JP2001086396A - Image-pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence on exposure adjustment of the luminance value of an image other than a main object and to improve the accuracy of the exposure adjustment to the main object, by estimating and excluding the image other than the main object within an image-pickup screen and adjusting an exposure, based on the luminance value of a remaining area. SOLUTION: First a photographing mode is set in a photographing mode setting part 33. By the setting, various kinds of parameters, corresponding to the set photographing mode, are called to an arithmetic part 13. Then, when photographing preparation is instructed in a photographing instruction part 31, focus is adjusted by an AF mechanism 26. Then, when photographing is instructed in the photographing instruction part 31, preliminary photographing is performed first, the exposure is adjusted based on a preliminarily photographed image-pickup screen, and succeeding main photographing is performed. In this case, in this device, an area satisfying prescribed conditions based on the luminance value is excluded from a base area which is predetermined within the screen, so that exposure is adjusted based on the luminance value of the remaining area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus for automatically adjusting exposure when taking an image using photoelectric conversion, for example, a digital still camera or a digital moving picture photographing apparatus having an automatic exposure adjustment function. And so on.

[0002]

2. Description of the Related Art With the recent miniaturization and high performance of CCD elements, the number of image pickup apparatuses using photoelectric conversion equipped with CCD elements has been increasing. As a method of automatic exposure adjustment in this type of imaging apparatus, Japanese Patent Publication No. Hei 7-26874
As disclosed in Japanese Patent Application Publication No.
There is a method of performing exposure adjustment using a D element as a photometric unit for exposure adjustment. According to this method, since the photometry can be performed based on the information of the captured image itself, there is an advantage that the exposure can be adjusted more accurately than when a photometry mechanism is separately provided.

[0003]

However, in such a conventional imaging apparatus which automatically performs exposure adjustment, the exposure adjustment is always performed based on image information of the entire imaging screen. When the contrast in the imaging screen is large, for example, when a light source such as the sun is included therein, there has been a problem that the exposure adjustment cannot always be performed accurately for the main subject.

[0004]

SUMMARY OF THE INVENTION In view of the above problems, according to the present invention, there is provided an imaging apparatus for automatically adjusting exposure, comprising:
Since the exposure adjustment is performed based on the luminance value of the remaining area excluding the area that satisfies the predetermined condition based on the luminance value from the predetermined base area in the screen, the luminance value of the image other than the main subject is adjusted. The influence on the exposure adjustment can be reduced, and the accuracy of the exposure adjustment for the main subject can be improved.

Further, according to the present invention, in an image pickup apparatus for automatically performing exposure adjustment, an outline of an image in a screen is detected and exposure adjustment is performed based on a luminance value of the outline. It is possible to reduce the influence of the internal brightness value on the exposure adjustment, and it is possible to improve the accuracy of the exposure adjustment for the main subject.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment in which an imaging apparatus according to the present invention is applied to a digital still camera will be described. The schematic configuration of the present embodiment will be described with reference to FIG.

The digital still camera 1 has an imaging unit 11 for capturing an image as a signal by photoelectric conversion, for example, a CCD.
A device, an A / D converter 12 for A / D converting an image signal from the imaging unit 11, and an arithmetic unit 13 for performing various arithmetic processing such as an arithmetic operation in an exposure adjustment process on the A / D converted signal. For example, a CPU, a storage unit 14 that stores a captured image signal and various parameters in arithmetic processing, an imaging unit driving circuit 16 connected to the arithmetic unit 13 to control driving of the imaging unit 11, for example, a CCD driving circuit, Is provided. The image signal taken into the storage unit 14 is
The image is displayed on a display unit 15 such as a liquid crystal display connected to the arithmetic unit 13 and built in the digital still camera 1 or an external display unit (not shown) such as a CRT connected via the image signal interface 42.

The digital still camera 1 further includes a light emitting mechanism 22 externally connected to or incorporated in the camera, a light emitting mechanism driving circuit 21 for driving a strobe, a diaphragm mechanism 24 for freely setting a diaphragm, and a diaphragm mechanism. An aperture mechanism driving circuit 23 for driving the AF mechanism 24, an automatic focus adjustment mechanism (hereinafter, referred to as an AF mechanism) 26, and an AF mechanism driving circuit 25 for driving the AF mechanism 26 are provided. Each of these drive circuits is connected to the arithmetic unit 13 and is controlled thereby.

The digital still camera 1 further includes a photographing instruction unit 31 for inputting a photographing instruction operation, for example, a release button, and a parameter setting unit 32 for setting / changing various parameters related to the calculation in the calculation unit 13. A photographing mode setting unit 33 for selecting an operation processing pattern stored in the storage unit 14 and set in accordance with a photographing situation, and for performing external control of the operation unit or exchanging various parameters with the outside. And a control signal interface 41.

Next, a procedure for photographing an image according to the present embodiment will be described with reference to FIG. First, the shooting mode is set in the shooting mode setting section 33 (shooting mode setting step S11). In this shooting mode,
For example, there are a landscape photograph mode, a portrait photograph mode, a night scene mode, and the like. Various parameters used in the arithmetic processing are stored in the storage unit 14 corresponding to each of these modes. With this setting, various parameters corresponding to the set shooting mode are called by the calculation unit 13.

Next, when a photographing preparation instruction (for example, half-pressing of a release button) is performed in the photographing instruction section 31 (photographing preparation instruction step S12), focus adjustment is performed by the AF mechanism 26 (focus adjustment step S13). Next, when a shooting instruction (for example, full-pressing of a release button) is performed in the shooting instruction unit 31 (shooting instruction step S14), first, preliminary shooting is performed, and exposure adjustment is performed based on the captured screen in which the preliminary shooting is performed. (Exposure adjustment step S15), and then actual shooting of the image is performed (image shooting step S16).

Next, the procedure of the exposure adjusting step S15 in the present embodiment will be described with reference to FIG. It should be noted that the imaging screen in the description of this step indicates an imaging screen that has been preliminarily photographed.

First, a luminance value E (for example, an average luminance value of the entire imaging screen) of a predetermined base area in the imaging screen is calculated (base area luminance value calculating step S21). FIG. 4 shows an example of the block division of the base area. In this step, the base region 50 is divided into a plurality of regions (for example, 12 × 8).
(= 96) block 51), and this block 5
For each block luminance value, for example, the average luminance value L (i, j) (i = 1, 2,..., 12, j = 1,
2,..., 8) are calculated (block luminance value calculation step S22). Then, a log-normalized block luminance value L ′ obtained by normalizing and logarithmizing the block luminance value L (i, j).
(I, j) is calculated (step S23 for normalizing and logarithmic the block luminance value). Here, as shown in the following equation,
The normalization is performed so that the previously calculated base region brightness value E corresponds to the standardized brightness value (for example, the 18% reflectance brightness value X18), and the logarithm conversion is performed so that the base is 2. L ′ (i, j) = log2 (L (i, j) × X18 /
E) As described above, by normalizing or logarithmic the block luminance value, it is possible to process an imaged screen having any luminance value distribution at a uniform luminance value level. Processing accuracy in exposure adjustment can be improved.

Next, an unnecessary image area other than the main subject is estimated based on the luminance value, and this area is excluded (step of removing unnecessary area S24). By this process, for example, an unnecessary image region having a high luminance value or a low luminance value such as a locally dark portion such as a light source such as the sun or a black dress portion is estimated, and the source of the exposure adjustment index value is calculated. Is excluded from the target of calculation of the corrected index value, that is, the remaining area. The remaining area is identified by setting the remaining area index value FL. First, FL = 1 is given to the base region 50, and this is replaced with FL = 0 as needed when identifying the region to be excluded. In estimating the unnecessary area, the luminance value is weighted according to the position on the screen, so that an image element that is likely to be the main subject is not easily excluded. Explaining this process more specifically, the elimination of unnecessary areas having a high luminance value is performed by subtracting a value obtained by multiplying the luminance value by a position weighting coefficient WPu that is low at the center of the screen and increases toward the periphery of the screen. Is performed by setting the remaining area index value FL to 0 for a block having a threshold value Tu or more. Meanwhile,
Unnecessary areas with low luminance values are excluded from blocks whose value obtained by multiplying the luminance value by a position weighting coefficient WPd that is higher at the center of the screen and lower toward the periphery of the screen is equal to or less than a predetermined threshold value Td. This is performed by setting the area index value FL to 0. That is, the estimation of the unnecessary area in this step is performed by excluding the area satisfying the predetermined condition based on the luminance value. As described above, by estimating the area of the image that is not the main subject according to the luminance value and excluding it from the calculation of the exposure adjustment index value, the accuracy of the exposure adjustment for the main subject can be improved. In addition, by performing weighting according to the position at that time, it becomes possible to more accurately estimate and exclude images other than the main subject.

Next, a corrected index value based on the luminance value of the remaining area is calculated (corrected index value calculating step S25). First, a procedure for calculating a modified index value is determined based on the ratio of the area remaining so far to the predetermined area in the imaging screen due to the elimination of the unnecessary area, and the process is branched (the determining step of the modified index value calculating procedure). S26). If the ratio is large, the luminance value of the remaining area is calculated as a correction index value (remaining area luminance value calculating step S27). More specifically, when the number of remaining areas at this point (that is, the number of blocks whose remaining area index value is a value other than 0) ZB is larger than threshold value Tb, modified index value M is shown below. As in the formula, the logarithmic normalized luminance value L ′ of the remaining area is calculated as a weighted average value (remaining area luminance value) Ma obtained by performing weighting by the position in the screen and weighting by the brightness. The threshold value Tb is set to, for example, Tb = 31 with respect to the number of blocks (= 96) in the base area. Ma = Σ (Lk ′ × WPk × WLk) / Σ (WPk × W
Lk) Here, k (= 1, 2,..., ZB) is a number assigned to a block having a remaining area index value FL other than 0, WP
Is a weighting coefficient by position, and WL is a weighting coefficient by brightness. The position-based weighting coefficient WP is determined such that the maximum value is at the center of the screen and the value is reduced radially from the center toward the periphery. FIG. 5 shows an example of the position weighting coefficient WP determined for each block 51 that divides the base region 50. The numerical value shown in the frame of the block 51 indicates the position weighting coefficient WP for each block. There is a high possibility that the main subject is near the center of the screen, and thus, by giving greater weight to the vicinity of the center of the screen, the accuracy of exposure adjustment for the main subject can be improved. FIG. 6 shows an example of the weighting coefficient WL based on brightness determined according to the brightness value. In this example,
In a region where the luminance value L 'is lower than the first threshold value Tl1, the coefficient WL is higher as the luminance value L' is lower, and in a region where the luminance value L 'is higher than the second threshold value Tl2, the luminance value L' is higher. Are higher, the coefficient WL is higher and the luminance value L ′
Is set between the first threshold value T11 and the second threshold value T12, the coefficient WL is set to 1 and the coefficient WL is continuous within these ranges. In general, the range of the luminance value that can be received by the imaging unit 11 such as a CCD element is limited. When the luminance value of a captured image exceeds this range, the luminance value is saturated and is recognized as a luminance value lower than the actual value. Will be done. Therefore, by setting the threshold value in accordance with the light receiving range of the imaging unit and correcting the luminance value in the high range and the low range of the luminance value, it is possible to obtain a luminance value distribution closer to the actual one. The accuracy of exposure adjustment for the main subject can be further improved.

On the other hand, when the ratio of the remaining area to the predetermined area in the imaging screen is small, the modified base area luminance value obtained by weighting the remaining area based on the luminance value of the base area as the modified index value is used. Is calculated (corrected base area luminance value calculating step S28). More specifically, the modified index value M is weighted by weighting based on the position in the base region, weighting based on brightness, and increasing the weight in the region remaining up to this point, as in the following formula ( It is calculated as the corrected base area luminance value Mb). Mb = Σ (L ′ (i, j) × WP (i, j) × WL
(I, j) × WM (i, j)) / Σ (WP (i, j) ×
WL (i, j) × WM (i, j)) Here, WP is a weighting coefficient based on a position, and WL is a weighting coefficient based on brightness. For example, the same coefficients as those described in the previous step S27 are used. Can be WM is a weighting coefficient based on the remaining area index value FL. The weighting coefficient WM based on the remaining area index value FL is set to, for example, 2 in a block where the remaining area index value FL is other than 0, and is set to 1 in a block where the remaining area index value FL is 0. When the ratio of the remaining region to the base region is small, it is highly likely that a portion other than the remaining region is also photographed as the main subject. Therefore, in such a case, the correction index value used as the basis for the exposure adjustment is calculated based on the luminance value of the entire base region by weighting the remaining region portion instead of calculating only the luminance value of the remaining region. By performing the calculation, more accurate exposure adjustment can be performed for the main subject.

Next, an exposure adjustment index value as a basis of the exposure adjustment is calculated (exposure adjustment index value calculating step S29).
The exposure adjustment index value A is calculated based on the base area luminance value E and the correction index value M according to the ratio of the initial area to the base area from which the correction index value M is calculated. More specifically, for example, the exposure adjustment index value A is calculated by the following equation. A = (1−ω) × E ′ + ω × M ′ E ′ = log2E M ′ = M−log2 (X18 / E) where ω is the base of the original area from which the correction index value M was calculated. This is a weighting coefficient according to the ratio to the area, and for example, as shown in FIG.
4, when the number of remaining area blocks ZB is 0, the coefficient ω
Is 0, the coefficient ω is 1 when the threshold value is equal to or more than the threshold value Tz, and between 0 and the threshold value Tz, ω changes linearly between 0 and 1; Is determined to be continuous. Here, the threshold value Tz is, for example, Tz = Tz = 96 for the number of base area blocks.
It is set to 75. Further, here, in order to calculate the exposure adjustment index value A as a weighted average, a value E ′ obtained by logarithmizing the base region luminance value E and a value M ′ obtained by canceling the above-described normalization are used as the correction index value M. . As can be seen from this equation, the larger the number of remaining area blocks ZB, the greater the proportion of the modified index value (M ') in the exposure adjustment index value A,
When the number of remaining area blocks ZB is equal to or greater than the threshold value Tz, the correction index value (M ′) itself becomes the exposure adjustment index value A. If the ratio of the original region from which the correction index value is calculated to the base region is small, it is possible that a portion other than the original region from which the correction index value was calculated may have been photographed as the main subject. Get higher. Accordingly, as described above, the weight of the correction index value M in the exposure adjustment index value A increases as the ratio of the initial area from which the correction index value M is calculated to the base area increases, that is, the correction index in the exposure adjustment. By setting the contribution of the value M to be high, the accuracy of exposure adjustment for the main subject can be improved.

Next, exposure control is performed based on the value of the exposure adjustment index value A (exposure control step S30). The exposure control in this step is performed on the aperture mechanism driving circuit 23, the imaging unit driving circuit 16, the light emitting mechanism driving circuit 21, and the like. More specifically, when the exposure adjustment index value A is a low value, that is, when the exposure is insufficient, the aperture opening is increased in accordance with the exposure adjustment index value A, The period, that is, the light receiving period is lengthened, or the light emitting mechanism is controlled to emit light. Conversely, when the exposure adjustment index value A is a high value, the reverse control is performed. It is also possible to selectively control these according to the setting of the shooting mode or other various parameters.

Next, a second embodiment in which the present invention is applied to a digital still camera will be described. In the present embodiment, in the procedure of the exposure adjustment step, a second unnecessary area elimination step is provided after the unnecessary area elimination step in the first embodiment. In addition, the schematic configuration of the apparatus in this embodiment and the processing procedure other than the exposure adjustment step are the same as those in the above-described first embodiment. Hereinafter, only the exposure adjusting step S15 will be described. FIG. 8 shows a flowchart of the exposure adjusting step S15 in the present embodiment.

Before the second unnecessary area exclusion step S42,
Step S41 of detecting the vertical direction of the screen based on the luminance value distribution of the imaging screen is performed in advance. In this step,
A predetermined area in the imaging screen is divided into a plurality of areas, and the direction of the screen is determined based on the arrangement of the areas having a large luminance value. This example will be described with reference to FIG.
FIG. 9 is an example of a direction detection map used as a basis for screen direction detection. A predetermined base area in the imaging screen is divided into a large block of 2 × 3, and the arrangement of the large block having the largest luminance value and the second largest block is recognized. The arrangement of these two large blocks (61, 62) in the direction detection map 60 is compared, and the direction of the screen is determined based on the comparison. here,
When the arrangement of large blocks on the imaging screen corresponds to FIG. 9A, the direction of arrow A is indicated. When the arrangement of large blocks corresponds to FIG. 9B, the direction of arrow B is indicated. Arrow C
The direction is determined as the upward direction of the screen.

If the direction can be detected in step S41, a second unnecessary area to be excluded from the remaining area by further estimating an area that is not the main subject based on the luminance value and the direction of the image pickup screen. In the exclusion step S42, when the detection is impossible, the correction index value is calculated in the step S25.
Then, the process is branched.

In the second exclusion step S42, for example, the sky or shadow can be excluded from the remaining area. In other words, a region having a high luminance value above the imaging screen is detected as sky, while a region having a low luminance value below the imaging screen is detected as shadow and is excluded. More specifically, for example, the threshold value Tsk is a value obtained by multiplying the luminance value by a weighting coefficient WPl that increases from the lower side to the upper side in the imaging screen.
Higher blocks are identified as empty blocks, while
A block whose value is lower than the threshold value Tsd is recognized as a shadow block. In this way, since the sky or the shadow can be excluded based on the detected screen direction and the brightness value, the exposure adjustment for the main subject can be performed with high accuracy. This step S42 is performed, for example, using the threshold value Ts.
By setting k and Tsd, when excluding a bright area, an area having a lower luminance value than the previous excluding step S24 is excluded, and when excluding a dark area, the excluding step S24 is used. It is set so that an area having a high luminance value is excluded. In this step S42, the unnecessary area is excluded by taking the vertical direction of the imaging screen into account. With such a setting, it is possible to accurately exclude an area whose luminance value level is closer to the luminance value of the main subject. Thus, the accuracy of exposure adjustment can be improved.

Next, a third embodiment in which the present invention is applied to a digital still camera will be described. In the present embodiment, the contour of the image on the imaging screen is detected, and the exposure is adjusted based on the luminance value of the detected contour. The steps other than the schematic configuration of the apparatus and the exposure adjusting step in this embodiment are the same as those in the above-described first embodiment. Hereinafter, only the exposure adjustment step will be described. FIG. 10 shows a flowchart of the exposure adjustment step S15 in the present embodiment.

In the exposure adjustment step S15, after the base area luminance value calculation step S21, the block luminance value calculation step S22, and the block luminance value normalization and logarithmic step S23, which are the same as in the first embodiment, And detecting the outline of the image on the imaging screen S43. In this step, a contour area, for example, a contour block is identified based on the luminance value. More specifically, as shown in the following equation, the absolute value of the rate of change of the luminance value in the block (for example, the difference between the luminance value of the block and the block adjacent to the block) is larger than the contour threshold value Th1. Block is identified as a contour block. DB (i, j)> Th1 or DS (i, j)> T
h1 Here, DB (i, j), DS (i, j) (i = 1,
2,..., 12, j = 1, 2,..., 8) are the maximum value of the luminance value increase rate and the maximum value of the luminance value decrease rate in the block i, respectively. DB (i, j) = | maxAL-L '(i, j) | DS (i, j) = | minAL-L' (i, j) | maxAL = max (L '(i + 1, j + 1), L '(i
+ 1, j), L '(i + 1, j-1), L' (i, j +
1), L '(i, j-1), L' (i-1, j + 1),
L '(i-1, j), L' (i-1, j-1)) minAL = min (L '(i + 1, j + 1), L' (i
+ 1, j), L '(i + 1, j-1), L' (i, j +
1), L '(i, j-1), L' (i-1, j + 1),
L ′ (i−1, j), L ′ (i−1, j−1)). Then, the remaining area index value FL is determined according to the values of DB and DS. The remaining area index value FL is determined for each block, and FL = 1 is set for a contour block satisfying DB> DS, FL = 2 is set for a contour block satisfying DB <DS, and FL = 0 is set for other blocks. . That is, in this case, the remaining area which is obtained by estimating and removing an unnecessary image from the base area is set to be identifiable as an area where the remaining area index value FL takes a value other than 0,
Among the contours appearing at the boundary between a bright image area having a high luminance value and a dark image area having a low luminance value, a contour on the bright area side (remaining area index value FL = 2) and a contour on the dark area side (remaining area index value FL = 1) are set so as to be identifiable by the remaining area index value. FIG. 11 schematically shows an example of the detection of the contour. FIG.
In the base area 70 of the imaging screen shown in FIG. 1A, there are a block 71 assumed to be a main subject image area and a block 72 assumed to be sky. FIG. 11B shows the result of the detection of the contour on the image screen. The numbers in the blocks of the block in FIG.
L. However, blocks with a remaining area index value FL of 0 are shown as blank.

In this step, the outline region of the image is used as the remaining region. This makes it possible to limit the unnecessary area other than the main subject to only the outline and reduce the influence on the exposure adjustment of the luminance value distribution irrelevant to the main subject in the unnecessary area. The accuracy of the adjustment can be improved. In addition, this makes it possible to reduce the region in which the exposure adjustment index value is calculated, so that the exposure adjustment can be performed quickly.

Next, an image area other than the main subject is estimated based on the luminance value and excluded from the remaining area (unnecessary area exclusion step S24). Is detected, and the process is branched based on the screen direction detection result (screen vertical detection process S4
1). These steps are the same as those in the first or second embodiment except that the remaining area is a contour area, and have the same functions and effects.

In the second exclusion step S42, for example, the sky or shadow can be excluded from the remaining area, as in the second embodiment. First, a block in which the luminance value of the uppermost block based on the direction detected in the previous step is higher than the threshold value Tsk is recognized as an empty block. Further, all blocks in the same column as this block, which are further upward than the uppermost block having the remaining area index value of 1 and whose remaining area index value is 2 (that is, the outline on the light side), are empty blocks. And the remaining area index values of these blocks are all replaced with 0. Also, when there is no block in the column where the remaining area index value FL is 1, blocks having the remaining area index value FL of 2 are recognized as empty blocks, and the remaining area index values FL of these blocks are determined as empty blocks. Replace all with 0. For example, if this step is performed in the example of FIG.
The result is as shown in FIG. 11C (arrow A direction: upward direction of the screen). Numerical values and blanks in FIG.
The remaining area index value FL is shown similarly to (b). On the other hand, a block in which the luminance value of the lowermost block based on the direction detected in the previous step is lower than the threshold value Tsd is determined as a shadow block. On the other hand, all blocks in the same column as this block, which are further lower than the lowermost block having a remaining area index value FL of 2, and whose remaining area index value FL is 1 (that is, the contour on the dark side) are deleted. The blocks are identified as shadow blocks, and the remaining area index values FL of these blocks are all replaced with 0. Also, when there is no block having the remaining area index value FL of 2 in the column, the remaining area index value F
Blocks in which L is 1 are recognized as empty blocks, and the remaining area index values FL of these blocks are all replaced with 0.
By separately identifying the outline area on the bright side and the dark side in this way, the sky or shadow can be easily and accurately excluded, so that the exposure adjustment accuracy for the main subject can be reduced. Can be improved. If the second exclusion step S42 is performed in a state in which a light source such as the sun remains, for example, the outline region of the light source may be erroneously recognized as an empty outline region. By performing an unnecessary area exclusion step S24 that does not depend on the vertical direction of the screen before this step and excluding a light source, a dark area, and the like in advance, erroneous recognition of the exclusion area in this step S42 is prevented. Exposure adjustment with higher accuracy is realized.

Steps subsequent to the second unnecessary area elimination step S42 (S25, S26, S27, S28, S29, S3)
0) is the same as in the above-described first or second embodiment, and the operation and effect of these steps are the same as in the first or second embodiment.

In this embodiment, in the exposure adjustment index value calculating step S29, the weighting coefficient ω is
The determination may be made in accordance with the ratio of the contour region recognized in the contour detection step S43 to the base region (for example, the ratio of the number of contour blocks detected in the contour detection process to the number of base region blocks). In this case, in FIG. 7, the horizontal axis is changed from the number of remaining area blocks ZB to the number of contour blocks ZE, and the threshold value Tz is set to, for example,
Tz = 21 is set for the number of base area blocks (= 96).

The present invention is also applicable to a moving picture photographing apparatus. In this case, the exposure adjustment according to the present invention is performed at any time during moving image shooting. The order of performing the respective steps can be changed as appropriate. For example, the first and second exclusion steps may be performed after the step of detecting the direction of the imaging screen. In addition, various operations for exposure adjustment are performed on blocks obtained by dividing the base region. However, the operations may be performed on pixels. Further, each threshold value may be set for each shooting mode. In this way, exposure adjustment can be optimized for various shooting situations.
Further, a posture detector 43 (FIG. 1) for detecting a relative posture of the imaging device with respect to the vertical direction may be provided, so that the vertical direction of the screen may be detected.

Before the exposure adjustment step, the white balance gain may be adjusted by a known method based on the luminance value of the image preliminarily photographed by the imaging unit 11.
This white balance gain adjustment adjusts each gain of the luminance values of the three primary colors according to, for example, the shooting mode. Therefore, it is possible to reproduce a luminance value distribution in a form closer to the luminance value distribution of an actual image. Thus, the accuracy of the exposure adjustment can be further improved.

When the vertical direction of the image sensing screen is detected based on the result of the attitude detection by the attitude detector or the luminance value distribution of the image sensing screen, the weighting coefficient WP based on the position in each process is slightly changed to the central part. It may be set to have a local maximum value or a local minimum value below. FIG. 12 shows an example of such a position weighting coefficient WP (in the direction of arrow A:
On the screen). The value of the weighting coefficient WP at this position is shown in each frame of the block 51. In many cases, the main subject generally exists slightly below the center of the screen, and this can further improve the accuracy of exposure adjustment for the main subject.

The step S24 of eliminating unnecessary areas based on the luminance value is not limited to the above-described procedure. For example, in a case where a region belonging to a contour on the bright side whose luminance value is higher than a preset threshold value Tsk is surrounded by a region of a contour on the dark side, these contour regions are recognized as light sources and excluded. can do.

[0034]

As described above, according to the present invention, by adjusting the exposure based on the luminance value of the remaining area by estimating and excluding images other than the main subject in the imaging screen. Thus, excellent effects such as improvement of the accuracy of exposure adjustment for the main subject and reduction of the time required for exposure adjustment can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a digital still camera according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure of photographing by the digital still camera according to the embodiment of the present invention.

FIG. 3 is a flowchart illustrating an exposure adjustment process performed by the digital still camera according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an example of block division in a base region set on an image screen by the digital still camera according to the embodiment of the present invention.

FIG. 5 is a diagram showing an example of a weighting coefficient based on a position of an imaging screen set in the digital still camera according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of a weighting coefficient based on a luminance value of an imaging screen set in the digital still camera according to the embodiment of the present invention.

FIG. 7 is a diagram showing an example of a weighting coefficient for calculating an exposure adjustment index value set in the digital still camera according to the embodiment of the present invention.

FIG. 8 is a flowchart illustrating an exposure adjustment step performed by the digital still camera according to the second embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of a direction detection map set in the digital camera according to the second embodiment of the present invention.

FIG. 10 is a flowchart illustrating an exposure adjustment step performed by the digital still camera according to the third embodiment of the present invention.

FIG. 11 is a schematic diagram illustrating a contour detection step and an unnecessary area elimination step based on a luminance value and a vertical direction of an imaging screen by the digital still camera according to the third embodiment of the present invention.

FIG. 12 is a diagram illustrating an example of a weighting coefficient based on a position of an imaging screen set in the digital still camera according to the second or third embodiment of the present invention.

[Explanation of symbols]

50, 70 base region, 51 blocks, WL
A weighting coefficient based on a luminance value, a weighting coefficient for calculating an exposure index value, and a 60-direction detection map.

Claims (5)

[Claims] 1. An imaging apparatus for performing exposure adjustment based on a luminance value of an imaging screen by photoelectric conversion, wherein an area satisfying a predetermined condition based on the luminance value is excluded from a predetermined base area in the screen. An imaging device that performs exposure adjustment based on the luminance value of the remaining area. 2. The imaging apparatus according to claim 1, wherein the exposure adjustment is performed based on a luminance value of the remaining area and a luminance value of the base area. 3. The imaging device further detects an up-down direction of an imaging screen, and the remaining region is a base region that satisfies a predetermined condition based on a luminance value and a direction determined by the direction detection unit. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is a region remaining after being excluded from the image processing. 4. An imaging apparatus for performing exposure adjustment based on a luminance value of an imaging screen by photoelectric conversion, wherein an outline of an image in the screen is detected based on the luminance value, and an outline of the outline area detected by the outline detection means is detected. An imaging device that performs exposure adjustment based on a luminance value. 5. The imaging apparatus according to claim 4, wherein the exposure adjustment is performed based on a luminance value of a base region predetermined in a screen and a luminance value of the outline.