JP2003255429A - Exposure controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure controller capable of eliminating the variance of the exposed state of an image and also performing automatic exposure control at a high speed by picking up the image while automatically continuing the exposed state when the luminance state of a subject is maintained from the previous automatic exposure control. <P>SOLUTION: A CPU 24a controls a digital signal processing circuit 18 so as to acquire luminance information in image data obtained from a CCD 12. When the CPU 24a judges that the luminance state of the subject is maintained from the previous exposure control based on the comparison of the luminance information acquired this time with the luminance information acquired by the previous exposure control, it performs the exposure control by using the previous control value. Meanwhile, when it judges that the luminance state of the subject is not maintained, it performs the exposure control by using the control value arithmetically calculated from the luminance information acquired this time. <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 exposure control device, and more particularly, to an exposure control device for a camera that controls an exposure state such as a shutter speed and an aperture value during photographing.

[0002]

2. Description of the Related Art The above-described conventional exposure control apparatus calculates a control value for controlling an exposure state such as a shutter speed and an aperture value based on the result of photometry every time the photometry of a subject is performed. The photometry of the subject is performed, for example, when the photographer operates the release switch. Also,
In recent years, a digital camera equipped with a display device adopts a through image mode in which an image of a subject is displayed on the display device as a through image (moving image before shooting) and the composition is adjusted. The photometry of the subject is performed at regular intervals.

[0003]

However, if the control value is calculated based on the photometry result every time the subject is metered, it takes time to calculate the control value and the photographer operates the release switch. However, there is a problem that a release time lag occurs before the actual shooting is performed and a smooth through image cannot be displayed.

Further, for example, in the case of an exposure control device that calculates a control value based on the comparison between the subject brightness and a predetermined threshold value, even if the subject brightness does not change much, the subject brightness is close to the threshold value. If it changes, the comparison result also changes and the control value also changes. As a result, there is a problem that the exposure state of the image varies even though the subject brightness is similar.

Therefore, the present invention focuses on the above-mentioned problems, and when the brightness state of the subject is maintained from the previous automatic exposure control, the exposure state is automatically and continuously imaged. Accordingly, it is an object of the present invention to provide an exposure control device capable of eliminating variations in the exposure state of an image and performing high-speed automatic exposure control.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the invention according to claim 1 measures the brightness state of a subject and outputs the result of photometry, and the photometry by the photometry means is performed. Each time the exposure control value is obtained, an exposure control device that includes an exposure control means that controls the exposure using the obtained control value is used. An exposure control device characterized by further comprising a determination means for determining whether or not the brightness state of the subject is maintained from the previous exposure control based on a comparison between the current photometry result and the previous photometry result. Exist.

According to the first aspect of the invention, the photometric means measures the brightness state of the subject and outputs the photometric result.
The exposure control means obtains a control value for the exposure and controls the exposure using the obtained control value. Before the determination means controls the exposure control means, it is determined whether or not the brightness state of the subject is maintained from the previous exposure control based on the comparison between the current photometry result by the photometric means and the previous photometry result. to decide.

According to the above construction, when the judging means judges that the brightness state of the subject has been maintained since the previous exposure control, for example, the control value used for the previous exposure control is again used for the exposure control. By doing so, the same exposure state as the previous exposure control can be continuously imaged without performing the manual exposure switching operation or the automatic exposure control lock operation. Moreover, it becomes possible to omit the calculation of the control value based on the measurement result.

A second aspect of the invention is the exposure control apparatus according to the first aspect, wherein the exposure control means controls the exposure using a control value calculated based on the photometric result of this time. Means and a shortened exposure control means for controlling the exposure using the control value used in the previous exposure control, and when the judgment means judges that the exposure is maintained, the shortened exposure control means The exposure control apparatus further comprises control means for starting the exposure control and for starting the exposure control by the normal exposure control means when the judgment means judges NO.

According to the second aspect of the present invention, the normal exposure control means controls the exposure using the control value calculated based on the current photometric result. The shortened exposure control means controls the exposure using the control value used in the previous exposure control. When the control means determines that it is maintained by the determination means,
The exposure control by the shortened exposure control means is started, and when the determination means determines NO, the exposure control by the normal exposure control means is started. Therefore, the exposure control by the shortened exposure control means does not need to calculate the control value based on the photometric result.

The invention according to claim 3 is the exposure control device according to claim 1, wherein the exposure control means controls the exposure using a control value calculated based on the exposure result of this time. And a shortened exposure control means for performing exposure control using a control value calculated based on a plurality of control values each used for exposure control up to a predetermined number of times, and the determination means maintains the exposure. When the determination is continued for the predetermined number of times or more, the exposure control by the shortened exposure control unit is started, and when the determination is not continued for the predetermined number of times or more, the control unit for starting the exposure control by the normal exposure control unit is further provided. The present invention resides in an exposure control device.

According to the third aspect of the present invention, the normal exposure control means controls the exposure using the control value calculated based on the current photometric result. The shortened exposure control means controls the exposure using a control value (for example, an average value of the plurality of control values) calculated based on the plurality of control values each used in the exposure control up to a predetermined number of times. The control means starts the exposure control by the shortened exposure control means when the determination that the control means is maintained by the determination means continues for a predetermined number of times or more, and the exposure control by the normal exposure control means when the determination is not continued for a predetermined number of times or more. To start.

Accordingly, when it is determined that the same scene is continuously shot when it is determined that the exposure is continuously performed a predetermined number of times or more, the control values used in the exposure control up to the predetermined number of times before are determined. The exposure value can be controlled as an average value of the control values. Therefore, even if the photometric result changes up and down to some extent within the range determined to be maintained by the determining unit, the exposure is controlled by the control value calculated based on the photometric result of the upper limit and the lower limit of the range. Control does not continue. Moreover, the control value may be calculated based on the control value calculated previously, and the amount of calculation can be reduced as compared with the case where the control value is calculated again from the photometric result.

The invention according to claim 4 is the exposure control apparatus according to any one of claims 1 to 3, wherein the photometric means is
The subject is divided into a plurality of areas, and the photometric result is output for each of the plurality of areas, and the determination means is based on a comparison between the current photometric result in each area and the previous photometric result, The present invention resides in an exposure control device characterized by making the above determination.

According to the invention described in claim 4, the photometric means divides the subject into a plurality of areas, and outputs the photometric result for each of the plurality of areas. Judgment means, based on the comparison of the current photometric result and the previous photometric result in each area,
Make a decision. Therefore, by comparing the photometric results in each of the divided areas of the subject, it is possible to more accurately determine whether or not the luminance state of the subject has been maintained since the previous exposure control.

The invention according to claim 5 is the invention according to claim 2 or 3.
The exposure control apparatus according to claim 1, wherein the control by the control means is stopped, and every time the photometry is performed, the normal mode for starting the exposure control by the normal control means and the control by the control means are always performed. The exposure control apparatus further includes a switching unit that switches to the shortening mode.

According to the fifth aspect of the present invention, the switching means stops the control by the control means and always starts the exposure control by the normal control means every time the photometry is performed. Switch to the short mode in which control is performed. Therefore, by providing the switching means, the photographer can select the normal mode or the short mode as needed.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a digital camera incorporating the exposure control device of the present invention. As shown in the figure, the subject light passes through the taking lens 11 and the CCD 12
Is incident on. A diaphragm 13 that limits the amount of light incident on the image pickup surface of the CCD 12 and a mechanical shutter 14 that blocks light that enters the image pickup surface of the CCD 12 are arranged between the taking lens 11 and the CCD 12. In addition,
The photographing lens 11, the diaphragm 13 and the mechanical shutter 1 described above.
4 are each driven by a motor driver 15.

The above-mentioned CCD 12 has an image pickup surface in which a plurality of pixels for photoelectric conversion are arranged in a secondary matrix,
When the subject light is incident, the optical image formed on the imaging surface is converted into an electrical signal and output as analog image data. Further, as the CCD 12, for example, an interlaced type in which all pixels can be read by using the mechanical shutter 14 together is used, and the total number of pixels is 3.26 million (horizontal pixel number 2080, vertical pixel number 156).
8), 3.14 million effective pixels (2048 horizontal pixels,
A vertical pixel number of 1536) is adopted.

The image data output from the CCD 12 is
Noise components are removed by the CDS circuit 16, converted into digital values by the A / D converter 17, and then output to the digital signal processing circuit 18. The digital signal processing circuit 18 uses the frame memory 19 that temporarily stores image data to perform various signal processing such as RGB conversion processing and YUV conversion processing, and the signal processed image data is displayed on the display device 20. It is a circuit to display.

The image data that has been subjected to the various signal processes described above is recorded in the data recording memory 22 via the image compression / expansion circuit 21. The image compression / expansion circuit 21
Is a circuit that compresses the image data output from the digital signal processing circuit 18 and outputs the compressed image data to the data recording memory 22, and also expands the image data read from the data recording memory 22 and outputs the expanded image data to the digital signal processing circuit 18. Is.

The image compression / expansion circuit 21 uses a JPEG (Joint Photographic Exc) as an image compression encoding method.
perts Group) method is adopted. For this coding algorithm, ADCT (Adaptive Discrete Cosine) is used, and image path coding with low resolution is first performed, and hierarchical coding with gradually increasing resolution is also incorporated.

Further, the above-mentioned CCD 12 and CDS circuit 1
6. The operation timing of the A / D converter 17 is controlled by the microcomputer 24 (hereinafter, the microcomputer 24) via the Timing SG 23 that generates a timing pulse. Further, the digital signal processing circuit 18, the image compression / expansion circuit 21, the data recording memory 22.
Is also controlled by the microcomputer 24.

The above-mentioned microcomputer 24 is for controlling the entire camera, and is a CPU 24a for performing various arithmetic processes according to a program, a ROM 24b which is a read-only memory storing programs executed by the CPU 24a, and various processes in the CPU 24a. A RAM 24c, which is a readable / writable memory having a work area used in the process, a data storage area for storing various data, and the like, is built in, and these are interconnected by a bus line (not shown).

The microcomputer 24 described above stores a camera operating section 25 provided with a release switch and the like, an EEPROM 26 storing various set values, and various photographing information mainly composed of text information on the display device 20. An OSD 27 for displaying the image overlaid on it and a strobe 28 for illuminating a subject are connected.

The operation of the digital camera having the above configuration will be described below. When the power of the digital camera is turned on, the digital camera performs through image processing for displaying the subject image incident on the CCD 12 on the display device 20. In the through image processing, image data obtained by photoelectrically converting the optical image formed on the image pickup surface by the CCD 12 is, for example, every 1/30 second, the CDS circuit 16, A / D.
It is sent to the digital signal processing circuit 18 via the converter 17. The digital signal processing circuit 18 sends the received RGB signals.
The image data is stored in the frame memory 19.

The R stored in the frame memory 19
The GB image data is read again by the digital signal processing circuit 18, YUV converted by a YUV conversion unit (not shown) provided in the digital signal processing circuit 18, and written back to the frame memory 19. YUV converted YUV
The image data is sent to and displayed on the display device 20 via the digital signal processing circuit 18. This process is, for example, 1 /
It is repeated every 30 seconds.

Then, the CPU 24a controls the camera operating section 2
When the release switch in 5 is operated, the image pickup operation is started. In the image capturing operation, the CPU 24a controls the focus operation for moving the taking lens 11 to the in-focus position and the aperture 1
The aperture value AV of 3, the shutter speed TV of the electronic shutter performed in the CCD 12, the gain AGC of the amplifier for amplifying the output of the CCD 12, etc. are automatically set to appropriate values,
Performs an automatic exposure control operation that ensures proper exposure. Then, after performing the focus operation and the automatic exposure control operation, the signal-processed image data output from the digital signal processing circuit 18 is recorded in the data recording memory 22 via the image compression / expansion circuit 21, and the image is captured. The operation ends.

Next, details of the above-described automatic exposure control operation will be described with reference to the flowchart showing the processing procedure of the CPU 24a in FIG. The CPU 24a starts the automatic exposure control operation according to the operation of the release switch,
First, it is determined whether or not the release switch is operated for the first time after the power switch (not shown) is turned on (step S1).

If it is the first time (Y in step S1), CP
The U 24a controls the digital signal processing circuit 18 to perform YUV conversion on the image data output from the A / D converter 17 after the release switch is operated, and the luminance information (Y) (= photometry result) is included in the image data. ) Is obtained and the photometric processing of storing in the frame memory 19 is performed (step S2). From the above, the CCD 12 and the digital signal processing circuit 1
8. It can be seen that the CPU 24a constitutes the photometric means in the claims. At this time, the CPU 24a stores, in the frame memory 19, the brightness information (Y) of each area obtained by dividing the image data into four areas, as shown in FIG.

Next, the CPU 24a thereafter functions as a normal exposure control means, performs apex conversion of the luminance information (Y) of each area to calculate the subject luminance (LV) (step S3), and then the subject luminance. The proper exposure (EV) is calculated based on (LV) (step S4). Then the CPU
24a calculates the above-described aperture value AV, shutter speed TV, and gain AGC based on the calculated appropriate exposure (EV), and calculates the calculated aperture value AV, shutter speed TV, and gain A.
The diaphragm 13 and the CCD 12 are controlled using the GC (step S5).

On the other hand, if it is not the first time (N in step S1), the CPU 24a proceeds to step S6. The operation in step S6 is the same as that in step S2 described above, and thus details thereof will be omitted. Next, the CPU 24a works as a judgment means and a control means,
The luminance information Y obtained by the current photometric processing is compared with the luminance information Y obtained by the previous photometric processing, and as shown in FIG. 4A, if the arrangement patterns of the regions higher than the threshold value are the same, It is determined that the brightness state of the subject has been maintained since the previous automatic exposure control operation (Y in step S7), and the process proceeds to step S8.

In step S8, the CPU 24a
The aperture value AV, shutter speed TV, and gain AGC used in the previous automatic exposure control operation work as a shortened exposure control means.
Is used to control the diaphragm 13 and the CCD 12. On the other hand, for each of the areas ~, as a result of comparing the luminance information Y obtained by the current photometric processing with the luminance information Y obtained by the previous photometric processing, for example, as shown in FIG. When the arrangement patterns of the areas do not match, it is determined that the brightness state of the subject is not maintained (step S7).
N), the process proceeds to step S3.

According to the above operation, when the brightness state of the subject is maintained from the previous automatic exposure control operation,
The automatic exposure control operation can be performed again using the aperture value AV, the shutter speed TV, and the gain AGC used in the previous automatic exposure control operation. As a result, even if you do not perform manual exposure switching operation or automatic exposure control lock operation,
Since it is possible to continuously capture the same exposure state as the previous automatic exposure control operation, it is possible to eliminate variations in the exposure state of the image. Moreover, the calculation of the aperture value AV, the shutter speed TV, and the gain AGC (steps S3 to S5) based on the brightness information (Y) is not required,
High-speed automatic exposure control can be performed.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to the drawings. The difference between the second embodiment and the first embodiment is the automatic exposure control operation. Regarding the details of the automatic exposure control operation of the digital camera according to the second embodiment,
This will be described with reference to the flowchart showing the processing procedure of the CPU 24a in FIG.

The CPU 24a performs photometric processing (step S10). The photometric processing is performed in step S described in FIG.
Since it is the same as 2 and S6, detailed description thereof will be omitted. Next, when the CPU 24a determines that the brightness state of the subject has not been maintained since the previous automatic exposure control operation (N in step S11), the process immediately proceeds to steps S13 to S15. On the other hand, if it is determined that the value is maintained (step S1
Then, it is judged whether or not the judgment is continuous n times (= predetermined times) or more (step S12).

If it is not continued n times or more, step S1
3 to S15, the aperture value AV, the shutter speed TV, and the gain AGC are calculated based on the brightness information (Y) obtained by the photometric processing in step S10, and the calculated aperture value AV, shutter speed TV, and gain AGC are calculated. Based on the aperture 13 and C
Control the CD12.

On the other hand, in the case of continuous n times or more, n
Aperture value AV used in each automatic exposure control operation before
An average value of the shutter speed TV and the gain AGC (hereinafter, these three are abbreviated as control values) is calculated (step S1).
6) The aperture 13 and the CCD 12 are controlled using the calculated aperture value average AVave, shutter speed average TVave, and gain average AGCave (step S17).

According to the above operation, when it is determined that the exposure is continuously maintained n times or more, the apertures 13 and C are determined based on the average value of the control values used in the exposure control up to n times before.
CD12 can be controlled. Therefore, step S
Even if the luminance information (Y) changes up and down to some extent within the range determined to be maintained in 11, the control value calculated based on the upper and lower limit luminance information (Y) of the range is used. , The diaphragm 13 and the CCD 12 are not controlled. Therefore, the accuracy of exposure control can be improved.

Moreover, based on the previously calculated control value,
It suffices to calculate the control value used for the automatic exposure control operation this time, and the calculation amount can be reduced compared to the case where the control value is calculated again from the luminance information (Y), and the automatic exposure control can be performed at high speed. it can.

Further, according to the above-described first and second embodiments, the object, that is, each area obtained by dividing the image data
The luminance information (Y) is compared with each other. This makes it possible to more accurately determine whether or not the brightness state of the subject has been maintained since the previous automatic exposure control operation.

Further, in the above-described first and second embodiments, the exposure control is performed by using the previous control value or the average of the control values up to a predetermined number of times, and the exposure control is always performed every time the photometric processing is performed. It is also conceivable to provide a changeover switch (= switching means) for switching from the brightness information (Y) to the normal mode for performing exposure control. As described above, if the changeover switch is provided, the photographer can select the normal mode or the shortened mode as needed.

[0043]

As described above, according to the first aspect of the invention, when the judging means judges that the brightness state of the object has been maintained from the previous exposure control, for example, the previous exposure control. If the exposure control is performed again by using the control value used for the exposure, the same exposure state as the previous exposure control is continuously imaged without performing the manual exposure switching operation or the automatic exposure control lock operation. Because you can
It is possible to eliminate variations in the exposure state of the image. Moreover, since it becomes possible to omit the calculation of the control value based on the measurement result, it is possible to obtain an exposure control device capable of performing automatic exposure control at high speed.

According to the second aspect of the present invention, since the exposure control by the shortened exposure control means does not need to calculate the control value based on the photometric result, the exposure control device capable of performing high-speed automatic exposure control. Can be obtained.

According to the third aspect of the present invention, when it is determined that the same scene is continuously held for a predetermined number of times or more, it is determined that the same scene is continuously shot, and the exposure is performed a predetermined number of times before. The exposure control can be performed by using the average value of the control values used in the control as the control value. Therefore, even if the photometric result changes up and down to some extent within the range determined to be maintained by the determining unit, the exposure is controlled by the control value calculated based on the photometric result of the upper limit and the lower limit of the range. Since the control is not continued, it is possible to improve the accuracy of the exposure control. Moreover, it is only necessary to calculate the control value based on the previously calculated control value, and the amount of calculation can be reduced compared to the case where the control value is calculated again from the photometric result, so high-speed automatic exposure control should be performed. It is possible to obtain an exposure control device capable of

According to the fourth aspect of the present invention, by comparing the photometric results in each of the divided areas of the subject, it is possible to determine whether or not the luminance state of the subject has been maintained more accurately since the previous exposure control. It is possible to obtain an exposure control device that can judge.

According to the fifth aspect of the present invention, by providing the switching means, it is possible for the photographer to select the normal mode or the shortened mode as needed, which is convenient. An exposure control device can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a digital camera incorporating an exposure control device of the present invention.

FIG. 2 is a CPU 2 included in the digital camera shown in FIG.
It is a flow chart which shows a processing procedure in a 1st embodiment of 4a.

FIG. 3 is a diagram for explaining each region obtained by dividing image data.

FIG. 4 is a diagram for explaining a comparison between the luminance information Y obtained by the current photometric processing and the luminance information Y obtained by the previous photometric processing for each of the regions 1 to 3 described in FIG.

5 is a CPU 2 included in the digital camera shown in FIG.
It is a flow chart which shows a processing procedure in a 2nd embodiment of 4a.

[Explanation of symbols]

12 CCD (photometric means) 18 Digital signal processing circuit (photometric means) 24a CPU (photometric means, exposure control means, judgment means,
Normal exposure control means, shortened exposure control means, control means)

Claims (5)

[Claims] 1. A photometric means for photometrically measuring the brightness state of a subject and outputting a photometric result, and an exposure control value is calculated every time photometry is performed by the photometric means, and exposure is performed using the calculated control value. In an exposure control device including an exposure control unit for controlling, before performing the control by the exposure control unit, the brightness state of the subject is determined based on a comparison between the current photometry result and the previous photometry result by the photometry unit. The exposure control device further comprising a determination unit that determines whether or not the exposure control has been maintained since the previous exposure control. 2. The exposure control device according to claim 1, wherein the exposure control unit controls the exposure using a control value calculated based on the photometric result of this time, and the previous exposure control unit. And a shortened exposure control means for controlling the exposure using the control value used in the exposure control, and when it is judged that the above-mentioned is maintained by the judgment means, the exposure control by the shortened exposure control means is started,
An exposure control apparatus further comprising a control unit that starts exposure control by the normal exposure control unit when the determination unit determines NO. 3. The exposure control device according to claim 1, wherein the exposure control means controls the exposure using a control value calculated based on the exposure result of this time, and a predetermined number of times before. The exposure control using a control value calculated on the basis of a plurality of control values respectively used in the exposure control up to the exposure control, the determination by the determination means is the predetermined It further comprises control means for starting the exposure control by the shortened exposure control means when the exposure is continued more than once, and for starting the exposure control by the normal exposure control means when the exposure is not continued for the predetermined number of times or more. Exposure control device. 4. The exposure control device according to claim 1, wherein the photometric unit divides the subject into a plurality of areas and outputs the photometric result for each of the plurality of areas. The exposure control device, wherein the determination means makes the determination based on a comparison between a current photometric result and a previous photometric result in each region. 5. The exposure control device according to claim 2, wherein the control by the control means is stopped, and the exposure control by the normal exposure control means is always started every time the photometry is performed. The exposure control device further comprising a switching unit that switches between a normal mode and a shortening mode in which the control by the control unit is performed.