JP2780797B2 - Electronic imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electronic imaging device that captures and inputs an image of a subject using a solid-state imaging device such as a CCD.

2. Description of the Related Art Recently, an electronic imaging apparatus that electronically captures and inputs an image of a subject using a solid-state imaging device such as a CCD and records the image signal (electronic still image) on a floppy disk or a memory card has been developed. It is attracting attention as an electronic still camera.

This type of electronic still camera is essentially different from a conventional general still camera using a silver halide film in that a so-called element shutter can be used. This element shutter is realized by photoelectrically converting a subject image and controlling the accumulation time of signal charges in a solid-state imaging device that accumulates signal charges according to the light amount of the subject image. Specifically, a high-speed shutter is realized by setting the accumulation time of the signal charge in the solid-state imaging device to be short, and a low-speed shutter is realized by setting the accumulation time to be long.

[Problems to be Solved by the Invention] However, there are the following problems in an electronic imaging apparatus employing this type of element shutter. That is, in order to properly capture a subject image by the solid-state imaging device, it is necessary to accumulate signal charges suitable for the imaging sensitivity characteristics. For this reason, if the accumulation time of the signal charge is set short in order to realize the high-speed shutter operation by the element shutter, an object to be imaged on the imaging surface of the solid-state imaging device is inevitable in order to ensure proper accumulation of the signal charge. It is necessary to increase the amount of light of the image. That is, it is necessary to increase the amount of incident light of the subject image by an amount corresponding to the shorter accumulation period of the signal charge, increase the image plane illuminance of the subject image with respect to the solid-state imaging device, and accumulate the signal charges corresponding to the subject image.

However, in the case where the image illuminance of the subject image is increased in this way and an image is taken by a high-speed shutter, the image illuminance often exceeds the smear allowable limit image illuminance of the solid-state imaging device. . The smear is a phenomenon in which light applied to an imaging surface of a solid-state imaging device is mixed into a signal charge transfer path to generate extra charge, or diffusion of light that has entered the inside of an element substrate, resulting in an object. This is a phenomenon in which unnecessary charges are mixed into signal charges accumulated according to an image.

However, if a subject image exceeding the smear allowable limit image plane illuminance is input and imaged, there arises a problem that the quality of a captured image signal is significantly reduced due to the occurrence of smear.

The present invention has been made in view of such circumstances,
It is an object of the present invention to provide an electronic imaging apparatus capable of capturing an image of a subject with high quality by an element shutter using a solid-state imaging element without causing a problem of smear.

[Means for Solving the Problems] In order to solve the above problems and achieve the object, an electronic imaging apparatus of the present invention is configured as follows.

An electronic imaging apparatus according to the present invention includes: an imaging optical system that forms an image of a subject at a predetermined position; a light amount adjusting unit that adjusts an incident light amount of the subject image formed by the imaging optical system; A solid-state imaging device that is provided at an imaging position and photoelectrically converts a subject image formed at the position and accumulates signal charges corresponding to the light amount of the subject image; and accumulation and accumulation of signal charges by the solid-state imaging device Solid-state image sensor driving means for controlling reading of the read signal charges, photometric means for measuring the light quantity of the subject, and an image formed on the solid-state image sensor based on the light quantity of the subject measured by the photometric means. The light amount adjusting means is drive-controlled so that the image plane illuminance by the subject image is equal to or less than the smear allowable limit value, and the signal charge by the solid-state imaging device is related to the incident light amount adjustment amount by the light amount adjusting means. Adjust the accumulation time is characterized by comprising an exposure control means for controlling the solid-state imaging device driving means such storage amount of signal charge corresponding to the object image becomes a predetermined value, the by the solid-state imaging device.

[Operation] According to the solid-state imaging device of the present invention configured as described above, when the element shutter is realized by controlling the accumulation time of the signal charges in the solid-state imaging device, the incident light amount is adjusted according to the light amount of the subject. Therefore, the image plane illuminance of the subject image formed on the imaging surface of the solid-state imaging device is controlled to be equal to or less than a predetermined value which is the smear allowable limit image surface illuminance of the solid-state imaging device. In this state, it is possible to perform imaging after the subject, that is, accumulation of signal charges corresponding to the subject image by photoelectric conversion. Under the condition that the light amount (image surface illuminance) is properly controlled, the control of the accumulation time of the signal charge is variably controlled in accordance with the light amount of the subject, that is, in relation to the control of the incident light amount. Since the exposure control is performed so that the charge amount becomes a predetermined value (appropriate value), it is possible to effectively prevent the occurrence of smear and perform appropriate exposure (imaging) of the subject image.

Hereinafter, a solid-state imaging device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment apparatus, and 1 is an image pickup optical system that forms an image of a subject at a predetermined position. The imaging optical system 1 is generally composed of a plurality of optical lenses, and incorporates therein an aperture mechanism (light amount adjusting means) 2 for adjusting the incident light amount of the subject image.

Then, a CCD 3 which is a solid-state image sensor is provided at an image forming position of a subject image which is formed through the imaging optical system 1 and whose light amount is adjusted by the aperture mechanism 2 and input.
The CCD 3 photoelectrically converts the subject image and inputs the image. A half mirror 4 is provided in the optical path of the imaging system, and a subject image forming a part of the incident light reflected by the half mirror 4 is focused on a focusing glass 5.
The image is formed on the upper side and can be visually recognized through a finder system including the half mirror 6 and the eyepiece 7. The half mirror 6 guides a part of the subject image formed on the focus glass 5 to the photometric sensor 8 and measures the amount of incident light (the amount of the subject image).

This apparatus employs a single-lens reflex optical system using the half mirror 4 as described above, and is configured so that an image of a subject captured by the CCD 3 can be confirmed as it is via the finder system.

The light quantity (brightness) of the subject image detected and received by the photometric sensor 8 is measured by the photometric circuit 11. The exposure control circuit 12 controls the aperture drive circuit 13 and the shutter drive circuit 14 according to the photometric value of the subject image measured by the photometric circuit 11 so that the exposure value of the subject image captured by the CCD 3 becomes appropriate. To

The CCD 3 photoelectrically converts the subject image formed on the imaging surface, accumulates signal charges corresponding to the amount of light, and reads the accumulated signal charges to capture the subject image. In this way, the image signal of the subject image picked up and input by the CCD 3 is given to the image pickup circuit 15 and subjected to processing such as separation into respective color components of three primary colors. Then, the data is recorded and output on a predetermined recording medium (floppy disk or memory card) via the recording circuit 16.

The aperture drive circuit 13 drives the above-described aperture mechanism 2 under the control of the exposure control circuit 12 for such an imaging system, and is basically connected to the imaging surface of the CCD 3 via the imaging optical system 1. The amount of light of the subject image to be imaged is controlled to be smaller than a predetermined image plane illuminance, specifically, an appropriate amount equal to or smaller than the smear allowable limit image plane illuminance of the CCD 3. That is, the aperture blades of the aperture mechanism 2 are driven to variably control the aperture diameter of the aperture, whereby the incident light amount of the subject image is adjusted (suppressed) to satisfy the above condition.

Thus, the shutter drive circuit 14 realizes an element shutter by variably controlling the accumulation time of the signal charges by the CCD 3, and its operation is controlled under the control of the exposure control circuit 12. The control of the signal charge accumulation time by the shutter drive circuit 14, that is, the control of the exposure time for the subject image, is performed in connection with the adjustment of the incident light amount by the aperture mechanism 2 described above. The control is performed such that the aperture value and the exposure time (accumulation time of the signal charge) satisfy a predetermined relationship in accordance with the imaging capability possessed.

Specifically, the imaging capability Lv for a predetermined subject luminance
Is the sensitivity Sv of the imaging signal processing system including the subject brightness Bv and CCD3
Lv = Bv + Sv Bv = log ₂ (B / K) B; brightness value of the object [ft−L] K; exposure calibration coefficient (generally 1.1 to 1.4) Sv = log ₂ (ISO / 100) +5 As shown. However, ISO indicates the sensitivity of the image signal processing system as I
It is a value expressed in SO speed.

On the other hand, the exposure control capability Ev by the above-described aperture value control and exposure time (signal charge accumulation time) control is Ev = Av + Tv Av = log ₂ F ² Tv =, where the aperture capability is Av and the shutter capability is Tv. log ₂ (1 / T) F; aperture value T; shutter speed [sec]. Thus, the exposure control circuit 12 is a photometric circuit.
The aperture drive circuit 3 and the shutter drive circuit 14 are controlled so as to obtain the relationship of Ev = Lv (Av + Tv = Bv + Sv) in accordance with the luminance B of the subject measured at 11, so that proper exposure can be obtained. The exposure control is performed.

At this time, when the transmittance of the lens and the half mirror 4 in the imaging optical system 1 is τ (for example, τ = 0.6), the CCD
The image plane illuminance E of the subject image on the imaging surface of No. 3 is given as E = τπB / 4F ² B; luminance value of the subject [cd / m ² ]. The exposure control circuit 12 drives the aperture drive circuit 13 so that the image plane illuminance E is equal to or less than the smear allowable limit image plane illuminance Emax unique to the CCD 3, and preferentially adjusts the amount of incident light. Exposure control is performed.

In other words, since the brightness B of the subject is measured by the photometry circuit 11, the F value for controlling the narrowing down of the incident light amount of the subject image is set so as to satisfy the relationship of F ≧ (τπB / 4Emax) ^1/2. , The image surface light amount E is suppressed to the smear allowable limit image surface illuminance Emax or less.

Then, the exposure time (shutter speed) indicated by the accumulation time of the signal charge by the CCD 3 is set so as to satisfy the above-described relationship of Av + Tv = Bv + Sv, and the exposure is controlled.

Here, when the shutter release switch 18 is pressed, the system controller 17 controls a series of processing operations for driving the above-described units at the timing shown in FIG. 2 to capture and input a subject image. This system controller 17
The above-described operation control process includes the above-described characteristic aperture control in the present apparatus.

That is, the present apparatus is configured to perform the imaging operation in synchronization with a predetermined timing pulse VD, and to perform the imaging operation in synchronization with the next timing pulse VD after the detection of the turning-on of the shutter release switch 18. The operation starts.
This imaging operation is performed by first controlling the aperture driving circuit 13 in accordance with the brightness B of the subject measured by the photometric circuit 11 and controlling the amount of light of the subject image formed on the imaging surface of the CCD 3 via the imaging optical system 1. (Image surface illuminance) E is the smear allowable limit image surface illuminance of the CCD3
The process is performed by adjusting the incident light amount (aperture control) so as to be equal to or less than Emax and to obtain a proper exposure value [processing in FIG. 2]. In this aperture stop control, when the shutter speed is set with priority, the aperture value is set so as to match the shutter speed after satisfying the condition regarding the smear allowable limit image surface illuminance Emax described above. When the control is performed, or when the aperture value is preferentially determined, when the above-described condition regarding the smear allowable limit image surface illuminance Emax is satisfied, the aperture value is controlled to be reduced to the set aperture value. However, in this case, it is automatically determined according to the amount of incident light in accordance with a program diagram of a predetermined aperture value and shutter speed.

That is, the conditions for performing the appropriate exposure are realized as various combinations of the relationship between the image surface light amount determined by narrowing down the light amount of the subject image and the signal charge accumulation time (shutter speed) by photoelectric conversion in the CCD 3. .
Specifically, as shown in FIG. 3, when the shutter speed is increased by increasing the image surface light amount, and conversely, when the shutter speed is decreased by decreasing the image surface amount, The same exposure value is obtained as long as the areas indicating are equal. That is, in either case, the exposure is appropriate.

However, when the shutter speed is increased to T1,
Inevitably, the image surface light amount for obtaining proper exposure must be increased, and the image surface light amount E1 at this time may exceed the smear allowable limit image surface illuminance Emax described above.

In order to cope with such a problem, in this apparatus, as described above, the image surface light amount E is set to the smear allowable limit image surface illuminance Em.
After narrowing down the incident light amount of the subject image so as to be less than or equal to ax, the subject image is picked up as follows.

After performing the aperture control for the incident light amount of the subject image as described above, the present apparatus maintains the state and controls the shutter drive circuit 14 to control the accumulation (exposure) of signal charges corresponding to the subject image. Perform The signal charge accumulation control is performed in accordance with a program chart set as shown in FIG. 4, for example, according to a program chart set as shown in FIG. ) Is controlled.

FIG. 4 is a so-called EV chart showing the relationship between the aperture value for obtaining proper exposure and the shutter speed with the amount of light of the subject as an oblique axis. As shown in this figure, in the present apparatus, a combination of an aperture value and a shutter speed is set so as to obtain an appropriate exposure within a range where the image plane illuminance is equal to or less than the smear limit.

It is preferable that the shutter speed be high unless the so-called camera shake phenomenon or the like during high-speed continuous shooting is considered, and that the aperture be open if the flash is not considered such as daytime synchro. On the other hand, regarding the depth of field,
Since the screen size of the CCD3 can be made sufficiently deeper than a normal silver halide camera using a 35 mm size film, there is not much effect. From this point of view, it can be said that it is desirable to shift the shutter speed as high as possible within a range where the image plane illuminance is equal to or less than the smear limit.

Therefore, in the present apparatus, in order to obtain an appropriate exposure, the combination (program diagram) of the aperture value and the shutter speed is set as shown in FIG.

Here, in the program diagram in FIG. 4, the supplementary explanation that the upper limit of the shutter speed for satisfying the condition relating to the smear allowable limit image surface illuminance Emax is set to 1/1000 second is described.

Smear allowable limit image plane illuminance Emax in actual imaging device
Was measured to obtain Emax (= 75 Lx) data. Therefore, for example, τ (= 0.6), K (= 1.4), ISO (= 10
0) is given by E = τπB / 4F ² (where B is the brightness value of the object [cd / m ² ]), and Ev = Lv, that is, log ₂ F ² + log ₂ (1 / T) = When T is calculated by substituting log ₂ (B / K) + log ₂ (32 ISO / 100) (where B is the brightness value of the subject [ft-L]), T601060 is obtained, and the smear allowable limit image is obtained. The upper limit of the shutter speed for satisfying the condition of the surface illuminance Emax is required to be 1/1000 second. The above-mentioned program chart is set in consideration of such a thing.

Under such conditions, the subject image is photoelectrically converted, and the signal charge is controlled to be stored. Then, a pulse indicating the end of the exposure is detected, and the signal charge stored in the CCD 3 is read out (transfer output). Then, the recording circuit 16 is driven and controlled, and CC
A signal charge read from D3, that is, a recording process of a captured image signal is executed.

When reading out the signal charges from the CCD 3 in this way, the aperture driving circuit 13 described above is again controlled in parallel with the reading out of the signal charges, so that the light is more incident than when the subject image is exposed. Aperture control is performed to reduce the amount of light.

That is, when the above-described exposure end pulse is detected,
The exposure control circuit 12 is completely independent of the above-described exposure control,
The diaphragm mechanism 2 is driven over the period of reading out the signal charges from the CCD 3, and the incident light amount is controlled to be reduced / suppressed by, for example, setting the minimum diaphragm value [processing shown in FIG. 2]. The aperture control at this time is completely independent of the exposure control when capturing the subject image, and is intended to prevent unnecessary light that causes smear from being irradiated on the imaging surface of the CCD 3 after the exposure is completed. Is performed as needed.

After reading out the signal charges from the CCD 3 and recording the image signal under the condition that the aperture stop control of the incident light is performed, the above-described aperture drive circuit 13 is driven again to open the aperture value. [Process shown in FIG. 2].
Although this process is not related to the electronic imaging of the subject image by the CCD 3, the subject image formed on the focusing glass 5 is brightened to facilitate focusing (focusing) and composition determination. It is performed for the purpose of normalization.

Thus, according to the present apparatus configured as described above and performing the aperture control for the incident light amount as described above, the image plane illuminance of the subject image formed on the imaging surface of the CCD 3 is always suppressed to be lower than the smear allowable limit image plane illuminance. Therefore, smear does not occur during the exposure. Furthermore, according to the above embodiment, after a predetermined imaging process (exposure) by the CCD 3 is performed, when reading out the signal charges accumulated in the CCD 3 by this exposure, the amount of light incident on the imaging surface of the CCD 3 is also determined. Since the aperture is narrowed down, irradiation of an extra subject image after the exposure is completed can be effectively suppressed. As a result, it is not necessary to input a subject image with high image plane illuminance unintentionally or to input extra light after the end of exposure, so that the generation of smear is effectively prevented, and the signal charge accumulated in the CCD 3 is reduced. The reading can be performed without deteriorating the quality.

In particular, at the time of imaging at a high shutter speed, the imaging is performed by capturing a larger amount of light for the shorter signal accumulation time. Even in such a case, the focusing control for the subject image is performed, and Since the shutter speed is optimized, the occurrence of smear can be effectively prevented. In other words, without performing an undesired high-speed shutter operation in which the occurrence of smear cannot be denied, the image plane illuminance is reduced by narrowing down the subject image, and the shutter speed is reduced in connection with this, so that the smear caused by the high-speed shutter operation is reduced. Generation can be effectively prevented.

It is conceivable to use a mechanical shutter to prevent the occurrence of smear. However, if the function of the aperture mechanism 2 is used as it is as in the present apparatus, an extra mechanism such as a mechanical shutter is added. There is an effect that there is no need to carry out.

Note that the present invention is not limited to the above-described embodiment. For example, the program diagram is not limited to the above-described example. When adopting a structure in which the viewfinder system is provided separately from the imaging system, the CCD3
The aperture mechanism 2 may be appropriately controlled only during the signal charge accumulation period, and the aperture value may be minimized during the period from the end of the exposure to the start of the next exposure. . Although the aperture value after the exposure is set to the minimum aperture value to prevent the occurrence of smear, it is of course possible to control the aperture value to an appropriate aperture value other than the minimum aperture value. Further, in the above-described embodiment, the aperture value is controlled by a photometric circuit provided separately from the image sensor, but before performing a normal exposure operation, an output for photometry is read from the solid-state image sensor, and based on this, The aperture value may be controlled. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[Effects of the Invention] According to the present invention, the image plane illuminance of the subject image when the solid-state imaging device performs exposure of the subject image (imaging: accumulation of signal charges according to the amount of light of the subject image), The amount of incident light of the subject image is controlled so as to be equal to or less than the smear allowable limit value, so that the occurrence of smear is easily and effectively prevented. As a result, when shooting with a high-speed shutter using an element shutter, Also, a high-quality captured image without smear can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an electronic image pickup apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing an image pickup operation timing in the embodiment apparatus, and FIG. FIG. 4 is a program diagram showing the relationship between the aperture value and the shutter speed with respect to the amount of subject light for obtaining the proper exposure in the embodiment. 1 ... imaging optical system, 2 ... stop mechanism (light amount adjusting means),
3 ... CCD (solid-state imaging device), 8 ... Photometric sensor, 11 ...
... Photometric circuit, 12 ... Exposure control circuit, 18 ... Aperture drive circuit, 14 ... Shutter drive circuit, 15 ... Imaging circuit, 16 ...
Recording circuit, 17 System controller, 18 Shutter release switch.

Claims (1)

(57) [Claims] An imaging optical system that forms an image of a subject at a predetermined position; a light amount adjusting unit that adjusts an incident light amount of the subject image formed by the imaging optical system; and an imaging position of the subject image. A solid-state imaging device that photoelectrically converts a subject image formed at the position and accumulates a signal charge corresponding to the amount of light of the subject image; and accumulates and accumulates the signal charge by the solid-state imaging device. Solid-state image sensor driving means for controlling the reading of electric charges; photometric means for measuring the amount of light of the subject; and a subject image formed on the solid-state image sensor based on the quantity of light of the subject measured by the photometric means The light amount adjusting means is driven and controlled so that the image plane illuminance by the light amount becomes equal to or less than the smear allowable limit value, and the signal charge is accumulated by the solid-state imaging device in relation to the amount of incident light amount adjustment by the light amount adjusting means. Exposure control means for adjusting the interval and controlling the solid-state image sensor driving means so that the signal charge accumulation amount corresponding to the subject image by the solid-state image sensor becomes a predetermined value. Imaging device.