JPH01270481A - White balance correcting circuit - Google Patents

Abstract

PURPOSE:To execute a suitable correction even to the object of a monochromatic light and to execute an accurate correction by executing the correction with a difference signal between a chrominance signal and a prescribed level after correction and the color temperature of an external light. CONSTITUTION:The output of an image pickup element 10 is converted to a luminance signal YH, a low area luminance signal YL and color difference signals (R-YL) and (B-YL) with a luminance chromaticity forming circuit 12. The signal YL is added, subtracted and corrected to a color difference signal inputted to white balance correcting amplifiers 14 and 16. A color difference signal comparing circuit 34 outputs the difference between the average value of the color difference signal and an achromatic level after correction. A color temperature detecting circuit 32 detects the color temperature from the output of a color temperature sensor 30. A white balance correcting circuit 36 forms a correcting signal based on the output of the circuit 32 and the circuit 34 and controls the amplifiers 14 and 16. The luminance signal YH and the chrominance signal after the correction are inputted to an encoder 18 and converted to a standard TV signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a white balance correction circuit, and more specifically, to a white balance correction circuit in an imaging device such as a color video camera or an electronic still camera. This invention relates to a correction circuit.

[Conventional technology]

FIG. 2 shows a configuration block diagram of a conventional example of an imaging device incorporating a white balance correction circuit.

10 is an image sensor, 12 is a brightness/chromaticity forming circuit, 14.1
6 is a white balance correction amplifier, 18 is a luminance signal output from the luminance/chromaticity forming circuit 12 and a white balance correction amplifier;
A standard television digital signal (
20 is a color temperature sensor, and 22 is a white balance correction signal forming circuit that forms a white balance correction signal from the output of the color temperature sensor 20.

To briefly explain the operation shown in FIG. 2, the light incident on the image sensor 10 is photoelectrically converted and applied to the brightness/chromaticity forming circuit 12. The luminance/chromaticity forming circuit 12 sends a luminance signal YM to a signal line 12A, a low frequency luminance signal YL to a signal line 12B, a color difference signal (R-YL) to a signal line 12G, and a color difference signal (BYL) to a signal line 12D. ) is output. Signal '47A12c,
Each of the 12D color difference signals is applied to a white balance correction amplifier 14.16.

The white balance correction signal forming circuit 22 forms a white balance correction signal based on the output of the color temperature sensor 20, and the amplifier 14.16 outputs the low-range luminance of the signal line 12B according to the white balance correction signal. Signal YL is added to or subtracted from the color difference signal input. This makes the amplifier 14.1
The output of No. 6 is a white-balanced color difference signal.

The encoder 18 receives the luminance signal YH1 from the luminance/chromaticity forming circuit 12 and the color difference signals (R-YL), (B-
YL) to form and output a standard television signal.

However, in the conventional example shown in FIG. 2, the system for correcting white balance is an oven loop, which has the disadvantage of poor absolute accuracy. To eliminate this drawback,
The conventional example shown in FIG. 3 has a closed loop configuration. In FIG. 3, the same components as in FIG. 2 are given the same reference numerals. 24 is a white balance correction signal forming circuit corresponding to the white balance correction signal forming circuit 22 in FIG. 2, and the difference from that in FIG.
The point is that a white balance correction signal is generated by referring to the output of .

The operation of the imaging device shown in FIG. 3 will be explained. The luminance/chromaticity forming circuit 12 receives the luminance signal Y as described above.

It outputs YL and color difference signals (R-YL) and (B-yt), and the color difference signals (R-YL) and (B-YL) are applied to amplifiers 14 and 16, respectively. Amplifier 14°16
In response to the white balance correction signal from the white balance correction signal forming circuit 24, as in the case of FIG.
YL) and (B-YL), and outputs a white balance corrected color difference signal.

The white balance correction signal forming circuit 24 includes the amplifier 1
The average value of the color difference signal subjected to white balance correction according to 4.16 is compared with the achromatic color level of the color difference signal, and a white balance signal having the same level is formed and applied to the amplifier 14.16. This allows white
Balance correction is performed in a closed loop.

[Problem to be solved by the invention]

In the conventional example shown in FIG. 3, the white balance correction system is a closed loop, so the accuracy of the circuit system is high.

However, for example, when the incident light on the image sensor 100 does not reflect the color temperature (or spectral distribution) of the illumination light irradiating the subject, as in the case of a single chromatic subject, erroneous The drawback is that white balance correction is required.

Therefore, it is an object of the present invention to provide a conventional white balance correction circuit that performs appropriate wide balance correction even in such cases.

[Means to solve the problem]

A white balance correction circuit according to the present invention includes a correction means for correcting a color signal according to a white balance correction signal, and an arithmetic means for forming a signal regarding a difference from a predetermined level regarding the color signal after correction by the correction means. , a color temperature detection means for detecting the color temperature of external light, and when the calculation means indicates that the difference is substantially zero, the white balance correction is performed according to the output of the color temperature detection means. a white balance signal, and when the calculation means indicates that the difference is not substantially zero, the white balance correction signal is formed from the calculation result of the calculation means and the output of the color temperature detection means; It is characterized by comprising a correction signal forming means.

[Effect]

The color temperature detection means described above can detect the color temperature of external light,
The arithmetic means determines, so to speak, whether or not the color signal for which white balance correction is to be performed is monochromatic. In the case of a single color, for white balance correction,
As the object is illuminated, the information that is the basis for forming the white balance correction signal is switched. This makes it possible to achieve appropriate white balance correction according to the subject and illumination light.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of the present invention, in which the same components as in FIGS. 2 and 3 are given the same reference numerals.

In FIG. 1, 30 is a color temperature sensor consisting of a color filter of two or more colors and a photo sensor (for example, a photodiode, a phototransistor, etc.) for detecting the amount of light of each color component by the color filter; 32 is a color temperature sensor; , a color temperature detection circuit that calculates the light amount signal of each color component from the color temperature sensor 30 and detects the color temperature of the light incident on the color temperature sensor 30; A color difference signal comparison circuit 36 that compares the achromatic color level of the signal and outputs the difference amount forms a white balance correction signal according to the color temperature detected by the color temperature detection circuit 32 and the output of the color difference signal comparison circuit 34. This is a white balance correction signal forming circuit. The white balance correction signal output from the white balance correction signal forming circuit 36 controls the amplifiers 14 and 16.

The operation shown in FIG. 1 will be explained. The luminance/color difference forming circuit 12 is
As in the case of FIGS. 2 and 3, the luminance signals YH, YL
and outputs color difference signals (RYL) and (B-YL),
The color difference signals are applied to amplifiers 14 and 16, respectively. The amplifiers 14 and 16 perform white balance correction on the input signal according to the white balance correction signal from the white balance correction signal forming circuit 36, and output the resultant signal. The outputs of the amplifiers 14 and 16 are applied to the encoder 18 and the color difference signal comparison circuit 34. The encoder 18 forms and outputs a standard television signal as in the conventional example.

The color difference signal comparison circuit 34 compares the average value of the color difference signals (R-YL) and (B-YL) output from the amplifier 14.16 with the achromatic color level of each color difference signal, and indicates the difference. White balance correction signal forming circuit 3
6. On the other hand, the color temperature sensor 30 outputs signals of a plurality of color components of external light, and the color temperature detection circuit 32 determines the color temperature of the external light from the output of the color temperature sensor 30.

When the color difference signal comparison circuit 34 outputs a signal indicating zero difference, the white balance correction signal forming circuit 36
When a white balance correction signal is formed depending uniquely on the color temperature signal outputted by the color temperature detection circuit 32 and the color difference signal comparison circuit 34 outputs a signal indicating non-zero,
A white balance correction signal is formed from both the color temperature signal from the color temperature detection circuit 32 and the output of the color difference signal comparison circuit 34. The white balance correction signal thus formed is applied to the amplifier 14.16,
Amplifiers 14 and 16 are as in the case of Figs. 2 and 3,
The low-range luminance signal YL is input as a color difference signal (R-YL).
), (B-Y, ) and outputs a white balance corrected color difference signal.

In the embodiment shown in FIG. 1, color difference signals (RY), (B-Y)
By adding and subtracting the low-range luminance signal YL to
Although the configuration for performing balance has been shown, it goes without saying that the present invention may be applied to other generally known configurations (for example, a configuration for controlling the amplification gains of the R signal and the B signal).
The signal to be compared in the color difference signal comparison circuit 34 may be a signal obtained by performing some kind of calculation between the color difference signals, or a signal obtained by removing an abnormal portion (for example, a high brightness portion) of the color difference signal.

〔Effect of the invention〕

As can be easily understood from the above explanation, according to the present invention, a white light beam that takes external light into consideration and has good control accuracy can be achieved.
Balance correction can be performed.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of one embodiment of the present invention, and FIGS. 2 and 3 are configuration block diagrams of a conventional example. 10-・Image sensor 12-・Brightness/chromaticity forming circuit 1
4.16- White balance correction amplifier 18...
-Encoder 20...Color 1m sen +22.24°3
6.-White balance correction signal forming circuit 30.
・-Color temperature sensor 32-・-Color temperature detection circuit 34・
・−Color difference comparison circuit

Claims (1)

[Claims] a correction means for correcting a color signal according to a white balance correction signal; a calculation means for forming a signal regarding the difference from a predetermined level regarding the color signal after correction by the correction means; and a color temperature for detecting the color temperature of external light. When the detection means and the calculation means indicate that the difference is substantially zero, the white color temperature is determined according to the output of the color temperature detection means.
When a balance correction signal is formed and the calculation means indicates that the difference is not substantially zero, the calculation result of the calculation means and the output of the color temperature detection means are used to determine the white balance.
A white balance correction circuit comprising a white balance correction signal forming means for forming a balance correction signal.