JPH0998339A - Electronic still camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the camera to deal with high luminance image pickup even with a mechanical shutter. SOLUTION: An exposure control section 6 fully opens a blade 2 by using a motor 3 driving the blade 2 as preliminary processing. A photometry value Ev1, less than a 1st photometry value Ev1 obtd. through 1st photometry by using an amplified gain (a) from a signal reception conversion section 5 is obtd. and it is separated into an aperture Av1' and a shutter time Tv1'. The blade 2 is driven based on the aperture Av1' to revise the aperture, 2nd photometry is conducted and an exposure error ΔEv is obtained based on the 2nd photometry value Ev2 and the photometry value Ev1'. When a 1st shutter time Tv2 obtained based on the shutter time Tv1' and the exposure error Δev is higher than a prescribed shutter time Tv0, the amplifier gain (a) being a half of an amplifier gain (b) at image pickup is used. Then the image pickup is conducted with a 2nd shutter time Tv2' obtd. by slowing down the 1st shutter time Tv2 to obtain the same exposure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automatic exposure control in an electronic still camera.

[0002]

2. Description of the Related Art At present, an electronic still camera using a solid-state image sensor (CCD or the like) for converting an optical image into an electric signal has been put into practical use, and the focus and the exposure are automatically adjusted, so that the user can particularly adjust it. It is common that the shooting is performed without doing. According to the description of JP-A-2-117275, exposure 1
The exposure control is performed by the electronic shutter, and the exposure 2 is performed by the shutter that also serves as the aperture, electrically for starting charge accumulation and mechanically for ending charge accumulation. Further, according to Japanese Patent Laid-Open No. 5-115036, a diaphragm mechanism arranged in an incident optical path of a solid-state image sensor having an electronic shutter function, and this diaphragm mechanism is fed back in accordance with an image signal output from the solid-state image sensor. Equipped with a diaphragm drive circuit to control, the diaphragm is fully opened at the start of exposure of the solid-state image sensor, the subject light that has passed through the shooting lens is metered, and the diaphragm is fully opened before normal imaging operation according to the photometric value. After that, the exposure time of the solid-state image sensor is controlled according to the photometric value.

[0003]

However, in the exposure control having such a structure, when the mechanical shutter is used, the shutter speed may not be able to follow the shooting especially at high brightness. Further, in the mechanical shutter, since it takes time to close, there is a problem that an error occurs in the exposure amount corresponding to the mechanical delay.

The present invention is to solve the above-mentioned problems of the prior art, and to provide an electronic still camera capable of coping with high-luminance photographing even with a mechanical shutter and reducing an exposure error due to a mechanical delay. To aim.

[0005]

In order to achieve this object, the present invention is directed to an image pickup means for picking up an image of a subject and outputting image data, a diaphragm for regulating the amount of light incident on the image pickup means, and the diaphragm. Drive means, data processing means for encoding / decoding the image data, control means for controlling writing / reading of data to / from a storage medium, storage means for storing various setting values, and overall control of the apparatus. CP to do
In an electronic still camera having U and U, a pre-calculation for determining the first shutter speed from the second photometric value obtained by performing the second photometry by changing the aperture based on the first photometric value of the first photometry. When the first shutter time is faster than the constant shutter time, the amplifier gain output from the image pickup device is lowered, and the image is shot at the second shutter time which is slowed down accordingly. It is characterized by doing.

Further, the first shutter speed obtained from the exposure control means is shifted to a low speed by a mechanical delay time of closing the shutter at the time of photographing.

Further, the exposure control information is stored in the storage means.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an electronic still camera according to an embodiment of the present invention. Further, FIG. 2 is a flow chart showing the processing of exposure control in the present embodiment.

In FIG. 1, 1 is a CPU that controls the entire electronic still camera, 2 is a blade that controls the exposure of a diaphragm and a mechanical shutter that changes the diameter when adjusting the incident light flux, and 2a is a fully opened blade 2. At this time, a mechanical aperture limiting hole having an aperture value of F2.8, 3 is a motor for driving the blade 2 by a control signal from the CPU 1, 4 is a CCD (charge coupled device), and 5 is a signal from the CCD 4. , Interlaced readout with pixel mixture (for field image capture) or non-interlaced readout without pixel mixture (for frame image capture), amplified by an appropriate amplifier gain, and the amplified output is captured by CDS (correlated double sampling) Then, a signal acquisition converter for A / D (analog / digital) conversion, and 6 for the blade 2 by the signal from the CCD 4.
Exposure control unit that controls the aperture and shutter speed by driving the
Reference numeral 7 is a digital signal processing unit for performing image processing, 8 is a compression / expansion unit for performing compression processing on image data at the time of shooting, and decompression processing at reproduction, and 9 is an external storage device detachable from the electronic still camera body. A card controller that is an interface with the memory card 10, 11 is an EEPROM (nonvolatile memory) for storing setting data, and 12 is a switch unit for performing operations such as release.

In the electronic still camera having the above-mentioned structure, the first release is turned on for taking a picture, and the CP
When U1 is activated for exposure measurement, first, as a pre-process, the exposure control unit 6 fully opens the motor 2 for driving the blades 2 so that the aperture value becomes the hole 2a of F2.8. At this time,
In the first release, the output of the CCD 4 is output from the signal acquisition conversion unit 5 by the amplifier gain a by interlaced reading of pixel mixture, and when the second release is performed, the CCD 4 is shielded by the mechanical shutter and no pixel is mixed. The output of the amplifier gain b by non-interlaced reading is used.

First, the first photometry is performed and the first photometric value Ev1
Then, a photometric value Ev1 ′ that is lower than the first photometric value Ev1 is determined. Considering the dynamic range characteristic of the CCD 4 that it is narrower on the bright side, the CCD 4 is affected by variations in the mechanical position of the blade 2 during the second photometry.
This is to prevent the output from overflowing. From the obtained photometric value Ev1 ', the aperture value Av1' and the shutter speed Tv
Separate into 1 '. The blade 2 is driven by the aperture value Av1 'to change the aperture position. Then, the second photometry is performed, and the exposure error ΔEv due to the variation in the diameter of the blade 2 is calculated from the second photometric value Ev2 and the photometric value Ev1 ′ obtained thereby. The first shutter time Tv2 of the mechanical shutter is obtained from the shutter time Tv1 ′ and the exposure error ΔEv, and the preprocessing is completed.

Further, when the second release is turned on and the first shutter time Tv2 obtained by the pre-processing is faster than the constant shutter time Tv0, the output used during photographing is changed from the amplifier gain b to the amplifier gain a. Shooting is performed by the second shutter time Tv2 ', which is lowered by the same time to lower the first shutter time Tv2 to obtain the same exposure value.

Next, the exposure control process of the electronic still camera will be described with reference to the flowchart shown in FIG.

As a pre-process for exposure measurement for photographing, the first release is turned on (S1). The blade 2 is fully opened to obtain an aperture value of F2.8 (S2). Set feather 2 to F2.
The first photometry is performed at the diaphragm position of 8 to obtain the first photometry value Ev1. This is not so accurate in the case of F4.5, F8, F11, etc. diaphragms due to the diameter of the blades 2 that are used for diaphragming, so an aperture position of F2.8 that fully opens the blades 2 is used (S3). . From the first photometric value Ev1 obtained by the first photometry, a photometric value Ev1 'which is under by a preset predetermined value Ev0 is obtained (S4). The measured photometric value Ev1
′ Is separated into aperture value Av1 ′ and shutter speed Tv1 ′
(S5). From the aperture value Av1 ', it is determined whether the aperture position is F2.8 or not. If the aperture position is not F2.8, the aperture value is
The matching blade 2 is driven to the diaphragm position of (F4.5, F8, F11) (S6).

The second photometric value Ev obtained by performing the second photometry
The exposure error ΔEv of the variation due to the diameter of the blade 2 is calculated from 2 and the photometric value Ev1 ′ (S7). Since the aperture position is fixed, the calculated exposure error ΔEv and shutter speed Tv
The first shutter speed Tv2 is determined by 1 ', and the preprocessing is ended (S8).

Further, the second release is turned on for taking a picture (S9). The first shutter time Tv2 determined in the pre-processing is a constant shutter time Tv0 (at high speed limit time)
It is determined whether the speed is higher (S10). When the first shutter time Tv2 is higher than the constant shutter time Tv0 (high speed limit time), the amplifier gain b used as the output of the CCD 2 is lowered to the amplifier gain a, and the same exposure value is obtained accordingly. Second shutter speed Tv2 'slowed down
Is determined (S11). Second shutter time Tv determined
Photographing is performed by the output of 2'and the amplifier gain a (S1
2).

As described above, even when the follow-up area of the shutter speed of the low-speed mechanical shutter is exceeded, the amplifier gain is lowered to determine the second shutter time of the same exposure value, so that high-luminance photographing is performed. It becomes possible to respond.

FIG. 3 is a timing chart of the amplifier gain output cycle and the mechanical shutter at the first shutter speed in this embodiment. In FIG. 3, in the case of a mechanical shutter, if the shutter closing tilt time operates at the timing of the first shutter time Tv2, a delay of the shift amount occurs. For this reason,
As shown in FIG. 3, by adding a shift amount for the time delay to the first shutter time Tv2, the first shutter time Tv2 is shifted to a low speed recording time (first shutter time Tv2 + shift amount). And As a result, it is possible to reduce the exposure error due to the delay between the first shutter speed Tv2 obtained during the pre-processing and the shutter closing tilt time of the mechanical shutter.

Further, as condition information for the various types of exposure control, aperture value information at each aperture position, time from shutter motor activation to closing, shutter closing inclination time, etc. are stored in advance in the EEPROM 11 as a storage means. ing. As a result, it becomes possible to easily change the setting conditions without repeatedly setting each setting condition.

[0020]

As described above, according to the electronic still camera of the present invention, the output of the amplifier gain b is lowered to the amplifier gain a even when the tracking range of the slow mechanical shutter at the shutter speed is exceeded. Then, by setting the first shutter speed to the second shutter speed, which is reduced by that amount, the high shutter speed can be dealt with.

Further, the exposure error can be reduced by shifting the first shutter speed to a low speed by the delay of the first shutter speed obtained during the preprocessing and the mechanical operation delay in closing the mechanical shutter. it can.

Further, there is an effect that each set value of the exposure control is also stored in the EEPROM (nonvolatile memory), and it is possible to deal with the change of each set value.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing an exposure control process according to the present embodiment.

FIG. 3 is a timing chart of an amplifier gain output cycle and a mechanical shutter at a first shutter speed in the present embodiment.

[Explanation of symbols]

1 ... CPU, 2 ... blade, 2a ... hole, 3 ... motor,
4 ... CCD (charge coupled device), 5 ... signal acquisition conversion unit,
6 ... Exposure control section, 7 ... Digital signal processing section, 8 ... Compression / decompression section, 9 ... Card controller, 10 ... Memory card, 11 ... EEPROM (nonvolatile memory), 12 ... Switch section.

Claims (3)

[Claims] 1. An image pickup means for picking up an image of a subject and outputting image data, a diaphragm for regulating an amount of light incident on the image pickup means, a driving means for driving the diaphragm, and code decoding of the image data. In an electronic still camera having a data processing means, a control means for controlling writing and reading of data to and from a storage medium, a storage means for storing various setting values, and a control means for controlling the entire apparatus,
And an exposure control means for performing a pre-process for obtaining a first shutter speed from a second photometric value obtained by performing a second photometry by changing a diaphragm based on the first photometric value of the first photometric value. When the first shutter speed is faster than the constant shutter speed, the amplifier gain output from the image pickup device is reduced, and the second shutter speed is reduced by that amount, and an image is captured at the electronic still camera. . 2. The electronic still camera according to claim 1, wherein the first shutter speed obtained from the exposure control means is shifted to a low speed by a mechanical delay time of closing the shutter at the time of photographing. 3. The electronic still camera according to claim 1, wherein each exposure control information is stored in the storage means.