JP2002258345A - Automatic exposure controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic exposure controller which can properly control exposure even for a photographic image having both a high-luminance part and a low-luminance part together when the exposure is continuously adjusted. SOLUTION: The automatic exposure controller which divides the photographic image into many small areas and performs exposure control by center-weighted light reading or spot light reading by using evaluated values found from the integral value of light made incident from an optical system by intermediate areas each formed of small areas is equipped with an intermediate area setting means which sets an intermediate area for luminance difference decision making to upper and lower areas or right and left areas of the photographic image, a decision means which decides that the luminance difference between the intermediate areas for luminance difference decision making is larger than a certain determined luminance difference threshold and the value of the lighter area for luminance difference decision making is less than the threshold, and an exposure control means which controls the exposure according to an exposure evaluated value found from the intermediate area as an object of exposure evaluation after a correction value for making the photographic image lighter is added to the luminance of the photographic image when the mentioned state is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic exposure control device. It is suitably applied to an image input device using an image pickup device such as a digital video camera and a digital camera.

[0002]

2. Description of the Related Art Exposure determination methods in a conventional automatic exposure control apparatus include an average metering, a center-weighted metering, a spot metering,
There are methods such as multi-pattern photometry. In any case, a plurality of predetermined evaluation areas are set in the image area including the entire captured image, an exposure evaluation value is obtained from the average luminance information of the area, and the exposure is determined based on the exposure evaluation value. Exposure correction such as backlight correction is performed.

In determining an evaluation area, an image area is divided into a large number of grid-like areas (hereinafter, referred to as small areas) as shown by broken lines in FIG. 2, and an area obtained by combining the divided areas (hereinafter, referred to as a small area). , A middle area) is often used as an evaluation area. The region surrounded by the thick line in FIG. 2 is a combination of evaluation regions generally seen in the center-weighted system.
Evaluation value of this evaluation area (hereinafter, referred to as middle area evaluation value)
Is obtained by averaging the integrated values of the luminance signals of the small areas included therein.

In general, since the evaluation value is obtained by the average luminance, if there is a portion of the photographed image as shown in FIG.
The evaluation value will be high. Then, since the exposure matches the brighter one, the whole image becomes dark as shown in FIG. 7B. In particular, in the case of center-weighted exposure as shown in FIG. 2, if a bright portion such as a spotlight exists at the center, the effect is large.

[0005] JP-A-5-122600 and JP-A-7-122600
According to the technique disclosed in Japanese Patent No. -298131, when the luminance value of each small area exceeds a predetermined threshold (hereinafter, referred to as a high luminance threshold), the luminance value of the small area is set to a predetermined value ( Hereinafter, this value will be referred to as a “high luminance prescribed value.”

For example, a problem of the high luminance processing will be described with reference to FIG. FIG. 5A is a model of a landscape photograph in which a mountain or the like is photographed, and the sky, which is considerably brighter than the lower mountain or the ground, is located almost from the center of the screen to the upper side. . For this reason, when center-weighted photometry or spot photometry is performed, the effect of the high-luminance portion of the sky is large, resulting in a dark image as a whole as shown in FIG. Therefore, the influence of the high-brightness portion is eliminated by replacing the high-brightness portion with a specified high-brightness specified value (including zero) for a high-brightness portion that is equal to or greater than a predetermined threshold (high-brightness threshold), as shown in FIG. A bright image can be obtained.

[0007]

In such a conventional technique, the influence of a high-luminance portion such as a spot light can be suppressed. In an image in which a high-luminance part and a low-luminance part are mixed together, if the evaluation area is moved from the state where the evaluation area is aligned with the high-luminance part to the low-luminance side, the captured image becomes Since the exposure is on the side, it may not be possible to extract a high-luminance area.

If the high-luminance threshold for determining the high-luminance portion is fixed, the high-luminance portion does not exist depending on the situation, and the high-luminance processing may not be performed. This depends on whether the exposure of the camera changes from the dark side or from the bright side. For example, consider a case in which exposure control is continuously applied to display on an LCD monitor or the like. When the center of the image faces the dark ground as shown in FIG. 5B, the dark part of the ground is exposed. From this state, FIG.
When the camera direction moves to the angle of view as shown in FIG. 5C, the high-brightness processing at this time is performed with the high-brightness threshold for the dark portion of the ground, that is, the sky in FIG. The high luminance processing is performed in a state where the part is higher than the high luminance threshold.

Conversely, when the center of the image faces the sky as shown in FIG. 5 (d), the high brightness threshold is high because the exposure matches the high brightness of the sky. FIG. 5 (e)
When the direction of the camera is changed to a state as shown in FIG. 5, since the high-luminance processing is performed with the high-luminance threshold, the high-luminance portion of the image disappears, and the high-luminance processing is not performed. ), The whole image becomes dark.

Although an example of automatic exposure correction has been shown for display on an LCD monitor or the like, the same occurs when continuous exposure control is not performed. For example, in actual photographing, exposure is changed several times for exposure control such as coarse adjustment and fine adjustment, so that the same occurs without continuous exposure control.

Such a problem can be solved by changing a high-luminance threshold for determining a high-luminance portion in accordance with an image. However, in order to determine the high luminance threshold, it is necessary to grasp the situation of the entire image, and there is a new problem that processing time is required.

According to the present invention, in order to solve the above-mentioned problems, even when an image is made such that a wide high-luminance portion and a low-luminance portion coexist when the exposure is continuously adjusted. It is another object of the present invention to provide an automatic exposure control device capable of appropriately controlling the exposure of a captured image.

[0013]

In order to solve the above-mentioned problem, an automatic exposure control apparatus according to the first aspect of the present invention divides a photographed image into a number of small areas and combines a plurality of these small areas. In an automatic exposure control device that performs exposure control by central photometry or spot photometry using an evaluation value obtained from an integrated value of luminance of light incident from the optical system for each of a plurality of middle regions, It is determined that there is a middle area setting means for setting a middle area for brightness difference determination in the area, or a middle area for brightness difference determination in left and right areas of the captured image, and a brightness difference for each middle area for brightness difference determination. A determination unit that determines that the value of the brightness difference determination middle area that is equal to or greater than the brightness difference threshold is equal to or less than a predetermined threshold 1;
From the exposure evaluation value obtained from the middle area of the exposure evaluation target after adding a certain correction value such that the image taken becomes brighter, Exposure control means for controlling exposure.

According to a second aspect of the present invention, there is provided an automatic exposure control apparatus which divides a photographed image into a plurality of small areas, and sets a plurality of medium areas obtained by combining a plurality of the small areas into a plurality of medium areas. In an automatic exposure control device that performs exposure control by central photometry or spot photometry using an evaluation value obtained from an integrated value of luminance, a luminance difference determination middle area in the upper and lower portions of the captured image, or the captured image. Medium area setting means for setting a luminance difference determination medium area in the area of the left and right portions of,
Determining means for determining that the luminance difference for each of the luminance difference determination medium areas is equal to or greater than a predetermined luminance difference, and that the value of the brighter luminance difference determination medium area is equal to or less than a predetermined threshold 1; An evaluation area moving means for moving a set area of a middle area for performing central photometry or spot photometry in a direction of lower luminance when the judgment means determines that the evaluation is true; and an exposure after the evaluation area moving means has moved. An exposure control unit configured to control exposure from an exposure evaluation value obtained from a middle region to be evaluated.

According to a third aspect of the present invention, there is provided an automatic exposure control apparatus which divides a photographed image into a plurality of small areas, and sets a plurality of medium areas obtained by combining a plurality of the small areas into a plurality of medium areas. In an automatic exposure control device that performs exposure control by central photometry or spot photometry using an evaluation value obtained from an integrated value of luminance, a luminance difference determination middle area in the upper and lower portions of the captured image, or the captured image. A middle area for brightness difference determination in the area of the left and right portions and a middle area setting means for setting a center brightness area in the center of the captured image, and the value of the center brightness area is equal to or less than a predetermined threshold value, and Determining means for determining that the brighter value of the luminance difference determination medium area is smaller than a predetermined threshold; and determining that the image taken becomes brighter when the determining means determines that the value is true. Correction value Serial, characterized in that it comprises an exposure control means for controlling the exposure from the exposure evaluation value obtained from the region within the exposed evaluated after applying to the luminance of the captured image.

According to a fourth aspect of the present invention, there is provided an automatic exposure control apparatus for dividing a photographed image into a plurality of small areas, and combining a plurality of these small areas into a plurality of middle areas for light incident from an optical system. In an automatic exposure control device that performs exposure control by central photometry or spot photometry using an evaluation value obtained from an integrated value of luminance, a luminance difference determination middle area in the upper and lower portions of the captured image, or the captured image. A middle area for brightness difference determination in the area of the left and right portions and a middle area setting means for setting a center brightness area in the center of the captured image, and the value of the center brightness area is equal to or less than a predetermined threshold value, and Determining means for determining that the brighter value of the luminance difference determination medium area is smaller than a predetermined threshold value, and setting of the middle area for performing central photometry or spot photometry when the determination means determines true. region An evaluation area moving unit that moves in a direction in which the luminance is low, and an exposure control unit that controls exposure based on an exposure evaluation value obtained from an exposure evaluation target middle area after the movement by the evaluation area moving unit. And

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of an embodiment of the present invention will be described below in detail with reference to the drawings.

(1) Configuration of the Present Invention FIG. 1 is a block diagram showing the configuration of a digital camera provided with an automatic exposure control device according to an embodiment of the present invention.
The digital camera according to the present invention includes a photographing lens 1, an aperture 2,
CD (charge coupled device) 3, CDS (correlated double sampling) circuit 4, process processing circuit 5, A / D converter 6, aperture control unit 7, CCD drive unit 8, system control unit 9, digital signal processing unit 12 , Memory 14, image data processing unit 1
7, a memory card 18, an image display processing unit 23, and an image display device 24.

An image of a subject that has passed through the taking lens 1 and the aperture 2 is converted into an image signal by an image sensor C that converts the formed light amount into an electric signal.
An image signal is output by the CD3. Output CCD
3 is converted into a CC signal by the CDS circuit 4.
After the noise of D3 is removed and the gain is controlled by the process processing circuit 5, the A / D converter 6 sets the image signal to an optimal sampling frequency (for example, an integer multiple of the subcarrier frequency of the NTSC signal). To convert to a digital signal.

An aperture control unit 7 is connected to the aperture 2, and a CCD driving unit 8 is connected to the CCD 3. The aperture control unit 7 is controlled by the system control unit 9 and opens and closes the aperture of the aperture 2 so as to change the diameter of a light beam incident from the imaging lens 1 and reaching the CCD 3. Also, CCD
The drive unit 8 controls the operation of the CCD 3 so that the system control unit 9 can accumulate and extract the electric signal converted by the captured light image. That is, the CCD 3 is a CCD
The shutter operation is performed under the control of the drive unit 8. Therefore, images can be taken with various exposures using these two driving units.

The image information for one image on the CCD 3 is CDS
4 and passes through the process processing circuit 5 to A / D
It is sent to the converter 6. A digital signal processing unit 12 is connected to the A / D converter 6, and the digital signal processing unit 12
Performs digital image processing such as RGB signal conversion and image interpolation on the image signal converted by the A / D converter 6 into a digital image signal.

The image data created by the digital signal processing unit 12 is once stored in a memory 14 and then sent to an image data processing unit 17 where the image data is subjected to image processing such as gamma correction and compression. 18 is stored.

The image data created by the digital signal processing unit 12 is sent to an image display processing unit 23, where γ
After the image display processing such as the processing is performed, the image is displayed on the image display device 24 such as an LCD monitor, so that the user can confirm the captured image.

The digital signal processor 12 converts RGB signal data included in a small area into a luminance value, and integrates the luminance value for each small area. The luminance integrated value for each small area is sent to the system control unit 9, where a middle area evaluation value is obtained for each middle area. For example, as shown in FIG. 2, the small area is divided into 10 × 10 100 pieces.

The system control unit 9 averages the luminance integrated values of the small areas included in each medium area to obtain a medium area evaluation value. This middle area is the area 1 surrounded by the thick line in FIG.
As in the case of ~ 6, evaluation small areas can be combined. The reason why the processing of the middle area is performed by the system control unit 9 is to facilitate changing the shape of the middle area (how to combine small areas) according to the situation. At this time,
When the integrated value of the small area is larger than a certain threshold value, the integrated value is replaced with a specified value, or the small area is not included in the evaluation value of the middle area, and the middle area evaluation value is obtained. .

FIG. 6A shows a case where center-weighted photometry is performed, in which exposure control is performed in two middle areas surrounded by oblique lines, and focus is placed on a middle area near the center of the two middle areas. In general, exposure control is performed with weights applied. In the case of spot metering, exposure control is performed at the center by using an area having a range equal to or smaller than the central middle area shown in FIG. 6A. The present invention solves the problems associated with high-brightness processing by moving the center area and the middle area where spot metering is performed depending on the state of the image. The system control unit 9 obtains a photographing exposure from each of the middle area evaluation values thus obtained, and controls the CCD driving unit 8 and the aperture control unit 7 to perform exposure control.

(2) Exposure control of an image having a large luminance difference First, a middle area for judging the luminance difference in the vertical or horizontal direction and a central luminance area for judging the luminance of the central part. Is newly provided (FIG. 3A,
(B)). Here, FIG. 3A shows a middle area for determining a case where there is a luminance difference in the vertical direction, and the two upper and lower middle areas are for determining a luminance difference. The middle region of the central portion is a central luminance region for determining whether or not the central portion is dark.

FIG. 3B shows a middle area for judging a case where there is a luminance difference in the left-right direction, which is for photographing an image with a digital camera or the like with the camera set up vertically. The two middle regions on the left and right are used for determining a luminance difference, and the middle region in the center is a center brightness region for determining whether or not the center is dark.

It is desirable that the middle area for judging the luminance difference is separated to some extent vertically or horizontally. However, since the top and bottom middle regions are determined differently from the center luminance region, the middle region is set to be a peripheral portion of the center emphasis region as shown in FIGS. 3 (a) and 3 (b). Good to set.

When determining the luminance difference in the vertical direction, an image having a luminance difference in the horizontal direction is obtained by taking an area longer in the horizontal direction as shown in FIG. Can be prevented from being erroneously determined to be present. Similarly, in the case of judging in the left-right direction, as shown in FIG. 3 (a) and 3 (b)
As described above, the same can be said for these central luminance regions.

Next, with respect to the set area, the luminances of the luminance difference determination area and the central luminance area are obtained. At this time, the evaluation value of the central luminance area is different from the high luminance removal processing in the evaluation area for determining the exposure, so that the high luminance removal processing is performed without limiting the number of high luminance parts. If the entire central luminance area is assumed to be bright, the target area disappears when the high luminance part is excluded, but at this time, the determined value is used as an alternative evaluation value, and the luminance integrated values of the small area are collectively collected. Ask. On the other hand, as for the evaluation value of the area where the luminance difference is being determined, it is necessary to look at the raw luminance difference, so that the luminance integrated values of the included small areas are collectively obtained without performing high luminance removal.

When a middle area for judging luminance is provided in the vertical direction as shown in FIG. 4A, the luminance integrated value (T1) of the upper luminance difference judging area and the lower luminance difference judging area are determined. A luminance difference is obtained from the luminance integrated value (T2). The luminance difference is obtained by dividing the larger value of the integrated luminance value by the smaller value of the integrated luminance value. In the case where the middle area for determining the brightness difference is taken in the vertical direction, the value of T1 is generally increased because the sky is at the top, and it is obtained by T1 / T2. Since it is unclear which of the left and right values will be larger, the luminance difference is determined after determining which is larger. Even in the case where a middle area for luminance determination is provided in the left-right direction, it can be obtained in the same manner as described above.

The brightness difference obtained in this manner is equal to or greater than a certain brightness difference threshold value and a certain brightness integration value (the larger brightness integration value) is a certain threshold value (hereinafter referred to as a bright portion threshold value). If it is smaller than 2), a luminance correction process or an evaluation area moving process is performed.

The brighter one (the one with the larger integrated luminance value)
Is a predetermined threshold (hereinafter, a bright part threshold 1)
Call. (Here, the bright part threshold 1 ≧ the bright part threshold 2)
Also, when the luminance integrated value of the central luminance area is smaller than a predetermined threshold (hereinafter, referred to as a central threshold), the luminance correction processing or the evaluation area moving processing is performed. This is because the fact that the vicinity of the center becomes dark despite the center emphasis indicates that there is a high luminance portion in the center emphasis region which is not included in the center luminance region.

In the brightness correction processing, a predetermined exposure correction value for brightening the image is added, and the next evaluation image is brightened as shown in FIG. Higher. As a result, high brightness processing is performed, and a bright image as shown in FIG.

In the evaluation area moving process, the center-weighted evaluation area as shown in FIG. 4B is moved to a darker one as shown in FIG. 4C to obtain the next evaluation value for photographing. Therefore, in the next photographing, the high-brightness portion becomes higher than the high-brightness threshold, and FIG.
A bright image as shown in (e) can be obtained. For example, as shown in FIG. 6B when the lower side is dark, FIG. 6C when the right side is dark, and as shown in FIG.

The photographing exposure is obtained from the finally obtained middle area evaluation values, and the exposure control is performed by controlling the CCD driving section 8 and the aperture control section 7.

In the above manner, even when a high-luminance portion such as an empty space is formed near the center of the screen, high-luminance removal processing can be performed. In addition, continuous exposure control is performed by preparing two types of bright part threshold 1, bright part threshold 2, and central part threshold depending on whether the brightness correction processing or the evaluation area moving processing is being performed. Occasionally, a stable image without hunting, in which the screen becomes brighter or darker, can be obtained.

The processing for automatic exposure control, the processing for setting the evaluation area, the processing for correcting the luminance, the processing for moving the evaluation area, and the like in the present embodiment can also be realized by a program using a microprocessor or the like. It is.

[0040]

As described above, according to the present invention,
Even when the high-luminance portion is exposed and high-luminance removal is not performed, high-luminance removal can be performed by exposure correction.

Even when the high-luminance portion is exposed and the high-luminance removal is not performed, the high-luminance removal can be performed by moving the evaluation area.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital camera of the present invention.

FIG. 2 is a diagram for explaining a relationship between division of an image into small regions and a middle region.

FIG. 3 is a diagram for explaining setting of a luminance difference determination area and a central luminance area.

FIG. 4 is a diagram for explaining processing when a vertical luminance difference determination area is set.

FIG. 5 is a diagram for explaining high luminance processing.

FIG. 6 is a diagram for explaining setting and movement of an evaluation area of center-weighted photometry.

FIG. 7 is a diagram for explaining exposure control of a captured image having high luminance.

[Explanation of symbols]

 Reference Signs List 1 lens 2 aperture 3 CCD (charge coupled device) 4 CDS (correlated double sampling) circuit 5 process processing circuit 6 A / D converter 7 aperture control unit 8 CCD control unit 9 system control unit 12 digital signal processing unit 14 memory 17 Data processing unit 18 Memory card 23 Image display processing unit 24 Image display device

Claims (4)

[Claims] 1. A captured image is divided into a number of small areas, and an evaluation value obtained from an integrated value of luminance of light incident from an optical system is used for each of a plurality of medium areas obtained by combining a plurality of these small areas. In an automatic exposure control device that performs exposure control by central photometry or spot photometry, the brightness difference determination middle area in the upper and lower portions of the captured image, or the brightness difference determination middle region in the left and right portions of the captured image. The medium area setting means to be set, and the luminance difference for each of the luminance difference determination medium areas is equal to or greater than a predetermined luminance difference threshold, and the value of the brighter luminance difference determination medium area is equal to or less than the predetermined threshold. And an exposure evaluation target after adding a correction value that makes the image taken brighter when the determination unit determines that the image is true, to the luminance of the captured image. Dew from area An automatic exposure control device comprising: an exposure control unit configured to control exposure based on an output evaluation value. 2. A captured image is divided into a number of small areas, and an evaluation value obtained from an integrated value of luminance of light incident from an optical system is used for each of a plurality of middle areas obtained by combining a plurality of these small areas. In an automatic exposure control device that performs exposure control by central photometry or spot photometry, the brightness difference determination middle area in the upper and lower portions of the captured image, or the brightness difference determination middle region in the left and right portions of the captured image. The medium area setting means to be set, the luminance difference for each of the luminance difference determination medium areas is equal to or greater than a predetermined luminance difference, and the value of the brighter luminance difference determination medium area is equal to or less than a predetermined threshold. Determination means for determining that there is, when the determination means is determined to be true,
Evaluation area moving means for moving the set area of the middle area performing central photometry or spot photometry in the direction of lower luminance, and an exposure evaluation value obtained from the middle area of the exposure evaluation target after moving by the evaluation area moving means. An automatic exposure control device comprising: exposure control means for controlling exposure. 3. A captured image is divided into a number of small areas, and an evaluation value obtained from an integrated value of luminance of light incident from an optical system is used for each of a plurality of medium areas obtained by combining a plurality of these small areas. In an automatic exposure control device that performs exposure control by central photometry or spot photometry, the luminance difference determination middle area in the upper and lower portions of the captured image, or the brightness difference determination middle region in the left and right portions of the captured image. A middle area setting means for setting a central luminance area at the center of the captured image; and a value of the central luminance area being equal to or less than a predetermined threshold value, and having a brighter value of the luminance difference determination medium area. A determining unit that determines that the image is smaller than a predetermined threshold, and a correction value that, when determined to be true by the determining unit, adds a certain correction value such that an image captured becomes brighter to the luminance of the captured image. Exposure evaluation target An exposure control unit for controlling exposure from an exposure evaluation value obtained from the middle area. 4. A captured image is divided into a number of small areas, and an evaluation value obtained from an integrated value of luminance of light incident from an optical system is used for each of a plurality of medium areas obtained by combining a plurality of these small areas. In an automatic exposure control device that performs exposure control by central photometry or spot photometry, the luminance difference determination middle area in the upper and lower portions of the captured image, or the brightness difference determination middle region in the left and right portions of the captured image. A middle region setting means for setting a center luminance region at the center of the photographed image; and a value of the center luminance region being equal to or less than a predetermined threshold value, and having a brighter value of the luminance difference determination medium region. Judgment means for judging that the value is smaller than a predetermined threshold value, and evaluation area moving means for moving the set area of the middle area for central photometry or spot photometry in the direction of lower luminance when the judgment means judges true. When An exposure control means for controlling exposure from an exposure evaluation value obtained from a middle area of the exposure evaluation target after being moved by the evaluation area moving means.