JP3057756B2 - White balance adjustment circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a white balance adjustment circuit for a video camera.

[Summary of the Invention]

According to the present invention, a white balance adjustment circuit of a video camera compares a three-primary-color signal obtained by imaging with a sequentially changing reference signal to determine a white balance, and a white balance is determined with a simple configuration. Adjustment is possible.

[Conventional technology]

2. Description of the Related Art In a video camera that obtains a color video signal by imaging, it is necessary to perform white balance adjustment according to the color temperature of a light illuminating an object to be imaged. This white balance adjustment is performed by adjusting the level of each of the three primary color signals constituting the imaging signal.

FIG. 3 is a diagram showing an example of a conventional white balance adjustment circuit. In the figure, (1R), (1G), and (1B) depict images picked up by an image pickup means (not shown) such as a CCD imager. Input terminals of three primary color signals (ie, red signal R, green signal G, and blue signal B) separated from the signals are shown. Then, the red signal R obtained at the terminal (1R) is supplied to the output terminal (3R) via the white balance adjustment amplifier (2R), and the green signal G obtained at the terminal (1G) is directly output to the output terminal ( 3G) and terminal (1B)
Is supplied to an output terminal (3B) via a white balance adjustment amplifier (2B), and the three primary color signals obtained at the respective output terminals (3R), (3G), and (3B) are It is supplied to a subsequent image signal processing circuit (not shown).

Also, the red signal R output from the white balance adjustment amplifier (2R) and the green signal G obtained at the terminal (1G) are connected to the first signal.
The blue signal B output from the amplifier (2B) for white balance adjustment and the green signal G obtained at the terminal (1G) are supplied to the comparator (4A) shown in the figure and supplied to the second comparator (4B). The respective comparators (4A) and (4B) compare the signal levels.
Then, the comparison result is supplied to a microcomputer (hereinafter referred to as a CPU) (5).

The CPU (5) controls the white balance adjustment, and performs the white balance adjustment amplifier (2
The white balance is adjusted by controlling the gains of R) and (2B). That is, when the comparators (4A) and (4B) detect the same level, it is determined that the white balance adjustment is appropriate, and at least one of the comparators (4A) or (4B) detects a level difference. When it is determined that the white balance adjustment is not appropriate, the gains of the white balance adjustment amplifiers (2R) and (2B) are changed, and the same level can be detected by the comparators (4A) and (4B). Adjust as follows.

The circuit of FIG. 3 enables white balance adjustment. In the case of the circuit of FIG. 3,
There was an inconvenience that fine white balance could not be adjusted. That is, the CPU (5) can determine only the magnitude relationship between the red signal R and the green signal G and the magnitude relationship between the green signal G and the blue signal B, and cannot determine the degree of the difference. When the level difference between the red signal R and the blue signal B is large, for example, when the level difference between the red signal R and the blue signal B is large, the gain of the amplifier for amplifying the red signal R or the blue signal B greatly changes. White balance adjustment was not possible.

For this reason, when high-precision white balance adjustment is required, for example, a circuit shown in FIG. 4 is used (see Japanese Patent Application Laid-Open No. 61-105991).

4, parts corresponding to those in FIG. 3 are denoted by the same reference numerals, and in this example, the red signal R output from the white balance adjustment amplifier (2R) is converted to a first analog / signal.
It is supplied to a digital converter (6R) and converted to digital data.
The green signal G obtained at the terminal (1G) is supplied to a second analog / digital converter (6G) to be converted into digital data, and the blue signal B output from the white balance adjustment amplifier (2B)
Is supplied to a first analog / digital converter (6B) to be converted into digital data. Then, the digital data of each color output from each of the analog / digital converters (6R), (6G), and (6B) is provided to the CPU (7). The CPU (7) directly determines the signal level of each color from the supplied digital data, and determines whether the white balance is appropriate based on the level difference. Then, based on the result of the determination, the CPU (7) operates the white balance adjusting amplifier (2R).
And white balance adjustment by adjusting the gain of (2B).

According to the example of FIG. 4, the CPU (7) can directly determine the level of each color, so that the white balance can be accurately determined, and strict white balance adjustment can be automatically performed.

[Problems to be solved by the invention]

However, in the case of the example of FIG. 4, it is necessary to use three analog / digital converters only for white balance adjustment, and a white balance adjustment circuit for automatically performing good white balance adjustment is configured. Was complicated.

An object of the present invention is to enable automatic and accurate white balance adjustment with a simple configuration.

[Means for solving the problem]

The present invention, for example, as shown in FIG. 1 and FIG.
In a white balance adjustment circuit that adjusts the white balance between the three primary color signals R, G, and B formed from the imaging signal output from the video output means, the circuit has one and the other pair of input terminals, and has one input terminal One of the three primary color signals R, G, and B is supplied, and a first, second, and third comparison output signal indicating a positive or negative signal is output.
The first and second comparators (8R), (8G), and (8B)
2. A microcomputer (10) that supplies a third comparison output signal and outputs a digital signal whose value changes with time, converts the digital signal into an analog signal, and converts the analog signal into the first and second analog signals. The second and third comparators (8
R), (8G), and (8B) digital / analog converters (9) for supplying to the other input terminals, respectively.
2. The white balance of the three primary color signals is adjusted based on the level ratio of the digital signal value when the third comparison output signal is inverted from positive to negative or from negative to positive, respectively. is there.

[Action]

By doing so, the microcomputer (10)
Then, by simply monitoring the change in the comparison output, each primary color signal R, G,
The level of B can be determined, and three comparators (8R), (8G),
(8B), a simple configuration using only one digital / analog converter (9) and a microcomputer (10) makes it possible to realize a white balance adjustment circuit capable of performing accurate adjustment.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1 and FIG. 1 and 2, parts corresponding to those in FIGS. 3 and 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a diagram showing a white balance adjustment circuit according to the present embodiment, in which input terminals (1R), (1G), and (1G) of three primary color signals separated from imaging signals output from imaging means such as a CCD imager.
Of the red signal R, green signal G, and blue signal B obtained at (1B), the red signal R obtained at the terminal (1R) and the blue signal B obtained at the terminal (1B) are respectively converted into white balance adjustment amplifiers (2
R) and (2B) are supplied to the output terminals (3R) and (3B), and the green signal G obtained at the terminal (1G) is directly supplied to the output terminal (3G).

The red signal R output from the white balance adjustment amplifier (2R) is supplied to one input terminal of the first comparator (8R), and the blue signal B obtained at the terminal (1B) is supplied to the second comparator ( 8G), and supplies the blue signal B output from the white balance adjustment amplifier (2B) to one input terminal of the third comparator (8B). The other input terminal of each of the comparators (8R), (8G), and (8B) is supplied with an output signal of a digital // analog converter (9) described later. Then, the comparison output of each of the comparators (8R), (8G), and (8B) is supplied to the CPU (10). The CPU (10) controls white balance adjustment, and performs white balance adjustment by controlling the gains of the white balance adjustment amplifiers (2R) and (2B) described above.

FIG. 2 shows a configuration example of the CPU (10) according to the present embodiment. Each of the comparators (8R), (8G), and (8B) obtained at the terminals (11R), (11G), and (11B). Are compared with the first, second and third fixed contacts (12R), (1
2G) and (12B). In this case, the movable contact (12A) of the changeover switch (12) connects the first, second, and third fixed contacts (12R), (12G), and (12B) in order at a relatively short predetermined cycle. Let it. Then, the signal obtained at the movable contact (12A) of the changeover switch (12) is converted into an arithmetic processing circuit (13)
To supply.

In the figure, reference numeral (14) denotes a reference signal generation circuit. The reference signal generation circuit (14) is a circuit for outputting a reference signal (digital data) that repeats a sequential increase and decrease at a predetermined cycle. The signal is supplied from (15) to the digital / analog converter (9) and to the arithmetic processing circuit (13) in the CPU (10).

Then, the reference signal supplied to the digital / analog converter (9) is converted into an analog signal voltage signal, and
It is supplied to the other input terminals of the second and third comparators (8R), (8G) and (8B). Therefore, each comparator (8R), (8G),
The other input terminal of (8B) is supplied with a voltage signal that repeatedly increases and decreases in a predetermined cycle.

The arithmetic processing circuit (13) in the CPU (10) determines the current white balance based on the supplied comparison output and the reference signal, and based on the determination, determines the gain control signal output terminal (16R) and The gain control signal is supplied from (16B) to the white balance adjustment amplifiers (2R) and (2B).

Here, the operation for determining the white balance performed in the CPU (10) will be described. The reference signal generation circuit (14) outputs a reference signal that repeats increasing and decreasing sequentially. Therefore, each comparator (8R) connected to the CPU (10),
In (8G) and (8B), the level of the reference signal supplied to the other input terminal sequentially increases and decreases. Therefore, when the level of the reference signal increases or decreases, each comparator (8R),
According to the level of the color signal supplied to (8G) and (8B),
Although the comparison output is inverted, the timing at which the comparison output is inverted depends on the level of the color signal, and the color signal level can be determined from the timing at which the comparison output is inverted.

For example, the movable contact (12A) of the changeover switch (12)
Assuming that the reference signal is connected to the first fixed contact (12R), the polarity of the comparison output of the first comparator (8R) when the level of the reference signal exceeds the level of the red signal R obtained from the imaging signal. Changes from positive to negative, for example. When the inverted comparison output is obtained by the arithmetic processing circuit (13) in the CPU (10), the arithmetic processing circuit (1) is output from the reference signal generation circuit (14).
The level of the reference signal supplied to 3) is determined as the level of the red signal R.

Similarly, the movable contact (12A) of the changeover switch (12)
However, when it is connected to the second fixed contact (12G), the level of the green signal G can be determined, and when it is connected to the third fixed contact (12B), the level of the blue signal B can be determined.

In this case, since the movable contact (12A) of the changeover switch (12) is sequentially switched at a predetermined cycle as described above, the levels of all the primary color signals R, G, B can be determined in a relatively short time by the arithmetic processing circuit (1).
3) can be judged. Then, the arithmetic processing circuit (1
When the levels of all the primary color signals R, G, B are determined in 3), the ratio of the levels of the respective color signals R, G, B is determined, and it is determined whether or not the ratio is within a predetermined range. When it is out of the predetermined range, the white balance adjustment amplifiers (2R) and (2B)
Is adjusted to perform white balance adjustment to converge within a predetermined range. In this case, in this example, the CPU (10) can determine the levels of all the primary color signals R, G, and B, and simply determine the magnitude relationship between the red signal R and the green signal G and the magnitude of the green signal G and the blue signal B. Since not only the relationship but also the magnitude of each difference can be determined, an accurate white balance can be determined, and the automatic white balance adjustment can be performed accurately.

Thus, according to the white balance adjustment circuit of this example, only three comparators (8R), (8G), and (8B) and one digital / analog converter (9) and a CPU (10) are required. In addition, the white balance of the image pickup signal can be accurately determined, and the white balance can be accurately determined as in the case of using three analog / digital converters and a CPU (example of FIG. 4). The circuit configuration is greatly simplified as compared with the conventional configuration using three analog / digital converters. In general, a digital / analog converter has a simpler circuit configuration than an analog / digital converter, and the circuit configuration is greatly simplified from this point as well.

The white balance adjustment does not need to be performed at high speed, and the adjustment circuit may be operated at a relatively low response speed, and the level determination of each primary color signal R, G, B is performed in a time-division manner as in this example. If you do, there is no problem.

In addition, the present invention is not limited to the above-described embodiment, but may take various other configurations.

〔The invention's effect〕

According to the present invention, the white balance can be accurately determined with a simple configuration using only three comparators, one digital / analog converter, and a microcomputer, and accurate white balance adjustment can be performed with a simple configuration. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of one embodiment of the present invention, FIG. 2 is a block diagram of a main part of one embodiment, and FIGS. 3 and 4 are each a block diagram showing a conventional example. (1R), (1G), (1B) are primary color signal input terminals, (2
R) and (2B) are white balance adjustment amplifiers, (3
R), (3G), and (3B) are primary color signal input terminals, (8R), (8
G), (8B) are first, second, and third comparators, (9) is a digital / analog converter, (10) is a microcomputer (CPU), (12) is a changeover switch, and (13) is The arithmetic processing circuit, (14) is a reference signal generation circuit.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 1-284087 (JP, A) JP-A 61-105991 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 9/73

Claims (1)

(57) [Claims] 1. A white balance adjusting circuit for adjusting a white balance between three primary color signals formed from a video signal output from a video output means, comprising: a pair of one input terminal and the other input terminal; To each of the three primary colors, and outputs first, second, and third comparison output signals indicating a positive or negative signal from the output terminal, respectively. And a microcomputer to which the first, second, and third comparison output signals are respectively supplied and that outputs a digital signal whose value changes with time; and a converter that converts the digital signal into an analog signal. A digital / analog converter that supplies the analog signal to the other input terminal of the first, second, and third comparators, respectively, and the first, second, and third comparison output signals Wherein the white balance of the three primary color signals is adjusted based on the level ratio of the value of the digital signal at the time when the color signals are inverted from positive to negative or from negative to positive, respectively. .