JPH0918889A - Automatic white balance correction device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the white balance correction with high accuracy by automatically switching the white balance correction method between a full screen average system and a void system in response to the incident light quantity of a solid state image pickup element. SOLUTION: The AGC control voltage is inputted to a comparator 12 from a process circuit 3, and the comparator 12 compares the AGC control voltage with a reference potential and outputs a decision signal. Based on this decision signal, a decision circuit 13 switches the output destination of the color difference signal received from the circuit 3 between a color temperature color detection circuit 5 and the integration circuits 6 and 7 respectively. Therefor, the color difference signal is directly integrated when the incident light quantity is equal or approximate to zero. Then the output of the circuit 5 is integrated when the incident light quantity is large. Thus the white balance is automatically corrected based on the integrated output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance correction apparatus and method used in an image pickup apparatus or the like.

[0002]

2. Description of the Related Art In recent years, CCD video cameras, surveillance cameras, door cameras, medical cameras, and the like have used CCD solid-state image pickup devices (hereinafter abbreviated as CCD) because of their features such as small size, light weight, high performance, and high image quality. It has become common to use such solid-state imaging devices.

Here, since the human eye has chromatic adaptation according to the illumination, a white subject looks white even if the color temperature of the light source changes, but in the case of a solid-state image pickup device such as a video camera, it can be used outdoors or indoors. In the case of (1), a difference in color temperature occurs between the light sources of sunlight and a fluorescent lamp, and a phenomenon occurs in which a white subject is colored due to the difference in color temperature. For example, when the color temperature of the light source is higher than the color temperature set for the camera, the proportion of short-wavelength light is high, so the captured image looks bluish, and when the color temperature of the light source is low, the proportion of long-wavelength light is high. It looks reddish because there are many. Therefore, it is necessary to match the characteristics of the camera with the characteristics of the human eye, and even if the color temperature of the light source changes, it is necessary to correct R = G = B when a white subject is imaged. This is generally called white balance correction, and what is automatically controlled is called auto white balance correction.

A conventional automatic white balance correction device will be described below. FIG. 2 is a block diagram of a conventional automatic white balance correction device. In FIG. 2, 1 is CC
D, 2 are color separation circuits, 3 is a process circuit, and 4 is an encoder. Reference numeral 5 is a color temperature color detection circuit, 6 is an RY integration circuit that integrates the RY signal, and 7 is B- that integrates the BY signal.
Y integration circuit, 8 R control signal generation circuit for outputting R signal gain control signal, 9 B control signal generation circuit for outputting B signal gain control signal, 10 R signal gain control circuit, 11 B signal gain control Circuits 14 and 15 are changeover switches.

The video signal obtained by the CCD 1 is sent to the color separation circuit 2. Here, the video signal is separated into three types of color signals of R, G and B, the G signal is sent directly, and the R and B signals are sent to the process circuit 3 through the respective gain control circuits 10 and 11. In this process circuit, the R, G and B signals are converted into a luminance signal Y and color difference signals RY and BY. Then, the luminance signal and the color difference signal are sent to the encoder 4, where they are converted into camera signals of the NTSC system or the like and output.

Next, two types of white balance correction methods having the configuration shown in FIG. 2 will be described. The first method is a method of performing white balance correction under the assumption that "achromatic color is obtained by integrating the entire screen" in order to extract achromatic color (color temperature color) data from a video signal. . First, the changeover switch 14 is set to the RY integration circuit 6 side, and the changeover switch 1
5 is switched to the BY integrating circuit 7 side. Then, the RY signal output from the process circuit 3 is directly input to the RY integrating circuit 6 without passing through the color temperature / color detecting circuit 5 and integrated so that the RY signal integrated value becomes zero. Feedback control for controlling the R signal gain is performed. In this case, R
The control signal generation circuit outputs an R signal gain control control signal in the direction of setting the value to 0 based on the RY signal integration value output from the RY integration circuit, and this signal is the R signal gain control circuit. Will be given to.

Similar control is performed for the BY signal.
In this way, the white balance is corrected by controlling the respective color signal gains so that the integrated values of the color difference signals RY and BY are both zero. Hereinafter, this white balance correction method is referred to as the "full screen averaging method".

A disadvantage of this full-screen averaging method is that the color difference signal includes not only the color temperature color indicating the change in color temperature but also the color signal of the subject itself, so that an error is likely to occur. There is.

Therefore, as a second white balance correction method for improving this drawback, there is the following method. First, in FIG. 2, the changeover switches 14 and 15 are changed over to the color temperature color detection circuit 5 side. As a result, the color difference signals RY and BY output from the process circuit 3 are input to the integration circuits 6 and 7 via the color temperature / color detection circuit 5.

In correcting the white balance, if only achromatic color (color temperature color) data can be extracted from the color difference signal and used, the above problem can be solved. On the color difference plane shown in FIG. 3, the achromatic color data shows the color temperature color change characteristic (solid line portion) according to the change in color temperature.
To move. Therefore, the color temperature / color detection circuit 5 sets the shaded portion in FIG. 3 which is approximated to the color temperature / color change characteristic, and from the RY signal and BY signal output from the process circuit 3, The data in the shaded area, that is, only the achromatic color is taken out and output to the RY integrating circuit 6 and the BY integrating circuit 7.

Then, similar to the operation described in the full screen averaging method, the R-Y signal and the BY signal are integrated, and the R signal gain and the B signal are adjusted so that the integrated values of these color difference signals become zero. White balance is achieved by controlling the gain independently. Hereinafter, this white balance correction method is referred to as "white extraction method".

[0012]

As described above, in the conventional configuration shown in FIG. 2, the changeover switches 14 and 15 are switched to select either the full screen averaging method or the white extraction method. can do. However, normally, the changeover switches 14 and 15 are fixed to either of the changeover positions. With the full screen averaging method,
For the above-mentioned reason, when a color of a specific hue occupies a large area in the screen, there is a possibility of malfunction such as fading of the color or coloring of white with another color. On the other hand, in the white extraction method, when the incident light is zero and a step is included between the black level of the color difference signal and the color signal due to an adjustment error, etc. A problem arises.

That is, in the above case, since the automatic gain control (hereinafter, abbreviated as AGC) has the maximum value, the step becomes large. Then, this step difference is regarded as a deviation of the color temperature and feedback is applied, and the color temperature moves to the correction limit in the direction of absorbing the step difference. When light is rapidly incident in this state, the AGC is maximized, and therefore the influence of the white balance fluctuation that has moved to the above limit is maximized, and the point representing white deviates from the shaded portion in FIG. . In this case, white that is out of the shaded area cannot be extracted from the color difference signal, so the color difference information for white balance is lost,
As a result, auto white balance is lost.

The present invention has been made in order to solve the above-mentioned conventional problems, and a white balance correction method and a white extraction method are used as a white balance correction method according to the amount of incident light entering a solid-state image pickup device. It is an object of the present invention to provide an automatic white balance correction device that realizes highly accurate white balance correction by automatically switching between the methods.

[0015]

To achieve this object, an automatic white balance correction apparatus according to the present invention inputs a solid-state image sensor and a video signal output from the solid-state image sensor into a basic color signal. A color separating means for separating, a color temperature compensating means for inputting a basic color signal output from the color separating means and adjusting a gain according to a change in color temperature of illumination light with respect to a subject, and a gain for the color temperature compensating means. The adjusted basic color signal is input and the color difference signal, luminance signal and AG
C means for generating a control voltage, an encoder for generating a camera signal from the color difference signal and a luminance signal, a color temperature color detecting means for extracting only a specific color temperature component from the color difference signal, the color difference signal or the color It is provided with an integrating means for integrating a temperature component, and a controlling means for generating a control signal for the color temperature compensating means by the output of the integrating means, which is characterized by a reference potential arbitrarily set and In comparison with the AGC control voltage, there is provided a comparing means and a judging means for switching the output destination of the color difference signal between the color temperature color detecting means and the integrating means based on the output of the comparing means. is there.

A feature of the auto white balance correction method of the present invention performed by using the above apparatus is that when the amount of incident light entering the solid-state image pickup device is zero or in the vicinity thereof, the output of the integrating means is used to integrate the color difference signals. The point is that the color temperature is corrected, and when the amount of incident light is large, the color temperature is corrected by using the output of the integrating means obtained by integrating the output of the color temperature color detecting means.

[0017]

According to the automatic white balance correction apparatus of the present invention having the above-described structure, the white balance correction method is automatically switched to a more appropriate method depending on the amount of incident light incident on the solid-state image sensor. As a result, highly accurate white balance correction can be performed.
Incidentally, when the color difference signal is sent to the integrating means via the color temperature / color detecting means, the white balance correction of the white extraction method is performed, and when the color difference signal is sent directly, the white balance correction of the full screen average method is performed.

According to the above automatic white balance correction method, when the incident light quantity is zero or in the vicinity thereof, the white balance correction of the whole screen average method is performed, and when the incident light quantity is large, the white extraction method white balance correction is performed. Will be done.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the automatic white balance correction apparatus of the present invention. In FIG. 1, 1 is CC
D solid-state image sensor, 2 color separation circuit, 3 process circuit,
Reference numeral 4 is an encoder. 5 is color temperature color detection circuit, 6 is R
RY integrating circuit for integrating -Y signal, 7 BY integrating circuit for integrating BY signal, 8 R control signal generating circuit for outputting R signal gain control signal, 9 B signal gain control signal Is a R signal gain control circuit, and 11 is a B signal gain control circuit. These components are the same as those of the conventional example shown in FIG.

Reference numeral 12 is a comparison circuit, which is a process circuit 3
The AGC control voltage output from the internal AGC circuit is input, this is compared with a reference potential, and a determination signal is output. This reference potential is adjusted and set with respect to the AGC control voltage when the AGC gain changes from 0 to the maximum value.

The judgment signal from the comparison circuit 12 is the judgment circuit 13
And the determination circuit 13 sends the color difference signals RY and BY input from the process circuit 3 to the color temperature color detection circuit 5 or R- based on the input determination signal.
It is determined whether or not it is directly sent to the Y integration circuit 6 and the BY integration circuit 7, and switching is performed. When the color difference signals R-Y and B-Y are sent to the R-Y integration circuit 6 and the BY integration circuit 7 via the color temperature / color detection circuit 5, the white balance correction by the white extraction method is performed, and When sent, white balance correction is performed by the full screen average method. The white extraction method and the full screen average method are as described in the conventional example.

The reference potential of the comparison circuit 12 is set as follows. That is, when the incident light is at or near zero, the determination circuit 13 sends the color difference signals RY and BY to the RY integration circuit 6 and BY integration circuit 7, and otherwise, the determination circuit 13. Is set to a potential such that the comparison circuit 12 outputs a determination signal for sending the color difference signals RY and BY to the color temperature / color detection circuit 5.

[0023]

As described above, according to the present invention, the white balance correction method is automatically switched between the full screen averaging method and the white extraction method according to the amount of incident light entering the solid-state image sensor. , For example, to prevent malfunction due to a step included between the black level of the color difference signal and the color signal,
Highly accurate white balance correction is possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an automatic white balance correction device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional auto white balance correction device.

FIG. 3 is a diagram for explaining a white extraction method of a white balance correction method.

[Explanation of symbols]

 1 CCD solid-state imaging device 2 color separation circuit 3 process circuit 4 encoder 5 color temperature color detection circuit 6 RY integration circuit 7 BY integration circuit 8 R control signal generation circuit 9 B control signal generation circuit 10 R signal gain control signal 11 B signal gain control signal 12 Comparison circuit 13 Judgment circuit 14 Changeover switch 15 Changeover switch

Claims (2)

[Claims] 1. A solid-state image sensor, color separation means for inputting a video signal output from the solid-state image sensor and performing color separation into basic color signals, and a basic color signal output from the color separation means. A color temperature compensating unit that performs gain adjustment according to a change in color temperature of illumination light with respect to an object, and a basic color signal whose gain has been adjusted by the color temperature compensating unit are input to generate a color difference signal, a luminance signal, and an AGC control voltage. A processing means, an encoder for generating a camera signal from the color difference signal and the luminance signal, a color temperature color detecting means for extracting only a specific color temperature component from the color difference signal, and an integration for integrating the color difference signal or the color temperature component. An automatic white balance correction device comprising: means and a control means for generating a control signal for the color temperature compensating means by the output of the integrating means. Comparing means for comparing the reference potential and the AGC control voltage, and judging means for switching the output destination of the color difference signal between the color temperature color detecting means and the integrating means based on the output of the comparing means. An automatic white balance correction device characterized by being provided. 2. An auto white balance correction method using the auto white balance correction apparatus according to claim 1, wherein when the amount of incident light entering the solid-state image sensor is at or near zero, integration that integrates color difference signals is performed. An automatic white balance correction method characterized in that color temperature correction is carried out using means output, and when the amount of incident light is large, color temperature correction is carried out using integrating means output obtained by integrating the color temperature color detection means output.