JPH0226193A - White balance control circuit - Google Patents

Abstract

PURPOSE:To prevent an unnatural white balance condition by providing a condition adapting circuit, obtain a deciding signal to relieve the condition of color and temperature control, controlling a gate circuit with this deciding signal and obtaining a white balance signal. CONSTITUTION:When a power source is turned on to a video camera and the output of a white area detecting circuit 15 can not detect a signal corresponding to a white subject and goes to be an L level, the output of a condition adapting circuit 100 goes to an H level during a blanking period and goes to the L level during another scanning period. Accordingly, such a condition relieves a white detecting area. Next, when the signal of a white area is detected, since the output of the circuit 15 goes to the H level, the output of the circuit 100 maintains the H level and gate circuits 19-21 are controlled to a conductive condition. Accordingly, the white balance control of high accuracy can be executed. Especially, when there is no chance to image pick-up the white subject after the power source is inputted, the unnatural white balance condition can be prevented from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a white balance control circuit used in a color television camera.

(Prior Art) An automatic color temperature tracking system, so-called a fully automatic white balance control system, is one of the important features in home color video cameras.

A color television camera is provided with a white balance control system so that when a white subject is imaged, the color reproduction looks natural.

White balance control systems can be roughly divided into two types: an external color temperature sensor type, and an i'l11 type, which determines color temperature from a captured video signal. Each method has advantages and disadvantages, but since the present invention belongs to the a11 method, that method will be explained below.

In the 4-1 method, a white balance is determined using a captured video signal, a control signal is generated, and the balance is adjusted. Does this method provide more accurate white balance than a single external color temperature sensor? It is expected that stability will be improved as well.

Furthermore, since there is no need to provide a sensor, it has many advantages, such as making it easy to miniaturize the camera head. However, the biggest drawback is that the white balance tends to change depending on the content of the video signal.

Generally, in the 1I11 method, it is desirable to extract only the signal of a portion corresponding to a white object from the video signal obtained by imaging, determine the white balance from this signal, and adjust the balance. However, it is a difficult technique to extract only the signal of a portion corresponding to a white object from a video signal that changes over time.

Furthermore, since the color temperature cannot be directly determined, it is difficult to accurately determine and extract a white object portion with intermittent color temperature changes from orange to blue. For this reason, the idea that if the entire screen is averaged, the white will be dispersed is adopted in simple video cameras that use a single focal length lens without a zoom-up function. However, when a close-up image of a monochromatic light portion is taken, the color changes are still severe, and in order to avoid this, an algorithm is required to determine the signal corresponding to the white object portion.

As a method for this, a width detection full autofocus balance control method has been proposed, which extracts only the signal of the part corresponding to the color temperature locus of the white subject part and uses that signal to control the white balance. Kosho 60-2
(See Publication No. 2952). This method will be explained below.

This method is based on the idea that when only the brightness of objects of the same color changes, the color difference signal as the video camera's color information and the luminance signal that distinguishes brightness and darkness are approximately proportional to each other. The value obtained by dividing the level by the luminance signal level can be a measure of color regardless of brightness, so
This method controls white balance by extracting a signal corresponding to a change in color temperature of a white object from a scale representing this color.

Figure 4 shows (RY)/Y on the vertical axis and (RY)/Y on the horizontal axis.
Y is taken, and the trajectory of the position indicated by each color light of the color par as the illumination light changes is plotted on two-dimensional coordinates.

Note that Y is a luminance signal, (RY) and (B-Y) are color difference signals, Mg is magenta, Ye is yellow, Cy is cyan, and G
is green and W is white. In Figure 4, 450
It is normalized to 0 so that white is in a well-balanced state.

From these coordinates, a signal in the range corresponding to the change in color temperature of a white subject is set (the area shown by diagonal lines), the signal in that area is determined and extracted, and the white balance is determined and adjusted using this. By doing so, it is possible to eliminate the influence of highly saturated objects and perform more accurate white balance control.

Calculations and conditional judgments for width detection can be performed as follows.

1(RY)/Y l > a
...(1) 1(B-Y)/Y l>b
...(2)(1/b)Xi(R-Y
)/Yl+(1/a)Xi(B-Y)/Yl>1 −
C3>(1/e)X 1(RY)/Yl +(1/d
)
) >Y − (la) (1/b
) (R-Y) >Y-(2
a) (1/b) (RY) + (1/a) (B-Y
) >Y −(3a)(1/c) (RY
) + (1/d) (B −Y) <Y
-(4a) The area where all of the above equations (la) to (4a) hold true becomes the width detection area, and this area can be detected by a simple comparison circuit. In Figure 4, the above formula (la) ~
The portion corresponding to (4a) is shown as a boundary line.

FIG. 5 shows a conventional control circuit that detects the above-mentioned white area signal, extracts it, and automatically performs white balance control.

The R and B signals obtained from the color video camera are respectively supplied to subtracters 13.14 via gain control amplifiers 11.12. The subtracters 13 and 14 are supplied with a Y signal obtained by a color video camera. Therefore, the information from the subtracters 13 and 1.4 is color difference signal information. (R
-Y) and (B-Y) signals are obtained. This (RY),
The (B-Y) signal and the Y signal are supplied to the white area detection circuit 15. The white area detection circuit 15 has the above-mentioned (la) to
By performing calculations based on equation (4a), a signal corresponding to a white object can be determined, and a determination signal can be obtained.

On the other hand, the previous (RY) and (B-Y) signals are supplied to clamp circuits 16 and 18, respectively. Also, clamp circuit 1
7 outputs a reference level signal. here,
The outputs of the clamp circuits 16 and 17゜18 are passed through gate circuits 19 and 20゜21 to a low-pass filter (LPF).
22, 23° and 24 for smoothing.

The output of the low-pass filter 22 and the output of the low-pass filter 23 are compared in a comparator 25, and the outputs of the low-pass filter 23 and low-pass filter 24 are compared in a comparator 26. Outputs J of comparators 25 and 26 are respectively supplied to control terminals of up/down counters 27 and 28 to control the counting direction. The count outputs of the up/down counters 27 and 28 are respectively converted into analog signals by digital-to-analog converters 29 and 30. Each analog signal is sent to an amplifier 31
．． via respective gain control amplifiers 11.32.
12 control terminals.

As a result, the signals in the shaded area in FIG. 4, that is, the (RY) and (B-Y) signals as color information, are controlled to match the reference level, and the white object signal is Balance is achieved.

(Problems to be Solved by the Invention) According to the above-described white balance control circuit, the narrower the target width detection area, the more accurate white balance control is possible. However, this also increases the risk of erroneous control when used under special imaging conditions.

In other words, if the camera detects a signal corresponding to a white object even at -degrees after the power is turned on, and normal white balance control operation is obtained, the correct color will be obtained even when capturing a color outside the white detection area. Reproducibility can be maintained. However, if the camera continues to capture images of objects outside the white detection area after the power is turned on, and a signal corresponding to a white object cannot be detected, the result will be that appropriate white balance control will not be obtained for a long time.

FIG. 6 shows an example of a phenomenon that occurs when white balance control is not performed. For example, when the color temperature is very high (over 10,000) under special conditions such as at dusk, red (R)
If you continue to image green or green (G) colors and track the white balance in the initial state, R'd in Figure 6
, Gv are in a balanced state, and the reproduced image is reproduced as an extremely bluish color, which is unnatural.

Therefore, this invention takes advantage of the fact that automatic white balance control provides accurate balance control, and takes advantage of the fact that automatic white balance control can provide accurate balance control. An object of the present invention is to provide a white balance control circuit that can prevent a white balance state from occurring.

[Structure of the Invention] (Means for Solving the Problems) The present invention uses a gate section to which color information corresponding to multiple types of colored lights of a color video camera device is supplied, and a signal passed through this gate section. a white balance control circuit comprising: a means for obtaining a control signal for white balance control; means, a second means for storing and storing that color information of a white object has been detected in response to the first determination signal from the first means, and a first determination signal from the first means. The second method relaxes the conditions for eight-color portion control when there is no judgment signal.
a third means for obtaining a determination signal; a second determination signal from the third means and a first determination signal from the first means; Until a determination signal is obtained, the second determination signal is used as a control signal for the gate circuit, and once the first determination signal is obtained, thereafter, the first determination signal is used as a control signal for the gate circuit. and a fourth means for use.

(Function) With the above means, even if there is no chance of detecting a signal corresponding to a white object after the power is turned on, it is possible to obtain a second determination signal that relaxes the conditions for color temperature control, and this second determination signal Since the gate circuit is controlled by the determination signal and a white balance control signal can be obtained, an extremely unnatural color image will not be obtained.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The method of applying a white balance control signal to the gain control amplifiers 11 and 12 in order to control white balance is the same as the conventional method. The circuit shown in FIG. 1 differs from the conventional one in that it is provided with a condition adaptation circuit 100 that processes the detection output of the white area detection circuit 15, and the control signal from this condition application circuit 100 is transmitted to the gate circuits 19, 20, 21, The point is that it is configured to control. The other parts are basically the same as the circuit in FIG. 5, and are designated by the same reference numerals as in FIG.

Further, the difference from the circuit of FIG. 5 is that the combination of signals supplied to the comparator 26 is different, and the outputs of the low-pass filters 22 and 24 are supplied to the comparator 26.

The reason for this connection will be described later.

The condition adaptation circuit 100 includes a flip-flop 50 and a NOR circuit 54 to which the output of the white area detection circuit 15 is supplied. Flip-flop 50 is composed of NOR circuits 51 and 52, and its output is connected to one input section of NOR circuit 53. The other input portion of this NOR circuit 53 is supplied with, for example, a blanking pulse BL.

The operation of the condition adaptation circuit 100 will be explained below.

Now, the output of the white area detection circuit 15 becomes high level when a signal corresponding to the shaded area in FIG. 4 is detected.
In other cases, the level shall be low. Further, it is assumed that the blanking pulse BL is at a high level during the blanking period and at a low level during other periods (scanning periods).

When the video camera is powered on and the output of the white area detection circuit 15 cannot detect a signal corresponding to a white object and is at a low level, the flip-flop 50
is not inverted, and the output of the NOR circuit 52 maintains a low level. Therefore, in this state, the output of the NOR circuit 53 is
The pulse output is at a high level during the scanning period, but becomes a low level every time there is a blanking period. Therefore,
The output of the NOR circuit 54 is at a high level during the blanking period, and at a low level during other scanning periods. Here, the gate circuits 19, 20, and 21 are set to output their inputs when a low-level control signal is supplied to their control terminals.

Therefore, after the power is turned on, while the white area detection circuit 15 does not detect a signal corresponding to a white object, all color difference signals in the scanning line period are used as information for obtaining a white balance control signal. In other words, in this state, the white detection area is relaxed.

Next, when a white area signal is detected, the white area detection circuit 1
5 becomes a high level, the flip-flop 50 is inverted, and the output of the NOR circuit 52 becomes a high level. Therefore, the output of the NOR circuit 53 always maintains a low level. As a result, the NOR circuit 54 outputs the blanking pulse B
Thereafter, it will respond to the output from the white area detection circuit 15 without responding to L. In other words, the output of the NOR circuit 54 normally maintains a high level, and the output of the white area detection circuit 15
In response to the high-level output obtained when detecting a signal corresponding to a white object, the gate circuits 19, 20.2
1 is controlled to be conductive. In other words, in this state, a white balance control signal can be obtained using only the signal corresponding to a white object, and highly accurate white balance control can be performed.

In the above embodiment, the condition adaptation circuit 100 is configured by hardware using a NOR circuit, but the point is to determine the state of the input signal and finally obtain the signal for controlling the gate circuit. Therefore, various logic circuits or software-based determination means may be used.

By the way, if a signal corresponding to the first white object is not obtained after the power is turned on, all the color difference signals in the scanning period are used to obtain the white balance control signal as described above, but at this time, It is necessary to limit the control signal so that even if a monochromatic image is captured, it will not become entirely white.

Due to this limitation, in this embodiment, the comparator 26 (R-
Y) signal information and (B-Y) signal information are input and compared. A control loop based on this system obtains a control operation such that R-B. On the other hand, the system of comparator 25 is R-Y
Obtain a control operation such that Therefore, overall Y-R-
The white balance state becomes B.

When such control is performed, R-B
A control operation such as RY can be obtained in a region along a pale white color temperature change locus, and a control action RY can have the effect of correcting color temperature deviations in fluorescent lights and the like.

In the above circuit, a and b in the above equation.

Select c and d (inside the white area detection circuit 15) and set 3000
If you limit tracking up to ~6000k, the second
The corresponding signal in the shaded area in the figure is adjusted to a signal corresponding to white, and changes in hue and saturation of other colors can be alleviated. In other words, even if white balance control is performed by temporarily using all the color difference signals during the scanning period, there will be no adverse effect on signals of colors that are originally different from those of the mill.

FIG. 3 shows another embodiment of the present invention, showing another example of the white area detection circuit 15 and the condition adaptation circuit 100.

The white area detection circuit 15 of the previous embodiment is based on the equation (l
When all of a) to (4a) are satisfied, a high level output is obtained from one output terminal, and this is the condition adaptation circuit 10.
0, but in this example, equations (1a) and (2a
) is established, terminal 1 receives a high level output.
5a, and a terminal 15b which obtains a high level output when both equations (3a) and (4a) are satisfied. The terminal 15a is connected to one terminal of the AND circuit 101, and the output terminal 15b is connected to the other terminal of the AND circuit 101.
It is connected to one terminal of the AND circuit 102. The output of the NOR circuit 103 is supplied to the other terminal of the AND circuit 102. This NOR circuit 103 is a flip-flop 1
If the output of 04 is low level, it normally remains high level and outputs a pulse that becomes low level only when the blanking pulse BL is manually generated. However, when the output of the flip-flop 104 is at a high level, the output of the NAND circuit 103 always maintains a low level.

The output of the NAND circuit 102 is supplied to one side of the NOR circuit 107. Also, the output of the NOR circuit 101 is the output of the AND circuit 10
6 and is also supplied to one side of the comparator 109 via the integrator 108. The comparator 109 inverts the flip-flop 104 when the output of the integrator 108 exceeds the reference voltage 110.
output can be made high level.

The output of the flip-flop 104 is also supplied to the other input of the AND circuit 106.
The output of is supplied to the other input of the NOR circuit 107.

According to the above condition adaptation circuit 100, first, after the power is turned on, the white object detection area is the boundary (la), (2a) in FIG.
) can be canceled and limited to the direction of the color temperature change trajectory. In other words, after the power is turned on and the output of the flip-flop 104 is at a low level, (3a)
, (4a), the AND circuit 102 obtains a high-level output during the scanning period. As a result, a control signal that becomes low level during the scanning period is obtained from the NAND circuit 107, and the gate circuit passes all color difference signals during the scanning period. Therefore, the detection area of the signal corresponding to the white object is more limited than in the previous embodiment. In this case, the boundaries (3a) and (4a) in Figure 4
White balance control is performed using signals in the range surrounded by , but under this control situation, signals corresponding to objects in the magenta or green direction, whose color temperature is difficult to estimate, are used for white balance control. This will not be adopted as information, and the quality of control balance can be improved.

Next, when equations (1a) and (2a) are established, the AND circuit 1
The output of 01 becomes high level. Here, flip-flop 104 is not inverted immediately, but waits until the output level of integrator 108 is sufficient.

This means that, for safety's sake, high-precision control must be waited until the signal corresponding to the white object is advanced enough times to take white balance.

When the flip-flop 104 is inverted, the AND circuit 10
The output of the NOR circuit 107 becomes a high level, and the output of the NOR circuit 107 becomes a low level, that is, a control signal that makes the gate circuit conductive. In this state, each boundary (la) to (4a) in FIG.
) is used as a white balance control signal.

[Effects of the Invention] As explained above, according to the present invention, by taking advantage of the fact that automatic white balance control allows accurate balance control, it is possible to take pictures of white subjects under special imaging conditions, especially after turning on the power. When there is no chance to capture an image, it is possible to prevent an unnatural white balance state.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a circuit diagram showing another embodiment of the present invention; FIG. 4 is an explanatory diagram of the color temperature locus; FIG. 6 is a diagram showing a conventional white balance control circuit, and FIG. 6 is an explanatory diagram of a color temperature locus shown to explain the problem of the circuit of FIG. 5. 11.12...Gain control amplifier, 13.14...Subtractor, 15...White area detection circuit, 16,17°18...Clamp circuit, 19,20.21... Gate circuit, 22.23.24...Low pass filter, 25.
26...Comparator, 27.28...Up/down counter, 29.30...Digital analog converter, 31
．． 32...Amplifier, 100...Condition adaptation circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Scope of Claims] A gate section to which color information corresponding to a plurality of types of colored lights of a color video camera device is supplied, and means for obtaining a control signal for white balance control using a signal passing through the gate section. A white balance control circuit comprising: a first means for determining color information of a white subject necessary for target color temperature control from the color information and obtaining a first determination signal; A second determination signal that stores and retains that color information of a white object has been detected in response to the first determination signal.
means for obtaining a second determination signal that relaxes the conditions for color temperature control when there is no first determination signal from the first means; 2 and a first judgment signal from the first means, and the second judgment signal is used to control the gate circuit until the first judgment signal is obtained after power is turned on. and fourth means for using the first determination signal as a control signal for the gate circuit after the first determination signal is obtained.