JP2001045363A - Automatic exposing device for camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic exposing device for a camera capable of preventing the photographic image of even a white subject from being darkened by photographing a subject by correcting an exposure value calculated from light quantity in plural regions according to a difference between the exposure value and the maximum value of the light quantity in the plural regions. SOLUTION: This device is provided with a photometry means for measuring a photometric value by dividing a subject into plural regions, an exposure value calculating means for calculating the first exposure value of the subject based on the photometric value, a maximum value detecting means 24 for detecting the maximum value of the photometric values in plural regions, an arithmetic means for calculating a difference between the maximum value and the first exposure value, and an exposure control means 28 for controlling exposure by correcting the first exposure value according to the calculated difference when the difference is not more than a normal value, and calculating a second exposure value for photographing the subject more brightly than the first exposure value. Thus, photographing validly making the most of the dynamic range of an image to be photographed can be realized, and the photographic image of even a white subject can be prevented from being darkened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic exposure device for a camera, and more particularly, to an automatic exposure device for a camera which compares the light amount information in a specific photometry area and the maximum light amount information in a subject image to correct the exposure value and shoots. Related to the device.

[0002]

2. Description of the Related Art Exposure determination methods in a conventional automatic exposure controller include an average metering, a center-weighted metering, a spot metering,
There are methods such as multi-pattern photometry. The average metering method is
This is a method in which the exposure that provides an exposure amount at which the average value of the luminance signal of the entire image becomes a predetermined value is determined as an appropriate exposure. Center-weighted metering is a metering method that weights an area near the center of an image when obtaining an average value of luminance signals of the image in the average metering method. The spot metering method is a method in which a photographer selects a very narrow area of an image and controls the average value of the luminance signal in the area to be a specified value. Multi-pattern photometry divides an image into a plurality of areas, performs pattern recognition processing by a microcomputer, predicts the most important area, and sets the average value of the luminance signal in that area to a specified value. To control.

An exposure control method for setting the maximum value of luminance to 70 to 100% of the dynamic range is disclosed in Japanese Patent Laid-Open No.
No. 274062.

A method of detecting exposure by controlling color components of an image is disclosed in Japanese Patent Application Laid-Open No. Hei 6-281994.

[0005]

However, in the exposure control method disclosed in Japanese Patent Application Laid-Open No. 7-270462, in which the maximum value of the luminance is set to 70 to 100% of the dynamic range, the saturation of the image sensor is prevented. The key factor of adjusting the exposure to the main subject has been lost because of the implications for performing. Further, a method of judging a backlight state based on a luminance ratio between a central region and a peripheral region of an input image has been proposed at the same time. However, there is a problem that a small change in an angle of view greatly changes an exposure control amount. . Furthermore, although exposure correction is performed using a luminance signal of an image, when the control target is a high-saturation subject, there is a problem that the possibility that the signal of each color component exceeds the dynamic range increases.

In the method disclosed in Japanese Patent Application Laid-Open No. 6-281994, in which color components of an image are detected and exposure control is performed, signals for each color are simply weighted, so that a white subject is The exposure could not be set to shoot white.

In the average photometry method in the conventional automatic exposure control device, the exposure is determined by the average value of the luminance signal of the entire image. Therefore, the user wants to adjust the exposure to the subject existing in the center of the image. However, if a dark background includes a small bright subject, the entire subject is overexposed due to the influence of the surrounding brightness. When the brightness cannot be obtained and the whole subject is whitish, the reflectance is 1
There was a problem that the exposure was adjusted to about 8% gray.

In addition, in the center-weighted photometry, when an average value of the luminance signal of the image is obtained, the area near the center of the image is weighted and photometry is performed. The problem that the exposure does not match the subject existing in the center in response to this is solved. However, when the subject in the center where the weighting is heavy is white, the center is grayed with a reflectance of about 18%. Since the exposure was adjusted, there was a problem that a white subject was recorded in gray.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and makes it possible to effectively utilize the dynamic range of an image to be captured, and to prevent a captured image from becoming dark even with a white subject. It is intended to provide an automatic exposure device for a camera.

[0010]

In order to achieve the above object, a photometric means for dividing a subject into a plurality of areas and measuring a photometric value for each of the plurality of areas, based on the photometric values of the plurality of areas. Exposure calculating means for calculating a first exposure value of the subject; maximum value detecting means for detecting a maximum value of the photometric values in the plurality of areas; and the detected maximum value and the calculated first exposure value Calculating means for calculating the difference between the first exposure value and the second exposure value, and correcting the first exposure value in accordance with the difference when the obtained difference is equal to or less than a specified value, and photographing the image brighter than the first exposure value. Correcting means for calculating an exposure value; and controlling the exposure based on the first exposure value when the obtained difference is equal to or greater than a specified value, and controlling the exposure when the obtained difference is equal to or less than a specified value. Exposure control means for controlling exposure based on the exposure value. There.

According to the present invention, the subject is divided into a plurality of areas, and photometric means for measuring the photometric value for each of the plurality of areas, and the first exposure value of the subject is determined based on the photometric values of the plurality of areas. Exposure calculation means for calculating, maximum value detection means for detecting a maximum value of the photometric values in the plurality of areas, and calculation means for calculating a difference between the detected maximum value and the calculated first exposure value. Correction means for correcting the first exposure value according to the difference when the obtained difference is equal to or less than a specified value, and obtaining a second exposure value for photographing brighter than the first exposure value; If the obtained difference is equal to or larger than a specified value, the first
And an exposure control means for controlling the exposure based on the second exposure value if the obtained difference is equal to or less than a specified value. It is possible to take a picture by effectively utilizing the dynamic range, and it is possible to prevent a photographic image from becoming dark even with a white subject.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an automatic exposure device for a camera according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a first embodiment of an electronic camera to which a camera automatic exposure apparatus according to the present invention is applied.

The optical system of the electronic camera 10 includes a photographing lens 12 capable of adjusting a focus and an aperture 1 for adjusting a light amount.
4 and a solid-state imaging device (CCD) 16 for converting an image of the subject 15 into an electric signal. A matrix circuit 18 for converting R, G, B image signals obtained by the CCD 16 into video signals of Y, Cr, Cb luminance signals and color difference signals, and an image display device for displaying and recording the video signals / Recording device 20 and Y of the video signal,
An area divider 22 that divides a captured image into a plurality of predetermined areas from at least one signal of Cr and Cb and integrates the obtained images to obtain a luminance level of a subject; A maximum value detecting means 24 for detecting a region having the maximum luminance from the middle and a maximum luminance value; and weighting such as center-weighted photometry for the luminance signal divided into regions by the region divider 22 when determining the exposure at the time of photographing. The exposure necessary for photographing is calculated from the luminance level of the subject obtained by calculating the weighting table 26 for performing the calculation, the luminance signal obtained by dividing the area, the weighting table value, and the maximum luminance signal.
Exposure control means 28 for controlling the exposure of the aperture 16 and the aperture 14 is provided.

The main image signal processing of the electronic camera 10 configured as described above will be described.

The image of the subject 15 to be photographed is
An image is formed on a light receiving surface of a solid-state imaging device (CCD) 16 through the aperture 2 and the aperture 14. And the image of the formed subject is C
Each photoelectric conversion element in the CD 16 photoelectrically converts the charge signal into an amount corresponding to the amount of incident light. A timing pulse is output from the CCD drive circuit based on a signal output from a control unit (not shown), whereby the charge signals accumulated in the CCD 16 are sequentially output to the matrix circuit 18.
Is forwarded to The matrix circuit 18 amplifies the R, G, and B signals of the image data and reduces noise, and then performs A / D conversion to obtain digital data. And the A
The / D-converted R, G, and B signals are temporarily stored in a temporary storage memory, and at the same time, are transmitted to a high-frequency component extraction circuit (not shown) to determine the focus when performing autofocus. The image data stored in the temporary storage memory is extracted as necessary, and Y, Cr, C
The signal b is YC-converted and output from the matrix circuit 18.

Y, output from the matrix circuit 18,
The data of Cr and Cb is displayed or recorded by the image display / recording device 20 as needed.

Weighting is performed on the luminance information for each region obtained by dividing the region using a weighting table 26 as necessary. FIG. 2 is a diagram showing an array of constants in the weighting table 26 when the average photometry is designated as the photometry means. According to the figure, the first exposure value is calculated for the exposure control means 28 by multiplying the luminance information (photometric value) for each area obtained by dividing the area by a factor of 1/16. Output. Therefore, the exposure is determined equally for all the regions, and the average photometry is obtained.

FIG. 3 is a diagram showing an example of an array of constants in the weighting table 26 when the center-weighted photometry is designated as the photometry means. According to the figure, 1 is mainly located in the central portion where the ratio of the subject desired to be photographed is high (the area of the f, g, j, and k areas of the weighting table 26 shown in FIG. 1).
The first exposure value is calculated and output to the exposure control means 28 by multiplying it by a large coefficient of 3/64. Therefore,
An exposure value is set mainly for the central area.

FIG. 4 is a diagram showing an example of an array of constants in the weighting table 26 when the lower priority photometry is designated as the photometry means. According to the figure, a large coefficient of 10/64 is applied to the central portion where the proportion of the subject is high (the portion of the f, g, j, and k regions of the weighting table 26 shown in FIG. 1), and the central portion of the subject is A first exposure value is calculated and output to the exposure control means 28 by multiplying the lower half excluding the above by a relatively high coefficient of 3/64. The reason why a large weight is placed on the lower half of the subject is to prevent the calculated exposure value from becoming lower than the required exposure when the subject is photographed in a landscape in which the upper half of the subject generally becomes a bright sky.

In the above-described example, an example has been described in which an image is divided into rectangular regions in the vertical and horizontal directions when photometry is performed. However, the present invention is not limited to this. The object of the present invention can be achieved even with a combination of free shapes such as a half-moon shape.

In the present invention, the first exposure value obtained by the above-described divided photometry method is appropriately corrected in accordance with the maximum luminance in the subject image in order to photograph a white subject in white. The method is described below.

Since the position of the subject to be photographed is mainly located near the center in many cases, the present embodiment will be described by using an example in which the subject brightness information in the central region of the subject image to be compared is adopted. The present invention is not limited to this, and the luminance information of any part in the image may be used, or the user may specify the position of the specific luminance information.

FIG. 5 shows an example of a subject image which is photographed by correcting the first exposure value using the automatic exposure device for a camera according to the present invention.

The subject image 40 shown in FIG. 3 includes a white building 42 as a target to be photographed, a sky 44 and a dark gray building 4.
6, 48 are present. The white building 42 is a subject that looks brighter than the sky 44 by about +2 EV because it is illuminated by normal light. In the subject image 40, the names of the regions a to p divided into regions for photometry and the average EV of each region are shown.
The values are also shown. In the subject image 40, the first weighting method shown in FIG.
Is obtained, the exposure EV value is EVoldＶ13.
8 EV. White building 42 with photometric value of 15EV
If you try to make the image white, it must be exposed at 13 EV, but if it is exposed at EVold@13.8 EV determined by average photometry, it will be grayish. The subject image 4
When the first exposure value is obtained by using the center-weighted photometry method for weighting 0 as shown in FIG. 3, EVold ≒ 14.7E
V. Further, even when the first exposure value is obtained by using the weighted lower priority photometry method shown in FIG.
$ 14.3EV, and the color of the white building 42 obtained from the captured image becomes gray. That is, the exposure EV value calculated using center-weighted photometry or the like means that the maximum luminance is generally taken at a prescribed brightness with a reflectance of 18%, and the taken image is taken dark. This means that the histogram of the captured image data is biased toward the smaller output, and the dynamic range of the digital data of the captured image is not sufficiently used, and data for the image is wasted.

Therefore, in this embodiment, the maximum value of the subject luminance information in the divided area of the subject image 40 is defined as maxE.
The exposure control means 28 calculates the second exposure value recEv, which is the second exposure value, using v as the exposure EV value. When the center-weighted photometry shown in FIG. 3 is performed on the subject image 40 shown in FIG.
Vol is 14.7EV, and f, g, j,
The maximum value maxEv = 15EV of the object luminance information exists in k.

[0027]

In the case of maxEv−EVold> k, recEv = EVol (1) where maxEv is the maximum value of subject luminance information in the subject image. Exposure value) k: exposure constant recEv: shooting exposure (second exposure value)

[0028]

ΔEv = (k− (maxEv−EVold)) × n when maxEv−EVold ≦ k (2)

[0029]

RecEv = EVold−ΔEv (3) where ΔEv: Exposure correction amount n: Exposure correction coefficient Note that the exposure constant is a numerical value of about k = 2 (preferably in the range of 1 to 3 EV) depending on the environment to be used. Should be substituted for the exposure correction coefficient. Note that n (exposure correction coefficient) is a value determined according to the difference between the average value and the maximum value of the amount of light in the divided area measured at the time of obtaining the first exposure. Set a small value for. By setting these constants, FIG.
The photographing exposure recEv of the subject image 40 shown in FIG. First, using the above equations (2) and (3), ΔEv =
1.7 EV is obtained, and by using this ΔEv value to correct the first exposure value by 1.7 EV and reduce recEv to 13 EV, the white building 42 as a target in the subject 15 is photographed in white. Becomes possible.

FIG. 6 shows a backlit subject image 50 taken at the same angle as the subject image 40.

In the subject image 50 shown in FIG. 1, there are a building 52 and a sunset 54 that appear gray due to backlight. In the subject image 50, regions a to p divided into regions for photometry and the average EV value of each region are also shown. When the first exposure value is obtained for this subject image 50 using the average photometry method shown in FIG. 2, about 11.3 EV
Becomes Building 5 that looks gray with photometric value of 10EV actually
If you try to make it look as gray as you saw 2, 10EV-11
Since it is necessary to expose at about EV, if it is exposed at 11.3 EV determined by average photometry, the image looks almost gray as seen. When the first exposure value of the subject image 50 is obtained using the center-weighted metering method shown in FIG.
V and the first priority using the lower priority photometry shown in FIG.
Is about 10.4 EV, and the color of the building 52 which looks gray becomes gray as seen.

In this embodiment, the maximum value of the subject luminance information in the subject image 50 is defined as maxEv.
Calculated using values. Therefore, when center-weighted photometry is performed on the subject shown in FIG.
ld = 10.3EV, maxEv = 1 in region c
Since 6EV is present, the above equation (1) is used to determine the second exposure value, ie, the shooting exposure value. Accordingly, since recEv = 10.3EV is calculated, the building 52 which looks gray is recorded as gray as seen.

That is, by correcting the first exposure value in accordance with the luminance in the subject image shown in the equations (1) to (3), it is possible to photograph a white subject in white and perform appropriate exposure. Become.

Hereinafter, a second embodiment of the automatic exposure apparatus for a camera according to the present invention will be described in detail with reference to the accompanying drawings.

In the first embodiment, the first exposure value is corrected with the maximum value of the luminance signal in each area. However, in the case of a subject having high saturation and dark color, overcorrection is performed and an analog circuit is performed. The signal of the middle color component and the color component data of the captured image may exceed the dynamic range.
This is because the correction amount is evaluated only with the luminance signal. The luminance signal Y is generally expressed by the following equation (4) using three primary colors of green (G), red (R), and blue (B).

[0036]

Y = 0.59G + 0.3R + 0.11B (4) where Y: luminance level of luminance signal G: saturation level of green signal R: saturation level of red signal B: saturation level of blue signal In the above equation (4), when the subject has a large red (R) component and a small green (G) component, the level of the Y signal is low, and the Y signal is doubled with only the R (red) component. In this case, when the R (red) component is tripled, the Y signal is finally doubled, and the luminance becomes appropriate. Thus R
Attempting to correct the luminance only with (red) exceeds the dynamic range of R (red), and there is a possibility that the red gradation is lost.

FIG. 7 shows the relationship between the saturation and the luminance level when photographing a white subject, and FIG. 8 shows the relationship between the saturation and the luminance level when photographing a red subject.

FIG. 7 shows a red dynamic range 60, a green dynamic range 62, a blue dynamic range 64, a luminance dynamic range 66, and an exposure control means 28 output from the CCD 16. ing. Each dynamic range is represented by 8-bit (256) gradations that are often used in recent years. However, the present invention is not limited to this, and it is not limited to this.
It may be represented by a gradation such as a bit or 12 bits.

An object which is entirely white and has a luminance of Y = 100/25
In the case of 5, the saturation of each of the RGB colors is 100/255.
From the above equation (4), the following equation (5) is obtained.

[0040]

Y = 0.59G + 0.3R + 0.11B Y = 0.59 × 100 + 0.3 × 100 + 0.11 × 100 (5) = 100 where G: saturation level of green signal = 100/255 R: Saturation level of red signal = 100/255 B: Saturation level of blue signal = 100/255 When exposure correction is doubled by the above equation (5), Y = 200 /
255 and the saturation level of each color is 200
/ 255, but does not saturate because each saturation and luminance dynamic range is up to 255.

However, in the case of an object shown in FIG. 8 which is reddish overall and has a luminance Y = 100/255, the following equation (6) is obtained from the above equation (4).

[0042]

Y = 0.59G + 0.3R + 0.11B Y = 0.59 × 70 + 0.3 × 159 + 0.11 × 100 (6) = 100 where G: Saturation level of green signal = 70/255 R: Saturation level of red signal = 159/255 B: Saturation level of blue signal = 100/255 When exposure correction is doubled by the above equation (6), Y = 200 /
255, and the saturation level of the green signal is 124.
/ 255, the saturation level of the red signal is 318/255, and the saturation level of the blue signal is 200/255, and the saturation level of red is the maximum value of the dynamic range 2
Since it exceeds 55, a problem occurs that colors are not correctly reproduced.

The problem is that the saturation level of the red signal is large, but the level of the luminance signal is low, so that the red signal is overcorrected. Therefore, in the second embodiment according to the present invention, the maximum value among the divided regions of each color signal is used as a reference for correction.

FIG. 9 is a block diagram showing a second embodiment of an electronic camera to which the camera automatic exposure device according to the present invention is applied.

In the structure of the electronic camera 11, the description of the same parts as those of the electronic camera 10 shown in FIG. 1 is omitted. R obtained from the CCD 16 of the electronic camera 11,
The G and B chroma signals are transmitted to the matrix circuit 18 and the RGB area divider 23. In the RGB area divider 23, R
This is a block for performing photometry by performing area division for each of the GB signals. The RGB region divider 23 divides the captured image into a plurality of predetermined regions from at least one of the R, G, and B saturation signals and integrates the acquired images to obtain the saturation level of the subject. The maximum value detecting means 24 detects a maximum saturation area and a maximum saturation value from among the saturations in each of the divided areas.

Exposure control means 28 calculates the exposure required for photographing from the luminance level of the subject obtained by calculating the saturation signal, the weighting table value and the maximum luminance signal obtained by dividing the area, and controls the exposure of the CCD 16 and the aperture. 14 is performed.

An image signal processing portion which is a feature of the electronic camera 11 configured as described above will be described.

The formed subject image is photoelectrically converted by each photoelectric conversion element in the CCD 16 into a charge signal of an amount corresponding to the amount of incident light. A timing pulse is output from the CCD drive circuit 22 based on a signal output from a control unit (not shown), whereby the charge signals accumulated in the CCD 16 are sequentially output and transferred to the matrix circuit 18 and the RGB area divider 23. You. At least one of the saturations of the R, G, and B signals transferred to the RGB region divider 23 is divided for each region. Then, the average or maximum saturation is calculated for each region, and the region divider 22 is compared with the exposure EV value obtained from the weighting table. As a result of the comparison, the maximum saturation maxDi is calculated based on the following expression (7), and the second exposure value recDi which is the second exposure value is calculated by the expression (1).
Formulas (8), (9), and (10) obtained by modifying (2) and (3)
Find more. However, the unit is not (EV) but (saturation level) and (luminance level).

[0049]

MaxDi = MAX (maxR, maxG, maxB) (7) where MAX (A, B, C) represents a function for extracting the maximum value from A, B, and C and substituting it for maxDi. .

MaxDi: the maximum value of the subject saturation in the subject image maxR: the maximum value of the R (red) saturation signal divided into regions maxG: the maximum value of the G (green) saturation signal divided into regions maxB: the region division Maximum value of the extracted B (blue) chroma signal

[0051]

## EQU8 ## When log ₂ (maxDi / Diold)> kd, recDi = Diold (8) where maxDi: maximum value of chroma information in the subject image Diold: at the time of photographing obtained by the designated photometry method Kd: Exposure constant recDi: Saturation or luminance signal value at the time of shooting (second exposure value)

[0052]

## EQU9 ## log ₂ (maxDi / Diold) ≦ kd
In the case of ΔDi = (kd−log ₂ (maxDi / Diold)) × nd (9) where ΔDi: Exposure correction amount (EV) nd: Exposure correction coefficient

[0053]

## EQU10 ## recDi = Diold × 2 EXP (ΔDi) (10) where 2EXP (ΔDi) indicates 2 to the power of ΔDi.

It should be noted that the exposure constant is k according to the environment of use.
It is preferable to substitute a numerical value of about d = 1 and a numerical value near nd = 1 for the exposure correction coefficient. In the embodiment in which these constants are set and a white object shown in FIG.
i = 100/255 and Diold = 100/25
Since it is 5, ΔDi = 1 (EV) is obtained using Expression (9), and the exposure amount is increased (corresponding to lowering the exposure value) by using the correction value thus obtained. Then, the luminance recDi value (200/255) at the time of shooting can be obtained from Expression (10). Therefore, since the brightness is increased, it becomes possible to photograph a white subject in white.

On the other hand, in the embodiment shown in FIG. 8 for photographing a reddish subject, since maxR = 159/255, maxDi = 159/255 from equation (7). Also, since Diold = 100/255, equation (9)
Is used to determine ΔDi = 0.33 (EV).
The exposure amount is slightly increased using the i value (corresponding to lowering the exposure value). That is, 2 EXP is applied to each saturation signal.
By multiplying (ΔDi) = 2 ^0.33か け る 1.26, a new red exposure amount 200/255 (maxR × 1.26 = 159 /
255 × 1.26 ≒ 200/255). Since the exposure is slightly corrected in this manner, it is possible to accurately reproduce a reddish color and to correct the light amount. By the way, the new green exposure in this case is 8
8/255 (maxG × 1.26 = 70/255 × 1.
26/88/255), and the new blue exposure is 126 /
255 (maxB × 1.26 = 100/255 × 1.2
6 = 126/255), and the new luminance exposure amount is 126 /
255 (maxY × 1.26 = 100/255 × 1.2
6 = 126/255).

In the above description, the exposure correction amount .DELTA.Ev or .DELTA.Di has been described as an example of a linear function of (maxEv-EVold) or (maxDi-Diold). However, the present invention is not limited to this. Instead, the object of the present invention can be achieved even if the function is expressed by a function of a quadratic function or higher, a function of a logarithm or the like.

In the above description, an example has been described in which nd (exposure correction coefficient) used in equation (9) is represented as one constant, but the present invention is not limited to this. The nd (exposure correction coefficient) may be changed according to the color component having the maximum value. For example, in the examples of the above formulas (7) and (9), if the blue saturation shows the maximum value, maxDi = maxB, and the exposure correction coefficient is nd.
= NdB = 0.4, and if the saturation of red shows the maximum value, maxDi = maxR, so the exposure correction coefficient is set as nd = ndR = 0.5, and if the saturation of green is maximum, When the value is indicated, maxDi = maxG, so that the exposure correction coefficient is set to nd = ndG = 0.6 and ΔDi
Is calculated to correct the exposure value. By changing the exposure correction coefficient according to the color component showing the maximum saturation in this way, overcorrection of exposure can be prevented.

Although the above embodiment has been described with reference to an example of an embodiment of exposure correction in an electronic camera, the present invention is not limited to an electronic camera as long as it has photometric means for dividing a luminance or a color into regions and performing photometry. Even with a silver halide camera, it is possible to appropriately perform exposure correction using the camera automatic exposure device according to the present invention.

In the above equation (7), an example has been described in which the maximum saturation maxDi is obtained using the three primary colors of RGB. However, the present invention is not limited to this, and other color information may be added. , Only the G signal having a large coefficient may be used. Further, the object of the present invention is achieved even when the maximum luminance Y is entered as a parameter as shown in the following equation (11).

[0060]

MaxDi = MAX (maxR, maxG, maxB, maxY) (11) where MAX (A, B, C, D): The maximum value is extracted from A, B, C, D and maxDi. Represents a function to be assigned to.

MaxY: maximum value of Y (luminance) signal divided into regions

[0062]

As described above, according to the automatic exposure apparatus for a camera according to the present invention, a photometric means for dividing a subject into a plurality of areas and measuring a photometric value for each of the plurality of areas, Exposure calculation means for calculating a first exposure value of the subject based on the photometry value of the subject; maximum value detection means for detecting a maximum value of the photometry values in the plurality of regions; Calculating means for calculating a difference between the first exposure value and the calculated first exposure value, and correcting the first exposure value in accordance with the difference when the determined difference is equal to or less than a specified value, and taking a picture brighter than the first exposure value. Correction means for obtaining a second exposure value for controlling the exposure based on the first exposure value when the obtained difference is equal to or more than a specified value, and when the obtained difference is equal to or less than a specified value. Exposure control means for controlling the exposure based on the second exposure value; So equipped, it is possible to prevent that even white object enables effectively utilizing photographing the dynamic range captured image of the image to be photographed is dark.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of an electronic camera to which a camera automatic exposure apparatus according to the present invention is applied.

FIG. 2 is a diagram showing an array of constants in a weighting table when an average photometry is designated;

FIG. 3 is a diagram showing an example of an arrangement of constants in a weighting table when center-weighted photometry is designated;

FIG. 4 is a diagram showing an example of an arrangement of constants in a weighting table when downward priority photometry is designated;

FIG. 5 is a view showing an example of a subject image captured by correcting the first exposure value using the automatic exposure device of the camera according to the present invention;

FIG. 6 is a view showing a backlit subject image taken at the same angle as the subject image;

FIG. 7 is a diagram illustrating the levels of saturation and luminance when capturing a white subject;

FIG. 8 is a diagram illustrating a relationship between saturation and luminance level when a red subject is photographed.

FIG. 9 is a block diagram showing a second embodiment of an electronic camera to which the camera automatic exposure device according to the present invention is applied.

[Explanation of symbols]

10 ... electronic camera, 11 ... electronic camera, 12 ... lens,
14 aperture, 16 CCD (solid-state imaging device), 18 matrix circuit, 22 area divider, 23 RGB area divider, 24 maximum value detection means, 26 weighting table, 28 exposure control means, 60 ... red dynamic range, 62 ... green dynamic range, 64 ... blue dynamic range, 66 ... luminance dynamic range,

Claims (6)

[Claims] 1. A photometric unit that divides a subject into a plurality of regions and measures photometric values for each of the plurality of regions, and an exposure that calculates a first exposure value of the subject based on the photometric values of the plurality of regions. Calculating means; maximum value detecting means for detecting a maximum value of the photometric values in the plurality of regions; calculating means for calculating a difference between the detected maximum value and the calculated first exposure value; Correction means for correcting the first exposure value according to the difference when the difference is equal to or less than a prescribed value, and obtaining a second exposure value for photographing brighter than the first exposure value; If the difference is equal to or greater than a specified value, the exposure is controlled based on the first exposure value. If the determined difference is equal to or less than a specified value, the exposure is controlled based on the second exposure value. An automatic exposure device for a camera, comprising: control means; 2. The photometric unit calculates a luminance value for each of the plurality of regions, and the exposure calculating unit calculates an average photometric operation, a center-weighted photometric operation, a lower-priority photometric operation, 2. The automatic exposure device for a camera according to claim 1, wherein the first exposure value is calculated by performing at least one of pattern photometry calculations. 3. The photometric unit calculates a photometric value for each of one or more color components for each of the plurality of regions, and the maximum value detecting unit determines a photometric value of one or more color components of the plurality of regions. 3. The automatic exposure device for a camera according to claim 1, wherein a maximum value among the values is obtained. 4. The automatic exposure apparatus according to claim 3, wherein a photometric value of at least one of R, G, and B color components is obtained as the color component. 5. The automatic exposure device for a camera according to claim 1, wherein the specified value is a value in a range of 1 to 3 EV. 6. The correction means corrects the first exposure value according to the difference and the type of the color component having the maximum value when the obtained difference is equal to or less than a specified value. 6. The automatic exposure device for a camera according to claim 3, wherein a second exposure value for photographing a subject brighter than the exposure value is obtained.