JPH02181583A - Electronic image pickup device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory image pickup picture by suppressing the incident light quantity of an object so that the image surface illuminance of the object can be the smear tolerance limit image surface illuminance of a solid-state image pickup device (CCD) or below when the object is image picked up, and signal charges are accumulated according to the light quantity of the object. CONSTITUTION:For an image pickup system, a diaphragm driving circuit 13 drives a diaphragm mechanism 2 and converge-controls the light quantity of the object image-formed through an image pickup optical system 1 on the image pickup surface of a CCD 3 so that the light quantity can be prescribed image surface illuminance or below, namely, the light quantity can be proper quantity which is the smear tolerance limit image surface illuminance of the CCD 3 or below. Consequently, the signal charges corresponding to the object can be accumulated under a state where the occurrence of a smear never causes trouble. Further, the exposure of the object can be controlled so that the accumulating signal charge quantity can be a prescribed value under a condition in which the light quantity is properly controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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.

[Prior Art] Recently, electronic imaging devices that electronically capture and input the image of a subject using a solid-state imaging device such as a COD and record the image signal (electronic still image) on a floppy disk or memory card have become popular. It is attracting attention as an electronic still camera.

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

[Problems to be Solved by the Invention] However, electronic imaging devices that employ this type of element shutter have the following problems. That is, in order to properly capture an object image using a solid-state imaging device, it is necessary to accumulate signal charges that match the imaging sensitivity characteristics of the solid-state imaging device. For this reason, when the signal charge accumulation time is set short in order to achieve high-speed shutter operation using an element shutter, in order to ensure proper signal charge accumulation, it is necessary to focus on the object that is imaged on the imaging surface of the solid-state image sensor. It is necessary to increase the light intensity of the image. In other words, it is necessary to increase the amount of light incident on the subject image by the shorter signal charge accumulation period, thereby increasing the image plane illuminance of the subject image on the solid-state image sensor, and to accumulate signal charges corresponding to the subject image.

However, when attempting to capture images using a high-speed shutter by increasing the image plane illuminance of the subject image in this way, the image plane illuminance often exceeds the smear permissible limit image plane illuminance of the solid-state image sensor. .

This smear is caused by the light irradiated on the imaging surface of the solid-state image sensor getting mixed into the signal charge transfer path and generating excess charge, or by the diffusion of light entering the inside of the device substrate. This is a phenomenon that causes unnecessary charges to be mixed into signal charges accumulated in accordance with an image.

However, when a subject image exceeding the smear permissible image plane illuminance is input and captured, a problem arises in that the quality of the captured image signal is significantly degraded due to the occurrence of smear.

The present invention has been made in consideration of these circumstances, and its purpose is to provide an electronic device that can capture a high-quality image of a subject using an element shutter using a solid-state image sensor without causing the problem of smear. An object of the present invention is to provide an imaging device.

[Means for Solving the Problems] The present invention provides an imaging optical system that forms an image of a subject at a predetermined position, a light amount adjustment means that adjusts the amount of incident light of the subject image formed by the imaging optical system, a solid-state image sensor that is provided at an imaging position of the subject image and photoelectrically converts the subject image formed at the position and accumulates a signal charge according to the amount of light of the subject image; and a solid-state image sensor that measures the amount of light of the subject. In the electronic imaging device, the electronic imaging device is equipped with a photometric means, and controls the accumulation of signal charges by the solid-state image sensor and the readout of the accumulated signal charges according to the photometry results, based on the light intensity of the subject measured by the photometry means. (1) driving and controlling the light amount adjusting means so that the image plane illuminance due to the subject image formed on the solid-state image pickup device is below a predetermined value; means for adjusting the accumulation time of signal charges by the solid-state image sensor and controlling the solid-state image sensor driving means so that the amount of signal charge accumulated by the solid-state image sensor according to the object image becomes a predetermined value; It is characterized by preventing the occurrence of smear.

[Function] According to the solid-state imaging device of the present invention configured as described above,
When realizing an element shutter by controlling the accumulation time of signal charges in a solid-state image sensor, the amount of incident light is adjusted according to the amount of light from the object, and the image surface illuminance of the object image formed on the imaging surface of the solid-state image sensor is adjusted. Since the image plane illuminance is controlled to be below a predetermined value, which is the smear permissible limit image illuminance of the solid-state image sensor,
Capturing a subject image without smearing,
In other words, it becomes possible to accumulate signal charges corresponding to the subject image by photoelectric conversion. Under conditions in which the amount of light (image surface illuminance) is properly controlled, the accumulation time of the signal charge is variably controlled according to the amount of light from the subject, that is, in relation to the control of the amount of incident light, and the accumulated signal Since the exposure control is performed so that the amount of charge becomes a predetermined value (appropriate value), it is possible to effectively prevent the occurrence of smear and perform proper exposure (imaging) of the subject image.

[Embodiment] A solid-state imaging device according to an embodiment of the present invention will be explained below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment apparatus, in which numeral 1 denotes an imaging 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 has a diaphragm mechanism (light amount adjusting means) 2 built therein for adjusting the amount of incident light of the subject image.

However, a CCD 3, which is a solid-state image sensor, is provided at the imaging position of the subject image that is formed through the lever imaging optical system 1 and inputted after adjusting the amount of light by the diaphragm mechanism 2. The subject image is photoelectrically converted and input as an image. Further, a half mirror 4 is provided in the optical path of this imaging system, and a subject image forming part of the incident light reflected by this half mirror 4 is formed on a focusing glass 5, and the half mirror 6 and eyepiece lens It can be visually recognized through a finder system consisting of 7. The half mirror 6 guides a portion of the subject image formed on the focusing glass 5 to the photometric sensor 8, and is used to measure the amount of incident light (the amount of light of the subject image).

As described above, this device employs a single-lens flex optical system using the half mirror 4, and is configured so that the image of the subject captured by the CCD 3 can be confirmed directly through the finder system.

Now, the amount of light (brightness) of the subject image received and detected 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, respectively, based on all diameter values of the subject image measured by the nj optical circuit 11, and controls the aperture drive circuit 13 and the shutter drive circuit 14, respectively.
The exposure value of the subject image imaged by D3 is made appropriate.

The CCD 3 photoelectrically converts the subject image formed on its imaging surface, accumulates signal charges corresponding to the amount of light, and reads out the accumulated signal charges to capture the subject image. The image signal of the subject image imaged and inputted by the CCD 3 in this manner is given to the imaging circuit 15,
For example, processing such as separation into each of the three primary color components is performed. The data is then recorded and output to a predetermined recording medium (floppy disk or memory card) via the recording circuit 16.

For such an imaging system, the aperture drive circuit 13 drives the aperture mechanism 2 described above under the control of the exposure control circuit 12, and basically focuses on the imaging surface of the CCD 3 via the imaging optical system 1. The light amount is narrowed down and controlled so that the light amount of the imaged object image is below a predetermined image plane illuminance, specifically, an appropriate amount that is below the smear permissible limit image plane illuminance of the CCD 3.

That is, the diaphragm blades of the diaphragm mechanism 2 are driven to variably control the diameter of the aperture, thereby adjusting (suppressing) the amount of light incident on the subject image so as to satisfy the above conditions.

The shutter drive circuit 14 implements an element shutter by variably controlling the accumulation time of signal charges by the CCD 3, and its operation is controlled under the control of the exposure control circuit 12. This shutter drive circuit 14
The control of the signal charge accumulation time, that is, the control of the exposure time for the subject image, is performed in conjunction with the adjustment of the amount of incident light by the aperture mechanism 2 described above, and is controlled according to the imaging capability of the imaging signal processing system including the CCD 3. Control is performed so that the aperture value and exposure time (signal charge accumulation time) satisfy a predetermined relationship.

Specifically, the imaging capability Lv for a predetermined subject brightness is the sum of the subject brightness By and the sensitivity Sv of the imaging signal processing system including the CCD 3: Lv = By + Sv B v = log2 (B / K ) B; Value [f't-L] K: Exposure calibration coefficient (-1.1 to 1.4 for boat fishing) Sv
= log2(ISO/100) + 5. However, ISO is a value expressing the sensitivity of the imaging signal processing system in terms of ISO speed.

On the other hand, the exposure regulation ability Ev by the aperture value control and exposure time (signal charge accumulation time) control described above is Ev −Av +Tv Av −log2F Tv −log2( 1/T) F; aperture value T; shutter speed [indicated by seC]. Accordingly, the exposure control circuit 12 has a function of 4-1.
Depending on the brightness B of the subject measured by the optical circuit 11, E
v 7mLv (Av +Tv -Bv +Sv)
The aperture drive circuit 3 and the shutter drive circuit 14 are each controlled to obtain the following relationship, and exposure control is performed to obtain proper exposure.

At this time, when the transmittance of the lens and half mirror 4 in the imaging optical system 1 is τ (e.g. -0,6), C
The image plane illuminance E of the subject image on the imaging surface of CD3 is E-τπB74F2 B; brightness value of the subject [cd/rr? ] is given as . The exposure control circuit 12 controls this image plane illuminance E.
is the smear permissible limit image illuminance E m specific to the CCD 3
Drive the aperture drive circuit 13 so that the aperture is equal to or less than ax,
The amount of incident light is adjusted preferentially and then the exposure is controlled.

In other words, the brightness B of the subject is calculated by the photometry circuit 11.
Therefore, by setting the F value that narrows down and controls the incident light amount of the subject image to satisfy the relationship F≧(r yr B/4Emax) 1/2, the image plane light amount E can be adjusted to the above-mentioned smear tolerance. The image plane illuminance is kept below the limit Ewax.

Then, the exposure time (shutter speed) indicated by the signal charge accumulation time by the CCD 3 is set to the above-mentioned Av + Tv.
The exposure is controlled so as to satisfy the following relationship: -By +Sv.

Here, when the shirt release switch 18 is pressed, the system controller 17 controls a series of processing operations for driving each of the above-mentioned parts at the timing shown in FIG. 2 to capture and input a subject image. The operation control process by the system controller 17 includes the above-mentioned characteristic aperture control in this apparatus.

That is, this device is configured to perform its imaging operation in synchronization with a predetermined timing pulse VD, and is configured to perform its imaging operation in synchronization with the next timing pulse VD after the activation of the shirt release switch 18 is detected. Then, the imaging operation is started. In this imaging operation, first, the aperture drive circuit 13 is controlled according to the brightness B of the subject measured by the photometry circuit 11, and the amount of light of the subject image formed on the imaging surface of the CCD 3 via the imaging optical system 1 is controlled. (Image surface illuminance) E is less than or equal to the smear permissible limit image surface illuminance Eff1ax of the CCD 3, and the amount of incident light is determined to be a value to obtain an appropriate exposure value: J! This is performed by JfJ (narrowing down control) [processing marked with ■ in FIG. 2]. Note that in this aperture control, when the shutter speed is set with priority, the aperture value is set to match the above-mentioned shutter speed after satisfying the conditions regarding the smear permissible limit image plane illuminance E 1llaX described above. In some cases, the control is carried out by
Alternatively, if the aperture value is determined preferentially, the above-mentioned smear allowable limit image plane illuminance E I! In some cases, the aperture value is controlled to a preset aperture value after satisfying the conditions related to ax, but in this case, the aperture value is automatically determined according to the amount of incident light according to a program diagram of a predetermined aperture value and shutter speed. It is done.

In other words, the conditions for proper exposure are the image surface light amount determined by the aperture for the light amount of the subject image, and the CCD 3
Various combinations are realized in relation to the signal charge accumulation time (shutter speed) by photoelectric conversion. Specifically, as shown in Figure 3, when the amount of light on the image plane is increased and the shutter speed is increased, and when the amount of light on the image surface is decreased and the shutter speed is slowed, the amount of exposure changes. The exposure value will be the same as long as the areas showing the values are the same. In other words, the exposure will be correct in either case.

However, when the shutter speed is increased to T1,
Inevitably, the amount of image surface light must be increased to obtain proper exposure, and the image surface light ff1El at this time may exceed the above-mentioned smear permissible limit image surface illuminance E max.

In order to deal with such problems, this device narrows down and controls the incident light amount of the subject image so that the image plane light ff1E becomes equal to or less than the smear permissible limit image plane illuminance EIIlax, as described above, and then Imaging is performed as follows.

Now, after performing narrowing down control on the amount of light incident on the subject image as described above, this apparatus next maintains this state and controls the shutter drive circuit 14 to control the accumulation (exposure) of signal charges corresponding to the subject image. Do this. This signal charge accumulation control is carried out over the time set in relation to the aperture value described above, for example, according to a program diagram set as shown in FIG. ).

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

It is preferable that the shutter speed be high, unless consideration is given to the so-called camera shake phenomenon during high-speed snapshot photography, and it is desirable that the aperture is open, unless consideration is given to strobe photography such as daylight synchronization. On the other hand, regarding depth of field, C
Since the screen size of the CD3 can be made much deeper than that of a normal silver halide camera using a film of 35Iffl size, there is not much of a shadow. Based on this viewpoint, it can be said that it is desirable to shift the shutter speed to the high speed side as much as possible within the range where the image plane illuminance is below the smear limit.

Therefore, in this apparatus, the combination of aperture value and shutter speed (program diagram) is set as shown in FIG. 4 in order to obtain proper exposure.

Here, a supplementary explanation will be given regarding the fact that in the program diagram in FIG. 4, the upper limit of the shutter speed to satisfy the condition regarding the smear permissible limit image plane illuminance Eff1aX is set to 1/1000 second.

Smear permissible limit image plane illuminance E w in an actual imaging device
When ax was evaluated n1, E a+ax (=
75Lx) was obtained. At 6, for example, (-
0,6).

K(~1.4), ISO(-100) is expressed as E-τπB/4F2 (where B is the brightness value of the subject [cd/go]), and v-Lv, that is, 1og F +log2(1/T)-log2
(B/K) + log2 (32180/100) (
However, B; Substituting the brightness value of the subject [rt-Ll), T
When calculated, T'=; 1060, and the upper limit of the shutter speed to satisfy the condition of the smear permissible limit image plane illuminance Eff1ax is required to be 1/1000 second. The above-mentioned program chart has been designed with this in mind.

After photoelectrically converting the object image under these conditions and controlling the accumulation of the signal charges, a pulse indicating the end of exposure is detected and the signal charges accumulated in the CCD 3 are read out (transferred and output). Then, drive control of the recording circuit 16,
Recording processing of the signal charge read out from the CCD 3, that is, the captured image signal is executed.

In addition, in this apparatus, when reading out the signal charges from the CCD 3 in this way, the aperture drive circuit 13 mentioned above is controlled again in parallel with the reading out of the signal charges, so that the incident light is further controlled than when the subject image is exposed. Aperture control is performed to reduce the amount of light.

That is, the above-mentioned exposure end pulse force (when detected,
The exposure control circuit 12 drives the aperture mechanism 2 during the reading period of the signal charge from the CCD 3, completely independently of the exposure control described above, and sets the aperture value to the minimum aperture value to reduce the amount of incident light. Inhibition control is being carried out [processing shown in ■ in FIG. 2]. The aperture control at this time is completely independent of the exposure control when capturing the subject image, and its purpose is to prevent unnecessary light that may cause smear from being irradiated onto the imaging surface of the CCD 3 after the exposure is completed. This will be done as necessary.

Signal charges are read from the CCD 3 under conditions where such narrowing control of incident light is performed.

After recording the captured image signal, the aperture drive circuit 13 described above is driven again to open the aperture value (processing shown in (2) in FIG. 2). Although this processing is unrelated to the electronic imaging of the subject image by the CCD 3, it brightens the subject image formed on the focusing glass 5 and brings it into focus (
This is done for the purpose of making it easier to determine focus and composition.

According to this apparatus configured in this way and performing narrowing control on the amount of incident light as described above, the CCD 3
Since the image plane illuminance of the subject image formed on the imaging plane is always kept lower than the smear permissible limit image plane illuminance, smear does not occur during exposure. Moreover, according to the above embodiment, after the predetermined imaging processing (exposure) is performed by the CCD 3, even when reading out the signal charges accumulated in the C0D3 by this exposure, the amount of light incident on the imaging surface of the CCD 3 is reduced. Since the aperture is narrowed down, it is possible to effectively suppress unnecessary illumination of the subject image after the exposure is completed. As a result, it is no longer possible to inadvertently input a subject image with high image plane illuminance or to inject extra light after exposure, effectively preventing the occurrence of smear and
It becomes possible to read out the signal charges accumulated in the memory without impairing their quality.

In particular, when capturing an image with a high shutter speed, the signal accumulation time is short, so a large amount of light is taken in and the image is captured. Since the shutter speed can be optimized, it is possible to effectively prevent the occurrence of smear.

In other words, the illuminance on the image plane is reduced by narrowing down the subject image, and the shutter speed is accordingly slowed down, without causing undesired high-speed shutter operation that inevitably causes smear. It becomes possible to effectively prevent the occurrence.

Although it is conceivable to use a mechanical shutter to prevent the occurrence of this smear, if the function of the aperture mechanism 2 is used as is in this device, it is unnecessary to use an extra mechanism such as a mechanical shutter. Effects such as no need to add .

Note that the present invention is not limited to the embodiments described above. For example, it goes without saying that the program diagram is not limited to the example described above. In addition, when adopting a structure in which the viewfinder system is provided separately from the imaging system, the CCD
Even if the aperture mechanism 2 is properly controlled only during the signal charge accumulation period according to 3, and the aperture value is minimized from the time the exposure ends until the next exposure starts. good. Furthermore, here, the aperture value after exposure is set to the minimum aperture value to prevent the occurrence of smear, but it is of course possible to control the aperture value to an appropriate aperture value other than the minimum aperture value. Furthermore, in the embodiment described above, the aperture value is controlled by a photometric circuit provided separately from the image sensor, but before performing the normal exposure operation, the output for photometry is read from the solid-state image sensor, and based on this, the aperture value is controlled. The aperture value may also be controlled.

In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, when exposing a subject image (imaging: accumulation of signal charges according to the amount of light of the subject image) using a solid-state imaging device such as a COD, Since the amount of light incident on the subject image is suppressed and controlled so that the image plane illuminance is below the smear permissible limit image plane illuminance of the solid-state image sensor,
The occurrence of smear can be easily and effectively prevented. As a result, great practical effects can be achieved, such as being able to obtain good captured images without smearing even when photographing with a high-speed shutter using an element shutter.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an electronic imaging device according to an embodiment of the present invention, FIG. 2 is a diagram showing imaging operation timing in the embodiment device, and FIG. 3 is a diagram showing exposure amount depending on image surface light amount and shutter speed. FIG. 4 is a diagram showing the relationship between the aperture value and the shutter speed with respect to the amount of light of the object for obtaining proper exposure in the implementation device. . ■... Imaging optical system, 2... Aperture mechanism (light amount adjustment means), 3... CCD (solid-state image sensor), 8... Photometric sensor, II... Photometric circuit, 12... Exposure control circuit,
13... Aperture drive circuit, 14... Shutter drive circuit, I5... Imaging circuit, 16... Recording circuit, II...
・System controller, I8...shirt release switch.

Claims (1)

[Scope of Claims] An imaging optical system that forms an image of a subject at a predetermined position, a light amount adjustment means that adjusts the amount of incident light of the subject image formed by the imaging optical system, and a formation of the subject image. A solid-state image sensor that is installed at a position and photoelectrically converts a subject image formed at the position and accumulates signal charges according to the amount of light of the subject image; solid-state image sensor driving means for controlling readout of signal charges;
In an electronic imaging device comprising a photometric means for measuring the amount of light of the subject, based on the amount of light of the subject measured by the photometer,
The light amount adjusting means is drive-controlled so that the image plane illuminance due to the subject image formed on the solid-state image pickup device is equal to or less than a predetermined value. An electronic imaging device characterized in that a solid-state imaging device driving means is controlled so that the accumulation time of signal charges by the imaging device is adjusted, and the amount of signal charge accumulated by the solid-state imaging device according to a subject image becomes a predetermined value. .