Wide-angle imaging apparatus

Abstract

To provide a wide-angle imaging apparatus capable of acquiring a wide-angle image with reduced image distortion caused by lens field curvature, and with inconspicuous seams when images are stitched together.SOLUTION: The wide-angle imaging apparatus includes an imaging device 2 having a semi-cylindrical surface shape, a plurality of element lenses 4 arranged around the outer periphery of the imaging device 2, and a partial element image stitching unit 6 that extracts a partial region including the central area from each element image 9 formed on the imaging device 2 for each of the plurality of element lenses 4, and stitches the resulting plurality of partial element images.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus for capturing images with a wide field of view (angle of view), such as a panoramic image, and more particularly to a wide-field-of-view imaging apparatus in which multiple lenses are arranged around the periphery of a curved imaging device. [Background technology]

[0002] In recent years, there has been a demand for acquiring images with a wider viewing angle than those captured using wide-angle lenses such as fisheye lenses, and in response to this demand, progress has been made in the development of technologies to realize viewing that provides a higher level of immersion than conventional flat, high-definition images, such as 4K and 8K. It is anticipated that wide-viewing-angle images acquired in this manner will be utilized as immersive content, for example, by displaying them on a curved wide-viewing-angle display or viewing them on a head-mounted display.

[0003] As a technology for acquiring such wide-viewing-angle images, for example, a technology using one or more cameras equipped with an ultra-wide-angle (fisheye) lens is known (see Patent Document 1 below). Furthermore, in a camera device for a drive recorder that contributes to safe driving, a device is known that achieves wide-field shooting by stitching together images obtained using two cameras, one for the front and one for the rear, and two cameras for blind spot compensation, based on information obtained using a separate wide-angle lens (see Patent Document 2 below). Furthermore, a photography technique using a group of multiple lenses (lens array) has been proposed for a camera of an overlapping image system called TOMBO (see Patent Document 3 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-315380 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-250193 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-61109 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology described in Patent Document 1, due to the characteristics of the super-wide-angle (fisheye) lens, the occurrence of curved image distortion (field curvature) is unavoidable, particularly in the peripheral areas of the image. Furthermore, with the technology described in Patent Document 2, like the technology described in Patent Document 1, it is impossible to avoid the occurrence of field curvature due to the lens. Furthermore, when combining images from multiple cameras into a single image (performing a process of stitching the images together), the seams between the images become noticeable, and a satisfactory image is not necessarily obtained.

[0006] Furthermore, the technology described in Patent Document 3 employs a method of dividing a planar imaging element into multiple imaging areas and combining the individual images. However, because the imaging element itself is planar and the angle difference (parallax) between the shooting directions of the individual images is extremely small, it is difficult to achieve wide-field imaging, and for the same reason as the technology described in Patent Document 2, the seams between the images become noticeable, which is a problem.

[0007] The present invention has been made to solve the above problems, and aims to provide a wide-field-of-view imaging device that can obtain an image with a wide field of view while reducing image distortion associated with field curvature at the periphery of the lens, and with inconspicuous seams when combined. [Means for solving the problem]

[0008] The wide-viewing-angle imaging device of the present invention comprises: The imaging device has a cross section that is circular or a part of a circle, a plurality of element lenses arranged along the outer circumferential surface of the imaging device, and a partial element image stitching unit that cuts out a partial region including a central region of each element image obtained by forming an image on the imaging device for each element lens to obtain a partial element image, and stitches together the obtained partial element images, When the area on the imaging device where the element images corresponding to each of the element lenses are obtained is defined as a pixel area, the pixel area is shaped to have a recess that can reduce the field curvature caused by the element lenses.

[0009] It is also desirable that the imaging device has a cylindrical or partially cylindrical shape, where the "partial cylindrical shape" refers to a shape in which the central angle θ in a cross section is in the range of 0<θ<360°. In addition, it is desirable that the pixel areas of the imaging device corresponding to the respective element lenses are formed as a continuum. It is also preferable that the plurality of element lenses be formed in a cylindrical or cylindrical trapezoidal shape as a whole, with central axes coinciding with the central axes of the corresponding pixel areas.

[0010] It is also desirable that the element lens formed in a cylindrical or cylindrical trapezoidal shape as a whole and the recess of the pixel area corresponding to this element lens are formed coaxially. It is also desirable that a partition wall for preventing crosstalk be provided between adjacent lens elements. Furthermore, it is desirable that the imaging device be attached to the outer peripheral surface of a base having a circular or partial circular cross section. The above-mentioned "element lens" includes not only a single lens but also a lens system made up of a combination of multiple lenses. [Effects of the Invention]

[0011] According to the wide-field-of-view imaging device of the present invention, an imaging device having a cross section that is circular or part of a circle, and a plurality of element lenses arranged along the outer peripheral surface of the imaging device, a partial element image is obtained by cutting out a portion including the central region of each element image obtained for each element lens, and the obtained plurality of partial element images are stitched together, so that it is possible to obtain an image with a wide field of view but with inconspicuous seams when combined, and it is possible to eliminate image distortion associated with extreme field curvature. Furthermore, the pixel area is formed in a concave shape that can reduce the curvature of field caused by the element lenses, so that the image distortion caused by the curvature of field at the periphery of the lens can be reduced while still providing a wide field of view. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a wide-viewing-angle imaging device according to an embodiment of the present invention. [Figure 2] 2 is an enlarged cross-sectional view of a portion of the wide-viewing-angle imaging device shown in FIG. 1. FIG. [Figure 3] 3 is a schematic diagram showing how element lenses and pixel areas overlap when a part of the wide-viewing-angle imaging device shown in FIG. 2 is viewed from the light incident direction. [Figure 4] 2 is a diagram for explaining the processing content in the partial element image joining unit shown in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a specific configuration of a wide-viewing-angle imaging device according to an embodiment of the present invention will be described with reference to the drawings. The wide-viewing-angle imaging device according to this embodiment is a device that can capture an image with a wider field of view (angle of view) than any other imaging method used in television cameras.

[0014] <Basic configuration of wide-viewing-angle imaging device> Fig. 1 shows a cross-sectional view of a wide-view angle imaging device according to an embodiment of the present invention, and Fig. 2 shows an enlarged cross-sectional view of a portion of the wide-view angle imaging device of Fig. 1. That is, an imaging device 2 (with a radius of curvature R) curved into a semicylindrical surface shape (with an axis passing through the center of curvature O of the imaging device 2 in the depth direction of the paper in Fig. 1) is attached and fixed to a base 1 formed in a semicylindrical shape (with an axis passing through the center of curvature O of the imaging device 2 in the depth direction of the paper in Fig. 1), and a plurality of element lenses 4 are arranged around the imaging device 2 concentrically and fixed to each other by lens fixing members 3. Although this element lens 4 is shown in a cylindrical shape, it may also be formed in a cylindrical trapezoid shape in which one of the light incident end face and light emitting end face has a larger diameter than the other.

[0015] Each pixel area 5 of the imaging device 2, which is curved into a semi-cylindrical surface shape, and its corresponding element lens 4 are configured so that the central axis position of each coincides with the direction of light incidence, and so that each pixel area 5 is regularly arranged on the imaging device 2. Furthermore, each pixel area 5 is formed to have a recess 8 that can reduce the field curvature caused by the corresponding element lens 4. Specifically, the recess 8 is formed to be able to compensate for the amount of field curvature based on the lens data at the time of optical design of the element lens 4. The recess 8 is formed to follow a recess provided in advance on the surface of the base 1, but it may be molded after the imaging device 2 is attached onto the base 1.

[0016] The element lens 4 is positioned using the lens fixing member 3 so that the distance between the element lens 4 and the center of the concavely curved pixel area 5 (center of the recess 8) matches the design value of the back focus BFL of the element lens 4. The radius of curvature R of the imaging device 2 is the distance from the center of curvature O of the imaging device 2 to the center of the concavely curved pixel area 5 (center of the recess 8). Furthermore, it is preferable that the element lenses 4 are held by the lens fixing member 3 using a mechanism that allows for back focus adjustment, for example.

[0017] Furthermore, although the number of element lenses 4 is set to 12 and the angle of view per element lens 4 is set to 15 degrees in FIG. 1, it is possible to increase the number of element lenses 4 and make the imaging range covered by one element lens 4 smaller, and it is possible to set the number of element lenses 4 and the angle of view per element lens 4 to desired values.

[0018] In addition, the pixel size, number of pixels, aspect ratio, etc. in the pixel area 5 can be selected arbitrarily as long as no loss occurs in the stitched image formed by the image cutting and stitching processes. For example, when the pixel area 5 is square, the number of pixels arranged in the pixel area 5 is, for example, one hundred to several thousand in both the vertical and horizontal directions. Of course, the shape of the pixel area 5 can be other than a square, and in that case, the number of pixels arranged in the vertical and horizontal directions can be adjusted according to the shape (aspect ratio).

[0019] Furthermore, it is desirable that the semi-cylindrical base 1 is not easily deformed by external forces, and that the cylindrical side surface to which the imaging device 2 is attached is made of a material that absorbs incident light and does not reflect light in the direction of the incident light (for example, a metal material that has been black anodized).

[0020] Figure 2 shows an enlarged view of the structure of each element lens 4 of the wide-viewing-angle imaging device 100 shown in Figure 1, and shows how, in order from the light incident direction, the element lens 4, a predetermined area (central angle 15 degrees) of the imaging device 2 corresponding to this element lens 4, and a predetermined area (central angle 15 degrees) of the base 1 to which the imaging device 2 is attached are arranged.

[0021] Specifically, a solid-state imaging element such as a CMOS (Complementary Metal-Oxide-Semiconductor) sensor, a CCD (Charge-Coupled Device) sensor, or a TFT (Thin-Film Transistor) sensor can be used as the imaging device 2. Alternatively, a photosensitive material such as film can be used. Furthermore, it is preferable that the imaging device 2 be configured to form a continuous body (a single piece) of pixel areas 5 on a flexible substrate so that the pixel positions can be identified, and be attached to the base 1; however, it is also possible to configure the imaging device 2 such that, for example, a flexible substrate on which each pixel area 5 is formed individually is attached to the base 1, or a flexible substrate on which multiple pixel areas 5 are formed in an array is attached so that they are joined together on the base 1.

[0022] Furthermore, the design values ​​of the focal length, aperture, etc. of the element lenses 4 may be the same for all element lenses 4, or some element lenses 4 may be different from the other element lenses 4. Furthermore, it is preferable to provide a partition 7 (not shown in FIG. 1) to prevent crosstalk between adjacent lens elements 4, but it is also possible to adopt a mode in which the partition 7 is not provided. The partitions 7 may be provided only in the upper portions such as between the element lenses 4, or only in the lower portions such as between the element lenses 4 and the imaging device 2, or may be provided in both the upper and lower portions. Fig. 2 shows an embodiment in which the partitions 7 are provided in both the upper and lower portions, and these portions are integrated. Furthermore, although FIG. 2 shows the element lenses 4 held by the lens fixing members 3 supported by the partition walls 7, the element lenses 4 may be configured to be held directly by the partition walls 7.

[0023] 1, the wide-viewing-angle imaging device 100 also includes a partial pixel image stitching unit 6. For each of the plurality of elemental lenses 4, the partial elemental image stitching unit 6 obtains a partial elemental image by cutting out a portion including a central region of each elemental image 9 (see FIG. 3) obtained by image formation on the corresponding pixel area 5 on the imaging device 2, performs processing to stitch together the obtained partial elemental images corresponding to each elemental lens 4, and outputs the wide-viewing-angle image obtained in a predetermined data format.

[0024] FIG. 3 is a schematic diagram showing the overlapping state between the lens elements 4 and the pixel area 5 of the imaging device 2 when a part of the wide viewing angle imaging device shown in FIG. 2 is viewed from the light incident direction. That is, each element lens 4 (showing a projected image of the output end surface of the element lens 4 in FIG. 3) is arranged so as to include a rectangular pixel area 5 with a concave curved shape (having a recess 8), and is configured so that the optical axis of the element lens 4 coincides with the central axis of the corresponding pixel area 5. Element images 9 obtained by these pixel areas 5 are output to the partial element image stitching unit 6 via the output unit of the imaging device 2, respectively.

[0025] Each pixel area 5 has approximately the same number of pixels arranged vertically and horizontally, and as described above, has a spherical recess 8, which corrects the field curvature caused by the element lens 4. The shape of this recess 8 (particularly the curvature and depth) is adjusted according to the state and magnitude of the field curvature of the element lens 4 (obtained from the design values ​​of the element lens 4). The recess 8 that forms the concave shape of the pixel area 5 may extend outside the pixel area 5, as long as at least the area of ​​the pixel area 5 has the shape of the recess 8. However, each pixel area 5 is configured to fit within the area of ​​the image projected on the output end surface of the corresponding element lens 4, as shown in FIG. 3. The elemental images 9 formed by the output from each pixel 8 in the pixel area 5 are sequentially output from the output section of the imaging device to the partial elemental image joining section 6.

[0026] Next, the processing performed in the partial element image joining unit 6 will be described with reference to FIG. As described above, field curvature can be significantly improved by forming each pixel area 5 to have a recess 8 that can reduce the field curvature caused by the corresponding element lens 4, but extreme field curvature that exists in the peripheral region of the pixel area 5 can be eliminated by the following process, which extracts the central region of the image in the partial element image stitching unit 6. That is, the partial element image stitching unit 6 performs a cutout process to extract the central region of each of the N element images (element image 1 to element image N) input from the imaging device 2, and then performs a process to stitch together the N partial element images (partial element image 1 to partial element image N) with significantly improved field curvature as described above. Here, the corresponding edges of adjacent partial element images are joined together in an abutting state, and in this case, the abutting state means that images relating to the same subject area located on the corresponding edges of adjacent partial element images are superimposed on each other.

[0027] In this way, by performing a simple image combining process of joining adjacent partial element images together while they are in contact with each other, it is possible to obtain a wide-viewing-angle image in which the seams between adjacent partial element images are inconspicuous. Furthermore, the pixel area 5 is shaped to have recesses 8 that can reduce the curvature of field caused by the element lenses 4, so that it is possible to reduce image distortion caused by the curvature of field at the periphery of the element lenses 4 while still providing a wide field of view. This generally makes it possible to reduce peripheral shading as well as image distortion caused by the curvature of field. Note that while Figure 4 describes the process of joining partial element images that are adjacent in the horizontal direction, the process of joining partial element images that are adjacent in the vertical direction can also be performed in a similar manner, and the same effects can be achieved by this process.

[0028] (Modifications) The wide-viewing-angle imaging device of the present invention is not limited to the above-described embodiment, and various other modifications are possible. For example, in the above-described embodiment, an imaging device having a cross section shaped like a semi-cylindrical surface is used, but instead, an imaging device having a cross section shaped like a partial cylindrical surface with any central angle θ (0 degrees < θ ≦ 360 degrees (excluding 180 degrees)) can be used, and the same effects as those achieved by using an imaging device having a cross section shaped like a semi-cylindrical surface can be achieved. In addition, instead of an imaging device having a cylindrical surface shape or the above-mentioned partial cylindrical surface shape, it is also possible to use an imaging device having a spherical surface shape or a partial spherical surface shape such as a hemispherical surface shape, and the same effects as those obtained when an imaging device having a cylindrical surface shape or the above-mentioned partial cylindrical surface shape is used can be achieved. Furthermore, the shape of the base to which the imaging device is attached can be either a circular cross section or a partially circular shape with an arbitrary central angle, depending on the shape of the imaging device.

[0029] When the specifications of a lens element are changed, it is necessary to change the back focus BFL of the lens element. Therefore, when there is a possibility of changing the lens specifications, it is preferable to have a configuration in which the lens element is indirectly or directly locked to the imaging device and can be moved perpendicular to the light incident surface of the imaging device as necessary, as described above. Furthermore, the image to be acquired may be not only visible light but also infrared light, ultraviolet light, or other radiation, and can be selected depending on the use of the image to be acquired. [Explanation of symbols]

[0030] 1 pedestal 2. Imaging device 3 Lens fixing member 4-element lens 5 pixel area 6. Partial element image stitching 7 Bulkhead 8 recess 9 Element Images 100 Wide-field imaging device

Claims

1. The imaging device has a cross section that is circular or a part of a circle, a plurality of element lenses arranged along the outer circumferential surface of the imaging device, and a partial element image stitching unit that cuts out a partial region including a central region of each element image obtained by forming an image on the imaging device for each element lens to obtain a partial element image, and stitches together the obtained partial element images, A wide-viewing-angle imaging device characterized in that, when an area on the imaging device where the element images corresponding to each of the element lenses are obtained is defined as a pixel area, the pixel area is shaped to have a recess that can reduce the field curvature caused by the element lenses.

2. 2. The wide-viewing-angle imaging device according to claim 1, wherein the imaging device has a cylindrical or partially cylindrical shape.

3. 2. The wide-viewing-angle imaging device according to claim 1, wherein the imaging device has a continuum of pixel areas corresponding to the lens elements.

4. 2. The wide-viewing-angle imaging device according to claim 1, wherein the plurality of element lenses are formed into an overall cylindrical or cylindrical trapezoidal shape having central axes that coincide with the central axes of the corresponding pixel areas.

5. 5. The wide-viewing-angle imaging device according to claim 4, wherein the element lens formed in an overall cylindrical or cylindrical trapezoidal shape and the recess in the pixel area corresponding to this element lens are formed coaxially.

6. 2. The wide-viewing-angle imaging device according to claim 1, wherein a partition wall for preventing crosstalk is provided between adjacent lens elements.

7. A wide-field-of-view imaging device according to any one of claims 1 to 6, characterized in that the imaging device is attached to the outer peripheral surface of a base having a circular or partial circular cross section.

Images