JP2003069891A - Electronic still camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic still camera by which photographing is performed by effectively utilizing a little remaining amount of a battery concerning the electronic still camera to be used with the battery as a power source. SOLUTION: The electronic still camera is provided with a photographing means for obtaining image data corresponding to a subject image by picking up the image of the subject, the battery for supplying a driving voltage to the photographing means, a voltage lowering amount detecting means for detecting a voltage lowering amount in the battery while driving the photographing means and a driving method changing means for changing a method for driving the photographing means in response to the voltage lowering amount which is detected by the voltage lowering amount detecting means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera that uses a battery (including a dry battery and a rechargeable battery) as a power source.

[0002]

2. Description of the Related Art In an electronic camera using a battery as a power source, it is known that the amount of voltage drop at the time of shooting increases as the remaining amount of the battery decreases. FIG. 5 is a diagram showing a change in the amount of voltage drop at the time of shooting with a decrease in the remaining amount of the battery. From FIG. 5, it can be seen that the voltage drop amount at the n-th shooting in which the output voltage of the battery in the standby state has dropped is considerably larger than the voltage drop amount at the first shooting.

Therefore, in the conventional electronic camera, photographing is prohibited in a state where the remaining amount of the battery has a margin (for example, in a state where the output voltage of the battery in the standby state becomes Vn in FIG. 5).

[0004]

By the way, the power consumption of the image pickup device provided in the electronic camera largely depends on the driving frequency thereof, and the power consumption at the time of photographing is reduced by lowering the drive frequency of the image pickup device. be able to. That is, even if the remaining battery level is low, if the drive frequency of the image pickup device is lowered, there is a high possibility that further shooting can be performed.

However, in the conventional electronic camera, even if photographing is possible by lowering the driving frequency of the image pickup device as described above, the photographing function is completely stopped,
It was not easy to use. Therefore, an object of the present invention is to provide an electronic camera capable of taking a picture by effectively utilizing a small remaining amount of a battery.

[0006]

According to another aspect of the present invention, there is provided an electronic camera having a photographing means for photographing a subject image to obtain image data corresponding to the subject image, and a driving voltage to the photographing means. A battery, a voltage drop amount detecting means for detecting a voltage drop amount of the battery when the image taking means is driven, and a voltage drop amount of the image taking means according to the voltage drop amount detected by the voltage drop amount detecting means. And a driving method changing means for changing the driving method.

Note that the photographing means described in claim 1 may have a function of recording the acquired image data in a predetermined recording medium. An electronic camera according to a second aspect is the electronic camera according to the first aspect, wherein the driving method changing means is configured to operate the photographing means in accordance with an increase in a voltage drop amount detected by the voltage drop amount detecting means. It is characterized in that the driving method is changed to a driving method with a lower driving voltage than the normal driving method.

The electronic camera according to claim 3 is the electronic camera according to claim 1.
Alternatively, in the electronic camera according to claim 2, the photographing means includes a plurality of constituent members that are driven in a predetermined order, and the voltage drop amount detecting means includes the battery when each of the constituent members is driven. Is detected. In addition, as a constituent member that constitutes the photographing means, a mechanism portion such as a mirror and a shutter, an image sensor that reads out signal charges generated by a plurality of pixels to generate image data, and image data in a predetermined recording medium. It is also possible to include a recording unit for recording in.

An electronic camera according to a fourth aspect is the electronic camera according to the first aspect.
Alternatively, in the electronic camera according to claim 2, the voltage drop amount detecting means detects the voltage drop amount of the battery based on the output voltage of the battery.
An electronic camera according to a fifth aspect is the electronic camera according to the third aspect, further comprising a voltage conversion member that converts an output voltage of the battery into a voltage for driving each constituent member of the photographing unit. It is characterized in that the voltage drop amount detecting means detects the voltage drop amount of the battery when each of the constituent members is driven, based on the output voltage of the voltage conversion member.

An electronic camera according to a sixth aspect is the electronic camera according to the first aspect.
The electronic camera according to claim 5, further comprising a notification unit that notifies the operator that the drive method of the image capturing unit has been changed by the drive method changing unit. . The electronic camera according to claim 7, wherein an image capturing unit that acquires image data corresponding to a subject image through an image sensor that reads out signal charges generated by a plurality of pixels to generate image data, and the image capturing unit. A battery for supplying a drive voltage to the device, a voltage drop amount detecting means for detecting a voltage drop amount of the battery when the image sensor is driven, and a driving time of the image sensor in a state where the voltage of the battery shows the maximum. A reference amount that indicates the amount of voltage drop of
The latest voltage drop amount detected by the voltage drop amount detecting means is compared, and when the increase rate of the latest voltage drop amount with respect to the reference amount exceeds a predetermined value, the driving method of the image pickup device is set to a normal value. And a driving method changing means for changing the driving frequency to a driving method lower than the driving method.

According to another aspect of the present invention, there is provided an electronic camera.
In the electronic camera described in [1], the driving method changing unit determines a reduction rate of the driving frequency of the imaging unit based on the increase rate. The electronic camera according to claim 9, wherein an image capturing unit that acquires image data corresponding to a subject image via an image sensor that reads out signal charges generated by a plurality of pixels to generate image data, and the image capturing unit. A battery for supplying a drive voltage to the device, a voltage drop amount detecting means for detecting a voltage drop amount of the battery when the image sensor is driven, and a driving time of the image sensor in a state where the voltage of the battery shows the maximum. When a reference amount indicating the amount of voltage drop and a latest voltage drop amount detected by the voltage drop amount detecting means are compared, and an increase rate of the latest voltage drop amount with respect to the reference amount exceeds a predetermined value. And a driving method changing means for changing the driving method of the image pickup device to a driving method for thinning out signal charges from some pixels to generate image data.

An electronic camera according to a tenth aspect of the present invention is the electronic camera according to the ninth aspect, wherein the driving method changing means determines a thinning rate of signal charge reading based on the increasing rate. .

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a functional block diagram of an electronic camera corresponding to the first and second embodiments. In FIG. 1, the electronic camera 10 includes a CPU 11 and a lens 1.
2, mechanism section 13 such as mirror and shutter, image sensor 1
4, analog signal processing unit 15, A / D conversion unit 16, TG
(Timing Generator) 17,
Digital signal processing unit 18, compression recording unit 19, motor 2
0, operation unit 21 corresponding to a release button, DC-D
The C converter 22 and the battery 23 are provided. Also,
A removable memory card (card-shaped removable memory) 24 is loaded in the electronic camera 10.

In the electronic camera 10 having such a structure, the lens 12 and the mechanism portion 13 are driven via the motor 20 based on an instruction from the CPU 11. Image sensor 1
An optical image is formed on the lens 4 through the lens 12 and the mechanism unit 13. The image sensor 14 generates a signal charge corresponding to the optical image by an internal pixel, reads the signal charge, and generates analog image data. Further, the analog signal processing unit 15 performs predetermined signal processing on the image data generated by the image sensor 14, and the A / D conversion unit 16 digitally processes the image data subjected to the signal processing by the analog signal processing unit 15. Turn into. The timing of driving the image pickup device 14, the analog signal processing unit 15, and the A / D conversion unit 16 is controlled by the TG 17 based on an instruction from the CPU 11.

The digital signal processing section 18 subjects the image data digitized by the A / D conversion section 16 to predetermined image processing (for example, gradation conversion and edge enhancement), and the compression recording section 19 The image data processed by the digital signal processing unit 18 is compressed into a predetermined format and recorded in the memory card 24. The digital signal processing unit 18 and the compression recording unit 19 as described above are driven based on an instruction from the CPU 11.

The CPU 11 gives an instruction to drive each of the above-mentioned units in accordance with an operation performed by the photographer through the operation unit 21, and supplies a drive voltage required for driving each unit to the DC-DC converter 22. Give instructions. Based on such an instruction from the CPU 11, the DC-DC converter 22 converts the output voltage of the battery 23 into a drive voltage for driving each unit in the electronic camera 10, and supplies the drive voltage to each unit.

Further, the DC-DC converter 22 notifies the output voltage of the battery 23 to the CPU 11, but the output voltage of the battery 23 is notified to the CPU 11 as digital data via an A / D conversion section (not shown). I shall. Hereinafter, the output voltage of the battery 23 notified to the CPU 11 in this manner will be referred to as a battery voltage.

By the way, the electronic camera 10 corresponding to the first and second embodiments is provided with a finder eyepiece window (not shown). Inside the viewfinder eyepiece window, a "non-photographable lamp" is provided to inform the photographer that photographing is impossible due to insufficient remaining battery 23. Also, inside the viewfinder eyepiece window, a "low speed mode execution lamp" for notifying the photographer that the "low speed mode" described later is being executed,
A "thinning-out mode execution lamp" is provided to notify the photographer that the "thinning-out mode" is being executed. Such a lamp is turned on according to an instruction from the CPU 11.

Here, the "low speed mode" is a mode in which the image pickup device 14, the analog signal processing section 15, the A / D conversion section 16 and the like are driven at a frequency lower than the driving frequency during normal photographing, The “thinning-out mode” means the image sensor 14
This is a mode in which signal charges are read out from some pixel columns in the vertical direction by thinning out. It should be noted that a plurality of "low-speed mode execution lamps" may be provided in association with the drive frequency reduction rate of each unit.
May be provided in association with the thinning rate.

<< Description of Operation of First Embodiment >> FIG. 2 is an operation flowchart of the first embodiment. In particular, FIG.
Shows the operation of the CPU 11 in a state in which a shooting mode for realizing still shooting is set. The operation of the first embodiment will be described below, but of the operations of the electronic camera 10, the operation of the CPU 11 shown in FIG. 2 will be described below, and description of other operations will be omitted.

First, the CPU 11 determines whether or not the release button has been pressed via the operation unit 21 (FIG. 2).
S1). The CPU 11 executes the processing of FIG. 2S1 as described above.
Repeat until the release button is pressed. And
When the release button is pressed, the CPU 11 causes the DC-D
It is determined whether or not the battery voltage notified from the C converter 22 is equal to or lower than the lower limit voltage Vs (S2 in FIG. 2).

Here, the lower limit voltage Vs is a voltage at which driving of the CPU 11 is expected to be difficult. For example, the lower limit voltage Vs is 1 of the battery voltage in the standby state when the battery 23 is fully charged. It can be / 2. When the battery voltage is equal to or lower than the lower limit voltage Vs, the CPU 11 turns on the above-mentioned “imaging disabled lamp” (FIG. 2S3), and ends the operation.

On the other hand, when the battery voltage exceeds the lower limit voltage Vs, the CPU 11 starts driving each part related to photographing and detects the maximum voltage drop amount X (S4 in FIG. 2). Here, the maximum voltage drop amount X is the maximum voltage drop amount among the voltage drop amounts at the time of driving each unit related to shooting. For example, the CPU 11 drives the respective units as shown in FIG. 3 based on the battery voltage notified from the DC-DC converter 22 (when the lens 12 and the mechanism unit 13 are driven by the motor 20, the charge of the image sensor 14 is changed). The amount of voltage drop at the time of reading, at the time of recording image data on the memory card 24, etc.) is detected, and the maximum voltage drop amount out of such voltage drop amounts is defined as the maximum voltage drop amount X. If a member (for example, a mirror of the mechanism unit 13) that can maximize the voltage drop during driving is known in advance, only the voltage drop during driving of the member is detected to determine the maximum voltage drop. The quantity X may be used.

Next, the CPU 11 causes the maximum voltage drop X
Is less than twice the reference amount X0 (Fig. 2
S5). Here, the reference value X0 is the amount of voltage drop when photographing is performed with the battery 23 fully charged.

When the maximum voltage drop amount X is less than twice the reference amount X0, the CPU 11 drives each part related to shooting in the normal shooting mode (S6 in FIG. 2). On the other hand, when the maximum voltage drop amount X is twice or more the reference amount X0, the CPU 11
Determines whether the maximum voltage drop amount X is less than four times the reference amount X0 (S7 in FIG. 2). Then, the CPU 11
When the maximum voltage drop amount X is more than twice the reference amount X0 and less than four times, the "low-speed mode execution lamp" described above is turned on (FIG. 2S8) and the drive frequency is 1 / normal.
In the low-speed mode, which is 2, each part related to shooting is driven (S9 in FIG. 2).

When the maximum voltage drop amount X is four times the reference amount X0 or more, the CPU 11 turns on the "low-speed mode execution lamp" (FIG. 2S10), and the drive frequency is the normal 1
In the low speed mode of / 4, each unit related to shooting is driven (S11 in FIG. 2). When the driving of each part is completed, C
PU11 performs the process of FIG. 2S1 again. As described above, the electronic camera 10 corresponding to the first embodiment is
By comparing the maximum voltage drop amount X, which is the maximum voltage drop amount that occurs during the shooting process, with twice the reference amount X0, it is determined whether normal shooting is possible. When the maximum voltage drop amount X is more than twice the reference amount X0, it is determined that normal shooting is impossible due to the increase in the voltage drop amount due to the decrease in the remaining amount of the battery 23, and is involved in shooting. The driving frequency of each part is gradually reduced.

The driving with the driving frequency lowered as described above can reduce the power consumption as compared with the normal photographing. That is, the power consumption at the time of shooting decreases in proportion to the reduction rate of the drive frequency of each unit. Therefore, according to the electronic camera 10 corresponding to the first embodiment, the battery 23
Even when the amount of voltage drop increases as the remaining amount of the battery decreases, it is possible to perform shooting.

Further, the electronic camera 10 corresponding to the first embodiment turns on the "low-speed mode execution lamp" while driving in the low-speed mode in which the drive frequency is lowered, so that normal photographing is performed. The photographer who desires can promptly take measures such as replacement of the battery 23. In the first embodiment, the maximum voltage drop amount X is 2 which is the reference amount X0.
It is two times or more and less than four times, and the maximum voltage drop amount X is four times or more of the reference amount X0. However, the drive frequency of each part may be lowered steplessly according to the ratio of the maximum voltage drop amount X to the reference amount X0.

<< Description of Operation of Second Embodiment >> FIG. 4 is an operation flowchart of the second embodiment. In particular, FIG.
Shows the operation of the CPU 11 in a state in which a shooting mode for realizing still shooting is set. The operation of the second embodiment will be described below, but of the operations of the electronic camera 10, the operation of the CPU 11 shown in FIG. 4 will be described below, and description of the other operations will be omitted. In addition, the processes of FIGS. 4S1 to 4S7 are the same as those of FIGS. 2S1 to 2S8.
Corresponding to the first embodiment and is the same as the first embodiment. Therefore, the description will be simplified below.

When the release button is pressed (YES side in FIG. 4S1), the CPU 11 performs the same operation as in the first embodiment.
It is determined whether the battery voltage notified from the DC-DC converter 22 is equal to or lower than the lower limit voltage Vs (FIG. 4S).
2). Then, when the battery voltage is equal to or lower than the lower limit voltage Vs, the CPU 11 performs the same operation as in the first embodiment.
The “non-shooting lamp” is turned on (S3 in FIG. 4), and the operation ends.

On the other hand, when the battery voltage exceeds the lower limit voltage Vs, the CPU 11 starts driving each part related to photographing and detects the maximum voltage drop amount X (S4 in FIG. 4), as in the first embodiment. It is determined whether the maximum voltage drop amount X is less than twice the reference amount X0 (S5 in FIG. 4).

Then, the CPU 11 causes the maximum voltage drop amount X
Is less than twice the reference amount X0, each unit related to shooting is driven in the normal shooting mode as in the first embodiment (S6 in FIG. 4). On the other hand, when the maximum voltage drop amount X is twice or more the reference amount X0, the CPU 11 determines whether the maximum voltage drop amount X is less than four times the reference amount X0, as in the first embodiment. (Fig. 4 S7).

The CPU 11 then determines the maximum voltage drop amount X
Is more than twice the reference amount X0 and less than four times, the above-described “thinning-out mode execution lamp” is turned on (S8 in FIG. 4), and the thinning-out rate is ½ in the thinning-out mode. Each part is driven (S9 in FIG. 4). Also, CPU
When the maximum voltage drop amount X is four times or more of the reference amount X0, 11 turns on the "thinning mode execution lamp" and the "low speed mode execution lamp" (FIG. 4S10), and the thinning rate is 1 /.
The thinning-out mode 2 and the low-speed mode in which the driving frequency is ½ of the normal frequency drives each part related to shooting (FIG. 4S).
11).

That is, the electronic camera 10 corresponding to the second embodiment is the electronic camera 1 corresponding to the first embodiment.
Similar to 0, when the maximum voltage drop amount X is equal to or more than twice the reference amount X0, it is determined that normal photographing is impossible due to the increase in the voltage drop amount due to the decrease in the remaining amount of the battery 23. When the maximum voltage drop amount X is equal to or more than twice the reference amount X0 and less than four times the reference amount X0, the thinning rate drives each unit related to shooting in the thinning mode of 1/2, and the maximum When the voltage drop amount X is four times or more of the reference amount X0, the thinning-out rate is reduced to ½ in addition to the low-speed mode in which the driving frequency is reduced to ½ to drive the respective units involved in photographing.

Driving in such a thinning mode or a low speed mode can reduce power consumption as compared with normal photographing. That is, the power consumption at the time of shooting decreases in proportion to the thinning rate and the reduction rate of the drive frequency of each unit related to the shooting.

Therefore, according to the electronic camera 10 corresponding to the second embodiment, it is possible to take an image even when the amount of voltage drop increases as the remaining amount of the battery 23 decreases. Further, the electronic camera 10 corresponding to the second embodiment turns on the “thinning-out mode execution lamp” when driving in the thinning-out mode, and “when driving in the low-speed mode”. Since the "low-speed mode execution lamp" is turned on, a photographer who desires normal photographing can promptly take measures such as replacement of the battery 23.

In the second embodiment, when the maximum voltage drop amount X is four times or more of the reference amount X0, the thinning rate is reduced to 1 /.
2 and the reduction rate of the driving frequency of each part related to photographing is halved, but if the power consumption at the time of photographing can be reduced to the same extent as in this case, the thinning rate and the driving frequency can be reduced. The reduction rate may be any combination of values.

In the second embodiment, the maximum voltage drop amount X is more than twice the reference amount X0 and less than four times the reference amount X0, and the maximum voltage drop amount X is the reference amount. X0
The power consumption at the time of shooting is reduced step by step in two steps, that is, four times or more, and the thinning rate and the driving frequency reduction rate of each part related to shooting are combined with various values. As a result, the power consumption at the time of shooting can be reduced steplessly according to the ratio between the maximum voltage drop amount X and the reference amount X0.

Further, in the above-described first and second embodiments, when it is determined that the maximum voltage drop amount X is more than twice the reference amount X0 and normal photographing is impossible. Although different processing is performed, the photographer may be able to set which processing is to be performed. Also, the first
In the first embodiment and the second embodiment, it is determined whether or not photographing is impossible by comparing the battery voltage and the lower limit voltage Vs. However, it is determined whether or not photographing is impossible. May be performed using the maximum voltage drop amount X.
For example, when the maximum voltage drop amount X is 5 times or more of the reference amount X0, it can be determined that photographing is impossible.

Furthermore, in the first and second embodiments, the maximum voltage drop amount X is calculated based on the battery voltage.
Is detected, the maximum voltage drop X is DC-DC
It may be detected based on the drive voltage supplied from the converter 22 to each unit. In addition, the first embodiment and the second
In the embodiment of the present invention, the lighting of various lamps provided inside the viewfinder eyepiece window informs the photographer that photography is impossible and the type of mode being executed. Instead of this, a mark corresponding to each lamp may be displayed on the liquid crystal display panel.

[0042]

As described above, according to the first aspect of the invention, since the driving method of the photographing means can be changed according to the voltage drop amount of the battery, for example, the voltage drop amount of the battery increases. Then, even if it becomes impossible to drive the photographing means by the normal driving method, it is possible to drive the photographing means by another driving method.

According to the second aspect of the present invention, the driving method of the photographing means can be changed to a driving method with a smaller driving voltage than the normal driving method according to an increase in the voltage drop amount of the battery. Therefore, according to the invention of claim 2,
Even if the amount of voltage drop of the battery increases and it becomes impossible to drive the photographing means by a normal driving method, the photographing means can be reliably driven by the driving method with a small driving voltage.

Further, in the invention described in claim 3, when the photographing means is composed of a plurality of constituent members driven in a predetermined order, the voltage drop amount of the battery when each constituent member is driven is detected. Therefore, according to the invention described in claim 3, it is possible to improve the detection accuracy of the voltage drop amount of the battery. Further, in the invention described in claim 4, the voltage drop amount of the battery is detected based on the output voltage of the battery. In the invention described in claim 5, the photographing means is driven by a plurality of constituent members in a predetermined order. In the case of (1), the voltage drop amount of the battery is detected based on the output voltage of the voltage conversion member that converts the output voltage of the battery into a voltage for driving each component. Therefore, according to the inventions of claims 4 and 5, the voltage drop amount of the battery can be reliably detected.

Further, in the invention described in claim 6, since it is possible to notify the operator that the driving method of the photographing means has been changed, the operator can drive the photographing means by a normal driving method, for example. If desired, actions such as battery replacement can be taken promptly. Further, according to the invention described in claims 7 to 10, even if the image pickup device cannot be driven by the normal driving method due to an increase in the voltage drop amount, the driving method with the small driving voltage is used. The image pickup element can be driven reliably.

Therefore, according to the electronic camera of the present invention, even when the remaining amount of the battery is low, the remaining amount can be effectively used for shooting.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an electronic camera.

FIG. 2 is an operation flowchart of the first embodiment.

FIG. 3 is a diagram showing a voltage drop amount at the time of photographing.

FIG. 4 is an operation flowchart of the second embodiment.

FIG. 5 is a diagram showing a change in the amount of voltage drop at the time of shooting due to a decrease in battery voltage.

[Explanation of symbols]

10 electronic camera 11 CPU 12 lenses 13 Mechanism 14 Image sensor 15 Analog signal processor 16 A / D converter 17 TG 18 Digital signal processor 19 Compressed recording unit 20 motor 21 Operation part 22 DC-DC converter 23 Battery 24 memory card

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) // H04N 101: 00 H04N 101: 00

Claims (10)

[Claims] 1. A photographing means for acquiring image data corresponding to the subject image by picking up the subject image, a battery for supplying a driving voltage to the photographing means, and a battery for driving the photographing means. A voltage drop amount detecting means for detecting the voltage drop amount of the battery; and a driving method changing means for changing the driving method of the photographing means according to the voltage drop amount detected by the voltage drop amount detecting means. An electronic camera characterized by. 2. The electronic camera according to claim 1, wherein the driving method changing unit normally sets the driving method of the photographing unit according to an increase in a voltage drop amount detected by the voltage drop amount detecting unit. The electronic camera is characterized in that the driving method is changed to a driving method with a smaller driving voltage than the driving method. 3. The electronic camera according to claim 1, wherein the photographing unit is composed of a plurality of constituent members that are driven in a predetermined order, and the voltage drop amount detecting unit is one of the constituent members. An electronic camera characterized by detecting the amount of voltage drop of the battery when each is driven. 4. The electronic camera according to claim 1, wherein the voltage drop amount detection unit detects the voltage drop amount of the battery based on the output voltage of the battery. camera. 5. The electronic camera according to claim 3, further comprising a voltage conversion member that converts an output voltage of the battery into a voltage for driving each constituent member of the photographing unit, the voltage drop. The electronic camera, wherein the amount detecting means detects the amount of voltage drop of the battery when each of the constituent members is driven, based on the output voltage of the voltage converting member. 6. The electronic camera according to claim 1, wherein the driving method changing unit notifies an operator that the driving method of the photographing unit has been changed. An electronic camera characterized by having. 7. A photographing means for acquiring image data corresponding to a subject image through an image sensor for reading out signal charges generated by a plurality of pixels to generate image data, and a driving voltage is supplied to the photographing means. A battery, a voltage drop amount detecting means for detecting a voltage drop amount of the battery when the image pickup device is driven, and a voltage drop amount when the image pickup device is driven in a state where the voltage of the battery shows a maximum. The reference amount shown is compared with the latest voltage drop amount detected by the voltage drop amount detecting means, and when the increase rate of the latest voltage drop amount with respect to the reference amount exceeds a predetermined value, the image sensor is driven. An electronic camera comprising: a driving method changing unit that changes the driving method to a driving method in which a driving frequency is lower than that of a normal driving method. 8. The electronic camera according to claim 7, wherein the driving method changing unit determines a reduction rate of a driving frequency of the imaging unit based on the increase rate. 9. An imaging device for acquiring image data corresponding to a subject image through an imaging device which reads out signal charges generated by a plurality of pixels to generate image data, and supplies a drive voltage to the imaging device. A battery, a voltage drop amount detecting means for detecting a voltage drop amount of the battery when the image pickup device is driven, and a voltage drop amount when the image pickup device is driven in a state where the voltage of the battery shows a maximum. The reference amount shown is compared with the latest voltage drop amount detected by the voltage drop amount detecting means, and when the increase rate of the latest voltage drop amount with respect to the reference amount exceeds a predetermined value, the image sensor is driven. An electronic camera comprising: a driving method changing means for changing the method to a driving method for thinning out signal charges from some pixels to generate image data. 10. The electronic camera according to claim 9, wherein the driving method changing unit determines a thinning rate of reading signal charges based on the increase rate.