JP2003259231A - Automatic exposure controller and program thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately perform high luminance processing in an image with uneven luminance distribution. <P>SOLUTION: An automatic exposure controller is provided with a means for preparing a luminance histogram by using a luminance value of each small area of a photographed image obtained from image data, a high occurrence section extracting means for extracting a high occurrence section exceeding a occurrence threshold from the luminance histogram, a means for comparing an evaluation value for a bright part calculated on the basis of positional information of a small area included in a section equal to or more than a bright part high occurrence section with an evaluation value for a dark part calculated on the basis of positional information of a small area included in a section equal to or less than a dark part high occurrence section when there are a plurality of high occurrence sections and a bright part high occurrence section with the highest luminance is away from a dark part high quality section by a fixed section or more, and a means for performing high luminance processing according to a high luminance processing method selected on the basis of this judgement result. <P>COPYRIGHT: (C)2003,JPO

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 applied to an image input device using an image pickup device such as a digital video camera and a digital still camera, and a program therefor.

[0002]

2. Description of the Related Art The conventional exposure determination methods used in automatic exposure control devices include average metering, center-weighted metering, 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, the exposure evaluation value is acquired from the average brightness information of the area, and the exposure is determined based on that. In addition, exposure compensation such as backlight compensation is performed. In defining the evaluation area, the image area is often divided into a plurality of grid-like areas (small areas) as shown by the broken line in FIG. 2, and the divided areas are combined to form an evaluation area (medium area). . The area surrounded by the thick line in FIG. 3 is a combination of evaluation areas generally found in the center-weighted method.

By the way, if there is a sky-like high-luminance portion in the evaluation area as shown in FIG. 4, the exposure evaluation value becomes high due to the influence of the luminance of the sky portion, and the exposure is suitable for the brighter one.
The entire image may be dark. In particular, in the case of center-weighted photometry as shown in FIG. 3, if there is a bright portion such as the sky in the center, the effect is great. Therefore, a method of replacing the brightness value of the small area with a predetermined value when the brightness value of each small area exceeds a predetermined threshold value is disclosed in JP-A-5-122600 and JP-A-7-29.
As proposed in Japanese Patent No. 8131, etc., in the case of an image with a large luminance difference, high luminance processing is performed by replacing the high luminance portion with a predetermined value.

[0004]

As described above, when photographing outdoors, it is possible to suppress the influence of high brightness such as the sky by replacing or excluding the high brightness part with a predetermined position. Further, even when shooting indoors, it is possible to suppress the influence of indoor lighting. However, when shooting indoors,
If there are more than a certain percentage of black objects such as shadows and dark curtains that are not illuminated by the illumination light in the image, there will be a difference in brightness between the dark areas and the illuminated areas, and There was a problem that the subject part was judged to be a high-brightness part and the exposure was adjusted to the dark part, and the original subject part illuminated by the light was blown out.

The present invention has been made in consideration of the above-mentioned problems of the prior art, and provides an automatic exposure control device and its program capable of performing more appropriate high brightness processing on an image having a brightness difference. The purpose is to do.

[0006]

That is, an automatic exposure control apparatus according to the invention of claim 1 divides a photographed image into a plurality of small areas based on image data from an image pickup element, and the brightness of each small area. Brightness value calculating means for calculating a value, histogram creating means for creating a brightness histogram by dividing the brightness value for each small area into partitions, and high frequency for extracting a high-frequency partition having a frequency higher than a frequency threshold value from the brightness histogram When there are a plurality of partition extraction means and a plurality of high-frequency partitions and a bright part high-frequency partition having the highest brightness and a dark part high-frequency partition having the lowest brightness are separated by a certain number or more, the bright part high-frequency Evaluation values for bright areas calculated based on position information of target small areas included in sections equal to or larger than the dark section and dark areas calculated based on position information of target small areas included in sections equal to or lower than the dark section high frequency section A high-luminance process is performed according to a high-luminance processing method selected based on a determination result of comparing the evaluation value and determining which of the bright high-frequency segment and the dark high-frequency segment is important, and the determination result of the determination unit. And a calculation means for calculating an exposure control value.

According to the first aspect of the invention, when the evaluation value for the bright part is larger than the evaluation value for the dark part, it is determined that the high frequency part of the bright part is more important than the high frequency part of the dark part and corresponds to the high frequency part of the bright part. When the high brightness processing method that matches the high brightness area is selected, and conversely, when the evaluation value for dark areas is larger, the high brightness processing method that matches the low brightness area that corresponds to the dark area high frequency section is selected, and It is possible to perform appropriate high-luminance processing according to the subject even for images having a difference.

According to a second aspect of the present invention, in the automatic exposure control device according to the first aspect, the light area evaluation value and the dark area evaluation value are set for each small area in accordance with the distance from the designated area of the photographed image. It is characterized in that it is calculated using a weighting coefficient.

According to the second aspect of the present invention, the evaluation value for the bright area and the evaluation value for the dark area are calculated using all the weighting factors of the corresponding target small area, and the small value close to the designated area is included in the target small area. The more areas there are, the higher the evaluation value and the more important it is.

According to a third aspect of the present invention, in the automatic exposure control device according to the second aspect, the designated area of the photographed image can be arbitrarily changed. According to the present invention, when the photographer designates the subject, the weighting coefficient is set to be higher for a small area closer to the subject, and it is possible to more reliably perform appropriate high-luminance processing.

According to a fourth aspect of the present invention, in the automatic exposure control device according to the first aspect, the evaluation value for the bright area and the evaluation value for the dark area are corrected according to the luminance information of the corresponding small sub-areas. Is characterized by. In this invention,
By setting the weighting coefficient according to the brightness level,
It is possible to reflect the brightness information of the target small area in the evaluation value, and it is possible to more reliably perform appropriate high brightness processing.

According to a fifth aspect of the present invention, in the automatic exposure control device according to the first or fourth aspect, the light area evaluation value and the dark area evaluation value are corrected in accordance with the hue information of the corresponding small sub-areas. It is characterized by In the present invention, by setting the weighting coefficient depending on the hue,
It is possible to reflect the hue information of the target small area in the evaluation value, and it is possible to more reliably perform appropriate high-luminance processing.

According to a sixth aspect of the present invention, in the automatic exposure control device according to the first aspect, it is determined whether or not the small area included in the high-frequency section is achromatic, and when it is achromatic, the exposure control value is corrected. An achromatic color correction means is provided. In the present invention, when the captured image has an achromatic background such as a snow scene or white paper, the exposure is corrected by detecting this and preventing the entire image from becoming a gray image.

According to a seventh aspect of the invention, based on the image data from the image pickup device, the photographed image is divided into a plurality of small areas, and a brightness value is calculated for each of the small areas, and a brightness for each of the small areas. Creating a brightness histogram by dividing the values into partitions, extracting a high-frequency partition having a frequency higher than a frequency threshold from the brightness histogram, a plurality of the high-frequency partitions, and a bright part high frequency having the highest brightness For a bright part calculated based on the position information of the target small area included in the bright part high frequency partition or more when the partition and the dark part high frequency partition with the lowest brightness are separated by a certain number or more The evaluation value is compared with the evaluation value for the dark part calculated based on the position information of the target small area included in the section below the dark section high frequency section, and which of the bright section high frequency section and the dark section high frequency section is important? Process to judge Performs high luminance processing in accordance with the high luminance processing method is selected based on the determination result of this step,
A program for causing a computer to execute the step of calculating an exposure control value.

According to the seventh aspect of the invention, by causing a computer to execute this program, it is possible to easily realize an automatic exposure control device capable of performing more appropriate high-luminance processing on an image having a luminance difference. Is possible.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block configuration of an automatic exposure control device according to a first embodiment of the present invention. An object image that has passed through a taking lens 1 and an aperture 2 shows the amount of light formed as an electric signal. An image signal is output by the CCD 3 which converts the image signal into The output image signal is converted from an analog signal to a digital signal by the A / D converter 6 after the noise of the CCD 3 is removed by the CDS 4 and the gain is controlled by the process processing circuit 5. A diaphragm driving unit 7 is connected to the diaphragm 2, and a CCD driving unit 8 is connected to the CCD 3.

The diaphragm driving section 7 is controlled by the system control section 9 and opens and closes the hole diameter of the diaphragm 2 so as to change the diameter of the light beam entering from the imaging lens 1 and reaching the CCD 3.
Further, the CCD drive unit 8 controls the operation of the CCD 3 by the system control unit 9 so that the electric signal converted from the photographed light image can be accumulated and taken out. That is, CC
The shutter operation of the CCD 3 is executed under the control of the D drive unit 8. Therefore, it is possible to capture images with various exposures by these two driving units.

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

The image data created by the digital signal processing unit 12 is sent to the memory 13 once, and then sent to the image data processing unit 14 to be subjected to image processing such as gamma correction and compression, and then to the memory card 15. Memorized in. In addition, the signal from the digital signal processing unit 12 is
6, the image display processing such as γ processing is performed, and then the image is transmitted to the image display device 17 such as an LCD monitor, whereby the photographed image can be confirmed.

In addition, the digital signal processing unit 12 carries out a luminance integration process for each small area. This brightness integration process is
This is performed by converting the RGB signal data included in the small area into a brightness value and integrating the brightness value for each small area. The brightness integrated value for each small area is sent to the system control unit 9.

The system control unit 9 inputs the luminance integrated value for each small area to create a histogram based on the luminance distribution, and at the same time stores the number (position information) of the small area included in each section of the luminance histogram. Then, based on the result of the brightness histogram and the exposure conditions at the time of shooting, a high brightness threshold and a high brightness processing method are set, high brightness processing is performed, an exposure control value for exposure control is determined, and the CCD is determined by the exposure control value. Exposure control is performed by controlling the drive unit 8 and the diaphragm drive unit 7. In addition,
When a program for digital camera control is written in the memory card 16, if a special operation is performed on the camera side, the program is transferred to a camera control program memory (not shown) and the camera control program can be rewritten.

FIG. 2 shows an example of an evaluation small area divided into 10 × 10 100 areas and a middle area (portions surrounded by thick lines 1 to 6) formed by combining the evaluation small areas. ing. The brightness integrated value of the small region is calculated by the digital signal processing unit 12 as described above, and the processing for each medium region is performed by the system control unit 9. This is because it is easy to change the shape of the middle area (how to combine the small areas) depending on the situation. Here, FIG. 3 shows a case of performing center-weighted photometry, in which exposure control is performed in two middle regions indicated by hatched portions, and the middle regions near the center of the two middle regions are weighted with priority. Generally, exposure control is performed. In the case of spot metering, exposure control is performed by an area that is the same as or smaller than the middle area of the central portion shown in FIG.

The high brightness processing will be described with reference to FIGS. FIG. 4 is a model of a landscape photograph when a mountain or the like is photographed, and a sky having a considerably higher brightness than the lower mountain or the ground is located substantially above the center of the screen.
Since the high-brightness sky part is also located in the center of the screen, when center-weighted metering or spot metering is performed, the effect of the high-brightness part of the sky is large, and as shown in FIG. turn into.

Therefore, a method of eliminating the influence of the high-luminance portion by the high-luminance processing of replacing with the high-luminance prescribed value (including 0) defined for the high-luminance portion having a certain threshold value (high-luminance threshold value) or more is devised. (Japanese Patent Laid-Open No. 5-
122600 and Japanese Patent Application Laid-Open No. 7-298131), a bright image as shown in FIG. 4B can be obtained by performing such high brightness processing. Note that FIG.
FIG. 5B at the time of (a) shows the respective luminance histograms at the time of FIG. 4 (b). In FIG. 5, the horizontal axis represents the luminance partition number and the vertical axis represents the frequency. In FIG. 5A, the high luminance part (sky) is located at the center of the luminance histogram.
In (b), it can be seen that the low luminance part (ground) is at the center of the luminance histogram.

In an image having a luminance difference as shown in FIG. 5, there are two high frequency portions (high frequency sections) of the luminance histogram. Which of these two high-frequency sections is to be subjected to the high-luminance processing is also determined by the shooting conditions and the like. For example, in FIG. 5, high-luminance processing is performed according to the dark side. However, as shown in FIG. 6, when a dark curtain A or a dark portion A not illuminated by illumination light exists in an image indoors, a certain proportion or more exists in the image. As shown in FIG. 7, a distribution state of the luminance histogram similar to that of FIG. 5A is shown. At this time, if the exposure is adjusted to the low-luminance portion as shown in FIG. 5B, the subject portion B becomes too bright, resulting in an image called overexposure. In addition, in FIG. 6, the symbol C indicates spot light.

In order to prevent such a situation, in the present invention, an appropriate high brightness processing method is selected based on the position information of the small area included in the high frequency section of the brightness histogram. For example, when there are many small areas included in the bright high-frequency section near the center of the captured image, the high-intensity processing obtained from the bright high-frequency section is used instead of the high-luminance processing near the center of the captured image. In some cases, darker high brightness processing is performed.

That is, the system control unit 9 in the present embodiment performs high brightness processing according to the processing flow shown in FIGS. 8 and 9. For reference, a conventional high brightness processing operation is shown in FIG.

8 and 9, first, step 10
As 0, a histogram based on the brightness distribution is created based on the brightness integrated value for each evaluation small area from the digital signal processing unit 12. Here, 10 × 10 100 as shown in FIG.
An example will be given in which a histogram relating to luminance is created using the evaluation small areas divided into pieces. In this case, since the histogram has only 100 elements, the luminance section cannot be narrowed. This is because if the section is narrowed, the total number of sections increases and the frequency of entering one section becomes low. Therefore, the sensitivity of CCD is ± 3ev (Exposure Val
Since it is before and after ue), 1 section is set to 1 ev, and a histogram of 9 sections is created in consideration of correction such as exposure correction.
It has been found that the unit of division is less affected by the high-luminance portion when the unit of ev is used. When the exposure evaluation value of the small area is output as a linear value, the histogram is created by converting the ev value into a linear value for the luminance section when creating the histogram. For example, when the linear value at the time of the target exposure is 1000, the histogram section is set as follows. The linear value indicates the central value of the section.

[0030] -3ev; 125 -2ev; 250 -1ev; 500 0 ev; 1000 1ev; 2000 2ev; 4000 3ev; 8000

Further, in step 101, the position number of the small area for each section is stored. Actually, step 1
The position number of the small area is stored in the memory 13 or the like when the partition is determined when the histogram of 00 is created. FIG. 11 shows an example of the position number of each small area.

Next, in step 102, a section having a higher frequency than the high frequency threshold (high frequency section) is extracted from the created luminance histogram. In the case of the luminance histogram as shown in FIG. 12, section numbers 2 and 7 (sections surrounded by a square in the figure) apply.

Then, in step 103, it is checked whether or not there are two or more high frequency partitions. If there is no high-frequency division or 1
In one case, the process proceeds to step 104, and the first high-brightness process that determines the exposure control value is performed without using the brightness of the section equal to or higher than the high-brightness threshold set by another process. If there are three or more high-frequency partitions, the brightest partition and the darkest partition among them are the target partitions for the subsequent processing.

When there are two or more high-frequency partitions, it is determined in step 105 whether the two high-frequency partitions are more than a predetermined number of partitions, for example, two partitions (corresponding to 2 ev here). This is to determine whether the two high-frequency sections have a certain brightness difference. If they are not separated from each other, the first high-intensity processing of step 104 is performed as in the case where there is no high-frequency partition or when there is one.

If the two high-frequency partitions have a certain brightness difference, in step 106, the brighter (higher brightness) high-frequency partition (hereinafter referred to as bright part high-frequency partition). Find the position of the small area in the above high-intensity section,
From the position and the shooting conditions indicated by the section, the evaluation value for bright part a
Ask for. Further, in step 107, the position of the small area in the low-luminance side partition below the darker (lower brightness) high-frequency partition (hereinafter referred to as the dark part high-frequency partition) is obtained,
Based on the shooting conditions indicated by the position and the section, the evaluation value b for the dark area
Ask for.

The evaluation value a for bright areas and the evaluation value b for dark areas are obtained as follows. A weight table 20 according to the position of the small area as shown in FIG. 13 is prepared. FIG. 13 is an example in which the weighting factor is changed depending on the distance from the center of the image (the portion surrounded by the thick line). When obtaining the evaluation value a for bright areas, the weighting coefficient is obtained from the position of the small area included in the relevant section (high-luminance side section equal to or higher than the bright section high frequency section) by the weight table 20, and the weighting coefficient of all the relevant sections. The sum of the above is defined as the evaluation value a for the bright area. The dark area evaluation value b is similarly obtained.

The center position of the weight table 20 can be changed by the user. This may be designated directly with a touch pen or the like on the monitor, or may be designated with other cursors. FIG. 14 is an example in which the center position of the weight is moved to the left by two small areas from FIG. This is effective when the subject is located at a position displaced from the center position, such as when two people are lined up.

By the way, when actually photographing two people, for example, in order to adjust the focus, aim the camera so that one person is in the center of the image.
It is usual to press the shutter halfway to lock the focus. Then, when the shutter is pressed halfway,
The weighted table 20 from the center position as shown in FIG. 3 is used to obtain an evaluation value in advance, and whether the exposure is to be adjusted to the bright portion or the dark portion is obtained in advance. By carrying out the processing based on the above, it becomes possible to deal with only the weight table 20 from the center position as shown in FIG.

In addition to the image position weighting table 20, it is preferable to set weighting factors for each brightness value. In this case, a weighting coefficient is set low for a high-luminance portion such as the sky that is not a subject or a low-luminance portion such as a shadow, and a high weighting coefficient is set for a middle luminance portion. For example, 12 ev or more is set to 1, 1 ev is 7 ev to less than 12 ev is 4, 4 ev is less than 7 ev is 2, and 4 ev is less than 1. When obtaining the evaluation value a for the bright portion and the evaluation value b for the dark portion, first, a value obtained by multiplying the weighting coefficient by the brightness and the weighting coefficient by the position of the small area is obtained. Then, the sum of the values of all the target small areas is used as the evaluation value.

In step 108, the light area evaluation value a and the dark area evaluation value b obtained in steps 106 and 107 are compared, and the larger evaluation value is selected. In other words, when the bright part evaluation value a is high, it means that the brighter high-frequency segment is determined to be important, and therefore the bright part high-brightness process is performed. In the opposite case, high brightness processing for dark areas is performed.

If the bright portion evaluation value a is high, the process proceeds to step 109, and it is checked whether or not the luminance value indicated by the bright portion high frequency section is higher than a certain luminance value (bright portion threshold). The relationship between the section and the luminance value is obtained from the exposure control value at that time, which indicates the central section of the histogram (section circled in FIG. 12, section number 4). If it is equal to or more than the bright part threshold,
The bright high-frequency section is determined to be empty, but step 10
Since it is known from the determination of 8 that the exposure is adjusted to the bright part, the sky is considered to be the subject in this case. for that reason,
In step 110, the second high brightness processing is performed so that the high brightness portion is not removed so much. On the other hand, when the brightness value of the bright part high frequency section is smaller than the bright part threshold value, a predetermined third high brightness process is performed in step 111.

If the dark area evaluation value b is higher than the light area evaluation value a, the process proceeds to step 112, and it is checked whether the brightness value indicated by the dark area high frequency section is less than a certain brightness value (dark area threshold). If it is less than the dark area threshold value, it is determined to be indoors, and therefore, in step 113, the fourth high brightness processing in which the high brightness removal effect is suppressed is performed. On the other hand, when the brightness value of the dark part high frequency section is equal to or higher than the dark part threshold value, the third high brightness process of step 111 is performed.

From the above, in an image having a brightness difference,
A more appropriate high brightness process can be selected by determining which brightness part is important by determining the evaluation value a for the bright part and the evaluation value b for the dark part.

On the other hand, in the conventional high brightness processing, processing as shown in FIG. 10 is performed. That is, in steps 200 and 201, high-frequency sections are extracted from the luminance histogram in the same manner as steps 100 and 101. Then, in step 202, the extracted high-frequency segment is 2
It is determined whether there are two or more high-frequency sections, and if there are two or more high-frequency sections, it is determined in step 203 whether they are separated by a certain number or more. If there is no high-frequency partition, or if there is one, or if the two high-frequency partitions are not too far apart, then in step 204 the first high-intensity processing is performed.

On the other hand, if the two high-frequency sections are separated by a certain number or more, it is checked in step 205 whether the brightness value of the bright-section high-frequency section is equal to or more than the bright-section threshold. In the luminance histogram shown in FIG. 12, the bright part high frequency division is the division number 7, and shows the luminance value 13ev. FIG. 15 shows a case where the light area threshold is set to 12 ev and the dark area threshold is set to 7 ev. The white circles indicate the positions of the bright high-frequency sections, and the black circles indicate the positions of the dark high-frequency sections. FIG. 15A shows the sections of the histogram of FIG. Actually, the brightness histogram has seven sections according to the CCD sensitivity, and therefore, the result is as shown in FIG. In the case of FIG. 15 (b), the position of the white circle is larger than the bright portion threshold value, so it is judged to be almost outdoors, and for this reason, the fifth high brightness processing is performed to remove the high brightness portion (step 206).

If the brightness value of the bright part high frequency section is smaller than the bright part threshold value, it is checked in step 207 whether the brightness value of the dark part high frequency section is less than the dark part threshold value. Figure 15
In the case of (c), since the position of the black circle is smaller than the dark area luminance value, it is determined to be indoors, and the fourth high luminance processing in which the high luminance removing effect is suppressed is performed (step 208).

If the brightness value of the bright part high frequency section is less than the bright part threshold value and the brightness value of the dark part high frequency section is the dark part threshold value or more, the third high brightness processing is performed in step 209.

Here, the above-described high brightness processing methods will be summarized below. First high-intensity processing: Since the high-frequency sections are almost concentrated in the image, a high-intensity threshold that is brighter by a predetermined brightness is obtained from the brightness indicated by the high-frequency sections, and the image brightness evaluation value of a portion brighter than this high-intensity threshold is excluded Then, the shooting exposure evaluation value is obtained. Second high-brightness process: Since the subject is considered to be a high-brightness part such as the sky, a high-brightness threshold that is bright by a predetermined brightness is obtained from the brightness indicated by the bright part high-frequency section, and an image of a part brighter than this high-brightness threshold is obtained. The shooting exposure evaluation value is obtained by excluding the brightness evaluation value. In this case, there is practically no number of image areas equal to or higher than the bright part high-frequency section, and therefore, the processing in which the high luminance removal is almost suppressed is performed. Third high-brightness process: A high-brightness threshold is obtained from the brightness indicated by the bright high-frequency section and the brightness indicated by the dark high-frequency section, and the image exposure evaluation value is determined by excluding the image brightness evaluation value of a portion brighter than the high-brightness threshold. Ask. As an example of how to set the high brightness threshold,
There is a method in which the brightness indicated by the bright part high frequency section and the brightness indicated by the dark part high frequency section are set to the middle (average). In addition, you may perform similarly to the following 5th high brightness processing. Fourth high-brightness process: Since the subject is considered to be a low-brightness part indoors, a high-brightness threshold that is brighter by a predetermined brightness is obtained from the brightness indicated by the dark part high-frequency section, and image brightness evaluation of a part that is brighter than this high-brightness threshold The value is also replaced with a predetermined value (a value brighter than the high brightness threshold value) to obtain the photographing exposure evaluation value. Here, the high-luminance part is not excluded as in the first and second high-luminance processes. The reason is that if the high-luminance part is excluded and the exposure is adjusted to the low-luminance part, parts other than the subject cause whiteout. This is because it will end up. Although there is no problem in terms of image quality even if the sky such as the outdoors is blown out, it is not preferable as an image when it is indoors because the state of the room other than the subject is unknown. Therefore, the high-luminance removal effect is suppressed by replacing the evaluation value of the high-luminance portion with a certain value. Fifth high-brightness process: A high-brightness threshold that is brighter by a predetermined brightness is obtained from the brightness indicated by the dark part high-frequency section, and the image exposure evaluation value is obtained by excluding the image brightness evaluation value of the part that is brighter than this high-brightness threshold. By setting the high brightness threshold to be equal to or lower than the brightness indicated by the bright part high frequency section, the high brightness portion can be removed.

As is clear from the above description, in the present embodiment, in an image having a brightness difference, it is determined by using a brightness histogram whether the high brightness part or the low brightness part is important in the position information in the image. It is possible to select a more appropriate high brightness process by making a determination based on the brightness level or the brightness level.

Next, a second embodiment of the present invention will be described. The automatic exposure control device of the present embodiment has a common block configuration shown in FIG. 1 as compared with the first embodiment, but the system control unit 9 does not perform the processing shown in FIG. 8 and FIG. The difference is that the processes shown in FIGS. 16 and 17 are performed. In the present embodiment, the high luminance processing method can be more appropriately selected by adding the color information based on the hue of the portion corresponding to the high frequency section. Also, if you try to shoot a snow scene or characters written on white paper, it will try to adjust the exposure to snow or white paper, so the captured image may be shot in gray. In order to prevent this, achromatic processing is applied to necessary high-frequency sections so that the achromatic portion looks white instead of gray by using luminance information and hue or saturation information.

In order to carry out the above-mentioned processing in this embodiment, the digital signal processing section 12 includes R included in the small area.
Luminance integration processing is performed in which the GB signal data is converted into a luminance value and the luminance value is integrated for each small area. At this time, the hue and saturation for each small area are also obtained. The system control unit 9 receives the hue and saturation as well as the luminance integrated value for each small area from the digital signal processing unit 12, and performs high-luminance processing as shown in FIGS. 16 and 17.

The flow of processing of the system controller 9 will be described below with reference to FIGS. 16 and 17, steps common to those in FIGS. 8 and 9 are designated by the same reference numerals, and overlapping description will be omitted.

In steps 100 and 101, a brightness histogram is created, and the position numbers of the small areas included therein are stored in the memory 13 for each section of the brightness histogram. In step 102, the created brightness histogram is stored. Extract high-frequency parcels from. And step 10
In step 3, it is checked whether there are two or more high-frequency sections. If there is no high-frequency section or if there is one, a first high-luminance process is performed in step 104. Further, even when there are two or more high-frequency partitions, if the two high-frequency partitions are not separated from a predetermined number of partitions, for example, two partitions in the determination of step 105, the first high brightness is calculated in step 104. Perform processing.

On the other hand, if the two high-frequency sections, that is, the bright section high-frequency section and the dark section high-frequency section are separated from each other by a certain number of sections, in step 106 ', the sections are divided into bright section high-frequency sections and above. The position of a certain small area is obtained, and the evaluation value a for the bright portion is obtained from the photographing condition indicated by the position and the section and the hue and saturation of the small area. Furthermore, in step 107 ',
The position of the small area in the low-luminance side section below the dark section high frequency section is obtained, and the evaluation value b for the dark section is obtained from the position, the photographing condition indicated by the section, and the hue and saturation of the small area.

The bright portion evaluation value a and the dark portion evaluation value b in this embodiment are obtained by the following method, for example.
First, find the position of the small area, and if that position is at a specific position (eg, the upper part of the screen), check the hue, check if the color at that time is a specific color (eg, blue), and perform appropriate high-luminance processing. The evaluation value is determined so that

Further, a weight table 20 according to the position of a small area as shown in FIG. 13 and a weight table 22 in which a weight coefficient is set for each color as shown in FIG. 18 are prepared.
A weighting table 20 is used to obtain a weighting coefficient from the position of a small area included in the corresponding section (a high-luminance side section that is higher than the bright section high-frequency section).
A value obtained by multiplying the weighting coefficient obtained by Then, the sum of the values of all the small areas included in the relevant section is defined as the bright area evaluation value a or the dark area evaluation value b.

Further, the weighting coefficient can be set for each brightness value. In this case, the weighting coefficient is set low for a high-luminance portion such as the sky that is not a subject or a low-luminance portion such as a shadow, and a high weighting is set for the middle luminance portion. For example, 1 is set for 12 ev or more, 4 is set for 7 ev or more and less than 12 ev, 2 is set for 4 ev or more and less than 7 ev, and 1 is set for 4 ev or less. When obtaining the evaluation values a and b, first, a value obtained by multiplying the weighting coefficient by the luminance by the weighting coefficient by the position of the small area and the hue is obtained. Then, the sum of the values of all the target small areas is used as the evaluation value.

The bright part evaluation value a and the dark part evaluation value b thus obtained are compared in step 108, and the one having the larger evaluation value is judged to be important, and the high brightness suitable for each is obtained. Perform processing. That is, when the bright portion evaluation value a is high, it is determined in step 109 whether or not the brightness value indicated by the bright portion high frequency section is equal to or higher than the bright portion threshold value, and when the luminance value is equal to or higher than the bright portion threshold value, the sky is considered to be a subject. Therefore, in step 110, the second high-intensity processing is performed so that the high-intensity part is not removed so much. If it is less than the bright part threshold value, a predetermined third high brightness process is performed in step 111.

If the dark area evaluation value b is higher than the light area evaluation value a, it is determined in step 112 whether the luminance value indicated by the dark area high frequency section is less than the dark area threshold value. When it is determined to be indoors, the fourth high-intensity processing that suppresses the high-intensity removal effect is performed in step 113. When it is equal to or more than the dark space threshold value, a predetermined third high brightness process is performed in step 111.

Furthermore, in the present embodiment, after performing the first high-intensity processing and the second high-intensity processing, in step 120, it is determined whether the hue or saturation of the high-frequency section is achromatic. If it is determined that the color is achromatic, a correction value for achromatic color that brightens the image is set in step 121. This is a process for preventing the entire image from becoming a gray image when a snow scene or white paper is photographed. For example, an exposure correction process is performed. It should be noted that the brightness information is also used for the determination because it may be overexposed.

In the present embodiment, by performing the above-mentioned processing, even in a photographed image having a luminance difference, a more appropriate high-luminance processing is selected according to the photographing purpose and correction for achromatic color is performed. Since it can be performed, more appropriate automatic exposure control can be performed.

[0062]

As described above, according to the invention of claim 1, in an image having a brightness difference, which brightness part is important is determined by obtaining an evaluation value from each position information on the image, By selecting the high brightness processing method based on the result of the determination, more appropriate high brightness processing can be performed.

According to the second aspect of the present invention, a weighting coefficient is set for each small area into which the image is divided, according to the distance from the designated area of the image, and the evaluation value is calculated using this set weighting coefficient. As a result, in an image having a brightness difference, it is possible to perform high brightness processing in accordance with a brightness portion closer to the designated area on the image.

According to the third aspect of the present invention, by making it possible to arbitrarily change the designated area of the image, the photographer can set the subject to the designated area of the image, and it is possible to reliably set the high brightness to the subject. Processing can be performed.

According to the invention of claim 4, in an image having a luminance difference, the evaluation value of each luminance portion is calculated based on the position information and the luminance information on the image, so that an appropriate high luminance can be more surely obtained. Processing can be performed.

According to the invention of claim 5, in an image having a brightness difference, an evaluation value of each brightness portion is calculated based on position information and hue information on the image, or position information, brightness information and hue information. As a result, it is possible to more reliably perform appropriate high brightness processing.

According to the sixth aspect of the invention, when the high-luminance portion corresponding to the high-frequency section of the luminance histogram is achromatic,
By performing the achromatic color correction for the high brightness processing, it is possible to prevent the captured image having an achromatic background such as a snow scene or white paper from becoming a gray image as a whole.

According to the seventh aspect of the invention, it is possible to cause the computer to execute automatic exposure control capable of performing more appropriate high-luminance processing on an image having a luminance difference.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an automatic exposure control device according to first and second embodiments of the present invention.

FIG. 2 is a diagram showing an example of dividing a captured image.

FIG. 3 is a diagram showing areas when center-weighted photometry is performed.

FIG. 4 is a diagram modeling a landscape photograph when a mountain or the like is photographed.

5 is a diagram showing a luminance histogram of the captured image shown in FIG.

FIG. 6 is a diagram modeling an indoor photograph.

7 is a diagram showing a luminance histogram of the photographed image shown in FIG.

FIG. 8 is a flowchart (part 1) showing the processing operation of the system control unit according to the first embodiment of the present invention.

FIG. 9 is a flowchart (No. 2) showing the processing operation of the system control unit according to the first embodiment of the present invention.

FIG. 10 is a flowchart showing a processing operation related to conventional high brightness processing.

FIG. 11 is a diagram showing an example of position numbers of small areas.

FIG. 12 is a diagram showing an example of a luminance histogram of an image having a luminance difference.

FIG. 13 is a diagram showing an example of a weight table 20 according to the position of a small area.

FIG. 14 is a diagram illustrating an example in which weighting factors are changed depending on a distance from a designated area (a portion surrounded by a thick line) of an image.

FIG. 15 is a diagram showing a relationship between a high frequency section of a luminance histogram and a bright part threshold value and a dark part threshold value.

FIG. 16 is a flowchart (part 1) showing the processing operation of the system control unit according to the second embodiment of the present invention.

FIG. 17 is a flowchart (No. 2) showing the processing operation of the system control unit according to the second embodiment of the present invention.

FIG. 18 is a diagram showing an example of a weight table 22 in which a weight coefficient is set for each color.

[Explanation of symbols]

20, 22 ... Weight table

Claims (7)

[Claims] 1. Based on image data from an image sensor,
A brightness value calculating unit that divides a captured image into a plurality of small areas and calculates a brightness value for each of the small areas; a histogram creating unit that creates a brightness histogram by dividing the brightness value of each of the small areas into sections; A high-frequency partition extraction unit that extracts a high-frequency partition having a frequency higher than a frequency threshold from a brightness histogram, a plurality of the high-frequency partitions, and a bright part high-frequency partition having the highest brightness and a dark part high-frequency partition having the lowest brightness. When the distance between them is equal to or more than a certain number of sections, the evaluation value for the light section calculated based on the position information of the target small area included in the section of the high frequency section of the bright section and the section of the high frequency section of the dark section or less Comparing with the evaluation value for the dark part calculated based on the position information of the target small area contained in, the determination means for determining which of the bright high frequency section and the dark high frequency section is important, and the determination means Size An automatic exposure control apparatus comprising: a high-luminance processing method that is selected based on a constant result; and a calculation unit that calculates an exposure control value. 2. The evaluation value for the bright area and the evaluation value for the dark area are:
The automatic exposure control device according to claim 1, wherein the automatic exposure control device is calculated using a weighting coefficient set for each small area in accordance with a distance from a designated area of the captured image. 3. The automatic exposure control device according to claim 2, wherein the designated area of the photographed image can be arbitrarily changed. 4. The light area evaluation value and the dark area evaluation value are:
The automatic exposure control device according to claim 1, wherein the correction is performed according to the brightness information of the corresponding small target areas. 5. The evaluation value for light and the evaluation value for dark are:
5. The automatic exposure control device according to claim 1, wherein the correction is performed according to the hue information of the corresponding target small areas. 6. The achromatic color correction means for determining whether or not a small area included in the high frequency section is achromatic and correcting the exposure control value when the achromatic color is achromatic.
The automatic exposure device described. 7. Based on image data from the image sensor,
Dividing the captured image into a plurality of small areas, calculating a brightness value for each small area; creating a brightness histogram by dividing the brightness value of each small area into sections; and a frequency threshold from the brightness histogram. A step of extracting a high-frequency section having a higher frequency, and a plurality of the high-frequency sections, and the bright section high-frequency section with the highest brightness and the dark section high-frequency section with the lowest brightness are separated by a certain number or more. When there is, the light portion evaluation value calculated based on the position information of the target small areas included in the bright part high frequency partition or higher and the position information of the target small areas included in the dark part high frequency partition or lower And a dark part evaluation value calculated based on the above, and determining which of the bright part high frequency partition and the dark part high frequency partition is important, and a high brightness process selected based on the determination result of this process. According to the method A program for causing a computer to perform a process of performing high brightness processing and calculating an exposure control value.