JP2001119716A - White balance adjustment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a white balance adjustment device to cope with control requiring immediacy such as photographing of a still picture by reducing the delay time required for white level convergence in white balance adjustment. SOLUTION: Chrominance signals R, B passing through variable gain circuits 3, 4 are fed to subtractor circuits 5a, 5b, where the signals are converted into color difference signals B-G, R-G, and a white region detection circuit 9 detects a white region of a photographed image from the color difference signals. Gate circuits 6a, 6b extract the white region of the color difference signals B-G, R-G and integration circuits 7a, 7b integrate the white region in the unit of one or a plurality of image patterns. On the other hand, a white area detection circuit 10 detects an area of the integration unit in the white area detected by the white region detection circuit 9 and normalizing circuits 11a, 11b normalize the integral values from the integration circuits 7a, 7b on the basis of the detected area. Generating circuits 8a, 8b generate a white balance correction signal to control the gain of the gain variable circuits 3, 4 by using the normalized integral value for a white offset.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white balance adjustment method and apparatus in a color image pickup apparatus such as a video camera and an electronic camera.

[0002]

2. Description of the Related Art A so-called internal colorimetric white balance adjusting device which detects and corrects a white shift of a photographing screen using a color component in a video signal is an external colorimeter using a dedicated colorimetric sensor for this. Compared to a color-type device, it has advantages in terms of structure and cost, but has a disadvantage that the adjustment accuracy may be reduced depending on the subject. In order to reduce the influence of the subject and stabilize the adjustment accuracy, for example, Japanese Patent Application Laid-Open Nos. 1-256890 and 4-35
As described in Japanese Patent No. 186, by extracting only a signal of a white portion in a screen and performing white adjustment using the extracted signal,
A method has been proposed that makes it less likely to be affected by a colored subject.

FIG. 5 is a block diagram showing the configuration of such a conventional white balance adjusting device, wherein 1 is a CCD image pickup device,
2 is a signal processing circuit, 3 and 4 are variable gain circuits, 5a and 5b
Is a subtraction circuit, 6a and 6b are gate circuits, 7a and 7b are integration circuits, 8a and 8b are white balance correction signal generation circuits, 9
Is a white area detection circuit.

In FIG. 1, an output signal of a CCD image pickup device 1 for picking up an image of a subject (not shown) is processed by a signal processing circuit 2 to be separated and generated into a luminance signal Y and color signals R, G, B. Among these color signals, the color signals R and B are supplied to variable gain circuits 3 and 4, respectively, and the gain control of the variable gain circuits 3 and 4 is performed according to a white balance correction value described later, so that the white balance is adjusted. . These color signals R and B whose white balance has been adjusted are output as video signals together with the luminance signal Y and the color signal G, but are also used for generating a white balance correction value.

That is, these color signals R and B are added to the subtractor 5
The color signals G are converted into two color difference signals RG and BG that are substantially orthogonal on a color plane by using the color signal G, and the white area detection circuit 9 outputs these color difference signals RG and BG. From the luminance signal Y, a white region (hereinafter, referred to as a white region) in an imaging range of the CCD imaging device 1 is detected. The gate circuits 6a and 6b are controlled by a gate signal representing a white area from the white area detection circuit 9, and are detected by the white area detection circuit 9 of the color difference signals RG and BG from the subtraction circuits 5a and 5b. The white area is extracted. The color difference signals RG and BG in the white area are integrated by integration circuits 7a and 7b for one to several field periods. The white balance correction signal generation circuits 8a and 8b are provided with these integration circuits 7a and 7
The shift amount (white shift amount) of the white balance is determined according to the integral value obtained in b, and a white balance correction signal corresponding to the white shift amount is generated. The gain of the variable gain circuits 3 and 4 is controlled by the white balance correction signal, and the white balance is adjusted.

[0006]

As described above, in the conventional white balance adjusting device, a white area in a screen is detected and the white balance is adjusted using only the signal of the area. The effect of a colored subject, which causes an adjustment error, is reduced, and a stable white balance can be obtained regardless of shooting conditions.

However, in this type of white balance adjusting device of the closed-loop feedback control, as described in the above-mentioned known example, an integration period of a certain degree (several fields) or more, and furthermore, It is necessary to have a control time constant. Here, the control time constant is related to the white balance adjustment speed, and may be a period from the start of the white shift amount detection operation to the completion of the white balance adjustment operation based on the white shift amount. it can.

The delay time until the convergence of the white balance due to the control time constant is such that, in a moving image camera such as a movie, a screen condition that fluctuates from time to time is integrated, which has an effect on stabilization of control. In a still image camera such as an electronic camera, the above-described integration effect of the screen state cannot always be expected.

In other words, in such a white area detection type white balance adjusting apparatus, the amount of deviation of the white balance of the screen is integrated by integrating one to several screens of the color signal amount corresponding to the white portion in the photographing screen. Measure. At this time, the integrated value is obtained as a value that also depends on the area of the white region, and is adjusted according to the zoom angle of view and the occupation ratio of the colored object even if the amount of white balance shift or the lighting condition is constant. Therefore, the area is not constant because the area of the white region changes. That is, the area of the white area fluctuates due to the zoom angle of view, the movement of the subject, and the like, and the fluctuation of the integral value due to this fluctuates.

For this reason, in many conventional white balance adjusting devices, a feedback control system is formed to aim at a target (in which the integrated value is 0 and does not depend on the area of the white region), and an appropriate value is obtained. The time constant is provided so that the white balance gradually converges. Therefore, it takes a considerable amount of time (for example, several tens of minutes) for the white balance to be obtained.
Screen period).

As described above, when the time until the white balance is achieved, that is, the period of the control time constant becomes longer,
If there is a photo opportunity during this period, the user naturally presses the shutter. However, if the shutter does not operate until the white balance converges, the photo opportunity will be missed. If the shutter is activated at the same time when the button is pressed, a still image in a state where the white balance adjustment is not completed is captured. As described above, in particular, in the case of an unexpected shutter chance, the white balance has a delay time until convergence, which is a disadvantage of the conventional white balance adjustment device in which the white balance is adjusted as described above. I was

An object of the present invention is to provide a white balance adjusting apparatus which can solve such a problem and can cope with control requiring immediacy such as still image shooting.

[0013]

In order to achieve the above object, the present invention normalizes the integrated value of the color signal amount corresponding to a white area in a screen by the area of the white area. is there. As a result, almost unique information can be obtained for the white balance deviation regardless of the area of the white region (or the occupation ratio of the area of the colored subject), and the correction amount for white balance adjustment can be obtained. Since it is almost uniquely obtained, the white balance can be adjusted only by the integration result for one screen (to several screens), and the time required for the convergence of the white balance can be reduced.

Also, in some cases, a still image camera has a sufficient pre-shooting time until the shutter is pressed, and can be handled almost in the same manner as a moving image camera. In such a case, it is also possible to use the average value of the integrated data (or the white balance correction value) obtained a plurality of times during the pre-shooting.

Therefore, the present invention derives a correction value for white balance adjustment from an appropriate weighted average value of the average value and the white balance correction value obtained as described above.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of a white balance adjustment device according to the present invention, wherein 10 is a white area detection circuit, 11a and 11b are normalization circuits,
Parts corresponding to those in FIG. 5 are denoted by the same reference numerals, and redundant description will be omitted.

In FIG. 1, information on a white area detected by a white area detection circuit 9 is supplied to a white area detection circuit 10, which outputs this information to the white area detection circuit 9.
Detects the area of the white region detected in. As a method of detecting this area, for example, the white area detection circuit 9 uses the color difference signal R
-G, BG and the luminance signal Y are used to determine whether or not each pixel belongs to a white area.
A gate signal for controlling a and 6b is generated.
At the same time, a pulse is output to the white area detection circuit 10 every time a pixel belonging to the white area is detected, and the white area detection circuit 10 counts the pulses to detect the white area detected by the white area detection circuit 9. The value of the area of is detected.

The integration circuits 7a and 7b may set the integration period of the color difference signals RG and BG from the gate circuits 6a and 6b to one screen (one field or one frame) or a plurality of screens. However, the area of the white region detected by the white area detection circuit 10 is also changed to the area in the integration period (accordingly, if the integration period is a period of a plurality of screens, (The sum of the areas of the white areas on the screen).

The normalizing circuits 11a and 11b include an integrating circuit 7
a, 7b, the color difference signal R- of the white area during the integration period.
The integral value ∫ (RG) of G and the integral value ∫ (BG) of the color difference signal BG are also divided by the area of the white area detected by the white area detection circuit 10 to obtain That is, an integral value that does not depend on the white area is obtained as the white shift amount. The white balance correction signal generation circuits 8a and 8b respectively generate white balance correction signals for the variable gain circuits 2 and 3 from the white shift amount.

In this manner, in this embodiment, a white shift amount independent of the area of the white region is obtained, and the white balance is adjusted based on the white shift amount. The white balance is adjusted without being affected by the change, or even if the area of the white area in the imaging range changes due to the movement of the subject or the change of the shooting direction, etc. Will be. Therefore, the white balance adjustment period can be made very short, about one screen period. Even if the white balance adjustment accuracy is improved, the white balance should be adjusted in about several screen periods. The stillness of an electronic camera or the like becomes effective even with a camera or the like.

Next, the function of the first embodiment will be described with reference to FIG.

FIG. 2A shows a photographing screen. As shown, it is assumed that a white subject A and colored subjects B and C exist in the photographing screen. D is the background. In such an imaging screen, the subject A is a white area. Here, it is assumed that the background D has no white area.

FIG. 2B is a diagram schematically showing the state of the image pickup screen in FIG. 2A on a color plane (RG, BG).

In the white region, the relationship between the color signals R, G, and B is substantially R = B = G, and the color difference signals RG and BG are substantially 0, and the color plane (R-G , BG), the white area is in the area including its origin 0. Therefore, in the white area detection circuit 9 in FIG. 1, a threshold value close to 0 level is provided for each of the color difference signals RG, BG, and the color difference signals RG, BG supplied from the subtracters 5a, 5b. Are both equal to or lower than the respective threshold values and the luminance signal Y is equal to or higher than a predetermined threshold value provided for the luminance signal Y, a white area is determined. In this case, the luminance signal Y is used to determine that it is a signal existing area (if the luminance signal Y is not determined, the CCD
A black area where no output signal is obtained from the image sensor 1 is also erroneously determined as a white area.

Returning to FIG. 2B, when the white balance is lost due to a change in the light source or the like (white displacement), the color plane (R
−G, BG), the white area A is shifted from its origin 0, and accordingly, the subjects B, C, and the background D also have a regular shape on the color plane (RG, BG). As a result, a reddish reproduction screen or a bluish reproduction screen is obtained.

Now, the white area A due to the white shift
Is shifted from its origin 0 at the color plane (RG, BG), and the color difference signal R-
Assuming that the level change amounts of G and BG (hereinafter referred to as white shift amounts) are x and y, respectively, the integrated values ∫ (BG) and ∫ (RG) obtained from the integrating circuits 7a and 7b are respectively. ∫ (BG) = y · S∫ (RG) = x · S where S is the area of the white region. Here, this area S is independent of white shift,
This is a value that fluctuates every moment due to the shooting angle of view and the movement of the subject itself. In other words, depending on the shooting conditions, the white shift amounts x, y
Is a value that does not uniquely correspond to

In the conventional white balance adjusting device shown in FIG. 5, the white balance correction signal generating circuits 8a and 8b use the integrated values y.S and x.S from the integrating circuits 7a and 7b to generate a white balance correction signal. Which is shown in FIG.
In the color plane (RG, BG) shown in (b), the white shift amount is not the white region A of x, y, but the white shift amount x · S, ys · S shifted from the white region A in the direction of the broken arrow. This means that the white balance is adjusted for the white area A. In this case, the white area A is positioned at the origin 0 of the color plane (RG, BG) with the white shift amounts x · S, y · S (that is, the white shift amounts x · S, y).・ S must be 0)
Although the correction is performed, the white shift amounts x · S and y · S differ depending on the value of the area S, and are correct in one white balance adjustment operation (that is, the integration period of one to several screens). White balance cannot be obtained. Therefore, the white balance adjustment operation is performed a plurality of times, and a sufficiently long control time constant (the time constant of the white balance control system, ie, the integration circuits 7a and 7b
It is necessary to smooth the variation in the amount of white shift due to the variation in the area S.

On the other hand, in the first embodiment, the integrated values y.S, x.S obtained by the integrating circuits 7a and 7b are normalized by the area S by the normalizing circuits 11a and 11b (that is, the integrated values y.S and x.S). y · S and x · S are divided by the area S), and a white balance correction signal is obtained with the resulting white shift amounts y and x unaffected by the area S. Accordingly, the control time constant can be reduced, and a white balance can be obtained in one white balance adjustment operation (that is, an integration period of one to several screens).
Almost instant control is possible.

FIG. 3 is a block diagram showing a second embodiment of the white balance adjusting device according to the present invention, wherein 12a, 1
2b is an integration circuit, 8a 'and 8b' are white balance correction signal generation circuits, and the same reference numerals are given to portions corresponding to the above-mentioned drawings, and redundant description will be omitted.

In the figure, the second embodiment differs from the first embodiment shown in FIG.
a, 6b, the color difference signals BG, R- in the white area.
In addition to adding integration circuits 12a and 12b for integrating G, instead of the white balance correction signal generation means 8a and 8b, weighting of the normalized integration value from the normalization circuit 11a and the integration value from the integration circuit 12a. An average value is obtained, and a white balance correction signal generation circuit 8a 'for generating a white balance correction signal of the variable gain circuit 4 using the weighted average value as a white shift amount.
And a weighted average value of the normalized integrated value from the normalizing circuit 11b and the integrated value from the integrating circuit 12b, and the weighted average value is used as a white shift amount to generate a white balance correction signal for the variable gain circuit 4. White balance correction signal generation circuit 8a '
Is used.

Here, the integration circuits 12a and 12b are arranged in the manner shown in FIG.
Has the same function as the integration circuits 7a and 7b, but has a sufficiently long integration time constant as compared with the integration circuits 7a and 7b (for example, a period corresponding to several tens of screens. The integration time constant of the circuits 7a and 7b is 1
During the period corresponding to several screens), the characteristics are close to those of the integration circuits 7a and 7b in the conventional white balance adjustment device shown in FIG. With the configuration in which the integrating circuits 7a and 7b and the normalizing circuits 11a and 11b are combined,
While characteristics suitable for immediate control of still image shooting can be obtained, by providing the integration circuits 12a and 12b having such characteristics, characteristics suitable for stable control of moving image shooting can also be obtained.

In the white balance correction signal generation circuit 8a ',
The weighted average value of the output values of the normalization circuit 11a and the integration circuit 12a is obtained, and the weighted average value of the output values of the normalization circuit 11b and the integration circuit 12b is obtained in the white balance correction signal generation circuit 8b '. The white balance correction signal is generated using these weighted average values as white shift amounts.

Therefore, the white balance correction signal generating circuits 8a 'and 8b' set the weighting coefficients in the weighted averaging process as appropriate, so that when a still image is shot depending on the product specifications and shooting conditions, the normal image is shot. Circuit 11a, 1
In the case where a white balance correction signal can be generated using the normalized integral value from 1b as the amount of white shift, an immediate control characteristic suitable for still image shooting can be selected, and when moving image shooting is performed In this method, a white balance correction signal can be generated using the integrated values from the integration circuits 12a and 12b as the white shift amount, and a stabilization control characteristic suitable for moving image shooting can be selected. Further, the normalization circuits 11a, 1
1b and integration circuits 12a and 12b
By using the average value of the integration value from b as the white shift amount, an intermediate characteristic between the characteristics of the above-described still image shooting and moving image shooting can be created.

Further, the weighting factor for determining which of the characteristics suitable for the still image shooting and the characteristics suitable for the moving image shooting is to be changed is sequentially determined according to the pre-shooting period from when the power is turned on to when the shutter is pressed. It is also possible to change it. Further, even during continuous moving image shooting, by appropriately taking into account the above-mentioned immediate control characteristics suitable for still image shooting, it is possible to realize white balance adjustment with good tracking performance to sudden changes in illumination and the like.

FIG. 4 is a block diagram showing a third embodiment of the white balance adjusting device according to the present invention. The same reference numerals are given to portions corresponding to those in FIG. The third embodiment is different from the second embodiment shown in FIG. 3 in that the white area detection circuit 10 and the normalization circuits 11a, 1
1b.

In FIG. 4, integrating circuits 7a and 7b and integrating circuits 12a and 12b are provided in parallel, and integrating circuit 7a
The integration value of the integration circuit 12a is supplied to the white balance correction signal generation circuit 8a ', and the integration value of the integration circuit 7b and the integration circuit 12b is supplied to the white balance correction signal generation circuit 8b'. In the white balance correction signal generation circuits 8a 'and 8b',
The two integrated values input are respectively weighted and averaged. However, the integration circuits 7a and 7b and the integration circuits 12a and 12b have different integration time constants (that is, control time constants), and the integration circuits 7a and 7b Is set so as to obtain characteristics close to the immediate control characteristics suitable for still image shooting (this is because the white shift amount is directly obtained by normalizing the white area (FIG. 2).
Although it takes a certain amount of integration period (for example, a period in which the integration period corresponds to several screens) as compared with obtaining the white shift amount x, y) in (b), only by changing the time constant, It is also possible to realize high-speed white balance adjustment), and the integration time constants of the integration circuits 12a and 12b are as follows:
Like the integration circuits 12a and 12b in FIG.
The period is set to a sufficiently long period of several tens of screens so as to obtain a stabilization control characteristic suitable for moving image shooting.

Also in the third embodiment, similar to the second embodiment, by switching or combining a plurality of characteristics, it is possible to obtain a suitable control characteristic between still image shooting and moving image shooting. In a hybrid video camera having a still image shooting function and a moving image shooting function,
It is possible to obtain a good white balance state according to each shooting mode.

[0038]

As described above, according to the present invention,
It is possible to obtain a shift amount of white balance independent of a shooting condition such as a zoom angle of view, an occupation ratio of a colored object on a shooting screen, and an area of a white region, and it is possible to obtain almost unique white correction information from the shift amount. As a result, the time required for convergence to the white balance state can be greatly reduced.

Further, according to the present invention, it is possible to take the characteristics of a moving image camera into consideration, thereby achieving both the stability of white balance in moving image shooting and the responsiveness of white balance in still image shooting. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a white balance adjusting device according to the present invention.

FIG. 2 is a schematic diagram for explaining functions of the embodiment shown in FIG. 1;

FIG. 3 is a block diagram showing a second embodiment of the white balance adjustment device according to the present invention.

FIG. 4 is a block diagram showing a third embodiment of the white balance adjustment device according to the present invention.

FIG. 5 is a block diagram illustrating an example of a conventional white balance adjustment device.

[Explanation of symbols]

Reference Signs List 1 CCD image pickup device 2 Signal processing circuit 3, 4 Variable gain circuit 5a, 5b Subtractor 6a, 6b Gate circuit 7a, 7b Integrating circuit 8a, 8b, 8a ', 8b' White balance correction signal generating circuit 9 White area detecting circuit 10 White area detection circuit 11a, 11b Normalization circuit 12a, 12b Integration circuit

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5C065 AA01 BB02 CC01 DD02 GG10 GG15 GG22 GG23 GG24 5C066 AA01 BA20 CA08 CA23 EA03 EA14 EF03 GA01 GA03 GA11 GA32 GA33 GB11 KA02 KA12 KD02 KD06 KE02 KE05 KM02 K02

Claims (6)

[Claims] 1. A signal processing means for processing an output signal of an image sensor to generate a luminance signal and a color signal; and a variable gain means for controlling the color signal from the signal processing means for white balance adjustment. A white area extracting means for extracting a white area on the photographing screen from the color signal; and a white shift amount corresponding to a white balance shift from the color signal in the white area extracted by the white area extracting means. , A white area detecting means for detecting an area of a white region on the photographing screen, and a white shift amount detected by the white area detecting means is detected by the white area detecting means. Normalizing means for normalizing with the area of the white region, and a white balance for generating a white balance correction signal for controlling the gain of the variable gain means according to the white shift amount normalized by the normalizing means. Correction signal generation means, and the amount of white balance deviation A white balance adjustment device configured to generate a white balance correction signal that uniquely corresponds to the white balance correction signal. 2. The integration unit according to claim 1, wherein the white shift amount detection unit integrates the color signal extracted by the white region portion extraction unit for one to several screens. A relatively short time constant of about one to several screens is obtained by using the integrated value over a plurality of screens as the white shift amount and normalizing the white shift amount with the area of the white area detected by the white area detecting means. Wherein the white balance adjusting operation is enabled and the white balance adjusting operation is converged in a short time. 3. A signal processing means for processing an output signal of an image sensor to generate a luminance signal and a color signal; and a variable gain means for controlling the color signal from the signal processing means for white balance adjustment. A white area extracting means for extracting a white area on the photographing screen from the color signal; and a white shift amount corresponding to a white balance shift from the color signal in the white area extracted by the white area extracting means. First white shift amount detecting means for detecting the white area, white area detecting means for detecting the area of a white region on the photographing screen, and white shift amount detected by the first white shift amount detecting means Normalizing means for normalizing with the area of the white area detected by the area detecting means; and a time constant larger than that of the first white shift amount detecting means, the white area extracted by the white area extracting means. A second method for detecting a white shift amount corresponding to a shift in white balance from the color signal;
And selecting one of the white shift amount normalized by the normalizing means and the white shift amount detected by the second white shift amount detecting means, or A white balance correction signal generating means for generating a white balance correction signal for controlling the gain of the variable gain means in accordance with the selected or weighted average white shift amount, using a weighted average using a weighting coefficient, A white balance adjustment device configured to generate a white balance correction signal corresponding to the white shift amount according to an imaging mode. 4. The white shift amount detecting device according to claim 1, wherein the first white shift amount detecting unit is an integrating unit that integrates the color signal extracted by the white region portion extracting unit. The white balance adjusting device is characterized in that the detecting means is integrating means for integrating the color signal extracted by the white area part extracting means with an integration time constant longer than that of the first white shift amount detecting means. 5. A signal processing means for processing an output signal of an image sensor to generate a luminance signal and a color signal; and a variable gain means for controlling the color signal from the signal processing means for white balance adjustment. A white area extracting means for extracting a white area on the photographing screen from the color signal; and a white shift amount corresponding to a white balance shift from the color signal in the white area extracted by the white area extracting means. First white shift amount detecting means for detecting a white balance shift from the color signal in the white area extracted by the white area extracting means with a longer time constant than the first white shift amount detecting means. A second white shift amount detecting means for detecting a corresponding white shift amount; and a time constant larger than that of the first white shift amount detecting means, wherein the color in the white area extracted by the white area extracting means is provided. A second method for detecting a white shift amount according to a white balance shift from a signal.
The white shift amount detecting means, and the white shift amount detected by the first and second white shift amount detecting means, or a weighted average using a variable weighting coefficient, and selecting or White balance correction signal generating means for generating a white balance correction signal for controlling the gain of the variable gain means in accordance with the weighted average white shift amount, the white balance correction signal corresponding to the imaging mode. A white balance adjustment signal for generating a white balance correction signal. 6. The device according to claim 5, wherein the first and second white shift amount detecting means are integrating means for integrating the color signals extracted by the white area portion extracting means, The integrating means as a white shift amount detecting means device has an integration time constant of several screens, and the integrating means as the second white shift amount detecting means device has an integration time constant of several tens screens. A white balance adjusting device, which is a period.