JP2015095857A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of obtaining an image without discomfort in accordance with a subject.SOLUTION: A digital camera which converts an optical image formed through an imaging lens 104 to an image signal by an imaging device 103 comprises an image processor 108 which corrects a distortion aberration characteristic to the imaging lens 104 by image processing. The image processor 108 varies a correction amount to use to correct the distortion aberration, in accordance with the focal distance of the imaging lens 104 and the incident angle of a beam from the subject to the imaging lens 104.

Description

  The present invention relates to an imaging apparatus, and more particularly to a technique for correcting distortion inherent in an imaging lens by image processing.

  In the imaging apparatus, the imaging magnification of the captured image changes depending on the image height of the imaging screen due to distortion inherent in the imaging lens, and thus a phenomenon occurs in which the captured image is distorted. On the other hand, in an imaging device such as a digital camera that performs image processing on a captured image, an image with reduced distortion is obtained by performing image processing for correcting distortion inherent in the imaging lens ( (See Patent Documents 1 and 2).

JP 2008-244803 A JP 2010-226157 A

  However, when correcting distortion inherent in the imaging lens by image processing such as the above-described prior art, it is possible to reduce image distortion if it is a planar subject, but if the subject is three-dimensional, Distortion peculiar to a three-dimensional subject occurs. In particular, when a large barrel distortion at the wide-angle position of the imaging lens is corrected, a good image can be obtained with a planar straight object, but an image distortion called wide-angle distortion occurs with a three-dimensional object. This wide-angle distortion is a phenomenon in which the subject at the periphery of the screen is stretched and photographed in the image height direction of the screen. End up. A specific example will be described with reference to FIG.

  FIG. 4A is an example of an image according to a conventional example in which distortion is favorably corrected. In FIG. 4A, the shape on the planar straight line is corrected well, but a three-dimensional object such as a person's face in the periphery of the screen has a wide-angle distortion and an uncomfortable image. I understand that. FIG. 4B is an example of an image according to a conventional example having barrel distortion. In FIG. 4 (B), the shape on the plane straight line is distorted, resulting in an uncomfortable image, but wide-angle distortion occurs in a three-dimensional object such as a human face around the screen. As a result, the image of the person's face is not uncomfortable.

  An object of the present invention is to provide an imaging apparatus capable of obtaining an image without a sense of incongruity according to a subject.

  An image pickup apparatus according to the present invention is an image pickup apparatus that converts an optical image formed through an image pickup lens into an image signal using an image pickup element, and includes a correction unit that corrects distortion inherent in the image pickup lens by image processing. The correction means changes a correction amount used when correcting the distortion according to a focal length of the imaging lens and an incident angle of a light beam from a subject to the imaging lens.

  According to the present invention, the amount of correction for correcting distortion inherent in the imaging lens by image processing is changed according to the focal length of the imaging lens and the incident angle of the light beam from the subject to the imaging lens. As a result, it is possible to obtain a good image without a sense of incongruity depending on the subject.

1 is a block diagram illustrating a configuration of a digital camera that is an example of an imaging apparatus according to an embodiment of the present invention. It is a figure which shows typically the distortion aberration and wide angle distortion of an imaging lens with which the digital camera of FIG. 1 is provided. It is a figure showing the relationship between the to-be-photographed object and to-be-photographed object distance in this embodiment, and a distortion aberration, (B), (C) is an appropriate correction example, (A), (D) is an inadequate correction example. is there. It is an example of the image which concerns on the conventional example in which distortion was correct | amended favorably, and an example of the image which concerns on a conventional example with barrel-shaped distortion.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, a so-called digital camera is taken up as the imaging apparatus according to the present invention.

<Configuration of imaging device>
FIG. 1 is a block diagram showing a configuration of a digital camera according to an embodiment of the present invention. The digital camera includes an operation unit 101, a control unit 102, an imaging element 103, an imaging lens 104, an aperture 105, a shutter 106, an A / D conversion unit 107, an image processing unit 108, and an EVF display unit 109. The digital camera also includes a format conversion unit 110, an image storage unit 111, an external connection unit 112, an AF processing unit 113, and an AE processing unit 114.

  The operation unit 101 includes switches, buttons, and the like that are operated by an operator of the digital camera to input various instructions to the digital camera, and includes a shutter switch. The control unit 102 includes a CPU, a ROM, a RAM, and the like, and performs overall control of the digital camera. In addition, the control unit 102 uses the digital image signal output from the image processing unit 108 to detect the face of a person included in the imaging screen and the shape of a building or a plant. It has a shape detection function. Note that a well-known determination technique is used for face detection and shape detection, and detailed description thereof is omitted here.

  A light beam (reflected light from a subject) incident through the imaging lens 104, the diaphragm 105 and the shutter 106 forms an optical image on the imaging surface of the imaging element 103. Note that the imaging lens 104 includes a plurality of lenses such as a focus lens, a zoom lens, and a shake correction lens. The image sensor 103 is an image sensor such as a CCD sensor or a CMOS sensor, and outputs a charge corresponding to the light amount of the optical image by photoelectric conversion. The A / D conversion unit 107 performs sampling, gain adjustment, A / D conversion, and the like on the analog image signal output from the image sensor 103, and outputs the digital image signal.

  The image processing unit 108 performs various types of image processing on the digital image signal output from the A / D conversion unit 107, and outputs the processed digital image signal. For example, the image processing unit 108 calculates an AF evaluation value based on the contrast value for each region of the digital image signal from the A / D conversion unit 107. The image processor 108 measures the distance (subject distance) from the position of the focus lens when the AF evaluation value is the maximum value to the subject in each region (subject distance) for each region of the digital image signal. Can do. The image processing unit 108 performs image processing such as white balance adjustment according to the subject and image processing for correcting distortion inherent in the imaging lens 104 on the digital image signal from the A / D conversion unit 107. . A correction amount for correcting distortion inherent in the imaging lens 104 is stored in advance in the RAM or the like of the control unit 102 with respect to the zoom stop position.

  The EVF display unit 109 is composed of a small liquid crystal panel or the like, and displays an image according to the image data processed by the image processing unit 108. The format conversion unit 110 converts the format of the digital image signal (image data) output from the image processing unit 108 into a format such as JPEG or MPEG, and outputs it to the image storage unit 111. The image storage unit 111 performs processing for storing the image data that has undergone format conversion received from the format conversion unit 110 in a memory (not shown) provided in the digital camera, an external memory (not shown) attached to the digital camera, or the like. The external connection unit 112 is an interface for connecting to an external device (not shown), and is, for example, a USB terminal. Examples of the external device include a personal computer and a printer.

<Shooting operation>
Next, the imaging operation by the digital camera will be described. Here, a case will be described in which shooting is performed while confirming a subject by executing a live view that displays the subject in real time on a small liquid crystal panel.

  First, when the control unit 102 detects that a power switch included in the operation unit 101 is turned on, the control unit 102 supplies power to each unit constituting the digital camera. As a result, the shutter 106 is opened, and the light beam enters the image sensor 103 via the imaging lens 104, the aperture 105, and the shutter 106. The control unit 102 reads out the electric charge accumulated in the image sensor 103 at regular time intervals. The analog electrical signal read from the image sensor 103 is input to the A / D conversion unit 107. The A / D conversion unit 107 performs sampling, gain adjustment, A / D conversion, and the like on the received analog image signal. The digital image signal that has been subjected to is output to the image processing unit 108.

  The image processing unit 108 measures the subject distance using the received digital image signal. Further, the image processing unit 108 performs various kinds of image processing such as image processing such as appropriate white balance according to the subject and image processing for correcting distortion inherent in the imaging lens 104 on the received digital image signal. . Then, the image processing unit 108 outputs the processed digital image signal to the EVF display unit 109. As a result, the subject is displayed on the EVF display unit 109. In the present embodiment, the image processing unit 108 changes the distortion aberration correction amount when the zoom position, the subject distance, or the subject changes.

  The control unit 102 controls the AF processing unit 113 to operate the imaging lens 104 to focus on the subject based on the image acquired by the image processing unit 108. In addition, the control unit 102 controls the AE processing unit 114 so as to operate the aperture 105 so as to display an appropriate image on the small liquid crystal panel. The control unit 102 repeats the above processing until receiving a signal from the operation unit 101 indicating that the shutter switch is half-pressed.

  When the control unit 102 receives a signal indicating that the shutter switch has been half-pressed from the operation unit 101, the control unit 102 performs AF processing and AE processing using the image at that time through the AF processing unit 113 and the AE processing unit 114. Get the best focus and exposure conditions for shooting. The control unit 102 repeats the above processing until it detects a signal indicating that the shutter switch has been fully pressed.

  When the control unit 102 receives a signal indicating that the shutter switch has been fully pressed from the operation unit 101, the control unit 102 performs exposure under the exposure conditions set for the image sensor 103, and thus performs A / D conversion from the image sensor 103. An analog image signal is output to the unit 107. The A / D conversion unit 107 performs sampling, gain adjustment, A / D conversion, and the like on the received analog image signal, and outputs the processed digital image signal to the image processing unit 108. The image processing unit 108 performs various types of image processing such as white balance corresponding to shooting conditions and image processing for correcting distortion aberration inherent to the imaging lens 104 on the received digital image signal, and the processed digital image The signal is output to the format conversion unit 110. At this time, by correcting the distortion aberration inherent to the imaging lens 104 with an optimal correction amount according to the subject and the subject distance, it is possible to obtain a good image without a sense of incongruity according to the subject.

  The format conversion unit 110 converts the format of the received digital image signal (image data) into a format such as JPEG or MPEG, and outputs it to the image storage unit 111. The image storage unit 111 performs processing for storing the received image data in a memory (not shown) or the like.

<Distortion correction>
Next, a description will be given of a method of obtaining a good image without a sense of incongruity according to a subject by changing a correction amount for correcting distortion inherent in the imaging lens 104 according to the subject and subject distance.

  FIG. 2 is a diagram schematically showing distortion and wide-angle distortion of the imaging lens 104. Usually, when the image height of the captured image is “y”, the incident angle from the subject to the imaging lens 104 is “θ”, and the focal length of the imaging lens 104 is “f”, the expression “y = f · tan θ” is obtained. A projection method called orthographic projection is used. In this projection method, it is possible to take a planar subject without distortion by eliminating the distortion aberration of the imaging lens 104. However, when photographing a three-dimensional object, distortion called wide-angle distortion occurs.

  The ideal image height “h” when there is no distortion due to the imaging lens 104 is represented by “h = β · H”. Here, “β” is the lateral magnification of the imaging lens 104, and “H” is the height of the subject. Note that “h = β · H = f · tan θ”. On the other hand, the image height “j” when there is distortion due to the imaging lens 104 is “j = β · (1 + δ) · H”. Here, “δ” is a distortion aberration of the imaging lens 104.

  When the diameter of the spherical subject on the subject side is “L”, the length in the image height direction becomes “Lm” due to distortion of the imaging lens 104 on the image side, and is orthogonal to the image height direction. The length in the direction is “Ls”. If the length “Lm” in the image height direction and the length “Ls” in the image height direction and the vertical direction are not equal, a phenomenon occurs in which the image expands or contracts in either direction, which is called wide-angle distortion. The wide-angle distortion can be expressed by “wide-angle distortion = (Lm−Ls) / Ls”. Therefore, in order for a spherical object on the object side to appear in a spherical shape on the image side, “Lm−Ls = It is desirable that the wide-angle distortion is “0”, that is, “0 (zero)”.

  The condition for setting the wide angle distortion to “0” is “(1) when the distortion in the image height direction is“ δ (h) ”and the distortion in the direction perpendicular to the image height direction is“ δ ′ (h) ”. / Cos θ) · [h · δ ′ (h) / (1 + δ (h)) + 1] = 1 ″ is satisfied. From this equation, “δ (h) = − tan 2 (θ / 2)”, and “y = 2f · tan (θ / 2)” can be calculated. A projection method that eliminates such wide-angle distortion is called three-dimensional projection.

  From the above, when correcting distortion inherent in the imaging lens 104, the distortion can be corrected by performing correction that satisfies the condition of “y = f · tan θ”. Further, wide angle distortion can be corrected by performing correction that satisfies the condition of “y = 2f · tan (θ / 2)”.

  Next, a description will be given of how an image is seen and distortion correction based on the subject, the subject distance, and distortion. FIG. 3 is a diagram illustrating the relationship between the subject, the subject distance, and the distortion, in which (B) and (C) are appropriate correction examples, and (A) and (D) are incorrect correction examples. .

  FIG. 3A shows an example in which a three-dimensional object such as a person's face is a main subject, the main subject is at a relatively close distance from the digital camera, and has a certain size in the imaging screen. When the distortion is an orthographic projection, a sense of incongruity is generated in the captured image due to wide-angle distortion. In this case, as shown in FIG. 3B, the distortion of the image is corrected so as to be a three-dimensional projection. As a result, the background is distorted due to distortion, but the wide-angle distortion is eliminated in the face of the person who is the main subject, and therefore, a sense of incongruity can be eliminated.

  In FIG. 3C, a three-dimensional object such as a person's face is reflected, but since this three-dimensional object is not the main subject and is at a relatively far distance from the digital camera, the size in the imaging screen is shown. This is an example of when is small. In this case, if the distortion is an orthographic projection, the straight object will not be distorted, and the image of a three-dimensional object such as a person's face to be photographed will be small on the screen. Absent. Even if there is no main three-dimensional object at such a short distance, if the distortion is made into a three-dimensional projection, a straight object appears to be bent due to distortion caused by the distortion of the flat object as shown in FIG. As a result, the image is uncomfortable. As described above, when the three-dimensional object is not the main subject but at a relatively far distance from the digital camera and the size in the imaging screen is small, the correction of the distortion aberration is corrected to be an orthogonal projection. .

  At this time, the distortion aberration correction amount may be weighted according to the subject, the subject distance, and the size of the subject in the imaging screen. In this case, the correction amount of the distortion aberration is between the orthogonal projection and the stereoscopic projection depending on the subject, the subject distance, and the size of the subject in the imaging screen (that is, 2f · tan (θ / 2) ≦ y). It is preferable to set so that the condition ≦ f · tan θ is satisfied.

  Many digital cameras have a plurality of shooting modes corresponding to different subjects. Examples of the shooting mode include a portrait (person) mode, a landscape mode, a sports mode, a flower (macro) mode, a night view mode, a fireworks mode, and the like. In such a digital camera, when a shooting mode is set assuming a scene in which a three-dimensional object such as a person is photographed at a short distance, the distortion aberration is corrected so that the stereoscopic projection is always performed. Also good. On the other hand, when a shooting mode is set that assumes a scene in which a subject close to a plane object is at a long distance, such as landscape shooting, distortion aberration correction may be performed so that the projection is always orthogonal. . Further, the photographer may be able to select a stereoscopic projection and an orthographic projection.

  Further, the condition “y ≦ 2f · tan (θ / 2)” is satisfied with respect to the image height y of the captured image, the incident angle θ from the subject to the imaging lens 104, and the focal length f of the imaging lens 104. It is also possible to design a digital camera. In this case, correction of distortion aberration inherent to the imaging lens 104 need only be corrected in the direction of enlarging the image, so that the correction circuit and the correction process can be simplified.

  As described above, according to the present invention, the amount of distortion correction for correcting distortion inherent in the imaging lens 104 is changed according to the subject and the subject distance. As a result, it is possible to obtain a good image without a sense of incongruity depending on the subject.

<Other embodiments>
Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of this invention, and it is also possible to combine each embodiment suitably.

  For example, in the above-described embodiment, a digital camera is taken up as an imaging device. However, the present invention is not limited to this, and is applied to other electronic devices equipped with a camera (imaging function) using an imaging element. Can do. That is, the present invention can also be applied to mobile communication terminals such as mobile phones and smartphones equipped with cameras, tablet PCs and notebook PCs equipped with cameras, and portable game machines equipped with cameras.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and the computer (or CPU, MPU, etc.) of the system or apparatus reads out and executes the program. It is processing to do. In this case, the program and the storage medium storing the program constitute the present invention.

DESCRIPTION OF SYMBOLS 101 Operation part 102 Control part 103 Image pick-up element 104 Imaging lens 108 Image processing part 113 AF process part 114 AE process part

Claims (8)

An imaging device that converts an optical image formed through an imaging lens into an image signal by an imaging device,
Correction means for correcting distortion inherent in the imaging lens by image processing;
The image pickup apparatus, wherein the correction unit changes a correction amount used when correcting the distortion aberration according to a focal length of the image pickup lens and an incident angle of a light beam from a subject to the image pickup lens. Equipped with measuring means to measure the distance to the subject,
The imaging apparatus according to claim 1, wherein the correction unit changes the correction amount according to a subject distance measured by the measurement unit. Measuring means for measuring the distance to the subject;
A face detection means for detecting a face in the imaging screen,
2. The correction unit according to claim 1, wherein the correction unit changes the correction amount according to a subject distance measured by the measurement unit and a position of the face detected by the face detection unit in the imaging screen. Imaging device. Measuring means for measuring the distance to the subject;
A shape detecting means for detecting the shape of the subject,
The imaging apparatus according to claim 1, wherein the correction unit changes the correction amount according to a subject distance measured by the measurement unit and a shape detected by the shape detection unit. It has multiple shooting modes depending on the subject,
5. The image pickup apparatus according to claim 1, wherein the correction unit changes the correction amount according to a difference in a shooting mode set from the plurality of shooting modes.   When the image height of the captured image is y, the incident angle from the subject to the imaging lens is θ, and the focal length of the imaging lens is f, the correction unit corrects to satisfy the condition y = f · tan θ. 6. The imaging according to claim 1, wherein the correction amount is changed so as to switch between a correction satisfying a condition of y = 2f · tan (θ / 2) and y = 2f · tan (θ / 2). apparatus.   When the image height of the captured image is y, the incident angle from the subject to the imaging lens is θ, and the focal length of the imaging lens is f, the correction unit is 2f · tan (θ / 2) ≦ y ≦ f The imaging apparatus according to claim 1, wherein the correction amount is changed so as to perform correction that satisfies the condition of tan θ.   When the image height of the captured image is y, the incident angle from the subject to the imaging lens is θ, and the focal length of the imaging lens is f, the distortion aberration inherent in the imaging lens is y ≦ 2f · tan (θ The imaging apparatus according to claim 1, wherein the condition (2) is satisfied.

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