JPH01231586A - Automatic white balancing device - Google Patents

Abstract

PURPOSE:To realize accurate white balance at low cost by correcting the level ratio of a color signal separated from a video signal based on a discriminated spectral characteristics at the value equal to the level ratio obtained with the natural light or the light of an incandescent lamp. CONSTITUTION:The spectral characteristics of photoelectric transducing elements 1a-1c are different from each other and scattered properly within a range of the spectral characteristics of an image pickup device 4. An arithmetic means 3 discriminates the spectral characteristics of the external beams incident on the elements 1a-1c based on the relation between the input signals Aa and Ac and also outputs the gain control signals Aa1 and Ac1 which are obtained by giving the correction to the input division values Aa and Ac respectively. In other words, the level ratios among color signals R, G and B are corrected in accordance with the discriminated spectral characteristics of an illumination light source. So the said level ratios are equal to those obtained with the natural illumination light. Thus it is possible to ensure an easy white balancing action even with an illumination light source having the special spectral characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic white balance device, and more particularly to an automatic white balance device that is used in a color video camera device to automatically adjust white balance.

[Conventional technology]

FIG. 3 is a block circuit diagram showing the configuration of a conventional automatic white balance device that is often used in home color video cameras.

In the figure, (lr), (Ig) and (1b) are each red.

A photoelectric conversion element having green and blue spectral sensitivity characteristics converts incident light into electrical signals Er, Bg, and Eb. (2
a) and (2b) are division circuits that calculate Eg/Er=Ar and Eg/Eb=Ab, output signal Ar is sent to the variable gain amplifier (6a), and output signal Ab is sent to the variable gain amplifier (6b). are respectively input as gain control signals. (4) is an imaging device, (5) is a color signal separation circuit,
The color signal R from the video signal input from the imaging device (4
Separate G and B. Of these color signals, the color signal R is input to the variable gain amplifier (6a), the color signal B is input to the variable gain amplifier (6b), and the color signal G is directly input to the encoder (7). Variable gain amplifier (6a
The color signal R1 adjusted to a level according to the gain control signal Ar is input to the encoder (7), and the variable gain amplifier (
Color signal B adjusted to a level according to gain control signal Ab.

is input to the encoder (7). The encoder (7) converts the input color signals R1, GJ:3 and B1 into signals suitable for subsequent processing.

Next, the operation of this conventional example will be explained. Photoelectric conversion element (1
r), (Ig) and (lb) Since the moon has red, green, and blue spectral sensitivity characteristics, respectively, the output voltage Er corresponding to the red, green, and 'A' components of the wavelength distribution of the incident light is
, Eg and Eb. For this reason, the division circuit (2
The output signals Ar and Ab output from a) and (2bJ) are signals representing the ratio of (green component)/(red component) and the ratio of (green component)/(blue component) of the incident light. , the level of the color signal R, output from the variable gain amplifier (6a) is adjusted to R1''-,RX(Eg/Er), and the color signal E, output from the variable gain amplifier (6b), is BI= The level is adjusted to Bx (Eg/Er).

In this way, in the conventional automatic white balance device, it is necessary to match the spectral characteristics of the R, G, and B outputs for the incident light of the imaging device (4) with the spectral characteristics of the light flux conversion elements (lr) and (IgL (lb)). Therefore, even if the color temperature of external light takes various values, the color signal input to the encoder (7) can be kept constant, and white balance can be automatically achieved.

[Problem to be solved by the invention]

Since the conventional automatic white balance device is configured as described above, it is necessary to accurately match the spectral characteristics of the photoelectric conversion element and the imaging device, which has led to the problem that the device is expensive.

In addition, when using an illumination light source with spectral characteristics different from incandescent light sources such as fluorescent lamps, there is a problem that accurate white balance cannot be achieved due to slight mismatch between the spectral characteristics of the photoelectric conversion element and the imaging device. There was a point.

This invention was made in order to solve the above-mentioned problems, and when the spectral characteristics are accurately matched using a photoelectric conversion element whose spectral characteristics have been managed only in a relatively genius way compared to conventional methods. An automatic white balance device that can perform white balance with the same level of accuracy as the standard white balance device, and can perform accurate white balance operations even for illumination light sources with special spectral characteristics such as fluorescent lights. The purpose is to obtain.

[Means to solve the problem]

An automatic white balance device according to the present invention includes at least eight light flux conversion elements each having different spectral characteristics into which illumination light is incident, means for calculating at least two ratios of output signals of these light flux conversion elements, and a means for calculating at least two ratios of output signals of these light flux conversion elements; A means for discriminating the spectral characteristics of the illumination light from the ratio value, and a level of the color signals R1G and B separated from the video signal photographed according to the discriminated spectral characteristics when an incandescent light source is used as the illumination light. The present invention is characterized in that it includes means for correcting so that the ratio becomes the same.

[Effect]

The means for discriminating the spectral characteristics of illumination light in this invention is as follows:
The spectral characteristics of the illumination light are discriminated from the relationship between the ratio values of the output signals of the photoelectric conversion elements. Color signal ratio.

The G, B level correction means corrects the level ratios of the color signals R, G, and E according to the spectral characteristics of the discriminated illumination light sources so that the level ratios of the color signals R, G, and E become the level ratios when the illumination light is natural light.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a block diagram showing the configuration of an embodiment of the present invention.
! In FIG. 1, the same components as those in the conventional example shown in FIG. 3 are given the same reference numerals.

In the figure, (la), (lb) and (IC) are
The photoelectric conversion elements each have different spectral characteristics, and the spectral characteristics of these elements may be appropriately dispersed within the range of the spectral characteristics of the imaging device (4).

(2a) is a division circuit that calculates Aa = (Ea/Bb), (2b) is a division circuit that calculates Ac = (Eb/Ec), and (3) is a calculation means that outputs input signals Aa and Ac.
From the relationship, photoelectric conversion elements (ia), (lb), (
In addition to distinguishing the spectral characteristics of external light incident on the lc),
Gain control signals Aa+ and Act are output by correcting the input division values Aa and Ac, respectively.

Next, the operation of this embodiment will be explained.

When the illumination light is natural light or incandescent light, the division values Aa and Ac output from the division circuits (2a) and (2b)
There is a certain relationship between them. In general, natural light and incandescent light bulbs emit light due to heat, and the emission spectrum of these light sources is based on the theory of black body radiation (known as plan
It follows k's law or Wien's law as an approximate solution. Therefore, for the change in color temperature, the division value A, a and A
There is a relationship with C such that if one increases, the other decreases. Experimentally, in the color temperature range that is normally photographed by a color video camera, as shown in Figure 2,
The values of og(Aa) and log(AC) or A, a and Ac exist on a straight line Ak.

However, if the illumination light is a light source with a special light spectrum such as a fluorescent lamp, the concept of so-called color temperature does not apply to the set of line spectra, so the point E and 0 are located off the straight line A in Figure 2. The values of Aa and Ac are as follows.

That is, the division value Aa+A located on the straight line A,
When C is input, the illumination light source is natural light or incandescent lamp light, and when it deviates from straight line A, it includes light other than natural light or incandescent light source, and when it is at a specific position, it is a discharge lamp with the spectral characteristics. It turns out that.

By the way, the photoelectric conversion element and the image sensor that make up the photographing device are manufactured by different processes (as they are often made in different processes, it is difficult to perfectly match their spectral characteristics, but natural light and incandescent light In the case of lamp light, even if there is a difference in the cutoff wavenumber of the spectral characteristics of the photoelectric conversion element and the image sensor, the division values Aa and Ac maintain a constant ratio, so
Can be easily adjusted to adulthood. On the contrary,
In the case of discharge lamp light, etc., the light spectrum is localized at a certain frequency as a line spectrum, so if there is a discrepancy in the cutoff wavenumber of the spectral characteristics of the photoelectric conversion element and the image sensor, the new cutoff wavenumber The white balance may shift significantly due to the influence of nearby line spectra.

When the division values Aa, A, and C are located on the straight line A shown in FIG.
a, Ac are output as they are as gain control signals Aat, Act. Also, the division values Aa, A, and c are shown in Figure 2.
3. If it deviates from the straight line A, as shown as point C, the correction value /2a is used to move it onto the straight line A, for example, as shown by the dashed-dotted arrow in the figure.

αC was added (direct Aa+ = A, a+aa, A
Gain control voltage Aa+ corresponding to ct = A, c+αC
, Outputs Act. The value of the correction value "a + "C is the photoelectric conversion element (la).

(lb), (lc) and the imaging device (4) may be experimentally determined to appropriate values depending on the difference in spectral characteristics.

The variable gain amplifiers (6a) and (6b) have a gain control voltage Aa+.

Since the gain is proportional to Acl, the same operation as the conventional example is performed in natural light or incandescent light, but in the case of discharge light such as a fluorescent lamp or natural light that includes discharge light, the corrected gain control voltage It is controlled by Aa+ and AC+, and malfunctions due to deviations in spectral characteristics that existed in the conventional example are avoided.

Note that the calculation means (3) can be constructed only by hardware, but it can be constructed more easily by using a D/A converter, an A/D converter, and a microcomputer.

In the first embodiment, the correction means in the arithmetic means (3) is configured to add the correction value, but other correction means, for example, Act-βaAa to which the multiplication values βa and βC are added
a, Ac+=βcAc +ac.

Alternatively, the correction means may be a table conversion method using a ROM. In this case, the calculation means (3) is 1
)/A converter, A/D converter, and microcomputer, table conversion that does not perform correction in the case of natural light or incandescent light bulbs, and uses the division values Aa and Ac as addresses only in the case of discharge lamp light sources, etc. Gain control voltage Aa+
, Act may be configured to output.

In the above example, three light w1 conversion elements were used, but if four or more photoelectric conversion elements each having different spectral characteristics are used, the spectral characteristics of external light can be discriminated more accurately. An automatic white balance device with high viscosity can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the spectral characteristics of illumination light are discriminated based on the ratio of the output voltages of at least three charge conversion elements having different spectral characteristics, and when the spectral characteristics are not natural light or incandescent light source, In this method, the level ratio of the color signals R, G, and E separated from the isthmus image signal is corrected to the level ratio obtained in the case of natural light or an incandescent light source. Since it is not necessary to match the spectral characteristics as severely as in the past, costs can be reduced, and an automatic white balance device that can achieve accurate white balance under any illumination light can be obtained.

[Brief Description of the Drawings] Fig. 1 is a block circuit diagram of an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between the division values Aa and AC in this embodiment, and the spectral characteristics of illumination light. FIG. 3 is a block circuit diagram of a conventional automatic white balance device. (Ia), (lb,), (lc), , photoelectric conversion element, (2a), (2b piece... division circuit, (3)...
- Arithmetic means, (4)...imaging device, (5)...color signal separation circuit, (6a), (6b)...variable gain amplifier. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) means for calculating at least two ratios of output signals of at least three photoelectric conversion elements each having different spectral characteristics to which illumination light of a subject is incident; A means for discriminating the spectral characteristics of the illumination light based on the spectral characteristics of the illumination light, and a level ratio of color signals R, G, and B separated from the video signal of the photographed subject based on the discriminated spectral characteristics when the illumination light is natural light or incandescent light. an automatic white balance device comprising means for correcting the level ratio so as to obtain a level ratio obtained from the above.