.
are respectively input to variable time constant circuits 12 and 13 via
The time constant changes depending on the output value. The time constant controlled by this is controlled by the gain control circuits 5 and 6 according to the output value of the color temperature detection circuit 4. Control the white balance by changing l.

At this time, the variable time constant circuits 12 and 13 use the variable time constant circuits 12 and 13 to adjust the angle of view when the zoom is set to the zoom telephoto side. By increasing the time constant, the response to misaligned color temperatures is slowed down and a natural screen can be obtained.On the other hand, when the zoom is set to the wide side, the angle of view is wide, so the color temperature detection information is is accurate, so it shortens the time constant and improves responsiveness.

In the above embodiment, instead of the variable time constant circuit 12.13 controlling the gain, the variable gain circuit 14.15 reduces the overall gain of the gain control circuits 5 and 6 on the zoom telephoto side as shown in the third diagram. However, the same effect can be obtained by increasing the gain on the zoom wide side.

〔Effect of the invention〕

As explained above, the present invention provides a tracking type auto white balance that changes the angle of incident light for color temperature detection depending on the zoom angle, and a variable time constant for white balance control that changes according to the output value of the zoom angle detection circuit. Because the configuration includes a circuit, the time constant of white balance control is shortened at the wide-angle end and lengthened at the telephoto end, thereby correcting the white balance shift based on the shift in color temperature at the telephoto end, resulting in a natural This has the effect that it is possible to obtain a clear image.

[Brief explanation of drawings]

Figure 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 Figure 2 is a block diagram of an automatic white balance device that includes a variable time constant circuit according to the zoom angle according to the present invention. 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 Fig. 1 2 Fig. 2

Claims (1)

[Claims] In an auto white balance device that controls the incident light angle of υ white balance according to the zoom angle, detects the color temperature, and automatically adjusts the gain of the color signal circuit of a color television camera, the zoom angle is detected and the zoom angle is detected. A white balance device comprising a variable time constant circuit for white balance control that changes a time constant according to an output value of the circuit.