JP2008085772A - Curvature of field aberration correcting imaging apparatus and curvature of field aberration correcting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a curvature of field aberration correcting imaging apparatus that can satisfactorily correct curvature of field aberrations of an imaging optical system while suppressing the manufacturing cost, and that can obtain image information such that an image is sharp from the center of a subject to a peripheral edge part, and a curvature of field aberration correcting method. <P>SOLUTION: The curvature of field aberration correcting imaging apparatus comprises the imaging optical system 2; an image sensor 21 (imaging element) acquiring the image formed by the imaging optical system 2 as the image information; a drive unit 5 which varies a relative distance between the imaging optical system 2 and image sensor 21 in the optical axis O direction of the imaging optical system 2; and a data processing circuit 25 (image processor) which obtains partial images formed by cutting regions set according to the relative distance between the imaging optical system 2 and image sensor 21 in the optical axis O direction of the imaging optical system 2 respectively from a plurality of pieces of image information obtained by the image sensor 21 while varying the relative distance between the imaging optical system 2 and image sensor 21 in the optical axis O direction of the imaging optical system 2, and then combines those pieces of partial image information together to generate complete image information. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and an image surface distortion correction method for correcting image surface distortion.

  In an image pickup apparatus including an image pickup optical system, an image formed by the image pickup optical system is affected by image surface distortion.

Specifically, the image formed by the imaging optical system is shifted in the optical axis direction depending on the image height (distance from the center of the screen), so even if a flat subject is photographed as it is, it remains on the curved surface. The image will be tied.
In general, an image sensor that acquires an image formed by an imaging optical system as image information in an imaging apparatus has a flat light receiving surface. For this reason, if the imaging surface of the imaging optical system is curved as described above, for example, one of the subject image obtained at the periphery of the light receiving surface and the subject image obtained at the center is blurred. Therefore, it is difficult to acquire clear image information.

  As a technique for correcting such image surface distortion, for example, a zoom lens described in Patent Document 1 is known. This zoom lens is configured to use a plurality of groups of lenses including an expensive aspherical lens in order to correct the aberration of the spherical lens.

JP 2004-240222 A

However, since the imaging optical system configured by a plurality of groups (sheets) of lenses is expensive, the cost of the imaging apparatus increases. Further, in the imaging optical system that corrects the image surface distortion as described above, the lens design is complicated, which increases the cost of the imaging apparatus.
Further, even when an imaging optical system constituted by a plurality of lenses is used as described above, it is difficult to completely correct the field distortion.

  The present invention has been made in view of the above-described circumstances, and corrects the image surface distortion of the imaging optical system well while suppressing the manufacturing cost, and acquires clear image information from the center to the periphery. An object of the present invention is to provide an image plane distortion correction imaging apparatus and an image plane distortion correction method that can be performed.

In order to achieve the above object, the present invention provides the following means.
The present invention relates to an imaging optical system, an imaging element that acquires an image formed by the imaging optical system as image information, and a relative distance between the imaging optical system and the imaging element in the optical axis direction of the imaging optical system. And changing the relative distance between the image pickup optical system and the image pickup device, and changing the relative distance to obtain image information by the image pickup device. A plurality of control devices, and set according to each of the relative distances from a plurality of pieces of image information acquired by the imaging device by changing the relative distance between the imaging optical system and the imaging device. An image surface distortion correction imaging apparatus including an image processing apparatus that obtains a plurality of partial image information obtained by cutting out a region and generates completed image information by combining the partial image information.

In the image plane distortion correction imaging apparatus configured as described above, the relative distance between the imaging optical system and the imaging element in the optical axis direction of the imaging optical system can be changed by the driving device.
In this image plane distortion correction imaging apparatus, when photographing a subject, a plurality of pieces of image information are photographed by changing the relative distance between the imaging optical system and the imaging element in the optical axis direction of the imaging optical system.
Specifically, in this image plane distortion correction imaging apparatus, imaging is performed a plurality of times by changing the relative distance in the optical axis direction between the imaging optical system and the imaging element within a range in which at least a part of the image information is in focus. I do.

In the image information obtained in this way, for example, when shooting twice, the first image information in which only the center of the subject is in focus, and the second in which only the periphery of the subject is in focus Image information is obtained.
The image processing apparatus cuts out only the area corresponding to the relative distance in the optical axis direction between the imaging optical system and the imaging element (the focused area) from the image information obtained in this way, and the partial image information. Get.

The image processing device generates clear image information (completed image information) that is in focus from the center to the peripheral portion of the subject by combining the partial image information.
That is, this image plane distortion correction imaging apparatus can obtain clear image information that is in focus from the center to the periphery of the subject even if the imaging optical system has image plane distortion. it can. In other words, this image plane distortion correction imaging apparatus corrects the image plane distortion without making the imaging optical system complicated, and is in focus from the center to the periphery of the subject. Clear image information can be obtained.
Further, in the imaging apparatus according to the present invention, the adjustment operation of the relative distance between the imaging optical system and the imaging element and the imaging by the imaging element are automatically performed by the control device at the time of shooting. The completed image information can be easily obtained without performing any operation.

  The present invention also provides an image plane distortion correction method in an image pickup apparatus having an image pickup optical system and an image pickup device that acquires an image connected by the image pickup optical system as image information. The relative distance between the imaging optical system and the imaging element in the optical axis direction is changed, and the relative distance between the imaging optical system and the imaging element is changed, and image information is acquired by the imaging element a plurality of times. Partial image information obtained by cutting out regions set in accordance with the relative distances from a plurality of pieces of image information acquired by the imaging element by changing the relative distance between the imaging optical system and the imaging element is obtained. Thus, an image surface distortion correction method for generating completed image information by combining these pieces of partial image information is provided.

In this image plane distortion correction method, when photographing a subject, a plurality of pieces of image information are photographed by changing the relative distance between the imaging optical system and the imaging element in the optical axis direction of the imaging optical system.
Specifically, in this image plane distortion correction imaging apparatus, imaging is performed a plurality of times by changing the relative distance in the optical axis direction between the imaging optical system and the imaging element within a range in which at least a part of the image information is in focus. I do.
Partial image information is obtained by cutting out only a region (a focused region) corresponding to the relative distance in the optical axis direction between the imaging optical system and the imaging element from the image information obtained in this way.

By combining these pieces of partial image information, clear image information (completed image information) that is in focus from the center to the periphery of the subject is generated.
That is, with this image surface distortion correction method, even if the imaging optical system has image surface distortion, it is possible to obtain clear image information that is in focus from the center to the periphery of the subject. . In other words, with this image surface distortion correction method, the image surface distortion is corrected without making the imaging optical system complicated, and the entire object is focused from the center to the periphery of the subject. Image information can be obtained.

Here, the focused area in the captured image information is determined by the characteristics of the image plane distortion of the imaging optical system and the relative distance in the optical axis direction between the imaging optical system and the imaging element.
For this reason, based on the characteristics of the image plane distortion of the imaging optical system, the imaging optical system and the imaging element are arranged so that the overlap of the in-focus area between the image information acquired in each imaging is minimized. By determining the relative distance and the number of acquisition times of the image information, it is possible to acquire clear image information that is in focus from the center to the peripheral portion of the subject with the minimum number of acquisition times. .

  According to the image plane distortion correction imaging apparatus and the image plane distortion correction method according to the present invention, it is possible to satisfactorily correct the image plane distortion of the imaging optical system while simplifying the configuration of the imaging optical system and reducing the manufacturing cost. Thus, clear image information can be acquired from the center to the peripheral portion of the subject.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Here, an example in which the present invention is applied to a digital still camera will be described.
As shown in the block diagram of FIG. 1, the digital still camera 1 (image plane distortion correction imaging apparatus) according to this embodiment has an imaging optical system 2 and an imaging optical system 2 connected in a housing (not shown). An imaging function unit 3 that acquires an image as image information and an image information display panel that displays various image information such as image information acquired by the imaging function unit 3 are provided.

Here, the imaging optical system 2 may be configured by only one spherical convex lens, or may be configured by a lens unit including a plurality of lenses including a spherical lens.
Further, the imaging optical system 2 may be configured by a single-focus imaging optical system having a fixed magnification, or may be configured by a known zoom optical system whose magnification can be changed to an arbitrary magnification. In the present embodiment, a zoom optical system is used as the imaging optical system 2.
In addition, as the image information display panel, for example, an LCD (Liquid Crystal Display) panel or an organic or inorganic EL (electroluminescence) display panel can be used. In the present embodiment, the LCD panel 4 is used as the image information display panel.

The imaging function unit 3 is provided with a driving device 5 that changes a relative position between an image sensor 21 (imaging device), which will be described later, and the housing in the optical axis O direction of the imaging optical system 2.
The drive device 5 changes the relative distance between the image pickup optical system 2 and the image sensor 21 in the optical axis O direction by changing the relative position between the image sensor 21 and the housing. The drive device 5 can be configured by an arbitrary mechanism such as an actuator using a piezoelectric element or MEMS (Micro Electro Mechanical Systems) in addition to a screw feed mechanism and a cylinder mechanism.

Hereinafter, a detailed configuration of the imaging function unit 3 will be described.
The imaging function unit 3 includes a power supply unit PW that supplies power to each device constituting the digital still camera 1, a CPU (Central Processing Unit), and the like, and a system controller 20 that controls each unit of the digital still camera 1 ( Control device), a ROM 20a in which a control sequence program for controlling the operation of the system controller 20, various control parameters, and the like, and data necessary for the execution of the various sequences by the system controller 20 are temporarily stored. And a RAM 20b used as a work area.

The system controller 20 controls the operation of the power supply unit PW to control the supply of power to each device constituting the imaging apparatus main body 2.
When the power state of the imaging apparatus main body 2 is turned on, the system controller 20 reads programs, parameters, and the like from the ROM 20a and performs predetermined processing. As a result, the system of the digital still camera 1 is activated and is in a state where it can be electrically photographed.

A flat image sensor 21 (imaging device) is disposed behind the imaging optical system 3. Thereby, a subject image is formed on the flat light receiving area of the image sensor 21 by the imaging optical system 3.
As the image sensor 21, an arbitrary one such as one using a CCD (Charge Coupled Devices) or one using a CMOS (Complementary Metal Oxide Semiconductor) can be used. In addition, a global shutter type high-speed CMOS sensor, a high-speed CMOS sensor in which single-slope A / D converters are integrated for each pixel column, and the like can be used. In the present embodiment, an image sensor using a CCD is used as the image sensor 21.

The imaging apparatus main body 2 is provided with a CCD driver 22 that drives the image sensor 21. Thereby, the image sensor 21 converts the optical subject image obtained via the imaging optical system 3 into an electrical imaging signal and outputs the electrical imaging signal.
The imaging apparatus main body 2 is provided with an amplifier 23 that amplifies an imaging signal output from the image sensor 21 and an A / D converter 24 that digitally converts the output of the amplifier 23.

On the light receiving surface of the image sensor 21, minute micro color filters such as R, G, and B are arranged in a matrix. An imaging signal serially output for each color corresponding to each micro color filter from the image sensor 21 is amplified to an appropriate level by an amplifier 23, and then digitally converted by an A / D converter 24 to be red, green , Blue image data.
The CCD has a disk-shaped color rotation filter provided with a plurality of different filter portions in the circumferential direction in addition to the CCD using the color separation method of the color CCD method using the above-described micro color filter. It is possible to use a color filter switching type CCD that performs color separation of light incident on the light receiving surface by rotating the color rotation filter and switching a filter portion that covers the light receiving surface of the CCD. Further, as a CCD, it is also possible to use a monochrome photographing CCD that does not use these color filters.

  The imaging apparatus body 2 is processed by a data processing circuit 25 (image processing apparatus) that performs various data processing such as white balance adjustment and gamma correction on the image data obtained by the image sensor 21, and the data processing circuit 25. And an LCD driver 26 for displaying the image data on the LCD panel 4 as image information. When the imaging apparatus main body 2 is in the photographing mode, the image data from the A / D converter 24 is input to the data processing circuit 25, and one image on which necessary processing has been performed by the data processing circuit 25. Minute image data is sent to the LCD driver 26 one after another. As a result, the subject image being shot is displayed on the LCD panel 4 as a moving image. In the shooting mode, the system controller 20 can switch between a display mode in which an image being shot by the image sensor 21 is displayed on the LCD panel 4 and a non-display mode in which the image being shot is not displayed on the LCD panel 4. It can be done.

  The imaging apparatus body 2 is provided with an AE processing circuit 27 that performs automatic exposure control (AE control) during imaging. Image data from the data processing circuit 25 is also sent to the AE processing circuit 27. This AE processing circuit 27 is based on each input image data and the charge accumulation time of the image sensor 21 set in the CCD driver 22 at that time, that is, the shutter time of the electronic shutter. A luminance photometric value is calculated. Then, the system controller 20 determines the shutter time of a new electronic shutter based on this photometric value, and feeds back this shutter time to the CCD driver 22, whereby the drive of the image sensor 21 is adjusted, and AE Control is performed.

  As described above, the digital camera 1 measures subject luminance by a TTL (Through The Lens) photometry method using the image sensor 21 as a light receiving sensor. The aperture value may be changed with the shutter time of the electronic shutter. When changing the aperture value, it goes without saying that the photometric value corresponding to the subject brightness is calculated with the aperture value taken into account.

The imaging apparatus main body 2 is provided with an external storage device that records the image data output from the data processing circuit 25. In the present embodiment, a flash memory 28 is used as an external storage device. The flash memory 28 is provided so as to be detachable from the imaging apparatus main body 2.
The imaging apparatus main body 2 is provided with an I / O port 31 for exchanging data between the system controller 20 and other devices. Connected to the I / O port 31 are an input unit 32 that accepts user input and an external connection terminal group 33 to which external devices are connected.

  The input unit 32 includes, for example, a release switch, a zoom lever, a key operation unit, and the like, and signals corresponding to these operations are input to the system controller 20 via the I / O port 31. The system controller 20 performs various processes and controls according to the input signal. The external connection terminal group 33 includes a memory slot into which a memory card as an external storage device is mounted, a connector for connecting to an external computer, and the like. Data can be input / output through the I / O port 31 by connecting an external storage device or computer to the external connection terminal group 33.

  Here, in the reproduction mode, the system controller 20 displays image data to be displayed from the flash memory 28 or the external storage device connected to the external connection terminal group 33 based on a user instruction input to the input unit 32. Is sent to the data processing circuit 25. As a result, the image data to be displayed is sent to the LCD driver 26 and an image is displayed on the LCD panel 4.

Hereinafter, in the digital still camera 1, details of the photographing operation when the imaging optical system 2 is a zoom lens will be described with reference to the flowchart of FIG.
[First relative position adjustment]
When a shooting command is input from the user via the input unit 32, the system controller 20 operates a lens driving device (not shown) on the imaging optical system 2 at an arbitrary zoom position to operate the image sensor 21. The relative distance between the imaging optical system 2 and the image sensor 21 is adjusted so that at least a part of the region including the subject P (see FIG. 4) is focused on the light receiving area (step S1).
Next, the zoom position of the imaging optical system 2 is detected (step S2). Then, from the detected zoom position and the lens configuration of the imaging optical system 2, the number of times (2 to n times) at which an optimal subject image is obtained in accordance with the curvature state of the image plane calculated in advance is determined, The moving direction and the operation amount of the image sensor 21 are determined (step S3).

[First shot]
In this state, the system controller 20 issues an operation command to the CCD driver 22 to perform first shooting (step S4).
In this state, image information focused on at least a part of the subject P on the light receiving area is obtained.

[Second relative position adjustment]
When the first shooting is completed, the system controller 20 operates the driving device 5 to select a region different from that at the time of the first relative position adjustment in the region including the subject P on the light receiving area of the image sensor 21. The relative distance between the imaging optical system 2 and the image sensor 21 is adjusted so that the image is in focus (step S5).

[Second shot]
In this state, the system controller 20 issues an operation command to the CCD driver 22 and performs second shooting (step S6).
In this state, out-of-focus image information can be obtained in a region different from the image information obtained at the time of the first photographing in the subject P on the light receiving area.

  Thereafter, the system controller 20 repeats the relative position adjustment operation and the image capturing operation until images in focus are captured for all the areas including the subject P on the light receiving area of the image sensor 21 (step Sn). , Sn + 1).

  For example, when the system controller 20 is configured to perform shooting twice in response to a single shooting command, the relative distance between the imaging optical system 2 and the image sensor 21 is set to D1, as shown in FIG. As shown in FIG. 4, first image information G1 is obtained in which only the central portion P1 of the region including the subject P on the light receiving area is in focus. Also, as shown in FIG. 5, by setting the relative distance between the imaging optical system 2 and the image sensor 21 to D2, as shown in FIG. 6, only the peripheral portion P2 of the region including the subject P on the light receiving area is shown. The second image information G2 that is in focus is obtained.

  Next, the system controller 20 controls the operation of the data processing circuit 25, and from the image information obtained by each shooting, an area corresponding to the relative distance between the imaging optical system 2 and the image sensor 21 in the optical axis O direction. Only the (in-focus area) is cut out to obtain partial image information (step Sn + 2). Specifically, the data processing circuit 25 cuts out only the central portion P1 from the first image information G1, and cuts out only the peripheral portion P2 from the second image information G2, respectively, as partial image information.

Here, the relationship between the relative distance between the imaging optical system 2 and the image sensor 21 in the direction of the optical axis O and the focused area in the obtained image information is the optical characteristic of the imaging optical system 2 (imaging optical system 2). Field curvature characteristics calculated from lens data, etc.), optical characteristics at the zoom position at the time of shooting in the zoom optical system, field angle of the subject, and the like. Of the image information obtained by one-time shooting, the in-focus area is a concentric section from the center of the screen to the peripheral edge of the screen, depending on the image plane distortion of the imaging optical system 2. There may be one, but there may be a case where a plurality of regions out of regions concentrically divided from the center of the screen to the periphery of the screen are focused. In this way, when a plurality of areas are in focus, each of the in-focus areas can be cut out from the image information, and each can be used as partial image information.
Based on this information, the system controller 20 identifies an in-focus area in the image information obtained by each shooting, and causes the data processing circuit 25 to generate partial image information.

Thereafter, the system controller 20 controls the operation of the data processing circuit 25 to synthesize the obtained partial image information, and clear image information (completed image information) that is in focus from the center to the periphery. ) Is generated. Specifically, as shown in FIG. 7, the data processing circuit 25 synthesizes the central portion P1 of the first image information G1 and the peripheral portion P2 of the second image information G2, and the central portion is the first one. Image information G3 is generated in which the region P1 of the first image information G1 and the peripheral portion are formed of the region P2 of the second image information G2.
In addition, in each partial image information, the partial image information of the adjacent region and the information of the boundary portion of the region are partially overlapped for convenience of the synthesis process. And when combining each partial image information, the overlapping parts are mixed in the partial image information of an adjacent area | region. Specifically, in each partial image information, in the vicinity of the boundary with the adjacent region, the usage ratio of the partial image information is lower as the portion is closer to the adjacent region, and the usage ratio of each partial image is half on the boundary. Is set to be As a result, the seam of the image information at the boundary portion between adjacent regions becomes inconspicuous.

That is, in this digital still camera 1, even if the imaging optical system 2 has image surface distortion, clear image information that is in focus from the center to the periphery of the subject can be obtained. In other words, the digital still camera 1 corrects the image plane distortion without making the imaging optical system 2 complicated, and is in sharp focus from the center to the periphery of the subject. Image information can be obtained.
Thus, according to the digital still camera 1, the configuration of the imaging optical system 2 is simplified to reduce the manufacturing cost, and the image surface distortion of the imaging optical system 2 is corrected well, and the peripheral portion from the center of the subject is corrected. Until then, clear image information can be obtained.

  In the digital still camera 1, the system controller 20 automatically adjusts the relative distance between the imaging optical system 2 and the image sensor 21, and photographing with the image sensor 21. The completed image information can be easily obtained without performing any operation.

As described above, the photographing operation of the digital still camera 1 in the case where the imaging optical system 2 is a zoom lens has been described using the flowchart of FIG. 2, but in the case where the imaging optical system 2 is a short focus lens, in step S <b> 2. Since detection of the zoom position is unnecessary, step S2 is omitted, and the moving direction and amount of movement of the image sensor 21 are determined by the number of times of shooting determined in advance based on the lens characteristics of the imaging optical system 2 in step S3. Is done.
In the above embodiment, an example in which the driving device 5 that changes the relative position of the image sensor 21 with respect to the housing is used as the driving device that changes the relative distance between the imaging optical system 2 and the image sensor 21. However, the present invention is not limited to this, and a driving device having a configuration in which the relative distance between the imaging optical system 2 and the image sensor 21 is changed by changing the relative position of the imaging optical system 2 with respect to the housing is used. May be.
In the above embodiment, the example in which the present invention is applied to a digital still camera has been described. However, the present invention is not limited to this, and the present invention may be applied to various cameras that handle image data electronically, such as a video camera.

1 is a block diagram illustrating a configuration of a digital still camera (an image plane distortion correction imaging apparatus) according to an embodiment of the present invention. It is a flowchart explaining operation | movement of the digital still camera which concerns on one Embodiment of this invention. It is a figure which shows the specific example of operation | movement of the digital still camera which concerns on one Embodiment of this invention, Comprising: It is a figure which shows the state which image | photographs the image information which is focused only on the center part. It is a figure which shows the image information image | photographed in the state shown in FIG. It is a figure which shows the specific example of operation | movement of the digital still camera which concerns on one Embodiment of this invention, Comprising: It is a figure which shows the state which image | photographs the image information which is focused only on the peripheral part. It is a figure which shows the image information image | photographed in the state shown in FIG. FIG. 7 is a diagram illustrating completed image information obtained by combining the partial image information of the image information illustrated in FIG. 4 and the partial image information of the image information illustrated in FIG. 6.

Explanation of symbols

1 Digital still camera (image plane distortion correction imaging device)
3 Imaging Optical System 5 Drive Device 20 System Controller (Control Device)
21 Image sensor
25 Data processing circuit (image processing device)

Claims (3)

An imaging optical system;
An image sensor for acquiring an image formed by the imaging optical system as image information;
A driving device that changes a relative distance between the imaging optical system and the imaging element in an optical axis direction of the imaging optical system;
While controlling the operation of the driving device to change the relative distance between the imaging optical system and the imaging element,
A control device that changes the relative distance and performs acquisition of image information by the imaging device a plurality of times;
A plurality of pieces of partial image information obtained by cutting out regions set in accordance with the relative distances from a plurality of pieces of image information acquired by the imaging element by changing the relative distance between the imaging optical system and the imaging element. And an image processing device that combines the partial image information to generate completed image information. An image plane distortion correction method in an imaging apparatus including an imaging optical system and an imaging element that acquires an image connected by the imaging optical system as image information,
Changing the relative distance between the imaging optical system and the imaging element in the optical axis direction of the imaging optical system;
Changing the relative distance between the imaging optical system and the image sensor, performing image information acquisition by the image sensor multiple times,
Obtaining partial image information obtained by cutting out a region set in accordance with each relative distance from a plurality of pieces of image information acquired by the imaging element by changing the relative distance between the imaging optical system and the imaging element. ,
An image plane distortion correction method for generating completed image information by combining these pieces of partial image information.   The image plane distortion correction method according to claim 2, wherein the relative distance between the image pickup optical system and the image pickup device and the number of acquisition times of the image information are determined based on a characteristic of image plane distortion of the image pickup optical system. .

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