JPS62284594A - Automatic white balance circuit - Google Patents

Abstract

PURPOSE:To attain a high-accuracy automatic white balance adjustment by supplying a white balance control signal to 1st and 2nd gain control amplifiers in common and composing the 1st and the 2nd gain control amplifiers of the same components so as to have the same characteristics. CONSTITUTION:The color temperature at a photography place is detected by a color detecting element 20, the R component and B component of the detected illumination light are supplied to a control circuit 22 through the 1st preamplifier 21, and the voltage levels of the R component and B component are adjusted to reference voltage levels. The adjusted control signal is fed back to the 1st preamplifier 21 and a control circuit 22 corrects a balance adjustment value. Further, the control signal from the control circuit 2 is supplied to the 2nd preamplifier 23 as well and corrected successively to vary the gains of the R signal circuit and B signal circuit of a camera, thereby adjusting the automatic white balance. Consequently, the white balance can be adjusted with high accuracy.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an improved auto white balance circuit in a color video camera or the like.

(Prior Art) FIG. 3 shows an example of an imaging device incorporating a conventional auto white balance circuit.

This auto white balance circuit 100 includes two external sensors 10 provided separately from the bridge image system, and a color temperature detection side jT.
1 circuit 11 and a gain control amplifier 1 incorporated in the imaging system.
It consists of a composition including 2 and .

The two external sensors 10 detect, for example, R and B color components of the illumination light at the photographing location. The color temperature detection control circuit 11 receives this detected color information and uses the gain control circuit 11 to adjust the color balance of the R and B channels of the IIi & image system. 11 amplification! A control il signal is output to SL2 to perform white balance adjustment.

The auto white balance circuit configured in this way obtains color information from the external sensor 10, so it can automatically adjust the white balance as needed, regardless of the imaging system, even during image capture, and can improve the It has the advantage of being able to constantly track changes.

(Problems to be Solved by the Invention) However, as is clear from the figure, the auto white balance circuit had the drawback of poor accuracy because it was an open-loop control. That is, since the characteristics of the color temperature detection control circuit 11 and the gain control amplifier 12 do not match, an imbalance occurs between the R and B signals, and the white balance is disturbed.

The reason for this discrepancy in characteristics is that there is no correlation between the variations in the characteristics of the control circuit 11 and the amplifier 12, or that the temperature characteristics never fail.

The object of the present invention was achieved based on the above circumstances, and
An object of the present invention is to provide an auto white balance circuit applicable to a color video camera, etc., which enables highly accurate white balance adjustment and can be adjusted independently of an imaging system.

(Means and effects for solving the problems) That is, the above-mentioned object of the present invention is to provide a color detection element provided separately from an imaging means, and a color detection element provided separately from an imaging means in an auto white balance circuit in a color video camera or the like. a first gain control amplifier to which a color signal from the element is supplied; a color temperature detection control circuit that outputs a white balance control signal based on the output signal of the first gain control amplifier; a first gain control amplifier that adjusts the gain of each color channel; the white balance control signal is commonly supplied to the first and second gain control amplifiers; The control amplifier is achieved by an auto white balance circuit characterized by being made of the same components and having the same characteristics.

In this way, by providing two gain control amplifiers with the same configuration and having the same characteristics, and adjusting the color balance of the output from one gain control amplifier and feeding it back again, the color temperature detection control circuit and the gain control amplifier can be combined. Highly accurate balance adjustment is achieved by correcting differences in the characteristics of the two.

(Example) Hereinafter, the present invention will be described in detail based on the drawings. In the embodiment shown in FIG. 1, the auto white balance circuit includes two color detection elements 20 provided separately from an imaging system, which will be described later, and two first color detection elements 20 to which the outputs of the color detection elements 20 are respectively supplied.
a gain control amplifier (hereinafter simply referred to as a first preamplifier) 21, and a color temperature detection control circuit (hereinafter simply referred to as a first preamplifier) that receives the output from the first preamplifier 21 and outputs a white balance control signal. control circuit) 22, and two second gain control amplifiers (hereinafter simply referred to as second preamplifiers) 23 for white balance adjustment. It consists of a configuration in which a control signal is commonly input to the first and second preamplifiers 21,23. Further, the first and second preamplifiers 2
1.23 consists of the same components and has the same characteristics.

Note that the color detection element 20 is an optical sensor, and uses a solid-state image sensor like the first image element.

Next, a video camera of a single carrier frequency separation type will be described as an example of a photographing apparatus incorporating this automatic white balance circuit.

The imaging system separates and extracts a luminance signal (Y), a red component (R), and a blue component ([3)] from the optical signal of a subject image captured by one imaging device 24 through a separation circuit 25. ing. The color signals outputted to the R and B color channels are demodulated and sent to the second preamplifier 2, respectively.
3-1 and 23-2, and converts it into a luminance signal (Y).
The signal is also passed through a matrix circuit 26 and applied to a color encoder 27 to obtain an NTSC system composite color video signal.

When photographing with the video camera configured as described above, the color temperature of the photographing location is detected by the color detection element 20. The detected R component and B component of the illumination light are supplied to the control circuit 22 through the first preamplifier 21, and the voltage levels of the R component and B component are adjusted with respect to the reference voltage level, and this adjusted control The signal is fed back to the first preamplifier 21 again, and the control circuit 22 successively corrects the balance adjustment value again. Further, the control signal from the control circuit 22 is transmitted to the second preamplifier 23.
Therefore, the gains of the R signal circuit and B signal circuit of the camera are changed based on the successively corrected control signals to perform white balance adjustment.

The auto white balance circuit operates in conjunction with turning on the camera power, and performs adjustment immediately before drawing.
It is configured to make sequential adjustments during shooting to track the shooting situation.

The embodiment shown in FIG. 2 is applied to a primary color type color camera, and external sensors are used to detect R component, B component, and Three color detection elements 20 for detecting the G component and the G component are provided, and the rest is substantially the same as the embodiment shown in FIG. 1 above. The control circuit 22 is composed of two differential amplifiers 28, each of which has a G component signal inputted to its non-inverting input, and R component and B component signals inputted to its inverted input. By configuring this, the gains of the R signal circuit and the B signal circuit of the camera are respectively adjusted using control signals of the R component and the B component based on the G signal.

Although the first embodiment and the second embodiment are configured so that the white balance adjustment is automatically performed at all times, it is also possible to configure the white balance adjustment to be performed at any time by manual setting.

Further, in the first embodiment and the second embodiment, preferably the first preamplifier and the second preamplifier are
By configuring it in a C chip and keeping it under the same environment, there is almost no influence from temperature variations.

(Effects of the Invention) As described above, since the auto white balance circuit of the present invention forms a feedback loop between the preamplifier and the control circuit, disturbances in white balance may occur due to differences in the characteristics of the two. It is possible to make highly accurate adjustments by scratching.

Furthermore, since the optical signal for adjustment is obtained from an external sensor separate from the imaging system, the balance can be adjusted sequentially regardless of the photographing operation. This is especially advantageous for electronic still cameras that record single-shot image signals with one shutter operation, and white balance adjustment can be performed before shutter operation.

In addition, since the first preamplifier and the second preamplifier are made of the same components and have the same characteristics, stable and highly accurate white balance adjustment can be achieved without being affected by variations in characteristics or temperature changes. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining one embodiment of the present invention, FIG. 2 is a circuit diagram for explaining another embodiment of the present invention, and FIG. 3 is a diagram for explaining a conventional auto white balance circuit. 20... Color detection element, 21... First gain control amplifier, 22... Color temperature detection control circuit, 23... Second gain control amplifier, 24... Ti image element, 25 ... Separation circuit, 26.
...Matrix circuit, 27...Color encoder, 28...Differential amplifier. Figure 1 Demand Figure 2 Figure 3

Claims (1)

[Claims] 1) In an auto white balance circuit in a color video camera or the like, a color detection element provided separately from an imaging means, and a first color detection element to which a color signal from the color detection element is supplied.
a gain control amplifier, a color temperature detection control circuit that outputs a white balance control signal based on the output signal of the first gain control amplifier, and a second gain that is inserted into the imaging system and adjusts the gain of each color channel. a control amplifier, the white balance control signal is commonly supplied to the first and second gain control amplifiers, and the first and second gain control amplifiers are made of the same components and have the same characteristics. An auto white balance circuit characterized by having. 2) The auto white balance circuit according to claim 1, wherein the first gain control amplifier and the second gain control amplifier are provided within the same semiconductor chip.