JP2887814B2 - Automatic exposure control device - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to an automatic exposure control device in, for example, an electronic still camera using a solid-state imaging device such as a CCD (Charge Coupled Device).

[Prior Art and its Problems] Generally, when photographing a subject, an aperture value based on an appropriate exposure is determined according to the average luminance of an optical image of the subject that is incident through an imaging lens and an aperture.

For this reason, when a part of a predetermined photometry area in the photographing area for the luminance measurement (the whole photographing area at the time of total photometry) is extremely bright and has a high luminance, or when it is desired to photograph characters written on a white background, The average luminance value in the entire photometric area tends to increase, and the aperture is set to close.

In this case, there are problems such as a dark image in the entire photographing range and a character portion not being clearly displayed.

[Object of the Invention] The present invention has been made in view of the above problems,
For example, even when a part of the photometry area is extremely bright or a small character is photographed over a white background, an appropriate aperture value that matches the optical image of the subject can be obtained without setting the aperture value based on the average luminance of the entire photometry area. It is an object of the present invention to provide an automatic exposure control device capable of setting.

[Object of the Invention] That is, an automatic exposure control device according to the present invention includes an imaging lens, a diaphragm unit for adjusting an incident light amount of an optical image incident on the imaging lens, and an image formed through the diaphragm unit and the imaging lens. Imaging means for outputting an electric image signal based on the optical image to be obtained, and a luminance variance value for detecting a variance range of luminance contained in the optical image formed based on the image signal output by the imaging means. Detection means, and aperture control means for controlling the aperture of the aperture means such that the dispersion range of the luminance of the optical image formed on the imaging means detected by the luminance variance value detection means is maximized. It is provided with.

Embodiments of the Invention One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an electronic circuit in an electronic still camera equipped with an AE function. In FIG. 1, reference numeral 11 denotes a control unit, which controls the operation of each circuit unit.

Reference numeral 12 denotes an aperture, and reference numeral 13 denotes an imaging lens. The aperture of the aperture 12 is adjusted by an aperture drive motor 14 to open and close. The aperture drive motor 14 uses, for example, a step motor, and rotates stepwise in response to a motor drive pulse signal from a motor drive control unit 15. The motor drive control unit 15 includes the control unit 11 An aperture control signal corresponding to an aperture value set in accordance with the control operation is supplied.

On the other hand, the optical image of the subject incident through the aperture 12 and the imaging lens 13 is formed on a solid-state imaging device 16 composed of a CCD (Charge Coupled Device). This solid-state image sensor
Reference numeral 16 denotes a structure in which a large number of pixels composed of photoelectric conversion elements (photodiodes) are arranged in the horizontal and vertical directions. The solid-state imaging device 16
Is driven by the CCD control unit 17 for exposure. This CCD controller
Reference numeral 17 denotes each of the pixels of the solid-state imaging device 16 which is horizontally and vertically scanned and sequentially driven for exposure.
The exposure drive timing of the solid-state imaging device 16 by the control unit 17 corresponds to a shutter speed (exposure time) at the time of photographing the subject, and the CCD exposure time is set according to the control operation of the control unit 11.

Then, an image signal corresponding to the formed optical image from the solid-state imaging device 16 is transferred and supplied to the A / D converter 18. The A / D converter 18 performs A / D conversion of the accumulated charge output corresponding to each pixel of the solid-state imaging device 16 and converts the charge into a white / black binary digital image signal. The digital image signals from the D converter 18 are sequentially transferred to and stored in the image data memory 19. The control for specifying the write and read addresses for the image data memory 19 is performed by the control unit 11.

Further, the control unit 11 is connected to a measurement area designation unit 20, an exposure time conversion unit 21, a variance value detection unit 22, a data memory 23, and a calculation: comparison unit 24.

The photometry area designating section 20 designates a luminance photometry area for a subject for AE (automatic exposure) control as a partial photometry or a whole photometry. The image of the solid-state imaging device 16 from the photometry area designation section 20 is provided. By giving the designated area data corresponding to the area to the control unit 11,
The control unit 11 reads an image signal corresponding to the designated photometry area from the image data memory 19. In this case, the control unit 11 supplies the image signal of each pixel corresponding to the designated photometry area read out from the image data memory 19 to the calculation / comparison unit 24 and performs total addition to obtain the luminance addition data. Then, the exposure time conversion unit 21 performs the calculation:
The luminance addition value of the designated photometry area calculated and calculated in the step is input, and the proper exposure time of the solid-state imaging device 16 is obtained from the luminance addition value / exposure time conversion table. The time data is stored in the control unit 11
Is set in the CCD control unit 17 through.

Further, the variance value detection unit 22 is based on an image signal corresponding to the designated photometry area read from the image data memory 19 to the control unit 11, and detects a light / dark dispersion range of a luminance state in the designated photometry area. The dispersion value corresponding to the luminance dispersion range in the photometry area is stored in the dispersion value data storage unit 23a of the data memory 23 through the control unit 11. In this case, the control unit 11 compares the previously detected luminance variance value previously stored in the variance value data storage unit 23a with the variance value detection unit 22a.
The above-mentioned calculation: the comparing unit 24 performs the magnitude comparison judgment with the luminance variance value of the present detection detected by the above. When this calculation: the comparing unit 24 determines that the current detected variance value is “large”, This variance value detected this time is stored as a new luminance variance value in the variance value data storage unit 23a, and an iris control signal for driving the iris drive motor 14 in the one-step “aperture open” direction is sent to the motor drive control unit 15. Supply. Also,
Calculation: If the comparison unit 24 previously determined that the storage dispersion value is “large”, the aperture drive motor 14 is turned “step closed” by one step.
An aperture control signal for driving in the direction is supplied to the motor drive controller 15.

FIG. 2 shows a luminance distribution characteristic of an incident optical image with respect to the solid-state imaging device 16. In an exposure state obtained from a luminance distribution characteristic a shown by a solid line evenly inclined in the light and dark directions, when the aperture 12 is adjusted in the opening direction. , A luminance distribution characteristic b indicated by a dashed line concentrated on a high luminance (bright) portion is obtained.
Brightness is low (dark) when aperture 12 is adjusted to close
The luminance distribution characteristic c indicated by the two-dot chain line concentrated on the portion is obtained. In other words, as the dispersion range of the luminance corresponding to the designated photometry area detected by the dispersion value detection unit 22 is larger, the contrast of the subject can be expressed more faithfully, and the aperture opening is set so that the luminance dispersion value becomes maximum. Just set it.

Next, the automatic exposure control processing of the electronic still camera equipped with the AE function having the above configuration will be described.

FIG. 3 is a flowchart showing an automatic exposure control process by the electronic still camera. First, an operator captures a subject by looking through a finder (not shown), and specifies a photometric area for AE control by a photometric area specifying unit 20. When an instruction for AE and AF control is given by half-pressing a release switch (not shown), the automatic exposure control process is started.

That is, first, the diaphragm drive motor 14 is driven to rotate in the fully open direction by the diaphragm control signal from the control unit 11 to the motor drive control unit 15, and the diaphragm 12 is set to the fully open state (step S1). Further, a preset initial exposure time (for example, 1/250 sec) is set from the control unit 11 to the CCD control unit 17, and the solid-state imaging device 16 is exposed and driven according to the exposure time (step S2). Then, the aperture 12 and the imaging lens 13
Optical image of a subject incident through the solid-state imaging device
An image signal corresponding to the amount of incident light within the exposure time is output to the A / D converter 18 and transferred to the image data memory 19 as a binary black / white digital image signal (step S1). S3).

Here, the control unit 11 reads from the image data memory 19 the image signal of the imaging range corresponding to the photometry area specified in advance by the photometry area specification unit 20, and causes the comparison unit 24 to calculate the luminance added value. Then, this operation: The luminance addition data of the image pickup signal according to the initial exposure state obtained by the comparison unit 24 is sent to the exposure time conversion unit 21 (steps S4 to S6). Then, in the exposure time conversion unit 21, the control unit
According to the luminance addition data sent from 11, the luminance addition value /
The appropriate exposure time (shutter speed) of the solid-state imaging device 16 is selected from the exposure time conversion table. The appropriate exposure time data selected by the exposure time conversion unit 21 is the initial exposure time set in advance in step S2. The time is set in the CCD control unit 17 instead of the time (step S7). At this time, the aperture 12 is adjusted to the fully closed state by the aperture control signal from the control unit 11 to the motor drive control unit 15, and the variance value data storage unit 23a of the data memory 23
Is cleared and set by the control unit 11 (steps S8 and S8).
9).

Then, the aperture 12 is controlled in the opening direction by one step in the aperture drive motor 14 (step S10). And
With the stop 12 opened from the fully closed position by one motor step, an optical image of a subject incident through the stop 12 and the imaging lens 13 is formed on the solid-state image pickup device 16 and the incident light amount within the optimum exposure time is set. A / D conversion unit 1
The digital image signal is transferred to and stored in the image data memory 19 as a white / black binary digital image signal through step 8 (step S11). Then, in the same manner as in step S4, the control unit 11 reads out the image signal of the imaging range corresponding to the photometry area specified in advance by the photometry area specification unit 20 from the image data memory 19. The image signal corresponding to the designated photometry area read out is sent to the variance value detection unit 22 to detect the light / dark variance range of the luminance state (steps S12 and S13).

Here, the luminance variance value of the designated photometry area detected at the aperture opening in the first step from the fully closed position and the previously detected variance value data stored in the variance value data storage unit 23a are calculated as follows: The comparison is performed by the comparison unit 24.In this case, since the variance value data 23a is immediately after being cleared in the above step S9, it is determined as the luminance variance value “large” of the current detection, and this variance value is The data is written into the variance value data storage unit 23a (steps S14 and S15). At this time, based on the number of motor drive steps of the aperture drive motor 14, the control unit 11 determines whether or not the aperture 12 has reached the fully opened state. In this case, the aperture 12 is still opened by one step from fully closed. Is determined to be "No", and the process returns to the one-step aperture opening process of step S10 again (step S16).

Thereafter, by repeating the processes and determinations in steps S10 to S16, the aperture 12 is sequentially controlled to be opened one motor step at a time, and the luminance variance value of the imaging data at each aperture degree is determined by the variance value detection unit 22. The comparison and comparison with the previously detected variance value stored in the variance value data storage unit 23a are repeatedly performed in the calculation: comparing unit 24.

That is, after the optimal exposure time is set for the CCD control unit 17, when the stop 12 is controlled to be in the fully closed state or sequentially in the opening direction by one motor step, the brightness dispersion range of the subject optical image formed by the solid-state imaging device 16 becomes For example, the luminance distribution characteristic shifts from “c” to “a” in FIG. 2 at this time. At this time, “No” in step S14, that is, from the luminance variance value of the imaging data based on the currently set aperture degree, Also, if it is determined that the luminance variance value based on the previously set aperture opening is larger, and, for example, it is determined that the luminance distribution characteristic a in FIG. The unit 11 controls the aperture 12 in the closing direction by one motor step in response to the aperture control signal to the motor drive control unit 15, and determines the incident state of the subject optical image on the solid-state imaging device 16 so that the maximum luminance dispersion value is obtained. Is returned (step S17).

As a result, the aperture 12 is adjusted to the appropriate aperture and the CCD controller 1
7 is set to an appropriate exposure time, and by fully pressing a release switch (not shown), the subject optical image formed in the optimal exposure state on the solid-state imaging device 16 is
The data is written to the image data memory 19 as a digital image signal through the A / D converter 18.

Therefore, according to the electronic still camera equipped with the AE function of the above configuration, the opening movement control of the aperture 12 is performed so that the luminance dispersion range of the subject optical image incident on the solid-state imaging device 16 in advance shows the maximum range. Therefore, for example, when a part of the shooting area is extremely bright and high brightness, or when you want to shoot a small character written on a white background, the entire shooting range becomes a dark image, the character part does not appear clearly, etc. It is possible to perform a clear contrast imaging process in an optimal exposure state without causing the above-mentioned problem.

[Effects of the Invention] As described above, according to the present invention, an imaging lens, aperture means for adjusting the incident light amount of an optical image incident on the imaging lens, and an image is formed through the aperture means and the imaging lens. Imaging means for outputting an electrically suitable image signal based on an optical image, and luminance variance value detecting means for detecting a variance range of luminance contained in the formed optical image based on the image signal output by the imaging means And aperture control means for controlling the aperture of the aperture means so that the variance range of the luminance of the optical image formed on the imaging means detected by the luminance variance value detection means is maximized. Because we configured
For example, even when a part of the photometry area is extremely bright or a small character is photographed over a white background, an appropriate aperture value that matches the optical image of the subject can be obtained without setting the aperture value based on the average luminance of the entire photometry area. An automatic exposure control device capable of setting can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an electronic circuit in an electronic still camera according to an embodiment of the automatic exposure control device of the present invention, and FIG. 2 is a luminance distribution characteristic of an incident optical image with respect to a solid-state imaging device of the electronic still camera. FIG. 3 is a flowchart showing automatic exposure control processing by the electronic still camera. 11 ... Control unit, 12 ... Aperture, 13 ... Imaging lens, 14 ...
Aperture drive motor, 15 Motor drive controller, 16 Solid-state image sensor (CCD), 17 CCD controller, 18 A / D converter, 19 Image data memory, 20 Photometric area Designation unit, 21 Exposure time conversion unit, 22 Dispersion value detection unit, 23
... Data memory, 23a ... Dispersion value data storage unit, 24 ...
Operation: comparison section.

Claims (1)

(57) [Claims] An imaging lens; a diaphragm means for adjusting the amount of incident light of an optical image incident on the imaging lens; and an electric image signal based on the optical image formed through the diaphragm means and the imaging lens. And a luminance variance value detecting means for detecting a variance range of luminance contained in the formed optical image based on an image signal output by the image radiating means. Control means for controlling the aperture of the aperture means so that the dispersion range of the brightness of the optical image formed on the imaging means is maximized.