Patent Description:
Biometrics using an iris, that is, iris recognition, is known. In iris recognition, the iris of a person to be authenticated is photographed using an imaging device, and features are extracted from the pattern of the photographed iris. When the person is authenticated, the extracted features are compared with the features registered in a database in advance, and a pass or fail decision is made based on a matching score. When registering a person to be authenticated, the extracted features are registered in a database.

When performing iris recognition, if the distance between the iris (i.e., a subject) of an object and a camera changes while the object is being photographed, the camera may not be able to take an image in focus. In response to this problem, for example, a device has been proposed that moves the camera lens in the optical axis direction so that the camera focuses on each of a predetermined plurality of positions and photographs at each position (refer to patent literature <NUM>, for example). The device selects one image that is presumed to be in focus from a plurality of images after taking the plurality of images. The device then performs iris recognition using the selected image.

In addition, patent literature <NUM> describes a device that utilizes a liquid lens to perform image processing.

<CIT>, <CIT> and <CIT> represent related art.

<CIT> discloses an image acquisition apparatus including a first image capturing unit group including a plurality of image capturing units in which at least part of in-focus distance ranges overlap each other and a second image capturing unit group including a plurality of image capturing units in which at least part of in-focus distance ranges overlap each other.

<CIT> discloses a system with two cameras changing focus positions in opposite direction.

<CIT> discloses a stereoscopic camera system where the second camera is driven with a delay compared to first camera on a reduced search focus range common with the first camera.

In the device described in patent literature <NUM>, even if the first photographed image is a focused image, iris recognition does not start until multiple images have been photographed. In addition, if a part of the iris being the subject is hidden in the focused image due to blinking of the eyes or other reasons, iris recognition will not be performed correctly. In such cases, the device will have to redo the photographing of the multiple images itself. Therefore, when using the device described in patent literature <NUM>, iris recognition takes a long time.

It is an object of the present invention to provide an image acquiring device and an image acquiring method that can shorten the time until an image used for image processing is acquired. It is also an object of the present invention to provide an image processing device that can shorten the time until the process of acquiring an image suitable for image processing is completed.

The above objects are achieved with the features of the independent claims.

According to the present invention, the time until an image used for image processing such as iris recognition is acquired can be shortened. The time until the process of acquiring images suitable for image processing is completed can be also shortened.

<FIG> are explanatory diagrams showing an overview of control of the image acquiring device of the example embodiment.

As shown in <FIG>, the imaging unit (camera) <NUM> facing the object <NUM> to be authenticated is installed so that the eye area including both eyes (including the iris) of the object <NUM> can be photographed. The imaging unit <NUM> changes the focal length within a predetermined focus moving range. In other words, the imaging unit <NUM> changes the focal position. The focus moving range is a range in which at least the iris of the object <NUM> will match the focal position during the movement of the imaging unit <NUM>.

<FIG> shows an aspect where a single imaging unit <NUM> (in detail, the camera lens) changes focal length. <FIG> shows an aspect where two imaging units <NUM> change focal length. The change in focal position shown in <FIG> corresponds to the change of the following example embodiments. That is, the image acquiring device of the example embodiments controls the focal length of the two imaging units <NUM>. In <FIG>, "front" indicates the end closest to the imaging unit <NUM> in the focus moving range, and "rear" indicates the furthest end from the imaging unit <NUM> in the focus moving range. A liquid lens that changes its lens power (the reciprocal of the focal length) in response to an applied voltage is used as the lens of the imaging unit <NUM>. In other words, the focal length of the liquid lens changes according to the change of the applied voltage.

The case will be assumed where the focal length is controlled so that the focal position of the imaging unit <NUM> stepwisely changes from the "front" position to the "rear" position and then stepwisely changes from the "rear" position to the "front" position, i.e., the focal position goes and returns. The "time to return" indicates the time required for the focal point to make a round trip from the starting point at position P. In <FIG>, the focal position is shown to change linearly, however in the example embodiments, the value of the voltage applied to the imaging unit <NUM> sequentially changes stepwisely. Thus, in reality, the change in focal position is stepwise.

In the example shown in <FIG>, a single imaging unit <NUM> stepwisely changes focal length, and each time the focal length changes, the imaging unit <NUM> photographs the object <NUM> (specifically, the eye area).

In this specification, "in focus" means that the focal point P matches the position of the iris of the object <NUM>. Therefore, image processing (image analysis) such as iris recognition is performed using the image taken at the "in-focus" position. Hereafter, the image taken at the "in-focus" position is referred to as an in-focus image.

If the eyelids of the object <NUM> are closed due to blinking, etc., when an in-focus image is taken, iris recognition, etc., based on that image cannot be performed. In the example shown in <FIG>, if the in-focus image is acquired when the eyelids of the object are closed, an in-focus image must be acquired again after making a round trip of the focal point position starting from the point where the image was first in focus. Therefore, it takes time to complete iris recognition, etc..

In the example shown in <FIG>, for a change in the focal position of one imaging unit <NUM>, the other imaging unit <NUM> changes its focal position with a delay. In <FIG>, "T" indicates a delay time of the change in focal position of the other imaging unit <NUM>.

Even if the eyelids of the object <NUM> are closed due to blinking, etc., when an in-focus image is taken by one imaging unit <NUM>, there is a high possibility that an in-focus image in which the eyelids are not closed will be acquired immediately afterwards by the other imaging unit <NUM>. Therefore, the time until iris recognition, etc. is completed is shortened compared to the example shown in <FIG>. The delay time T is set to a time equivalent to the time required for a typical object <NUM> to blink. Since the time required for a blink of a typical subject <NUM> is any of <NUM> to <NUM>, it is preferable to select the delay time T from within that time interval (with a margin, for example, from <NUM> to <NUM>). As an example, the delay time T is set to <NUM>.

<FIG> is a block diagram showing an example of the configuration of the image acquiring device, together with an imaging unit.

The image acquiring device <NUM> shown in <FIG> controls a first imaging unit 200A and a second imaging unit 200B, and inputs images taken by the first imaging unit 200A and the second imaging unit 200B. The image acquiring device <NUM> includes a first voltage applying unit <NUM>, a second voltage applying unit <NUM>, a first voltage control unit <NUM>, a second voltage control unit (a delay unit) <NUM>, and an image judgment unit <NUM>.

The first imaging unit 200A and the second imaging unit <NUM> B are each installed in a position where faces of objects (at least, the area that includes both eyes) can be photographed. In this example embodiment, each of the first imaging unit 200A and the second imaging unit 200B includes a liquid lens whose focal length is determined according to an applied voltage. Variable-focus lenses other than liquid lenses may be used as long as the focal length is electrically changed.

The first voltage control unit <NUM> generates voltage information from control information (control data) input from the image judgment unit <NUM>. The first voltage control unit <NUM> outputs the voltage information to the first voltage applying unit <NUM> and the second voltage control unit <NUM>. The voltage information output by the first voltage control unit <NUM> corresponds to the first voltage information.

The control data includes, for example, a trigger for the start of voltage control and information indicating that an image has been captured from the first imaging unit 200A. The control data corresponds to data indicating timing for switching the voltage value applied to the liquid lens in the first imaging unit 200A.

The first voltage information is information that can identify a voltage value that the first voltage control unit <NUM> applies to the liquid lens in the first imaging unit 200A. The first voltage information is information that indicates a voltage value itself, such as 3V, for example. In the case where the pattern of time-sequentially changing voltages (for example, <NUM>. 5V change every <NUM> between <NUM> and 30V) is predetermined, the first voltage information may be information indicating only the point in time at which the voltage value is switched.

The second voltage control unit <NUM> generates voltage information based on the first voltage information and outputs the voltage information to the second voltage applying unit <NUM>. The voltage information output by the second voltage control unit <NUM> corresponds to the second voltage information.

When the delay time T elapses from the time when the first voltage information is input, the second voltage control unit <NUM> outputs the first voltage information to the second voltage applying unit <NUM> as the second voltage information.

When the first voltage information is input, the first voltage applying unit <NUM> applies a voltage of the value identified by the first voltage information to the liquid lens in the first imaging unit 200A. When the second voltage information is input, the second voltage applying unit <NUM> applies a voltage of the value identified in the second voltage information to the liquid lens in the second imaging unit 200B.

The image judging unit <NUM> inputs images taken by each of the first imaging unit 200A and the second imaging unit 200B. It is preferable that an image input cycle is about the same as a cycle for switching the voltage value applied to the liquid lens.

<FIG> is an explanatory diagram showing an example of the arrangement of the first imaging unit 200A and the second imaging unit 200B. In this example embodiment, assume that the position where the object <NUM> of iris recognition is predetermined to a default position, when iris recognition is performed. As shown in <FIG>, the first imaging unit 200A and the second imaging unit 200B are installed at positions where they can take iris images (images of a small area including the iris) of the object <NUM> at the default position. In consideration of multiple objects <NUM> of varying heights, multiple pairs of the first imaging unit 200A and the second imaging unit 200B are installed at different heights from the ground or floor. In that case, one pair matching the height of the object <NUM> is used for the authentication process. For example, a wide-area imaging camera (full overhead camera) capable of photographing the entire body of persons of various heights may be installed, and a pair of the first imaging unit 200A and the second imaging unit 200B which can take an iris image of the object <NUM> is selected based on a wide-area image supplied by the wide-area imaging camera.

The lighting devices 202A, 202B for irradiating light (for example, near-infrared light) to the object <NUM> are also installed. The lighting devices 202A, 202B include a light source (for example, LED: Light Emitting Diode). The lighting devices 202A, 202B may be controlled to irradiate light during the period from the start to the end of image input. Alternatively, the lighting devices 202A, 202B may be controlled to be under a state where they irradiate light at all times. In addition, the lighting devices 202A, 202B may be turned on only at the timing when the first imaging unit 200A and the second imaging unit 200B are photographing.

<FIG> is a block diagram showing an example of the configuration of of the first imaging unit 200A and the second imaging unit <NUM>. <FIG> shows an imaging unit <NUM> representing the first imaging unit 200A and the second imaging unit 200B.

The imaging unit <NUM> includes a liquid lens <NUM> and an image sensor <NUM>. The image sensor <NUM> is a CMOS (Complementary Metal Oxide Semiconductor) sensor for example, however it may also be a CCD (Charge Coupled Device) sensor.

Next, the operation of the image acquiring device <NUM> will be described with reference to the sequence diagram in <FIG>. Although the imaging unit, the voltage control unit, the voltage applying unit, and the image judgment unit are described in <FIG>, as described above, there are actually the first imaging unit 200A and the second imaging unit 200B as the imaging units. There are the first voltage control unit <NUM> and the second voltage control unit <NUM> as the voltage control units. There are the first voltage applying unit <NUM> and the second voltage applying unit <NUM> as voltage applying units. The image judging unit shown in <FIG> corresponds to the image judging unit <NUM> in <FIG>.

For example, assume that the imaging unit, the voltage control unit, the voltage applying unit, and the image judgment unit shown in <FIG> comprises a block of a system controlling the first imaging unit 200A and acquiring images from the first imaging unit 200A. That is, assume that the imaging unit, the voltage control unit, the voltage applying unit, and the image judging unit correspond to the first imaging unit 200A, the first voltage control unit <NUM>, the first voltage applying unit <NUM>, and the image judgment unit <NUM>. In that case, the second imaging unit 200B, the second voltage control unit <NUM>, the second voltage control unit <NUM>, the second voltage applying unit <NUM>, and the image judging unit <NUM> perform the same operations as those shown in <FIG>, with a delay time T delayed against the operations shown in <FIG>, for the second imaging unit 200B.

When the operation of the image acquiring device <NUM> is started, the first voltage control unit <NUM> receives control data (indicating the start of processing) from the image judgment unit <NUM>. The first voltage control unit <NUM> sets the voltage information (the first voltage information) representing the initial value and outputs it to the first voltage applying unit <NUM> and the second voltage control unit <NUM> (step S101).

The first voltage applying unit <NUM> applies an initial voltage to the liquid lens in the first imaging unit 200A according to the first voltage information (step S101). The initial voltage is, for example, a voltage for setting a camera focus to an initial position, for example, the edge closest to the camera in the focus moving range (refer to "front" in <FIG>). When a delay time T elapses from the time when the first voltage information is input, the second voltage applying unit <NUM> outputs inputted first voltage information to the second voltage applying unit <NUM> as the second voltage information. The second voltage applying unit <NUM> applies an initial voltage to the liquid lens in the second imaging unit 200B according to the second voltage information (step S101).

When the process of step S101 is executed, the first voltage applying unit <NUM> and the second voltage applying unit <NUM> output a lighting instruction to the lighting devices 202A, 202B. In response to the lighting instruction, the lighting devices 202A, 202B emit light (step S102). In this example embodiment, suppose that when the initial voltage is applied to the liquid lens, the lighting devices 202A, 202B start emitting light, and end emitting light when the image judgment unit <NUM> inputs an in-focus image. Therefore, in this example embodiment, the process of step S103 is performed only once. As mentioned above, the first voltage applying unit <NUM> and the second voltage applying unit <NUM> may output a lighting instruction at each of the timings at which the first imaging unit 200A and the second imaging unit 200B photographs.

In addition, the first voltage applying unit <NUM> and the second voltage applying unit <NUM> may output a lighting instruction to the lighting devices 202A, 202B before applying voltage to the first imaging unit 200A and the second imaging unit 200B. The first voltage applying unit <NUM> and the second voltage applying unit <NUM> may start applying voltage and outputting a lighting instruction at the same time.

The image judging unit <NUM> inputs images (iris images) taken by the first imaging unit 200A and the second imaging units 200B (step S103A). In other words, the image judging unit <NUM> acquire images taken by the first imaging unit 200A and the second imaging unit 200B. The image judging unit <NUM> acquires an image from the second imaging unit 200B after a delay time T has elapsed from the time when the image judging unit <NUM> acquires an image from the first imaging unit 200A.

The image judgment unit <NUM> determines whether the acquired image is appropriate (step S104A). The image judgment unit <NUM> determines whether the input image is appropriate or not using clarity of the image, for example, contrast. Specifically, the image judging unit <NUM> detects the contrast of the image. When the contrast exceeds a predetermined threshold value, the image judgment unit <NUM> determines that the acquired image is an in-focus image taken at the in-focus position and is an appropriate image. If both the image input from the first imaging unit 200A and the image input from the second imaging unit 200B are determined to be appropriate, the image judgment unit <NUM> assumes that the image with the higher contrast is the appropriate image.

Further, the image judgment unit <NUM> outputs control data indicating update of the applied voltage (increase or decrease of voltage value) to the first voltage control unit <NUM>. When the control data is input, the first voltage control unit <NUM> outputs voltage information (first voltage information) that can identify the updated voltage value to the first voltage applying unit <NUM> and the second voltage control unit <NUM> (step S105A).

When the image input cycle and the switching cycle of the voltage value applied to the liquid lens are set to be the same level, the image judgment unit <NUM> outputs the control data indicating update of the applied voltage when acquiring an image from the first imaging unit 200A. However, it is not essential for the image judging unit <NUM> to output control data indicating update of the applied voltage when acquiring an image. For example, the image judging unit <NUM> may output control data indicating update of the applied voltage asynchronous to the time of image acquisition (as an example, the image acquisition interval: <NUM>, while the voltage update interval: <NUM>). In such a case, the image judging unit <NUM> acquires multiple images between the time the voltage value is updated and the next update.

When the image judgment unit <NUM> determines that an appropriate image has been acquired, the process is terminated. <FIG> shows an example in which, after the process of step S 105A (updating and applying the voltage) is performed, an appropriate image is not acquired by the process of step S 104B. Further, <FIG> shows an example in which, after the process of step S105B (updating and applying voltage) is performed, an appropriate image is acquired by the process of step S104C.

In this example embodiment, even if the in-focus image is acquired when the eyelids of the object <NUM> are closed due to blinking, etc., that is, even if the in-focus image is not suitable for iris recognition, the possibility of obtaining an in-focus image that can be used for iris recognition, etc. immediately after becomes high. In the example shown in <FIG>, when an in-focus image acquired first is not suitable for iris recognition, the in-focus image suitable for iris recognition cannot be acquired until at least "time to return" has passed. However, in this example embodiment, if the in-focus image acquired first is not suitable for iris recognition, there is a possibility that an in-focus image suitable for iris recognition can be acquired after the delay time T elapses. In other words, in this example embodiment, the possibility of obtaining an in-focus image suitable for iris recognition in a short period of time increases. Therefore, as a result, the time until the image used for image processing is acquired can be shortened.

In this example embodiment, the first voltage control unit <NUM> and the second voltage control unit <NUM> are separately, however a voltage control unit that includes the functions of the first voltage control unit <NUM> and the second voltage control unit may be provided. Such a voltage control unit outputs the above first voltage information and also performs delay processing related to the second voltage information and outputs the above second voltage information.

In this example embodiment, the first imaging unit 200A and the second imaging unit 200B including a liquid lens are used, however it is also possible to use a lens that is physically driven by a motor in at least one of the first imaging unit 200A and the second imaging unit 200B.

Iris recognition involves two phases. One is a registration phase in which the iris features of a large number of objects <NUM> are registered in a database, etc. Another is an authentication phase in which the iris features of a object <NUM> are compared with iris features of a large number of subjects registered in a database, etc. In the authentication phase, <NUM> wavelength band and <NUM> wavelength band are widely used.

It is not desirable for the wavelength band used in the registration phase to be different from it used in the authentication phase.

Therefore, in the registration phase, it is desirable to register the iris features acquired from an image acquired using light in the <NUM> wavelength band and an image acquired using light in the <NUM> wavelength band, respectively, in a database or the like in the registration phase.

When registering iris features based on images acquired from each of those in a database or the like, two imaging units (the first imaging unit 200A and the second imaging unit 200B) is considered to be used. Specifically, the wavelengths of light emitted by the lighting devices 202A, 202B are differentiated. For example, one light has a wavelength of <NUM> and the other has a wavelength of <NUM>. Then, the first imaging unit 200A and the second imaging unit 200B are each equipped with a bandpass filter. The passband of one bandpass filter is the <NUM> band, and the passband of the other bandpass filter is the <NUM> band. When set up in such a way, the image judgment unit <NUM> can obtain both images acquired using light of the <NUM> wavelength band and using light of the <NUM> wavelength band.

The delay control as illustrated in <FIG> is not performed in this example embodiment. In other words, the two imaging units together change the focal length. In this example embodiment, the light of the <NUM> wavelength band and the light of the <NUM> wavelength band are used, however used wavelengths of light are not limited to those.

<FIG> is a block diagram showing the imaging processing device of the third example embodiment. The image processing device <NUM> shown in <FIG> includes the image acquiring device <NUM> of the first example embodiment and a feature extraction unit <NUM>.

The feature extraction unit <NUM> inputs an image which is determined as an appropriate image by the image judgment unit <NUM> in the image acquiring device <NUM>. The feature extraction unit <NUM> extracts the iris region (excluding the pupil) from the input image and generates features (iris features) of the iris region. The feature extraction unit <NUM> then stores the iris features in the database <NUM>. The imaging processing device <NUM> shown in <FIG> executes the registration phase process in iris recognition. The feature extraction unit <NUM> can use any existing feature generation algorithm when generating the iris features.

As mentioned above, the in-focus image output by the image acquiring device <NUM> is likely to be an image (an image suitable for iris recognition) acquired when the eyelids of the object <NUM> are not closed, etc. Therefore, in this example embodiment, the time required for processing the registration phase in iris recognition is shortened as a result.

<FIG> is a block diagram showing the image processing device of the fourth example embodiment. The image processing device <NUM> shown in <FIG> includes the image acquiring device <NUM> of the first example embodiment and a feature extraction and matching unit <NUM>. The database <NUM> stores iris features of a number of objects.

The feature extraction and matching unit <NUM> inputs an image which is determined as an appropriate image by the image judgment unit <NUM> in the image acquiring device <NUM>. The feature extraction and matching unit <NUM> extracts the iris region (excluding the pupil) from the input image and generates iris features of the iris region. Then, the feature extraction and matching unit <NUM> compares (matches) the generated iris features with a number of iris features stored in the database <NUM>. When the generated iris features matches any of the iris features stored in the database <NUM>, the feature extraction and matching unit <NUM> considers that the authentication of the object <NUM> succeeds.

The third and fourth example embodiments may be combined. That is, the image acquiring device <NUM>, the feature extraction unit <NUM>, and the feature extraction and matching unit <NUM> may form an image processing device.

Each component (except for the first voltage applying unit <NUM> and the second voltage applying unit <NUM>) in the image acquiring devices of each of the above example embodiments may be configured with a piece of hardware or a piece of software. Alternatively, the components may be configured with a plurality of pieces of hardware or a plurality of pieces of software. Further, part of the components may be configured with hardware and the other part with software.

The functions (processes) in the above example embodiments may be realized by a computer having a processor such as a CPU (Central Processing Unit), a memory, etc. For example, a program for performing the method (processing) in the above example embodiments may be stored in a storage device (storage medium), and the functions may be realized with the CPU executing the program stored in the storage device. In addition, instead of a CPU, a GPU (Graphics Processing Unit), an FPGA (Field-Programmable Gate Array ), a DSP (Digital Signal Processor (DSP), or an ASIC (Application Specific Integrated Circuit) may be used. Further, multiple out of a CPU, a GPU, a FPGA, a DSP and an ASIC may be used in parallel.

<FIG> is a block diagram of a computer with a CPU. The computer can be implemented in each of the image acquiring device <NUM> and the image processing devices <NUM>, <NUM>. The CPU <NUM> executes processing in accordance with a program (software element: codes) stored in a storage device <NUM> to realize the functions in the above exemplary embodiments. That is, the computer realizes the functions of the first voltage control unit <NUM>, the second voltage control unit <NUM>, image judgment unit <NUM>, feature extraction unit <NUM>, and feature extraction and matching unit <NUM> in the image acquiring device <NUM> and image processing devices <NUM>, <NUM>, the first voltage control unit <NUM>, the second voltage control unit <NUM>, image judgment unit <NUM>, feature extraction unit <NUM>, and feature extraction and matching unit <NUM> in <FIG>, <FIG>.

The storage device <NUM> is, for example, a non-transitory computer readable media. The non-transitory computer readable medium is one of various types of tangible storage media. Specific examples of the non-transitory computer readable media include a magnetic storage medium (for example, hard disk), a magneto-optical storage medium (for example, magneto-optical disk), a compact disc-read only memory (CD-ROM), a compact disc-recordable (CD-R), a compact disc-rewritable (CD-R/W), and a semiconductor memory (for example, a mask ROM, a PROM (programmable ROM), an EPROM (erasable PROM), a flash ROM). The storage device <NUM> can also be used as a database <NUM>.

The program may be stored in various types of transitory computer readable media. The transitory computer readable medium is supplied with the program through, for example, a wired or wireless communication channel, i.e., through electric signals, optical signals, or electromagnetic waves.

A memory <NUM> is a storage means implemented by a RAM (Random Access Memory), for example, and temporarily stores data when the CPU <NUM> executes processing. It can be assumed that a program held in the storage device <NUM> or a temporary computer readable medium is transferred to the memory <NUM> and the CPU <NUM> executes processing based on the program in the memory <NUM>.

<FIG> is a block diagram showing the main part of the image acquiring device. The image acquiring device <NUM> shown in <FIG> comprises the voltage control unit (voltage control means) <NUM> (in the example embodiments, realized by the first voltage control unit <NUM> and the second voltage control unit <NUM>) which generates first voltage information that can identify voltage applied to the first variable-focus lens 20A (in the example embodiments, realized by the liquid lens <NUM>) included in the first imaging unit (first imaging means) <NUM> (in the example embodiments, realized by the first imaging unit 200A) installed in a position where a subject can be photographed and whose focal length changes in accordance with an applied voltage, and generates second voltage information that can identify voltage applied to the second variable-focus lens 21A (in the example embodiments, realized by the liquid lens <NUM>) included in the second imaging unit (second imaging means) <NUM> (in the example embodiments, realized by the second imaging unit 200B installed in the position where the subject can be photographed and whose focal length changes in accordance with an applied voltage, and the image judgment unit (image judgment means) <NUM> (in the example embodiments, realized by the image judging unit <NUM>) which inputs images from the first imaging unit <NUM> and the second imaging unit <NUM>, and selects one image taken at an in-focus position among input images, wherein the voltage control unit <NUM> generates information, as the first voltage information, that can identify each voltage in a time series of voltages whose values change with time, and generates information, as the second voltage information, that can identify that each of the voltages identified by the first voltage information is applied to the second variable-focus lens 21A after a predetermined period of delay.

Claim 1:
An image acquiring device comprising:
voltage control means (<NUM>, <NUM>,<NUM>) for generating first voltage information that identifies voltage applied to a first variable-focus lens (20A) which is included in first imaging means (<NUM>, 200A) installed in a position where a subject is photographed and whose focal length changes in accordance with an applied voltage, and generating second voltage information that identifies voltage applied to a second variable-focus lens (21A) which is included in second imaging means (<NUM>, 200B) installed in the position where the subject is photographed and whose focal length changes in accordance with an applied voltage; and
image judgment means (<NUM>, <NUM>) for inputting images from the first imaging means (<NUM>, 200A) and the second imaging means (<NUM>, 200B), and selecting one image taken at an in-focus position among input images,
characterized in that the voltage control means (<NUM>, <NUM>, <NUM>)
generates information, as the first voltage information, that identifies each voltage in a time series of voltages whose values change with time, and
generates information, as the second voltage information, that identifies that each of the voltages identified by the first voltage information is applied to the second variable-focus lens (21A) after a predetermined period of delay, such that the second imaging means (<NUM>, 200B) captures images at the same focus positions as the first imaging means (<NUM>, 200A) but with the predetermined period of delay.