JP2000092380A - Camera, its exposure control method and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain real time display of a through-image even under a dark condition. SOLUTION: In the case that an exposure detected by using a CCD is less than a reference value when a through-image is displayed before photographing (NO in both S1 and S2), a shutter speed is sequentially decreased (S3). When the exposure is still less than the reference value even if the shutter speed is decreased up to a minimum speed for display (YES in S2), the exposure is secured by increasing a gain of an output signal of the CCD (S4) to prevent frame missing of the through-image. When the shutter is depressed and the gain at that point of time is not a default (NO in S6), a calculation to convert a gain increment at that point of time into an exposure time (shutter speed) is conducted (S8). Then the gain is restored to the default (S9) to prevent a noise from being mixed in a photographed image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera device, an exposure control method therefor, and a recording medium on which a program is recorded.

[0002]

2. Description of the Related Art Conventionally, for example, in a digital camera, the brightness of an object image in a frame is measured by using a CCD which is a solid-state image sensor, and an aperture value and a shutter value are determined based on an appropriate exposure value corresponding to the measured light value. Speed, CC
Gain value such as D (amplification rate of imaging signal output by CCD)
Is set (hereinafter referred to as AE control). As the shutter, an electronic shutter whose exposure time is the accumulation time of signal charges in the CCD is generally used. In addition, in such a digital camera, when in a shooting preparation state in which a predetermined mode such as a recording mode is set, a subject image is sequentially captured regardless of a shutter operation and displayed on a liquid crystal monitor as a through image, and a viewfinder is displayed on the liquid crystal monitor. Many have functions.

[0003]

However, in the AE control described above, the exposure time is lengthened when photographing under dark conditions. For example, in shooting fireworks, the shutter speed is set to about 1 second. In this case, the number of images (number of frames) per unit time is reduced. Therefore, it is not possible to display a through image on the LCD monitor in real time (dropped frames), and it takes time to determine the composition,
There is a problem that the usability is extremely reduced, for example, giving the photographer a sense of incongruity.

The present invention has been made in view of such a conventional problem, and has been made in view of the above circumstances. A camera apparatus capable of real-time display of a through-the-lens image even in a dark condition, an exposure control method thereof, and a recording in which a program is recorded The purpose is to provide a medium.

[0005]

According to a first aspect of the present invention, there is provided a display device for displaying an image screen based on an imaging signal supplied from an imaging device for imaging a subject image. And a camera device that records image data generated from the imaging signal in response to a shooting operation,
Exposure control means for controlling the exposure time of the image sensor in accordance with the brightness of the subject image and for increasing or decreasing the gain of the image signal around a reference value, and an extension side of the exposure time by the exposure control means. Limiting means for limiting a control range to a predetermined reference time; and responding to the photographing operation in a suppressed state in which the exposure time is suppressed to the reference time, controlling the gain control value by the exposure control means to the reference value. A photographing control unit that changes the exposure time, which has been suppressed to the reference time, to the value, and extends the exposure time according to an increase in the gain from the reference value immediately before responding to the photographing operation. did.

In such a configuration, the control range on the extension side of the exposure time by the exposure control means is always limited to the predetermined reference time by the restriction means, and the exposure time is always suppressed to the predetermined reference time. For this reason, by setting the predetermined reference time to be shorter than the exposure time in which the display interval of the imaging screen based on the imaging signal is noticeable, the frame drop of the imaging screen displayed on the display means even under dark conditions. Can be prevented. Moreover, when there is a shooting operation,
Since the gain is reduced to the reference value by the photographing control means, it is possible to prevent noise from being mixed into the recorded image screen. At the same time, since the exposure time is extended by the photographing control means in accordance with the increase in the gain just before the photographing operation with respect to the reference value, the exposure state when the proper exposure is obtained even under dark conditions And an appropriate exposure time for reproducing is easily obtained.

[0007] In addition, in the invention of claim 2,
A focusing unit for performing a focusing operation for driving a focus lens based on the image pickup signal is provided. In such a configuration, imaging is performed while moving the focus lens on the optical axis.However, since the control range on the extension side of the exposure time of the image sensor is always limited to a predetermined reference time,
The time required for imaging at each optical axis position can be shortened even in a dark condition.

According to a third aspect of the present invention, there is provided a display means for displaying an image pickup screen based on an image pickup signal supplied from an image pickup means for picking up an image of a subject. In an exposure control method for a camera device that records image data generated from a camera, the exposure time of the image sensor is controlled according to the brightness of the subject image, and the gain of the image signal is controlled to increase or decrease around a reference value. ,
The control range on the extension side of the exposure time is limited to a predetermined reference time, and while the exposure time is suppressed to the reference time, the control value of the gain is changed to the reference value in response to a shooting operation. The exposure time, which has been suppressed to the reference time, is extended in accordance with an increase in the gain from the reference value immediately before responding to the photographing operation.

In this method as well, even under dark conditions, it is possible to prevent frame dropping of the imaged screen displayed on the display means, prevent noise from being mixed into the recorded imaged screen, and to set an appropriate Exposure time is easily obtained.

According to a fourth aspect of the present invention, there is provided a display means for displaying an image pickup screen based on an image pickup signal supplied from an image pickup means for picking up an image of a subject. A computer provided in a camera device that records the image data generated from the camera, controls the exposure time of the image sensor according to the brightness of the subject image, and controls the gain of the image signal to increase or decrease around a reference value. Exposure control means, restriction means for restricting the control range on the extension side of the exposure time by the exposure control means to a predetermined reference time, and for the photographing operation in a suppressed state in which the exposure time is suppressed to the reference time. In response, the control value of the gain by the exposure control means is changed to the reference value, and the exposure time suppressed by the reference time is changed immediately before responding to the photographing operation. And a recording medium for recording a program to function on a photographing control means for extending in response to increase relative to the reference value of the gain.

By using the program recorded on the recording medium, the above-described camera device can perform the same operation as the camera device of the first aspect.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram schematically showing an electrical configuration of a camera device 1 according to the present invention.

That is, the digital camera 1 has a CCD 2 which is a solid-state image pickup device for picking up a subject image formed by an optical system (not shown) and outputting it as an image pickup signal, and converts the picked-up image to JPEG format. The MPU 3 is mainly provided with an image processing function such as.
An optical image of the subject is formed on the light receiving surface of the CCD 2 through the fixed lens 4, the focus lens 5, and the diaphragm 6.
The focus lens 5 is composed of an AF motor or the like, and is held by a drive mechanism 7 that constitutes a focusing unit of the present invention.
When a drive signal output from the AF driver 8 is supplied to the drive mechanism 7 according to the control signal from the controller 3, a focusing operation of moving back and forth on the optical axis is performed. The aperture 6 is driven by a drive signal generated by an aperture drive unit 9 based on a control signal from the MPU 3 and adjusts the light amount of the subject image incident on the CCD 2.

A timing generator (TG) 10 for generating a timing signal is connected to the MPU 3. A V driver 11 (vertical driver) drives the CCD 2 based on the timing signal generated by the TG 10. An analog imaging signal corresponding to the luminance of the subject image is output from the CCD 2 and sent to the unit circuit 12. The unit circuit 12 includes a CDS that holds an image signal output from the CCD 2 and a gain adjustment amplifier (AG) that is an analog amplifier supplied with the image signal from the CDS.
C), and an A / D converter (AD) for converting the image signal amplified and adjusted by the gain adjustment amplifier into image data. The output signal of the CCD 2 is sampled by adjusting the black level here to obtain a digital signal. Is sent to MPU3. The transmitted digital signal (imaging signal) is a DRAM1
3 is temporarily stored in the flash memory (FLASH) 14 after being subjected to various types of image processing by the MPU 3 and finally as a compressed video signal. The stored video signal is read by the MPU 3 as necessary, and is generated into a digital video signal or an analog video signal through processing such as expansion processing and addition of a luminance signal and a color signal.

Further, the MPU 3 includes an MROM 15, a power supply circuit 16, an operation key unit 17, and a TFT liquid crystal monitor 1.
8. Strobe 19 is connected. The MROM 15 is
Program RO in which the operation program of MPU3 is recorded
M, that is, the recording medium of the present invention. Also, MROM
Reference numeral 9 stores program AE data and the like constituting a program diagram showing a combination of an aperture value (F) corresponding to an appropriate exposure value (EV) at the time of shooting and a shutter speed. The MPU 3 functions as an exposure control unit, a limiting unit, and a photographing control unit of the present invention by operating the built-in RAM as a working memory according to the operation program, and according to the program diagram, the charge accumulation time of the CCD 2 and the aperture stop. 6, the gain setting of the gain adjustment amplifier (AGC) of the unit circuit 12, and the like. The charge accumulation time set by the MPU 3 is supplied as a shutter pulse to the V driver 11 via the TG 10, and the V driver 11 drives the CCD 2 in accordance therewith, thereby controlling the charge accumulation time, that is, the exposure time. That is, the CCD 2 functions as an electronic shutter.
The operation program stored in the MROM 9 includes a program relating to autofocus control. Based on the program, the MPU 3 compares the images of a plurality of frames taken while driving the focus lens 5 to focus. Perform alignment. That is, TTL
Controls autofocus by the method.

The operation key section 17 includes a power-on / off button.
A power key operated when turned off, a mode switching key for switching between a recording mode (REC mode) and a playback mode (PLAY mode), and a video capture key operated for storing an image captured in the flash memory 14 in the recording mode ( Various keys such as a shutter are provided. The TFT liquid crystal monitor 18 displays sequentially captured images as a through image in the recording mode, and displays an image based on an analog video signal generated from the image data recorded in the flash memory 14 in the reproduction mode. The strobe light 19 is driven as necessary to emit an auxiliary light when operating the image capturing key (at the time of photographing). Note that the program data and the like stored in the above-described MROM 15 may be separately provided in a fixed manner, or may be stored in another recording medium such as an IC card that can be detachably attached, if the recorded contents can be retained. The configuration may be such that the program data is recorded from another device such as a personal computer.

Next, the operation of the camera device 1 having the above configuration will be described with reference to the flowchart of FIG. This flowchart relates to exposure control by the MPU 3 in a state where the recording mode is set after the power is turned on. However, this flowchart assumes only a case where shooting is performed without using a strobe under dark conditions where it is necessary to fully open the aperture outdoors at night or the like.

In the following, when the recording mode is set, the digital camera 1 integrates the exposure amount detected by using the CCD 2, specifically, the brightness of the image signal converted into a digital signal by the unit circuit 12. It is determined whether or not the amount of exposure obtained is smaller than the reference value (step S
1). At this time, if it is not less than the reference value, the process proceeds to step S5 described below, and if it is less than the reference value, it is further determined whether or not the shutter speed is the minimum speed for display (step S2). The shutter speed is a speed corresponding to a predetermined reference time (exposure time) in the present invention, and is a speed programmed in advance (1/10 second in the present embodiment). If the shutter speed has not been set to the minimum display speed yet, the process proceeds to step S3, where the shutter speed is reduced by one step, and then returns to step S1 until the shutter speed becomes the minimum display speed. Steps S1 to S3 are repeated.

Eventually, while the exposure amount is less than the reference value,
When the shutter speed is reduced to the minimum speed for display, that is, the minimum exposure time (YES in step S2), the gain adjustment amplifier (AG) of the unit circuit 12 is turned on.
The gain of C) is increased (step S4), and the
Return to 1. Here, the default value of the gain before the increase is the reference value in the present invention, and is a value determined according to the characteristics of the CCD 2 and corresponding to the minimum speed. Further, if the exposure amount becomes equal to or more than the reference value and the determination result of step S1 becomes YES while the processes of step S1, step S2, and step S4 are repeated thereafter, the process proceeds to step S5 to determine whether or not the shutter is pressed. I do. If the shutter is not pressed, the process returns to step S1 and repeats the above-described processing.

That is, before the shutter is pressed, TF
While a through image is displayed on the T LCD monitor 18,
AE control is performed to always keep the shutter speed at the minimum speed and increase the gain to secure exposure. For this reason, if the minimum speed is set to about 1/10 second as in the present embodiment, it is possible to capture 10 frames of imaging screens per second, and to reduce the number of images captured per unit time so that dropping frames are not conspicuous. Number. Therefore, even in the case of shooting a fireworks display, for example, a live view image can be displayed on the TFT liquid crystal monitor 18 in real time, so that the composition can be easily determined without discomfort while watching the fireworks, and good usability can be secured. In addition,
Even if the minimum speed is not 1/10 second, the frame drop can be made inconspicuous if it is generally about 1/4 second to 1/10 second.

On the other hand, when the shutter is pressed and the actual photographing is performed (YES in step S5), it is first determined whether or not the gain value at that time remains the default value (step S5).
6). Here, when the value remains at the default value, that is, when the gain increasing process in step S4 has not been performed, shooting is performed with the shutter speed set in the normal AE operation (step S4).
7) Exposure control processing for one shot is completed. If the decision result in the step S6 is NO and the gain value at that time is increased from the default value, the exposure time is calculated based on the increase amount of the gain value set immediately before the actual photographing with respect to the default value. (Step S
8). This calculation is to extend the exposure time by converting the amount of gain increase into the exposure time (shutter speed). Specifically,

(Equation 1) To determine the exposure magnification,

(Equation 2) To determine the photographing exposure time. Thereafter, the gain at that time is returned to the default value, and photographing is performed at the shutter speed of the photographing exposure time calculated here (step S8), and the exposure control process for one photographing is completed.

That is, when the shutter is pressed in a state where the shutter speed is suppressed to the minimum speed for display when displaying a through image, the exposure according to the exposure amount of the CCD 2 is performed irrespective of the increase in the gain described above. Since the time is set, it is possible to prevent a noise from being mixed in the shot image and shoot a good image. Also, an auxiliary light such as a strobe light is not required at the time of photographing. In addition, since the exposure time is determined based on the amount of increase of the gain value set to the default value immediately before, the appropriate exposure time that can reproduce the exposure state when the proper exposure was obtained can be easily obtained. Can be Therefore, the burden on the MPU 3 at the time of photographing is light, and a MPU 3 having the same processing capacity as that of the conventional MPU 3 can be used. For the same reason, it is convenient to change the operation program of the computer when an existing camera apparatus in which the AE control is performed by the computer performs the above-described exposure control processing.

In addition to the above, in the above-described exposure control, the shutter speed does not become lower than the predetermined minimum shutter speed for display, and the image pickup per unit time is performed even in a dark condition. Since a fixed number of sheets can be secured, the above-mentioned TTL
When performing autofocus control by the method, the time for capturing a plurality of images to be compared does not become long. Therefore, a constant speed can always be secured for the focus speed. This also ensures good usability.

[0024]

As described above, in the present invention,
By setting the reference time of the image sensor to be shorter than the exposure time at which the display interval of the imaging screen based on the imaging signal is noticeable, dropping of the imaging screen displayed on the display means is prevented even under dark conditions. It becomes possible. That is, real-time display of a through image can be performed. Therefore, the composition can be easily determined without discomfort while looking at the display screen of the display means even under dark conditions, and the usability under dark conditions can be improved. Further, since it is possible to prevent noise from being mixed in the recorded imaging screen, a good image can be taken. In addition, even when shooting under dark conditions, an appropriate exposure time can be easily obtained, so that it is possible to reduce operation processing related to exposure control during shooting in the camera device.

In addition to this, in a camera device provided with focusing means for performing a focusing operation for driving a focus lens based on an image pickup signal, the control range on the extension side of the exposure time of the image pickup element is always a predetermined value. Even when the focusing operation is performed under dark conditions, the time required for imaging at each optical axis position can be shortened, so that the focus detection speed under dark conditions is improved. Therefore, usability under dark conditions can be improved.

[0026]

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital camera showing an embodiment of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Digital camera 2 CCD 3 MPU 5 Focus lens 7 Drive mechanism 15 MROM

Claims (4)

[Claims] 1. A camera device having display means for displaying an imaging screen based on an imaging signal supplied from an imaging means for imaging a subject image, and recording image data generated from the imaging signal in response to a shooting operation. An exposure control means for controlling an exposure time of the image sensor in accordance with the brightness of the subject image, and controlling a gain of the imaging signal to increase or decrease around a reference value; and extending the exposure time by the exposure control means. Limiting means for limiting the control range on the side to a predetermined reference time, and controlling the gain control value by the exposure control means in response to the photographing operation in a suppressed state in which the exposure time is suppressed to the reference time. The exposure time is changed to the reference value, and the exposure time, which has been suppressed by the reference time, is extended according to an increase in the gain from the reference value immediately before responding to the photographing operation. A camera device, comprising: a longer shooting control means. 2. The camera device according to claim 1, further comprising a focusing unit that performs a focusing operation for driving a focus lens based on the imaging signal. 3. A camera device having display means for displaying an imaging screen based on an imaging signal supplied from an imaging means for imaging a subject image, and recording image data generated from the imaging signal in response to a shooting operation. In the exposure control method, while controlling the exposure time of the imaging element according to the brightness of the subject image, while controlling the gain of the imaging signal to increase or decrease around a reference value, the control range on the extension side of the exposure time While limiting the exposure time to the reference time and restricting the exposure time to the reference time, the control value of the gain was changed to the reference value in response to the photographing operation, and was suppressed to the reference time. An exposure control method comprising: extending an exposure time in accordance with an increase in the gain from the reference value immediately before responding to a shooting operation. 4. A camera device having display means for displaying an imaging screen based on an imaging signal supplied from an imaging means for imaging a subject image, and recording image data generated from the imaging signal in response to a shooting operation. An exposure control unit that controls an exposure time of the image sensor in accordance with the brightness of the subject image, and controls a gain of the image signal to increase or decrease around a reference value; Limiting means for limiting the control range on the extension side of the exposure time to a predetermined reference time; and in response to the photographing operation in a suppressed state in which the exposure time is suppressed to the reference time, the exposure control means The control value of the gain is changed to the reference value, and the exposure time suppressed by the reference time is compared with the reference value of the gain immediately before responding to the photographing operation. A recording medium on which is recorded a program for causing a photographing control means to extend in accordance with an increase in the amount.