JP2003174583A - Camera device and automatic exposure control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform optimum automatic exposure control as much as possible even in the case of image pickup of a backlight state, an excessive light state or an object (all white) for which the entire image pickup surface is uniform or the like. <P>SOLUTION: First, a DSP 6 of a camera device is provided with an OPD (optical detection circuit) 13 detecting a luminance distribution (histogram) of image pickup signals. Then, a situation with a specified exposure state is set beforehand and the histogram detected in actually picking up the image in the situation and a luminance integrated value (exposure control amount) obtained from the OPD 13 enabling optimum exposure control at that time are set to one template as a reference value. Then, when the photographing is actually performed, the histogram in the exposure state is measured, a correlation of the histogram and the histogram included in two or more pieces of the templates is taken, a reference value of the exposure control amount preserved in the template is corrected by the correlation value, and the optimum exposure control in the present exposure state is performed. <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 a camera device and an automatic exposure control method for detecting a brightness distribution (histogram) of a picked-up image and performing optimum exposure control.

[0002]

2. Description of the Related Art Conventionally, there has been provided a camera device for picking up an image of a subject using various solid-state image pickup devices. As an AE (automatic exposure control) in this type of camera device, an optical detection circuit (optical detector; OPD) for detecting the brightness of the imaged image is provided in the processing circuit section of the image pickup signal, and this is detected by this OPD. A method of controlling the amount of exposure using luminance information is used.

[0003]

However, in the above-mentioned conventional AE (automatic exposure control), the optimized exposure control is performed by obtaining only the brightness information of the picked-up image from the OPD. When a subject (all white) or the like whose light state or the entire image pickup surface is uniform is imaged, a difference occurs between the optimum exposure value and the brightness information output from the OPD, and optimum exposure control may not be performed. There was a problem that would happen.

Therefore, an object of the present invention is to perform the optimum automatic exposure control as much as possible even in the case of shooting a backlit state, an over-forwarding state, or a subject (all white) having a uniform image pickup surface. A possible camera device and its automatic exposure control method are provided.

[0005]

In order to achieve the above object, the present invention provides a camera device for outputting an image signal picked up by an image pickup device, which performs predetermined signal processing on the image pickup signal outputted from the image pickup device. A signal processing unit, a brightness distribution detecting unit that detects a brightness distribution of a captured image based on an image pickup signal signal-processed by the signal processing unit, and a brightness distribution when an image is captured in a preset specific exposure state situation. And a template storage unit that stores an exposure control amount that enables optimum exposure control as a template, a brightness distribution obtained from the brightness distribution detection unit at the time of imaging, and a brightness distribution stored in the template storage unit. And an exposure control amount is corrected based on the correlation value obtained by the operation means for calculating the correlation value by comparing , And having an exposure control means for performing exposure control.

According to the present invention, in an automatic exposure control method of a camera device for outputting an image signal picked up by an image pickup device, a signal processing step for performing a predetermined signal processing on an image pickup signal outputted from the image pickup device, A brightness distribution detection step that detects the brightness distribution of the captured image based on the image-processed signal processed by the signal processing step, a brightness distribution when the image is captured in a preset specific exposure state situation, and at that time optimal A template storage step of storing an exposure control amount that enables exposure control in the template storage means as a template, a brightness distribution obtained from the brightness distribution detection step at the time of imaging, and a brightness distribution stored in the template storage means. The calculation step of comparing and calculating the correlation value, and Based on the correlation value to correct the exposure control amount, and having an exposure control step of performing exposure control.

In the camera device of the present invention, a luminance distribution detecting means for detecting the luminance distribution of the picked-up image based on the picked-up image signal is provided, and the luminance distribution when the image is picked up in a preset specific exposure state situation, At that time, the exposure control amount that enables the optimum exposure control is stored in the template storage means as a template, and the brightness distribution obtained from the brightness distribution detection means at the time of imaging and the brightness distribution stored in the template storage means are stored. Since the correlation value is calculated by comparison, the exposure control amount is corrected based on the correlation value, and the exposure control is performed, for example, a backlight condition, an over-forward condition, or a subject with a uniform imaging surface is used. Even if you take an image of (all white) etc., you can optimize the exposure control amount by using the template created using the approximate exposure state, and perform the optimum automatic exposure control. Ukoto is possible.

Also, in the automatic exposure method of the camera device of the present invention, similarly, a brightness distribution detection step for detecting the brightness distribution of the output image based on the image pickup signal is provided, and a preset specific exposure state situation is set. The brightness distribution at the time of image capturing and the exposure control amount that enables optimal exposure control at that time are stored as templates in the template storage means, and the brightness distribution obtained by the brightness distribution detection step at the time of image capturing and the template storage means are stored in the template storage means. A correlation value is calculated by comparing with the stored luminance distribution, the exposure control amount is corrected based on this correlation value, and since exposure control is performed, for example, a backlight condition, an over-forward condition, or Even when capturing an image of a subject (all white) with a uniform imaging surface, the exposure control is performed using a template created using similar exposure conditions. The amount can be optimized, it is possible to perform optimal automatic exposure control.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are given. However, the scope of the present invention is not limited to the present invention in the following description. Unless otherwise stated, the present invention is not limited to these embodiments. The camera device according to the present embodiment has the following AE
The feature is an (automatic exposure control) algorithm.

First, the present camera device is provided with an OPD (optical detection circuit) for detecting the luminance distribution (histogram) of the image pickup signal, a situation having a specific exposure state is set in advance, and an image is actually taken in this situation. A histogram that is sometimes detected and a luminance integrated value obtained from the OPD that enables optimum exposure control at that time (that is,
Exposure control amount) and a reference value (reference) are set in one template. A plurality of such templates are collected in various exposure states, and these templates are provided inside the exposure control program. Then, at the time of shooting with an actual camera device, a histogram in the exposure state is measured, the histogram is correlated with the histograms included in the plurality of templates, and the exposure stored in the template is obtained by the correlation value. The reference value of the control amount is modified so that optimum exposure control in the current exposure state is performed.

FIG. 1 is a block diagram showing the configuration of a camera device according to this embodiment. The camera device of this example includes a lens 1, a CCD image sensor 2, a CDS (correlation double sampling) circuit 3, and an AGC (automatic gain control) circuit 4.
, A / D converter 5, DSP (digital signal processor) 6, D / A converter 7, TG (timing generator) 8, iris diaphragm 9, diaphragm driving motor 11, and microcomputer (Μ-COM) 10
And has an internal bus 12. Further, the DSP 6 has the OPD (optical detection circuit) 13 described above, and the microcomputer 10 has an internal bus interface (I / F) 1.
4, a CPU 15, a ROM 16, and a RAM 17 are provided.

In such a camera device, light from a subject passes through the lens 1 and is photoelectrically converted by the CCD image pickup device 2 to be output as an image pickup signal. Then, this image pickup signal is sampled by the CDS circuit 3, controlled by the AGC circuit 4 to have an appropriate gain, and then converted into a digital signal by the A / D converter 5. This digital signal is processed by the DSP 6, converted into an analog signal by the D / A converter 7, and supplied as an image output to the image output unit in the subsequent stage. Also, TG8
Supplies various timing signals for performing the above-described operations to each unit.

Next, an AE (automatic exposure control) algorithm in the camera apparatus of this example will be described. The software that executes this algorithm is executed by the microcomputer 10, and the CPU 15 reads the program on the ROM 16 and supplies necessary commands and data to each unit via the I / F 14 and the internal bus 12. Execute each process. The exposure information necessary for this algorithm is obtained from the OPD (optical detection circuit) 13 in the DSP 6.

FIG. 2 and FIG. 3 are explanatory views showing a picked-up image, a luminance distribution (histogram), and an exposure control state when the normal AE control performed by the conventional camera device in various situations is performed and converged. It is a figure. First, FIG. 2A shows a case where a normal image in which the histogram is dispersed over the entire brightness is shot. In such a case, proper exposure can be obtained even with normal AE control. In this case, the difference Δref from the reference luminance integrated value is 0.

Further, FIG. 2B shows a case where a subject (all white) or the like having a uniform image pickup surface is picked up. In such a case, the histogram concentrates around a certain luminance and converges to an under (dark) appearance. In this case, it is necessary to increase the reference brightness integral value to obtain the optimum exposure. That is, Δref has a positive (+) value. Also,
FIG. 3C shows a case where an image is captured in a backlit state. Also in this case, since the histogram is concentrated on the low luminance side, it is necessary to increase the reference luminance integration value to obtain the optimum exposure, and Δref becomes a positive (+) value. Further, FIG. 3D shows a case where an image is taken in an over-forward light state. In this case, the histogram is biased toward the low-luminance side and the highest-luminance portion due to high-luminance saturation. For this reason,
In order to obtain the optimum exposure, it is necessary to reduce the reference brightness integral value, and Δref becomes a negative (−) value.

In the normal AE control, as shown in FIG. 4, the relationship between the brightness integrated value (OPD value) obtained from the OPD 13 and the reference brightness integrated value ref which is the output value of the OPD 13 when the exposure control is converged is grasped. If the OPD value <ref, it is judged as under, the gain of the AGC circuit 4 is increased, the iris diaphragm 9 is controlled to open, and the CCD storage time (electronic shutter time) by the TG 8 is lengthened. The gain is increased to obtain the optimum exposure. On the other hand, if the OPD value> ref, it is judged to be over, the gain of the AGC circuit 4 is increased, the iris diaphragm 9 is controlled to be closed, and the CCD accumulation time (electronic shutter time) by the TG 8 is shortened. Obtain the optimum exposure by reducing the device gain.

However, in this example, such a conventional AE is used.
In the control, the optimal exposure control can be performed even in the case of shooting a backlit state, an over-forward lighting state, or a subject (all white) whose entire image pickup surface is uniform. It performs various control processes. First, in this example, a histogram OPD for detecting the brightness distribution is provided in addition to the OPD for calculating the normal brightness integrated value. FIG. 5 is an explanatory diagram showing the principle of the histogram OPD used in this example. This histogram OPD has thresholds Th1, Th2,
The number of pixels in the luminance range delimited by Th3, Th4, ... Hist1, hist2, hist3, hist
4 has a histogram OPD for calculating hist5.

Then, using this OPD, the difference between the histogram when a situation of a certain exposure state is picked up and the luminance integrated value and the reference luminance integrated value that enables the optimum exposure control at that time is obtained as Δref. deep. The combination of this histogram and Δref is called one template. Then, templates for various situations with different exposure states are stored in the program as a database. It is preferable that this database is for an exposure state with different properties such as backlight and over-forward light.
Then, at the time of actual photographing, the template in this database is used to perform optimum exposure control in the current exposure state.

FIG. 6 and FIG. 7 are flow charts showing an algorithm of the present example at the time of actual photographing. First, the histogram in the current exposure state is matched with each of the templates 1 to N in the program, and each correlation value Δref is obtained. First, in steps S1 to S3, the correlation value Δref1 based on the template 1 is obtained. The method of obtaining the correlation value is, for example, a calculation as shown in FIG. That is, first, two variables indicating the order of the luminance range in the histogram are set to m and n, the evaluation values hist obtained by the current imaging, the template value Tist, and the following calculation is performed. Imn = (histm / histn) / (Tistm /
Tistn) When Imn> 1, the reciprocal of Imn is used.

Then, by multiplying a plurality of Imns calculated by such an operation with each other, it is possible to obtain a correlation value represented by a range of 0 to 1. In addition,
The method of obtaining such a correlation value is not limited to this example, and various methods can be adopted. Then, the difference Δref1 between the luminance integration value and the reference integration value that enables the optimum exposure control in the template 1 is obtained by multiplying Δref by the correlation value (step S3).

Such an operation is performed by another template 2 to N.
Is similarly performed (steps S4 and S5), Δref1 to N of the number of templates (N in this example) included in the program are obtained, and finally the sum of these is obtained (step S6). As a result, the difference between the integrated luminance value and the reference integrated luminance value that enables the final optimum exposure control is Δr.
Calculate as ef. After that, as shown in step S7, the sum of the reference luminance integrated value ref and Δref is set as the final reference integrated value, and the OPD is performed in the same manner as in the normal AE control.
Compared with the current brightness value obtained more, as a result, the system gain is controlled to obtain the optimum exposure (step S8).

The above-mentioned template database can be improved in performance by increasing and organizing and accumulating it in a program in a learning manner. For example,
When the reference value of the exposure control amount stored in the template is corrected when a new image is captured, the correction result is left as it is in the database as a new template or is replaced with another template. Also,
When the exposure amount is corrected by the user's manual operation,
Considering this exposure state as an optimized state, obtaining the brightness distribution etc. at the time of shooting, creating a new template,
It is also possible to add it to the database.
Also, by accumulating and organizing situations,
It is also possible to improve the performance of the AE. of course,
This kind of template modification is not an automatic process,
It is possible to artificially perform (data exchange, update).

The AE (automatic exposure control) of this example as described above
According to this method, the following effects can be obtained. That is, in the conventional AE (automatic exposure control), the optimum exposure control is performed by obtaining only the brightness information of the imaged image from the OPD, but it is a backlit state, an over-forwarding state, or a subject with a uniform image pickup surface. When you take an image of (all white),
A difference occurs between the optimum exposure value and the brightness information output from the OPD, which causes a situation in which proper exposure control is not performed. Therefore, as in this example, a histogram corresponding to various situations is stored in advance as a template, and the exposure state at the time of actual shooting is corrected using this, so the above-mentioned backlight condition, over-forward condition, Alternatively, optimal exposure control can be performed even when a subject (all white) or the like whose image pickup surface is uniform is picked up.

The camera device and the automatic exposure control method thereof according to the present invention are not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. For example, the various types of arithmetic processing described above are examples, and other arithmetic methods may be used. Further, with respect to the configuration of the CCD image pickup device, the iris diaphragm, etc. shown in FIG. 1, it is possible to use other image pickup devices and diaphragm mechanisms. Further, the template database described above has been described on the premise that it is created by the camera device itself, but the database created by another camera system is not limited to being created by the camera device itself. It may be configured to be used for.

[0025]

As described above, the camera device of the present invention is provided with the luminance distribution detecting means for detecting the luminance distribution of the picked-up image based on the picked-up image signal, and the image is picked up in the situation of the preset specific exposure state. The brightness distribution at the time of exposure and the exposure control amount that enables optimal exposure control at that time are stored as templates in the template storage means, and are stored in the template storage means and the brightness distribution obtained from the brightness distribution detection means at the time of imaging. The correlation value is calculated by comparing with the brightness distribution that has been set, and the exposure control amount is corrected based on the correlation value to perform the exposure control. Therefore, for example, even when a backlit state, an over-forward state, or a subject (all white) with a uniform image pickup surface is imaged, the exposure control amount is adjusted using a template created using an approximated exposure state. Can be optimized, and optimum automatic exposure control can be performed.

Further, in the automatic exposure method of the camera device of the present invention, a luminance distribution detection step for detecting the luminance distribution of the output image based on the image pickup signal is provided, and the image is picked up in a preset specific exposure state situation. The brightness distribution at that time and the exposure control amount that enables optimum exposure control at that time are stored as templates in the template storage means, and are stored in the template storage means and the brightness distribution obtained by the brightness distribution detection step at the time of imaging. The correlation value is calculated by comparing the brightness distribution with the brightness distribution, and the exposure control amount is corrected based on the correlation value to perform the exposure control. Therefore, for example, even when a backlit state, an over-forward state, or a subject (all white) with a uniform image pickup surface is imaged, the exposure control amount is adjusted using a template created using an approximated exposure state. Can be optimized, and optimum automatic exposure control can be performed.

[Brief description of drawings]

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

[Fig. 2] Normal AE when capturing images in various situations
It is explanatory drawing which shows the image pick-up image at the time of controlling and converging, its brightness | luminance distribution (histogram), and an exposure control state.

[Fig. 3] Normal AE at the time of imaging in various situations
It is explanatory drawing which shows the image pick-up image at the time of controlling and converging, its brightness | luminance distribution (histogram), and an exposure control state.

FIG. 4 is an explanatory diagram showing a control method by normal AE control.

5 is an explanatory diagram showing a histogram of the camera device shown in FIG. 1. FIG.

6 is a flowchart showing an operation example of the camera device shown in FIG.

7 is a flowchart showing an operation example of the camera device shown in FIG.

FIG. 8 is an explanatory diagram showing a calculation example of the camera device shown in FIG. 1.

[Explanation of symbols]

1 ... Lens, 2 ... CCD image sensor, 3 ... CDS circuit, 4 ... AGC circuit, 5 ... A / D converter, 6 ... D
SP, 7 ... D / A converter, 8 ... TG, 9 ... Iris type diaphragm, 10 ... Microcomputer, 11 ... Diaphragm drive motor, 12 ... Internal bus, 13 ... OPD,
14 ... I / F, 15 ... CPU, 16 ... ROM, 1
7 ... RAM.

Claims (10)

[Claims] 1. A camera device for outputting an image signal picked up by an image pickup device, comprising: signal processing means for performing a predetermined signal processing on an image pickup signal outputted from the image pickup device; and image pickup processed by the signal processing means. Luminance distribution detection means for detecting the luminance distribution of the picked-up image based on the signal, luminance distribution when the image is picked up in a preset specific exposure state situation, and exposure control amount that enables optimum exposure control at that time A template storing means for storing as a template, a computing means for calculating a correlation value by comparing a luminance distribution obtained from the luminance distribution detecting means at the time of imaging with a luminance distribution stored in the template storing means, Exposure control means for correcting the exposure control amount on the basis of the correlation value obtained by the computing means, and performing exposure control. Camera device characterized by. 2. The camera device according to claim 1, wherein the template storage means stores a plurality of templates corresponding to a plurality of situations. 3. The camera device according to claim 1, further comprising a correction unit that learnably corrects the template stored in the template storage unit. 4. The situation of the specific exposure state includes image pickup in a backlit state, image pickup in a super-forward light state, or image pickup of a subject whose entire image pickup surface is uniform. The described camera device. 5. The camera device according to claim 1, wherein the arithmetic means is means for performing arithmetic operations by software processing of a microcomputer. 6. An automatic exposure control method for a camera device, which outputs an image signal captured by an image sensor, comprising: a signal processing step of performing a predetermined signal process on the image signal output from the image sensor; Luminance distribution detection step that detects the luminance distribution of the captured image based on the signal-processed image pickup signal, luminance distribution when the image is captured in a preset specific exposure state situation, and optimal exposure control is possible at that time A template storage step of storing the exposure control amount as a template in the template storage means, and a correlation by comparing the brightness distribution obtained from the brightness distribution detection step during imaging with the brightness distribution stored in the template storage means. A calculation step for calculating the value, and a correlation value obtained by the calculation step. There Correct exposure control amount, the automatic exposure control method for a camera apparatus characterized by having an exposure control step of performing exposure control. 7. The method according to claim 6, wherein the template storing step stores a plurality of templates corresponding to a plurality of situations in the template storing means. 8. The automatic exposure control method for a camera device according to claim 6, further comprising a correction step of learning-correcting the template stored in said template storage means. 9. The situation of the specific exposure state includes image pickup in a backlit state, image pickup in an over-forward light state, or image pickup of a subject whose entire image pickup surface is uniform. An automatic exposure control method for the described camera device. 10. The automatic exposure control method for a camera device according to claim 6, wherein the calculation step is performed by software processing of a microcomputer.