JP2579939B2 - Still image pickup device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a still image capturing apparatus that displays an image captured by an image capturing unit on a display unit such as an electronic view finder.

2. Description of the Related Art In general, a finder using an optical finder or an electronic view finder is known as a finder system of a steal video camera. Note that there are a TTL (Through the taking the lens) type reflex finder and an external finder as optical finder.

The reflex finder focuses the light that has passed through the photographing lens on a focus plate via a movable total reflection mirror or a fixed semi-transmissive mirror, and observes the image.
There is an advantage that there is no change in parallax (parallax) due to a change in subject distance. However, when the operator performs focusing while looking at the viewfinder image, in order to place the focus plate and the image sensor on an optically equivalent surface,
Precise position adjustment of the focus plate is required.

Further, the device having a movable mirror between the focus plate and the image sensor has a disadvantage that the mechanism is complicated and a subject image cannot be seen at the moment of photographing. When a semi-transmissive mirror is used, the received light flux is divided between the image sensor and the finder, so that the finder becomes dark and the effective sensitivity of the image sensor is reduced. In any of the above-mentioned systems, since the mirror has a mirror, the back focus of the optical system must be lengthened, and from the viewpoint of miniaturization of the apparatus, the design of the short focus lens is restricted.

The external finder is provided with a finder optical system separately from the photographing optical system, and does not have the drawbacks of having a mirror like a reflex finder, but the parallax between the finder image and the actually shot image And this parallax varies with the subject distance.
Further, since focusing cannot be performed with the finder image itself, it is necessary to provide a distance measuring means.

On the other hand, the electronic viewfinder reproduces an image of the signal photoelectrically converted from the image pickup element by, for example, a liquid crystal display element, and observes the image. Therefore, it is most suitable for miniaturizing the apparatus without requiring the above-mentioned mirror and the like. Further, there is an advantage that the subject image can always be observed even at the moment of shooting.

[Problems to be Solved by the Invention] However, in a camera using an electronic viewfinder and particularly having an automatic exposure mechanism (AE) that determines an aperture shutter speed according to luminance, for example, a video camera, except for shooting. The shutter speed is fixed, and the aperture is automatically adjusted by an automatic exposure mechanism according to the brightness of the subject.

Therefore, when the subject is bright, the aperture is stopped down, so that the depth of field of the optical system lens is increased. As a result, the background of the subject displayed on the electronic viewfinder becomes clearer. Then, the operator thinks that focus has been achieved, and presses the shutter button. Then, the aperture and shutter speed determined by the automatic exposure mechanism are determined, and photographing is performed. However, this kind of conventional still video camera has the following problems.

That is, when the subject image is bright, a phenomenon occurs in which the background of the captured image is out of focus. This phenomenon is particularly remarkable when the AE mechanism has a shutter priority.

Therefore, an object of the present invention is to solve such problems.
It is an object of the present invention to provide a still image pickup device capable of obtaining a clearer image pickup result than an image displayed on an electronic viewfinder before photographing regardless of a difference in photographing conditions.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a stop that limits the amount of incident light, and an imaging unit that photoelectrically converts light incident through the stop. Release means, in response to operation of the release means, a still image capturing control means for capturing a still image with a preset aperture value, exposure time, and opening the aperture before operating the release means. Displaying a moving image obtained from the imaging unit by controlling the imaging unit by controlling the accumulation time of the imaging unit in response to the brightness of the subject; Display means,
The depth of field at the time of capturing a still image is made deeper than the depth of field at the time of capturing a moving image.

[Operation] In the present invention, the above-described configuration causes the conventional disadvantages, namely,
Although the image is clearly displayed during the moving image capturing, the drawback that the image is blurred when the actual still image is captured is solved. When performing the focus adjustment, the depth of field is smaller at the time of capturing a moving image than at the time of capturing a still image, so that more accurate focus adjustment can be performed.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of a basic configuration in the present embodiment. In FIG. 1, reference numeral 100 denotes a stop for limiting an incident light beam. Reference numeral 101 denotes an imaging unit that photoelectrically converts a light beam incident through the stop 100. 101 'is a supply unit for supplying the output of the imaging unit 101 to the display unit 102.

102 is a display means for displaying the output of the supply means 101 '. 103 is a recording unit for recording the output of the imaging unit 101.

Numeral 104 denotes a photometer for measuring the brightness of the surroundings. 105, other than when recording the output result of the imaging unit 101 by the recording unit 103, when displaying the output of the imaging unit 101 by the display unit 102, the aperture 100 is set to a predetermined size,
This is control means for variably setting the drive speed of the imaging means 101 in accordance with the amount of light measured by the photometric means 104.

 FIG. 2 shows an example of a specific configuration of this embodiment.

In FIG. 2, reference numerals 1 and 1 'denote lenses constituting an imaging optical system. Reference numeral 2 denotes an aperture mechanism.

Reference numeral 3 denotes an aperture control circuit that variably sets the size of the aperture in the aperture mechanism 2. The aperture control circuit 3 includes an exposure determination circuit 5
The aperture of the aperture mechanism 2 is set in accordance with the aperture information sent from. Reference numeral 4 denotes a solid-state imaging device (CCD) for photoelectrically converting an incident light beam. The individual imaging device 4 forms an imaging unit. Further, the CCD 4 also functions as a photometric means.

Reference numeral 5 denotes an exposure determination circuit as control means for determining an aperture and a shutter speed according to the brightness of a subject image.
The exposure determination circuit 5 includes an arithmetic processing unit (CPU), a random access memory (RAM), and a read-on memory (RO).
M) to determine the aperture and / or shutter speed by executing the control procedure shown in FIG.

Reference numeral 6 denotes an electronic viewfinder (EVF) having a liquid crystal display (CCD) as display means and a drive circuit as supply means. This liquid crystal element displays image information at a display field frequency of 1/60 second of a normal standard television.

Reference numeral 7 denotes a recording circuit as means for recording image information on a recording medium such as a floppy disk.

Reference numeral 8 denotes a drive circuit for driving the image pickup device 4. The drive circuit 8 forms an image pickup unit, and drives the image pickup device 4 at a drive speed corresponding to shutter speed information sent from the exposure determination circuit 5. The drive circuit 8 may be called an electronic shutter.

Reference numeral 9 denotes a signal processing circuit that amplifies a signal that has been photoelectrically converted by the image sensor 4. The signal processing circuit 9 is an automatic gain control (AGC)
With an AGC amplifier.

The operation of this embodiment in such a configuration will be described with reference to the flowchart of FIG.

In FIG. 3, when a signal (display start signal) for instructing the electronic viewfinder 6 to display an image is sent from a shutter button (not shown) to the exposure determination circuit 5, step S1 is performed.
In, and sends via the signal line l ₁ of the signal for instructing the open aperture to the control circuit 3 is exposed determining circuit 5 aperture. Then, the aperture control circuit 3 sets the aperture of the aperture mechanism 2 to the open position.

Next, in step S2, stores the predetermined initial values for shutter time in the internal register R of exposure determination circuit 5, and transmits through the signal line l ₂ The initial value in the drive 8. In this embodiment, this initial value is set to 1/60 second. When the image signal photoelectrically converted by the CCD 4 is sent to the exposure determination circuit 5, the output level of the image signal is compared with an appropriate level predetermined by the exposure determination circuit 5 in step S3.

In this comparison, if the output level of the image signal is within the range of a predetermined appropriate level, the shutter speed stored in the internal register R is set as the driving speed of the CCD 4,
The CCD 4 is driven at the selected drive speed until the exposure determination circuit 5 makes a selection and issues an imaging instruction, that is, until a shutter button (not shown) is pressed.

Therefore, the subject image is displayed with appropriate brightness on the EVF 6 (steps S3 → S6 → S3).

Next, in step S3, if the output level of the CCD 4 is lower than the predetermined appropriate level, the exposure determination circuit 5
Determines that the exposure is insufficient, and proceeds to step S4.

Exposure determination circuit at step S4 5 compares the rate of the internal register R to now have been set T _pre that when a predetermined configurable lowest shutter speed shutter time T _LO.

If the currently set shutter time T _pre is higher than the minimum settable shutter time T _LO , the exposure determination circuit 5 sets the currently set shutter time T low to a lower speed.
The determined shutter time is stored in the internal register R.
Note that the shutter time to be changed may be calculated by the exposure determination circuit 5 so that the output level of the CCD 4 rises to an appropriate level, or the steps S3 → S4 → S4-1 are sequentially repeated to set a predetermined shutter time. Change every second, CCD4
It may be confirmed in step S3 that the signal output has reached an appropriate level.

In the present embodiment, it is set to the set minimum level T _LO shutter time when the same 1/60 sec as the driving speed of the EVF. Therefore, while the shutter speed can follow the brightness of the subject image, the subject image is displayed on the EVF 6 with a constant brightness.

Next, in step S5, when it is determined that the currently set shutter speed has reached the set minimum level _TLO , the exposure determination circuit 5 determines that the exposure adjustment by changing the shutter speed is a limit, and The amplification degree (gain) of the image signal is adjusted by the processing circuit 9. For this purpose, the exposure determination circuit 5 uses the currently set automatic gain control circuit (AG
It is checked whether the gain Gpre of C) is smaller than the set maximum gain Gmax (step S5).

The gain Gpre currently set by the exposure determination circuit 5
Is smaller than the set maximum gain Gmax.
Sets the gain of the signal processing circuit 9 higher than the current gain (step S5-1).

Also, the currently set gain Gpre is equal to the set maximum gain Gm
If it has reached ax, it is determined that the limit of the exposure adjustment by the exposure determination circuit 5 has been exceeded, and the exposure determination circuit 5 displays a low-luminance warning on a display lamp or EVF 6 (not shown). Then, the currently set exposure value, that is, the shutter time and the gain value of the AGC circuit are maintained (step S
6).

Next, in step S3, when the signal output level of the CCD 4 is larger than a predetermined appropriate value, that is, when the subject has high luminance, the exposure determination circuit 5 sets the shutter time so that the shutter time becomes high. (Step S3 → S1
1 → S11-1). Only when the shutter time reaches the settable maximum time, the exposure determination circuit 5
However, the aperture value is changed so that the aperture is properly closed (step S12 → S12-1). Note that instead of the aperture, AG
It goes without saying that the gain of the C circuit may be adjusted. Further, when the current aperture value reaches the maximum value Amax determined from the degree of image quality deterioration due to a diffraction phenomenon or the like, the exposure determination circuit 5 issues a high luminance warning and maintains the current exposure setting value (step S13).

By such a procedure, the subject image can be displayed at a constant brightness according to the brightness.

Then, when the operator presses a shutter button (not shown) to perform photographing, a recording signal generated by pressing the shutter button is sent to the exposure determination circuit 5. Then, the exposure determination circuit 5 determines the brightness of the subject, that is, CC
Depending on the D4 signal output, predetermined aperture value, shutter speed, determine the exposure constant and the exposure amount E _V such AGC setpoint. The characteristic in which the relationship between the shutter time, the aperture, and the AGC set value is predetermined is called an AE diagram, which is determined by a calculation formula or stored in advance in the above-described read-only memory provided in the exposure determination circuit 5. You can keep.

As described above, the exposure constant and the exposure amount are determined by the exposure determination circuit 5.
, The exposure determination circuit 5 instructs the determined exposure constant to the aperture control circuit 3, the drive circuit 8, and the signal processing circuit 9 (steps S7 to S8).

After the exposure conditions are set as described above, the image signal photoelectrically converted by the CCD 4 is sent to the image recording circuit via the signal processing circuit 9 and recorded on the recording medium.

Note that the control value on the long-time side during shooting is not the minimum shutter speed set above, but the dark current unevenness that occurs in the CCD 4 during camera shake, subject shake or long-time exposure, and image quality deterioration due to the gain amplifier in the AGC amplifier. Factors such as are taken into account. Then, after the end of the photographing, the procedure after step S1 is repeated again to execute the fixed order.

In the present embodiment, the brightness of the subject was measured based on the magnitude of the signal output of the CCD 4, but as shown in FIG. 4, the exposure value was determined according to the photometric output of the photometric sensor 10 as shown in FIG. Is also good.

As described above, in this embodiment, the exposure amount of the CCD in the display state of the EVF is adjusted by the driving speed of the CCD, that is, the shutter speed, so that the aperture can be fixed to the open state. Therefore, the aperture is narrowed down at the time of photographing, so that the depth of field becomes large, and the photographing result becomes clearer than the image displayed on the electronic viewfinder before photographing. Further, in the present embodiment, when the exposure amount exceeds the range in which the exposure amount can be adjusted by changing the shutter speed, the adjustment of the aperture and the gain of the AGC are also performed, so that the range of the adjustable exposure amount is increased. I do. Further, in this embodiment, since the exposure amount can be adjusted according to the shutter speed, there is no need to provide a diaphragm mechanism,
In a camera where miniaturization is important, it is effective for further miniaturization.

[Effects of the Invention] As described above, according to the present invention, the aperture is closed and released before the release means is operated, and the depth of field when capturing a still image is changed to the depth of field when capturing a moving image. By performing control so that the depth becomes deeper, the recorded image becomes clearer, and when performing focus adjustment before capturing a still image, the depth of field is smaller when capturing a moving image than when capturing a still image. Focus adjustment can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of the configuration of the embodiment of the present invention, FIG. 2 is a block diagram showing an example of a specific configuration of the embodiment of the present invention, and FIG. 3 is an exposure determining circuit 5 of the embodiment of the present invention. FIG. 4 is a block diagram showing a configuration of a second embodiment of the present invention. Reference numeral 100: aperture, 101: imaging means, 101 ': supply means, 102: display means, 103: recording means, 104: photometric means, 105: control means, 2: aperture mechanism, 3: aperture control circuit, 4: CCD, 5 ...
Exposure determination circuit, 6: EVF, 7: recording circuit, 8: drive circuit, 9: signal processing circuit.

Claims (1)

(57) [Claims] A stop for limiting the amount of incident light; an imaging means for photoelectrically converting light incident through the stop; a release means; and a preset means in response to an operation of the release means. Aperture value, a still image capturing control unit that captures a still image with an exposure time, and the aperture is opened before the release unit is operated,
A moving image capturing control unit for controlling the accumulation time of the image capturing unit in response to the brightness of the subject; and displaying a moving image obtained from the image capturing unit by controlling the image capturing unit by the moving image capturing control unit. A still image pickup apparatus, comprising: display means; and wherein the depth of field when capturing a still image is made deeper than the depth of field when capturing a moving image.