Imaging system and imaging method

Abstract

Provided are an imaging system and an imaging method capable of forming a high-quality image. This imaging system comprises: an illumination unit that emits, at a first degree of polarization, light polarized in a first direction with respect to an imaging region; and an imaging unit that receives, at a second degree of polarization, light polarized in a second direction from the imaging region. The first direction and the second direction intersect each other, and at least one of the first degree of polarization and the second degree of polarization is 10%-90%.

Description

Imaging system and imaging method

[0001] The present invention relates to an imaging system and an imaging method, and more particularly to an imaging system and an imaging method that utilize polarized light.

[0002] Patent Document 1 describes a technique for suppressing the influence of specular reflection by using polarized light in imaging using illumination.

[0003] Japanese Patent Application Laid-Open No. 2001-133856

[0004] One embodiment of the technique of the present disclosure provides an imaging system and an imaging method that can capture high-quality images.

[0005] [1] An imaging system comprising an illumination unit that emits light polarized in a first direction toward an imaging area with a first degree of polarization, and an imaging unit that receives light polarized in a second direction from the imaging area with a second degree of polarization, wherein the first direction and the second direction intersect, and at least one of the first degree of polarization and the second degree of polarization is 10% or more and 90% or less.

[0006] [2] The imaging system described in [1], wherein the illumination unit includes a light source and a first polarizing plate that transmits light polarized in a first direction, and the imaging unit includes an imaging element and a second polarizing plate that transmits light polarized in a second direction.

[0007] [3] The imaging system according to [2], wherein the first polarizing plate is configured as a polarizing plate having a first polarization degree, and the second polarizing plate is configured as a polarizing plate having a second polarization degree.

[0008] [4] The imaging system according to [2], wherein at least one of the first polarizing plate and the second polarizing plate is composed of a polarizing plate having a different degree of polarization in parts.

[0009] [5] The imaging system according to [4], wherein the polarizing plate with a partially different polarization degree is a polarizing plate having a partially 0% polarization degree region.

[0010] [6] The imaging system according to [5], wherein the polarizing plate having a partially different degree of polarization is a polarizing plate having discrete regions with a degree of polarization of 0%.

[0011] [7] The polarizing plate having different degrees of polarization in parts is a polarizing plate having different degrees of polarization in a first region corresponding to the region where the light source is reflected and a second region different from the first region, and the degree of polarization in the second region is lower than that in the first region, in the imaging system described in [4].

[0012] [8] The imaging system according to [7], wherein the degree of polarization of the second region is 0%.

[0013] [9] The imaging system described in [4], wherein at least one of the first polarizing plate and the second polarizing plate has a lower degree of polarization in a fourth region on the periphery than in a third region on the central side.

[0014]

[10] The imaging system according to [9], wherein the degree of polarization of the fourth region is 0%.

[0015]

[11] The imaging system according to [2], wherein at least one of the first polarizing plate and the second polarizing plate is a polarizing plate that transmits light in a specific wavelength range.

[0016]

[12] The imaging system described in [2], further comprising a first drive unit that moves the first polarizing plate in and out of the optical path, and / or a second drive unit that moves the second polarizing plate in and out of the optical path.

[0017]

[13] An imaging system as described in

[12] , comprising a processor, the processor controlling the first driving unit and / or the second driving unit to move the first polarizing plate and / or the second polarizing plate out of the optical path during exposure of the imaging unit.

[0018]

[14] The imaging system described in

[12] includes a processor, which controls the first driving unit and / or the second driving unit and the imaging unit to cause the imaging unit to perform imaging with the first polarizing plate and / or the second polarizing plate inserted into the optical path, and imaging with the first polarizing plate and / or the second polarizing plate retracted from the optical path.

[0019]

[15] The imaging system according to any one of [1] to

[14] , wherein the first direction and the second direction intersect at an angle of 90°±10°.

[0020]

[16] The imaging system according to any one of [1] to

[15] , wherein at least one of the first polarization degree and the second polarization degree is 30% or more and 70% or less.

[0021]

[17] The imaging system according to any one of [1] to

[16] , wherein the first polarization degree and the second polarization degree are 10% or more and 90% or less.

[0022]

[18] The imaging system according to any one of [1] to

[17] , which includes a plurality of illumination units for one imaging unit.

[0023]

[19] An imaging method using an illumination unit that emits light polarized in a first direction toward an imaging area with a first degree of polarization, and an imaging unit that receives light polarized in a second direction from the imaging area with a second degree of polarization, in which the first direction and the second direction are crossed to suppress reflection of the light source, and imaging is performed with at least one of the first degree of polarization and the second degree of polarization set to 10% or more and 90% or less.

[0024]

[20] The imaging method described in

[19] , in which the degree of polarization in the imaging area is reduced spatially, temporally, or wavelength-wise to make at least one of the first degree of polarization and the second degree of polarization 10% or more and 90% or less.

[0025] 11-11 sectional view of FIG. 10. Diagram showing the connection structure between the multi-eye imaging device and the control device. Diagram showing an example of the hardware configuration of the control device. Block diagram of the main functions of the control device regarding the imaging control function. Block diagram of the main functions of the camera control unit. Live view table. FIG. 1 is a diagram showing an example of a configuration of a control device; FIG. 2 is a block diagram of the main functions of the control device with regard to the image processing function; FIG. 3 is a conceptual diagram of composition processing by feature point matching; FIG. 4 is a conceptual diagram of imaging with one imaging unit; FIG. 5 is a conceptual diagram of imaging with one imaging unit; FIG. 6 is a diagram showing another example of setting the polarized and non-polarized regions; FIG. 7 is a diagram showing another example of setting the polarized and non-polarized regions;

[0026] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0027] Stitching is a known technique for generating a single image that captures a wide range of area. In stitching, an object is divided into multiple parts and captured, and the resulting images are stitched together to generate a single image (a so-called panoramic composite image). Feature point matching (corresponding point search) is generally used to synthesize images. Image synthesis using feature point matching involves extracting feature points from each image, matching similar feature points, and generating synthesis parameters based on the correspondence between the extracted feature points to synthesize the images. For this reason, synthesis may fail if a sufficient number of feature points cannot be extracted from the images.

[0028] Photogrammetry is also known as a technique for reconstructing the three-dimensional shape of an object. Photogrammetry involves capturing images of an object from multiple viewpoints (multi-viewpoints) and reconstructing the three-dimensional shape of the object from the resulting images (multi-viewpoint images). Photogrammetry performs feature point matching between each image and uses the processing results to reconstruct the three-dimensional shape of the object. For this reason, if a sufficient number of feature points cannot be extracted from the images, reconstruction may fail.

[0029] One of the factors that hinders the extraction of feature points is the reflection of the light source when capturing an image using lighting. That is, when capturing an image using lighting, reflection from the surface of the subject can cause parts of the image to appear white (overexposed), making it impossible to extract feature points.

[0030] It is known that the reflection of light sources can be suppressed by using polarized light. Polarized light imaging utilizes the polarization properties of reflected light from the subject (when light is specularly reflected, the polarization of the incident light is maintained during reflection), and by placing polarizers on both the illumination side and the imaging side, reflection of light sources in the captured image is suppressed. In this case, the polarization axes of the polarizers on the illumination side and the imaging side are placed orthogonal to each other. This allows the specularly reflected light from the subject to be removed by the polarizer on the imaging side, suppressing reflection of light sources in the captured image.

[0031] However, conventional imaging using polarized light involves a configuration in which the light used is completely polarized, resulting in a significant reduction in the amount of light incident on the imaging element. Specifically, completely polarizing the illumination light halves the illumination intensity, and further halves the transmittance on the imaging side, resulting in a problem in that the amount of light ultimately incident on the imaging element is one-fourth of that normally (imaging without polarized light). As a result, there is a problem in that imaging cannot be performed with sufficient brightness. If imaging cannot be performed with sufficient brightness, it is necessary to extend the exposure time or increase the sensitivity, resulting in a problem in that high-quality images (especially images from which feature points can be extracted) cannot be captured.

[0032] Hereinafter, an imaging system and an imaging method that can capture an image with sufficient brightness while suppressing reflection of a light source will be described as one embodiment of the present invention.

[0033] First Embodiment Here, an example in which the present invention is applied to an imaging system used for inspecting a tunnel structure will be described.

[0034] Tunnel structures (hereinafter referred to as "tunnels"), such as water conduits for hydroelectric power plants and subway tunnels, are inspected periodically to ensure their safety. Recently, visual inspections have been replaced by image-based inspections. Image-based inspections involve capturing images of the tunnel's inner wall with a camera and then visually or by image processing to detect damage such as cracks in the images.

[0035] The area to be inspected is divided into multiple areas for imaging. The images of each area are stitched together to form a single image (a panoramic composite image). For this reason, the images of each area are captured with some overlapping with the images of adjacent areas.

[0036] Furthermore, imaging is performed using illumination, that is, an imaging area is irradiated with illumination light from an illumination device, and an image of the imaging area is captured.

[0037] [Configuration of Imaging System] FIG. 1 is a diagram showing a schematic overall configuration of an imaging system.

[0038] The imaging system 1 of this embodiment is configured as a system that captures images of the entire inner wall surface (inner wall surface excluding the floor surface) of the tunnel 2 for the purpose of inspecting the tunnel 2 using images.

[0039] As shown in FIG. 1, the imaging system 1 includes a multi-lens imaging device 10 and a control device 500, and is configured as a system that captures images of an inner wall surface 2A of a tunnel 2 while moving within the tunnel 2 on a cart 3.

[0040] The cart 3 may be a so-called push type (a type that is moved by pushing it by hand) or a self-propelled type equipped with power. The cart 3 in FIG. 1 shows an example of a push type. In this case, the cart 3 moves through the tunnel 2 while being pushed by a person. If rails are laid in the tunnel 2, it is preferable that the cart 3 be configured to run on the rails.

[0041] [Multi-eye imaging device] FIG. 2 is a perspective view showing the configuration of the multi-eye imaging device. FIG. 3 is a front view showing the configuration of the multi-eye imaging device. FIG. 4 is a rear view showing the configuration of the multi-eye imaging device. FIG. 5 is a side view showing the configuration of the multi-eye imaging device. FIG. 6 is a plan view showing the configuration of the multi-eye imaging device. In FIGS. 2 to 6, the x-axis, y-axis, and z-axis are three mutually orthogonal axes. The plane including the x-axis and y-axis is the horizontal plane, and the z-axis is the vertical direction. Also, in FIGS. 2 to 6, the x-axis direction is the front-to-rear direction of the multi-eye imaging device 10, the y-axis direction is the left-to-right direction (lateral direction) of the multi-eye imaging device 10, and the z-axis direction is the up-to-down direction of the multi-eye imaging device 10. The multi-eye imaging device 10 moves in the front-to-back direction to capture an image of the inner wall surface 2A of the tunnel 2. Note that in FIGS. 2, 5, and 6, the direction indicated by arrow F is the forward direction of the multi-eye imaging device 10, and the direction indicated by arrow R is the rearward direction of the multi-eye imaging device 10.

[0042] The multi-lens imaging device 10 is configured by combining multiple imaging units 20. The number of imaging units 20 used can be increased or decreased as needed depending on the subject to be imaged, etc. Here, an example in which five imaging units 20 are used will be described.

[0043] Each imaging unit 20 is attached to the frame 11 and arranged at a predetermined position. In this embodiment, the inner wall surface 2A of the tunnel 2 is the object to be imaged, so the multiple imaging units 20 are arranged in an arc shape.

[0044] The frame 11 is mainly composed of a flat base 12 , a rectangular column 13 standing vertically on the base 12 , and a disk-shaped mounting base 14 attached to the column 13 .

[0045] The mounting base 14 is a mounting portion for the imaging device 100 and the lighting devices 200F, L1R to L1R. The mounting base 14 is installed perpendicular to the base 12. The mounting base 14 is attached to the column 13 so that its height can be adjusted by changing its attachment position. An axis Ax that passes through the center of the mounting base 14 and is parallel to the x-axis is defined as the axis of the multi-eye imaging device 10.

[0046] FIG. 7 is a perspective view showing the configuration of the imaging unit.

[0047] The imaging unit 20 includes at least one imaging device and at least one lighting device. In this embodiment, an example will be described in which the imaging unit 20 includes one imaging device 100 and two lighting devices 200F and 200R.

[0048] As shown in FIG. 7, the imaging device 100 and the lighting devices 200F and 200R are attached to a bracket 21 to form a unit.

[0049] The two lighting devices 200F, 200R are arranged symmetrically in the front and rear directions with the image capture device 100 in between. Hereinafter, as necessary, the lighting device 200F arranged in front of the image capture device 100 will be referred to as the "front-side lighting device 200F" and the lighting device 200R arranged behind the image capture device 100 will be referred to as the "rear-side lighting device 200R" to distinguish between the two.

[0050] The imaging device 100 and the illumination devices 200F and 200R are arranged with their orientations aligned, i.e., with the imaging direction and the illumination light irradiation direction aligned.

[0051] The imaging unit 20 is attached to the frame 11 of the multi-eye imaging device 10 via a bracket 21. Specifically, as shown in Fig. 3, the bracket 21 is fixed to the mounting base 14 using a clamp 22, thereby attaching the imaging unit 20 to the frame 11.

[0052] The brackets 21 of each imaging unit 20 are attached on the same circumference centered on the axis Ax of the multi-eye imaging device 10. Furthermore, each bracket 21 is attached so that its position can be adjusted within a predetermined angular range (for example, 30°) in the circumferential direction around the axis Ax.

[0053] The imaging unit 20 assembled to the frame 11 is disposed at a predetermined position and in a predetermined orientation with respect to the axis Ax. Specifically, the imaging units 20 are disposed radially around the axis Ax in a plane perpendicular to the axis Ax (the zy plane). More specifically, the imaging optical axes of the imaging devices 100 are disposed so as to face radially outward of a circle centered on the axis Ax. Furthermore, the bottom surfaces of the imaging devices 100 (bottom surfaces of the imaging device bodies) are mounted parallel to the mounting base 14 (parallel to the zy plane). That is, the bottom sides of the light receiving surfaces of the imaging elements are mounted parallel to the zy plane. Because the illumination devices 200F and 200R are disposed so as to face the same direction as the imaging device 100, the illumination devices 200F and 200R are also disposed so as to face radially outward of a circle centered on the axis Ax.

[0054] As described above, the bracket 21 of each imaging unit 20 is attached so that its position can be adjusted in the circumferential direction. Figures 3 and 4 show a state in which the bracket 21 of each imaging unit 20 is fixed at a reference position (the center of the movable range). By fixing the bracket 21 at the reference position, the imaging units 20 are arranged at equal intervals. In this embodiment, as shown in Figure 3, the imaging units 20 are arranged at 60° intervals in the range from -30° to 210°. More specifically, the imaging units 20 are arranged at positions of -30°, 30°, 90°, 150°, and 210°.

[0055] The positions and / or imaging angles of view of the imaging devices 100 of the multiple imaging units 20 assembled to the frame 11 are adjusted so that the imaging areas of adjacent imaging devices overlap. At this time, the positions and / or imaging angles of view are adjusted so that an overlap rate of at least 10% or more is ensured. The overlap rate refers to the rate at which the imaging areas of adjacent imaging devices overlap (the rate at which the captured images overlap).

[0056] [Imaging Device] FIG. 8 is a diagram showing a schematic configuration of an imaging device.

[0057] The imaging device 100 is a digital camera. That is, it is a camera that records images electrically. As an example, in this embodiment, the imaging device 100 is a digital camera with an interchangeable lens, and includes an imaging lens 110 and an imaging device body 130. The imaging lens 110 is interchangeable and is attached to the imaging device body 130 via a lens mount.

[0058] As shown in FIG. 8, the imaging device 100 receives light that has passed through an imaging lens 110 with an imaging element 131, converts the light into digital data, and records the digital data.

[0059] The imaging lens 110 includes a polarizing filter 120 as part of its optical system. As an example, in this embodiment, the polarizing filter 120 is attached to the tip (the position closest to the object) of the imaging lens 110, and the polarizing filter 120 is incorporated into the optical system of the imaging lens 110. Generally, imaging lenses (interchangeable lenses) for interchangeable lens digital cameras are configured to allow an optical filter or the like to be attached to their tips. Specifically, the inner periphery of the tip of the lens barrel is provided with a female thread portion, and the female thread portion can be used to attach an optical filter or the like. Therefore, the polarizing filter 120 can be attached to the tip of the imaging lens 110 by utilizing the female thread portion at the tip of the lens barrel.

[0060] By including the polarizing filter 120 as part of the optical system, light that has passed through the polarizing filter 120 is incident on the image sensor 131. The polarizing filter 120 is combined with the polarizing filter 240 provided in the illumination devices 200F and 200R to suppress reflection of the light source due to specular reflection. This point will be described in detail later.

[0061] FIG. 9 is a diagram showing the electrical configuration of the imaging device.

[0062] The imaging lens 110 includes a lens group 111 , an aperture 112 , a lens driver 113 , an aperture driver 114 , a lens operation unit 115 , and a lens microcomputer 116 .

[0063] The lens driving unit 113 moves all or part of the lens group 111 back and forth along the optical axis, thereby performing focus adjustment.

[0064] The diaphragm 112 is configured by, for example, an iris diaphragm. The diaphragm driver 114 drives the diaphragm 112 to operate the diaphragm blades and change the opening diameter of the diaphragm 112. In this way, the amount of light is adjusted.

[0065] The lens operation unit 115 is an operation unit for the imaging lens 110. The lens operation unit 115 includes various operation members such as a focus ring and an aperture ring, and outputs signals to the lens microcomputer 116 according to the operation of each operation member.

[0066] The lens microcomputer 116 is composed of a microcontroller (Micro Controller Unit: MCU) equipped with a processor and memory. The lens microcomputer 116 functions as a control unit for the imaging lens 110 by the processor executing a predetermined program. The memory stores the program executed by the processor and various data. The lens microcomputer 116 controls the lens driver 113 and the aperture driver 114 in response to operation input from the lens operation unit 115 and commands from the camera microcomputer 138.

[0067] The imaging device main body 130 includes an imaging element 131, a mechanical shutter 132, a digital signal processing unit 133, a storage unit 134, a display unit 135, an interface (I / F) unit 136, a camera operation unit 137, a camera microcomputer 138, and the like.

[0068] The mechanical shutter 132 is configured by, for example, a focal plane shutter. The mechanical shutter 132 operates and opens and closes in response to commands from a camera microcomputer 138.

[0069] The image sensor 131 converts the image formed by the imaging lens 110 into an electrical signal. As an example, in this embodiment, the image sensor 131 is configured as a CMOS (Complementary Metal-Oxide-Semiconductor) color image sensor having a predetermined color filter array. The image sensor 131 operates in response to commands from the camera microcomputer 138 to capture an image. The image sensor 131 includes an ADC (Analog to Digital Converter) and converts the signal of each pixel (pixel signal) obtained by capturing an image into a digital signal and outputs the digital signal. The image sensor 131 also includes a signal processing unit and performs predetermined signal processing (e.g., correlated double sampling, gain processing, correction processing, etc.) on the pixel signal and outputs the digital signal.

[0070] The digital signal processing unit 133 performs predetermined signal processing (for example, pixel interpolation processing, demosaic processing, gamma correction processing, white balance adjustment processing, etc.) on the pixel signals output from the image sensor 131 to generate image data.

[0071] The storage unit 134 stores data in a readable and writable manner. The storage unit 134 is composed of, for example, an internal memory and / or an external memory. The internal memory is composed of, for example, a non-volatile semiconductor memory, and is built into the imaging device main body 130. The external memory is composed of, for example, a memory card, and is loaded into a card slot provided in the imaging device main body 130.

[0072] In this embodiment, the captured image data is recorded by the control device 500. That is, all image data captured by each imaging device 100 is output to the control device 500 and recorded in a storage unit (auxiliary storage device 514) of the control device 500.

[0073] The display unit 135 is used to play back captured images, and also to display live view images as needed during image capture, serving as a viewfinder. It is also used as a setting monitor for configuring various settings. The display unit 135 may be configured with, for example, a liquid crystal display (LCD) or an organic light emitting diode (OLED) display. The display unit 135 may also include a touch panel.

[0074] The interface unit 136 is a unit for connecting to external devices. The imaging device 100 is connected to the external devices via the interface unit 136 so as to be able to communicate with them. Connection methods include both wired and wireless methods. An example of a wired connection is USB (Universal Serial Bus). Examples of a wireless connection are Wi-Fi (registered trademark) and Bluetooth (registered trademark).

[0075] The camera operation unit 137 is an operation unit of the imaging device main body 130. The camera operation unit 137 includes various operation members such as a power button and a shutter button, and outputs information to the camera microcomputer 138 according to the operation of each operation member.

[0076] The camera microcomputer 138 is configured with a microcontroller equipped with a processor and memory. The camera microcomputer 138 functions as a control unit and signal processing unit of the imaging device 100 by the processor executing a predetermined program. The functions of the control unit include photometry control, distance measurement control, exposure control (imaging control), recording control, playback control, display control, setting control, and communication control. Exposure control includes drive control of the lens group 111, drive control of the diaphragm 112, drive control of the mechanical shutter 132, and drive control of the image sensor 131. Drive control of the lens group 111 and drive control of the diaphragm 112 is performed via the lens microcomputer 116. The camera microcomputer 138 communicates with the lens microcomputer 116 via a communication terminal provided on the lens mount. The camera microcomputer 138 communicates with external devices via the interface unit 136. The memory stores programs executed by the processor and various data.

[0077] [Lighting Device] Fig. 10 is a front view showing a schematic configuration of a lighting device, and Fig. 11 is a cross-sectional view taken along line 11-11 of Fig. 10.

[0078] Illumination devices 200F and 200R have a light source unit 220 inside a housing 210, and light from light source unit 220 is emitted from a rectangular light emitting unit 230 provided on the front surface of housing 210. As an example, in this embodiment, an LED (Light Emitting Diode) is used as the light source.

[0079] The light source unit 220 is configured with a plurality of LED elements 221. The plurality of LED elements 221 are arranged regularly within the housing 210. As an example, in this embodiment, the light source unit 220 is configured by arranging the plurality of LED elements 221 in a two-dimensional matrix within the housing 210.

[0080] The light emitting unit 230 is provided with a polarizing filter 240 and a light distributing lens 250. The light emitted from the light source unit 220 (light emitted from the LED element 221) is emitted from the light emitting unit 230 via the polarizing filter 240 and the light distributing lens 250.

[0081] The polarizing filter 240 is combined with the polarizing filter 120 provided in the image capturing device 100 to suppress reflection of the light source due to specular reflection, as will be described in detail later.

[0082] The light distribution lens 250 causes the light from the light source unit 220 to exit from the light emitting unit 230 at a predetermined light distribution angle (beam angle).

[0083] In this embodiment, two illumination devices 200F and 200R are combined to illuminate the imaging area of ​​one imaging device 100. Specifically, the imaging area of ​​imaging device 100 is divided into two in the front-to-rear direction, and the front imaging area is illuminated by front-side illumination device 200F and the rear imaging area is illuminated by rear-side illumination device 200R.

[0084] [Connection Between Multi-Eye Imaging Device and Control Device] FIG. 12 is a diagram showing a connection structure between the multi-eye imaging device and the control device.

[0085] As shown in FIG. 12, the multi-eye imaging device 10 includes a relay device 300, and is communicably connected to a control device 500 via the relay device 300.

[0086] The relay device 300 is configured, for example, by a computer with a communication function. Each of the image capture devices 100 and the lighting devices 200F, 200R is connected to the relay device 300. The connection form between each of the image capture devices 100 and the lighting devices 200F, 200R and the relay device 300 is not particularly limited. It may be wired or wireless. As an example, in this embodiment, each of the image capture devices 100 and the lighting devices 200F, 200R and the relay device 300 are connected to each other via a wire (for example, USB) so that they can communicate with each other.

[0087] There is also no particular limitation on the connection form between the control device 500 and the relay device 300. As an example, in the present embodiment, the control device 500 and the relay device 300 are connected to each other so as to be able to communicate wirelessly (for example, via a wireless local area network (LAN)).

[0088] [Control Device] FIG. 13 is a diagram illustrating an example of the hardware configuration of the control device.

[0089] 13, the control device 500 includes a processor 511, a memory 512, an auxiliary storage device 514, an input device 515, a display device 516, and a communication interface 517. Generally, this type of configuration can be realized by a computer. As an example, in this embodiment, the control device 500 is configured as a notebook personal computer.

[0090] The processor 511 is configured by, for example, a CPU (Central Processing Unit). The memory 512 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The processor 511 executes a predetermined program, causing the control device 500 to function as a control device. The program executed by the processor 511 is stored in the memory 512 or the auxiliary storage device 514.

[0091] The auxiliary storage device 514 constitutes a storage unit of the control device 500. The auxiliary storage device 514 is constituted by, for example, a hard disk drive (HDD), a solid state drive (SSD), or the like.

[0092] The input device 515 constitutes an operation unit of the control device 500. The input device 515 is constituted by, for example, a keyboard, a mouse, a touch panel, and the like.

[0093] The display device 516 constitutes a display unit of the control device 500. The display device 516 is constituted by, for example, a liquid crystal display, an organic EL display, or the like.

[0094] The communication interface 517 constitutes a communication unit of the control device 500. The communication interface 517 is configured to be able to communicate with at least the relay device 300 using a predetermined communication method.

[0095] [Functions of the Control Device] The control device 500 has a function of controlling the multi-eye imaging device 10 and a function (image processing function) of processing images captured by the multi-eye imaging device 10. The function of controlling the multi-eye imaging device 10 includes a function (imaging control function) of controlling imaging by the multi-eye imaging device 10.

[0096] [Imaging Control Function] FIG. 14 is a block diagram of the main functions of the control device regarding the imaging control function.

[0097] 14, the control device 500 mainly has functions of a camera control unit 511A and an illumination control unit 511B, etc., with respect to the function of controlling image capture by the multi-eye imaging device 10. The functions of the camera control unit 511A and the illumination control unit 511B are realized by the processor 511 executing a predetermined program.

[0098] FIG. 15 is a block diagram of the main functions of the camera control unit.

[0099] As shown in FIG. 15, the camera control unit 511A mainly has the functions of an imaging control unit 511A1, a captured image acquisition unit 511A2, a captured image display control unit 511A3, and a captured image recording control unit 511A4.

[0100] The imaging control unit 511A1 controls each imaging device 100 mounted on the multi-eye imaging device 10 to cause each imaging device 100 to perform imaging. Imaging includes both still image capturing and video capturing. Still image capturing also includes so-called interval imaging. Interval imaging is a function that repeatedly captures still images at regular intervals. The imaging control unit 511A1 causes each imaging device 100 to perform imaging based on operation input (instruction to perform imaging) from the input device 515. In the case of video image capturing and interval imaging, imaging is started in response to an instruction to start imaging, and imaging is ended in response to an instruction to end imaging.

[0101] Each imaging device 100 captures images synchronously. Therefore, when capturing a still image, each imaging device 100 captures an image simultaneously (including a range that can be considered as nearly simultaneous). Also, when capturing a moving image, each imaging device 100 starts capturing images simultaneously and finishes capturing images simultaneously.

[0102] The captured image acquisition unit 511A2 acquires images captured by each imaging device 100. The images here include so-called live view images as well as images that are actually captured (images obtained in response to an imaging instruction).

[0103] The captured image display control unit 511A3 controls the display of images captured by each imaging device 100 (including live view images).

[0104] FIG. 16 is a diagram showing an example of a live view display.

[0105] 16, live view images of the imaging devices 100 are displayed in five image display areas IDA1 to IDA5 set on the display screen of the display device 516. The image display areas IDA1 to IDA5 are arranged in a layout corresponding to the arrangement of the imaging devices 100 in the multi-eye imaging device 10. Therefore, in this embodiment, the image display areas IDA1 to IDA5 are arranged in an arc shape.

[0106] The captured image recording control unit 511A4 controls the recording of images captured by each imaging device 100. In this embodiment, an image database (DB) 520 is created in the auxiliary storage device 514, and images captured by each imaging device 100 are recorded therein.

[0107] The captured image recording control unit 511A4 records images of each imaging device 100 in the image database 520 in units of images. One unit of image capture is the capture required to generate one composite image (panoramic composite image). Therefore, for example, when generating a composite image of the entire length of a tunnel, images captured over the entire length of the tunnel are recorded as a single group (image group) in a manner that allows them to be distinguished from one another. The captured image recording control unit 511A4 associates information about the imaging device that captured the images and information about the order in which the images were captured with each imaging device 100 and records the images of each imaging device 100 in the image database 520. That is, the images of each imaging device 100 are recorded in a manner that allows distinguishing which imaging device 100 captured each image and in what order. The form of association is not particularly limited. It is sufficient that the imaging device that captured each image and the order in which the images were captured can be identified. As an example, in this embodiment, information about the imaging device that captured the images and information about the order in which the images were captured are added to the images as additional information (e.g., meta information) and the images captured by each imaging device 100 are recorded.

[0108] The illumination control unit 511B controls the illumination devices 200F, 200R mounted on the multi-eye imaging apparatus 10. That is, it controls the on / off of the emission of illumination light from the illumination devices 200F, 200R. The illumination control unit 511B emits illumination light based on operation input (on instruction and off instruction) from the input device 515.

[0109] [Image Processing Function] FIG. 17 is a block diagram showing the main functions of the control device regarding the image processing function.

[0110] The control device 500 has a function (image processing function) for processing images captured by the multi-eye imaging device 10, such as stitching together multiple images captured by the multi-eye imaging device 10 to generate a single image (panoramic composite image).

[0111] 17 , with regard to the function of generating a composite image (panoramic composite image), the control device 500 has functions such as a processing target image acquisition unit 511C, a synthesis processing unit 511D, a composite image recording control unit 511E, and a composite image display control unit 511F. The functions of each unit are realized by the processor 511 executing a predetermined program.

[0112] The processing target image acquisition unit 511C acquires a group of images to be processed in the compositing process. That is, it acquires a group of images for generating a composite image. The processing target image acquisition unit 511C acquires the group of images to be processed from the image database 520.

[0113] As described above, information about the imaging device that captured the image and the order in which the images were captured are added to the images recorded in the image database 520. This information provides information about the image capture position. Therefore, by acquiring the image group to be processed, information about the image capture position (approximate image capture position within the tunnel) of each image that makes up the image group can be obtained at the same time.

[0114] The synthesis processing unit 511D performs a predetermined synthesis process on the group of images acquired by the processing target image acquisition unit 511C to generate a synthesized image. In this embodiment, the synthesis process is performed by so-called feature point matching (corresponding point search). Feature point matching is a process of matching feature points that have a high degree of similarity between images. In general, feature points are detected and feature descriptors are calculated for two images, and feature points that have a high degree of similarity are matched.

[0115] In the synthesis process using feature point matching, parameters required for the synthesis process (synthesis parameters) are determined from the results of the feature point matching, and the synthesis process is performed based on the determined synthesis parameters. More specifically, an image is projected onto a shape model based on the determined synthesis parameters to generate a single synthesized image.

[0116] FIG. 18 is a conceptual diagram of the synthesis process using feature point matching.

[0117] In the synthesis process using feature point matching, the synthesis parameters are determined from the results of feature point matching between images: the orientation parameters of the shape model, the orientation parameters (rotation matrix, translation vector) of each imaging device corresponding to each image, and the lens distortion parameters of each imaging device corresponding to each image.

[0118] The shape model is selected according to the imaging target (subject). If the imaging target is a plane, a planar model is selected. In the case of the planar model, a rotation matrix and a translation vector are determined as pose parameters. If the imaging target is a curved surface, a cylindrical model is selected. In the case of the cylindrical model, a rotation matrix, a translation vector, and the radius of the cylinder are determined as pose parameters.

[0119] When the inner wall surface 2A of a tunnel is an arc-shaped (curved tunnel), a cylindrical model is selected as the shape model. Therefore, in this case, the rotation matrix, translation vector, and cylinder radius are determined as the orientation parameters of the shape model.

[0120] The compositing processing unit 511D performs feature point matching between images of the group of images acquired by the processing target image acquisition unit 511C and determines compositing parameters from the result of the feature point matching. Furthermore, the compositing processing unit 511D projects the images onto a shape model based on the determined compositing parameters to generate a single composite image. Furthermore, when a cylindrical model is selected as the shape model, the compositing processing unit 511D develops the image projected onto the shape model into a plane to generate a composite image.

[0121] The composite image recording control unit 511E controls the recording of the composite image generated by the composition processing unit 511D. The composite image recording control unit 511E associates the generated composite image with the original image group and records it in the image database 520. The composite image recording control unit 511E records the generated composite image in the image database 520 automatically or in response to a recording instruction from the user.

[0122] The composite image display control unit 511F controls the display of the composite image generated by the synthesis processing unit 511D. The composite image display control unit 511F displays the generated composite image on the display device 516. The composite image display control unit 511F enlarges, reduces, moves, etc. the composite image displayed on the display device 516 in response to an instruction from the user.

[0123] [Processing from imaging to generation of composite image] Here, an example will be described in which the inner wall surface 2A of the tunnel 2 is divided and imaged using the multi-eye imaging device 10, and a composite image of the inner wall surface 2A of the tunnel 2 is generated from the obtained images.

[0124] First, settings are made for the multi-eye imaging apparatus 10. Specifically, settings are made for each imaging device 100 and lighting devices 200F and 200R mounted on the multi-eye imaging apparatus 10.

[0125] The positions of the image capturing devices 100 are adjusted so that the overlap rate of captured images (overlap rate in the circumferential direction of the tunnel 2) between adjacent image capturing devices satisfies a specified condition. The overlap rate condition is determined from the perspective of the synthesis process. As an example, the overlap rate condition is 10% or more.

[0126] The orientations of the illumination devices 200F, 200R are adjusted so that illumination light is irradiated onto the imaging area of ​​the corresponding imaging device 100. As described above, in this embodiment, the imaging area of ​​the corresponding imaging device 100 is divided into two in the front-to-rear direction, and illumination light from the front-side illumination device 200F is irradiated onto the front imaging area, and illumination light from the rear-side illumination device 200R is irradiated onto the rear imaging area.

[0127] After the settings are complete, imaging begins. Imaging is performed by moving the multi-eye imaging device 10 using the dolly 3. For example, the dolly 3 is moved at a substantially constant speed to capture interval images of the inner wall surface 2A of the tunnel 2. In this case, the traveling speed of the dolly 3 and the imaging interval for interval imaging are set so that the image overlap rate in the direction of movement of the dolly 3 satisfies a specified condition (for example, 10% or more).

[0128] Furthermore, imaging is performed with illumination light emitted from the illumination devices 200F and 200R. That is, in this embodiment, light from the illumination devices 200F and 200R is reflected by the subject (the inner wall surface 2A of the tunnel 2), causing light to be emitted from the subject. The light is then collected by the imaging lens 110 and formed into an image on the light receiving surface of the imaging element 131.

[0129] When capturing images of the entire tunnel 2, the camera moves from one end of the tunnel 2 to the other end and captures images of the inner wall surface 2A of the tunnel 2.

[0130] After the image capturing is completed, a composite image is generated in response to an instruction from the user. A single image (a panoramic composite image) is generated by joining the individual images. In the image capturing system 1 of this embodiment, the composite image is generated by the control device 500.

[0131] As described above, in the imaging system 1 of the present embodiment, an image is captured by irradiating the subject (the inner wall surface 2A of the tunnel 2) with illumination light. That is, the imaging system 1 is configured to capture an image of the subject by utilizing reflected light of light irradiated from the lighting devices 200F and 200R.

[0132] As described above, in the imaging system 1 of this embodiment, the imaging device 100 and the illumination devices 200F and 200R are provided with the polarizing filters 120 and 240, respectively, and imaging is performed using polarized light.

[0133] In the following, where necessary, the polarizing filter 120 provided in the imaging device 100 will be referred to as the "imaging-side polarizing filter 120," and the polarizing filter 240 provided in the lighting devices 200F and 200R will be referred to as the "illumination-side polarizing filter 240," to distinguish between the polarizing filters 120 and 240.

[0134] In the present embodiment, the polarizing filter (illumination-side polarizing filter) 240 provided in the illumination devices 200F and 200R is an example of a first polarizing plate. The polarizing filter (image-capture-side polarizing filter) 120 provided in the image capture device 100 is an example of a second polarizing plate. The image capture device 100 is an example of an image capture unit, and the illumination devices 200F and 200R are an example of an illumination unit.

[0135] FIG. 19 is a conceptual diagram of imaging with one imaging unit.

[0136] 19 , light (illumination light) emitted from the light source unit 220 of each of the lighting devices 200F, 200R is irradiated onto the tunnel inner wall surface 2A via an illumination-side polarizing filter 240 provided in the light-emitting unit of each of the lighting devices 200F, 200R. The illumination light irradiated onto the tunnel inner wall surface 2A is reflected by the tunnel inner wall surface 2A, and the reflected light enters the imaging lens 110 via the imaging-side polarizing filter 120 and is received by the imaging element 131.

[0137] The illumination-side polarizing filter 240 is composed of a polarizing plate that transmits light polarized in a specific direction with a predetermined degree of polarization. As an example, in this embodiment, the illumination-side polarizing filter 240 is composed of a polarizing plate (linear polarizing plate) that uniformly transmits light linearly polarized in a specific direction with a predetermined degree of polarization. The specific direction is the direction of the polarization axis (also called the polarization transmission axis). "Uniformly" means that light is transmitted with a predetermined degree of polarization across the entire filter. In other words, it means that light is transmitted with the same degree of polarization at every position. Note that "uniform" here not only means completely uniform, but also includes the meaning of "almost uniform," which includes tolerances allowed in design and manufacturing. Therefore, "same" also includes the meaning of "almost the same," which includes tolerances allowed in design and manufacturing, in addition to the meaning of "completely the same." This also applies hereinafter.

[0138] The degree of polarization is an index that represents the polarization state of light. The degree of polarization is expressed as a percentage (or a number between 0 and 1), with 100% indicating fully polarized light and 0% indicating unpolarized light. In linear polarization, fully polarized light (fully linearly polarized light) refers to light that vibrates in only one direction. Unpolarized light refers to light that vibrates isotropically. Light that is in an intermediate state between fully polarized light and unpolarized light is called partially polarized light. The degree of polarization indicates the proportion of fully polarized light contained. Therefore, for example, a degree of polarization of 70% means that 70% of the light is fully polarized. In other words, this means that 70% is fully polarized light and the remaining 30% is unpolarized light.

[0139] By using the illumination-side polarizing filter 240 configured as described above, light that is linearly polarized in a specific direction is emitted from the illumination devices 200F, 200R with a predetermined degree of polarization. As a result, light with a predetermined degree of polarization (first degree of polarization) is irradiated onto the imaging area of ​​the imaging device 100 as illumination light. The illumination-side polarizing filter 240 of this embodiment is an example of a polarizing plate with a first degree of polarization.

[0140] Like the illumination-side polarizing filter 240, the imaging-side polarizing filter 120 is composed of a polarizing plate that transmits light polarized in a specific direction at a predetermined degree of polarization. As an example, in this embodiment, the imaging-side polarizing filter 120 is composed of a polarizing plate that uniformly transmits light that is linearly polarized in a specific direction (the direction of the polarization axis) at a predetermined degree of polarization.

[0141] By using an image-capturing-side polarizing filter 120 configured in this manner, light that is linearly polarized in a specific direction is received by the image sensor 131 at a predetermined degree of polarization (second degree of polarization) in the imaging device 100. The image-capturing-side polarizing filter 120 of this embodiment is an example of a polarizing plate with the second degree of polarization.

[0142] The illumination-side polarizing filter 240 and the imaging-side polarizing filter 120 are arranged with their polarization axes perpendicular to each other. That is, the polarization axes of the polarizing filter 240 on the front-side illumination device 200F side and the polarizing filter 240 on the rear-side illumination device 200R side are arranged perpendicular to the polarization axis of the polarizing filter 120 on the imaging device 100 side. For example, if the polarization axis of the polarizing filter 120 on the imaging device 100 side is tilted at 0°, the polarization axes of the polarizing filter 240 on the front-side illumination device 200F side and the polarizing filter 240 on the rear-side illumination device 200R side are arranged with their polarization axes tilted at 90°. Note that "orthogonal" here means not only completely orthogonal, but also includes the meaning of "almost orthogonal," which includes tolerances allowed in design and manufacturing. "Orthogonal" is an example of "crossed."

[0143] In this embodiment, the direction of the polarization axis of the illumination-side polarizing filter 240 is an example of a first direction, and the direction of the polarization axis of the imaging-side polarizing filter 120 is an example of a second direction.

[0144] When light is reflected specularly, the polarization of the incident light is maintained. By placing polarizing filters on both the illumination side and the imaging side and orthogonally ...

[0145] Furthermore, by transmitting light at a predetermined polarization degree rather than completely polarizing it (100% polarization), it is possible to suppress a decrease in the amount of light. This makes it possible to capture high-quality images. In other words, by ensuring the amount of light, it is no longer necessary to extend the exposure time or increase the sensitivity. This makes it possible to suppress the occurrence of image blur and noise, and to capture high-quality images.

[0146] As described above, the degree of polarization indicates the proportion of fully polarized light. The higher the degree of polarization, the higher the proportion of fully polarized light. Furthermore, the higher the proportion of fully polarized light, the greater the effect of suppressing light source glare. On the other hand, the higher the proportion of fully polarized light, the greater the rate of reduction in light intensity. Therefore, it is preferable to set the degree of polarization while considering the balance between the reduction in light intensity and the influence of light source glare. The influence of light source glare, for example, refers to the influence on feature point extraction in the case of image synthesis using feature point matching. In other words, the influence of light source glare, such as making it impossible to extract feature points, is the influence. Therefore, it is preferable to set the degree of polarization within a range that enables feature point extraction. In other words, it is not necessary to completely remove light source glare; it is sufficient to suppress it to a degree that allows feature points necessary for image synthesis to be extracted from the glare area.

[0147] As an example, the degree of polarization is set in the range of 10% or more and 90% or less. More preferably, it is set in the range of 70% or less. In scenes where it is desired to reduce the reflection of the light source even at the expense of some light intensity, a value close to the upper limit (90%) is set. Generally, the brightness of an area where the light source is reflected is about 3 to 10 times the brightness of other areas (areas where the light source is not reflected). For this reason, the degree of polarization that can reduce the intensity of the reflection of the light source to 1 / 10 is preferably 90% or less, more preferably 70% or less.

[0148] The method for adjusting the degree of polarization of the polarizing plate (polarizing filter) is not particularly limited. For example, a method of adjusting the degree of polarization by changing the thickness of the polarizing plate (a method of reducing the thickness of the polarizing plate to reduce the degree of polarization) or a method of adjusting the density of the polarizer (a method of reducing the density of the polarizer to reduce the degree of polarization) can be used.

[0149] In this embodiment, "reducing the degree of polarization" means reducing the degree of polarization by a certain amount or more from complete polarization (100% polarization), that is, reducing the degree of polarization to a certain amount or less. Specifically, it means reducing the degree of polarization to 90% or less.

[0150] In this embodiment, the degree of polarization of the illumination-side polarizing filter 240 is an example of a first degree of polarization, and the degree of polarization of the image-capturing-side polarizing filter 120 is an example of a second degree of polarization.

[0151] As described above, in the imaging system 1 of this embodiment, while completely polarized light is normally used to suppress reflection of the light source, the degree of polarization is intentionally reduced to perform polarized imaging (imaging using polarized light). This makes it possible to capture an image with a sufficient amount of light while suppressing reflection of the light source. This also makes it possible to capture high-quality images. In other words, it is possible to capture images from which a sufficient number of feature points necessary for synthesis can be extracted.

[0152] [Modification] In the above embodiment, the degree of polarization of both the illumination-side polarizing filter 240 and the image-capturing-side polarizing filter 120 is reduced, but it is also possible to reduce the degree of polarization of only one of them.

[0153] Furthermore, when reducing the degree of polarization of both the illumination-side polarizing filter 240 and the imaging-side polarizing filter 120, they may be configured to be set to different degrees of polarization. For example, the degree of polarization of the illumination-side polarizing filter 240 may be configured to be lower than the degree of polarization of the imaging-side polarizing filter 120. The opposite setting is also possible.

[0154] [Second embodiment] In the first embodiment, a polarizing plate with a reduced degree of polarization is used to uniformly reduce the degree of polarization of light irradiating a subject and light reflected from the subject within the imaging field of view.

[0155] In this embodiment, the degree of polarization within the imaging field angle is spatially reduced, thereby achieving the same effect as the imaging system of the first embodiment.

[0156] In order to spatially reduce the degree of polarization within the imaging field angle, the present embodiment uses polarizing plates with partially different degrees of polarization.

[0157] Apart from the difference in the configuration of the polarizing plate used as the polarizing filter, the configuration is basically the same as that of the imaging system 1 of the first embodiment. Therefore, here, we will focus on one imaging unit and explain its configuration and effects.

[0158] FIG. 20 is a conceptual diagram of imaging with one imaging unit.

[0159] The arrangement of polarizing filters on both the illumination side and the imaging side is the same as in the imaging unit of the first embodiment. Illumination devices 200F and 200R are provided with an illumination-side polarizing filter 240 in the light output section 230, and imaging device 100 is provided with an imaging-side polarizing filter 120 at the tip of the imaging lens.

[0160] As shown in FIG. 20 , in this embodiment, the polarizing plate constituting the illumination-side polarizing filter 240 is composed of polarizing plates with different degrees of polarization in some areas. As an example, in this embodiment, the illumination-side polarizing filter 240 is composed of a polarizing plate with a polarization degree of 0% in some areas. The polarization degree in areas other than 0% is, for example, 100% (including nearly 100%). That is, the illumination-side polarizing filter 240 of this embodiment is configured to transmit a portion of the light emitted from the light source unit 220 as is and to output the remainder as fully polarized (including a state close to nearly fully polarized). The areas with a polarization degree of 0% may be configured with a transparent substrate with no polarizing effect, or may be configured as so-called transparent (nothing disposed therein). Placing a transparent polarizing plate in an area other than 0% is equivalent to disposing a polarizing plate in the area. A polarizing plate with a polarization degree of 100% (including nearly 100%) is a so-called general polarizing plate. Therefore, a general polarizing plate is disposed in areas other than the transparent area (area with a polarization degree of 0%). Hereinafter, for convenience, a region with a polarization degree of 0% will be referred to as a "non-polarized region," and a region other than the non-polarized region (a region that polarizes) will be referred to as a "polarized region."

[0161] The polarization region is set to correspond to the region where the light source is reflected in relation to the image capture device 100. When viewed from the illumination device side, light emitted from a region relatively closer to the image capture device 100 is reflected in the image due to specular reflection. Therefore, by designating the region relatively closer to the image capture device 100 as a polarization region, reflection of the light source can be effectively suppressed. As described above, in the multi-eye imaging device 10 of this embodiment, the two illumination devices 200F and 200R are arranged side by side in the front-to-back direction (the direction of the axis Ax of the multi-eye imaging device 10) with the image capture device 100 sandwiched between them. For this reason, the light output sections 230 of the illumination devices 200F and 200R are divided into two in the front-to-back direction, with the region closer to the image capture device 100 designated as a polarization region (the region hatched with vertical lines in FIG. 20 ) and the region away from the image capture device 100 designated as a non-polarization region. Specifically, in the front-side illumination device 200F, the light output section 230 is divided into two regions in the front-rear direction, with the rear region (region closer to the image capture device 100) being a polarized region and the front region (region farther from the image capture device 100) being a non-polarized region. On the other hand, in the rear-side illumination device 200R, the light output section 230 is divided into two regions in the front-rear direction, with the front region (region closer to the image capture device 100) being a polarized region and the rear region (region farther from the image capture device 100) being a non-polarized region. In this embodiment, the polarized region is an example of a first region, and the non-polarized region is an example of a second region. The polarized region has a polarization degree of 100%, and the non-polarized region has a polarization degree of 0%, so the non-polarized region (second region) has a lower polarization degree than the polarized region (first region).

[0162] Thus, the illumination-side polarizing filter 240 is composed of polarizing plates with different degrees of polarization in different parts. In this case, the degree of polarization (composite polarization degree) obtained by combining the light passing through each region is used as the overall degree of polarization. For example, if the polarizing plate constituting the illumination-side polarizing filter 240 has region A and region B with different degrees of polarization, the degree of polarization (composite polarization degree) of light passing through the polarizing plate is calculated by [polarization degree of region A x percentage of region A in the overall light] + [polarization degree of region B x percentage of region B in the overall light]. For example, if the polarization degree of region A is 100% (fully polarized), region A accounts for 70% of the overall light, region B has a polarization degree of 0% (non-polarized), and region B accounts for 30% of the overall light, then the combined degree of polarization is 1 x 0.7 + 0 x 0.3 = 0.7, and the combined degree of polarization is 70%.

[0163] The image-capturing-side polarizing filter 120 is made of a polarizing plate with a uniform degree of polarization. As an example, in this embodiment, the image-capturing-side polarizing filter 120 is made of a polarizing plate that completely polarizes the light that passes through it. In other words, it is made of a polarizing plate with a polarization degree of 100% (including nearly 100%).

[0164] As described above, the imaging system of this embodiment is configured to use polarizing plates with different degrees of polarization in different parts of the illumination side to spatially reduce the degree of polarization within the imaging field of view. This configuration, like the imaging system of the first embodiment, can also ensure sufficient light intensity while suppressing reflections of the light source. This allows high-quality images to be captured. In particular, the imaging system of this embodiment is configured to pinpoint polarizing plates in necessary areas, minimizing reductions in light intensity.

[0165] Generally, the range in which a light source is reflected (the range in which gloss, shine, etc. are generated by lighting) is about 30% of the imaging angle of view. From the viewpoint of image synthesis by feature point matching, if the range is about 10% of the imaging angle of view, synthesis is often possible even if the light source is reflected (the number of feature points required for image synthesis can be extracted). Therefore, the degree of polarization is preferably 10% or more, and more preferably 30% or more.

[0166] The degree of polarization (degree of polarization under actual use conditions) can be measured, for example, by the following method.

[0167] STEP 1: Illuminate without a polarizing plate, and measure the illuminance distribution on the surface of the object within the imaging angle of view. The sum of the measured illuminance distribution is defined as A.

[0168] STEP 2: Illuminate the subject under conditions of completely polarized light (including nearly completely polarized light), and measure the illuminance distribution on the subject surface within the photographing angle of view. The sum of the measured illuminance distributions is designated as B.

[0169] STEP 3: Illuminate under actual use conditions and measure the illuminance distribution on the surface of the object within the photographing angle of view. The sum of the measured illuminance distributions is defined as C.

[0170] STEP 4: Calculate the degree of polarization under actual use conditions using the following formula.

[0171] Degree of polarization under actual usage conditions = (C - B) / (A - B)

[0172] [Variations] [Setting of polarized and non-polarized regions] In the above embodiment, the region through which light passes is divided into two along the arrangement direction of the illumination devices 200F, 200R and the imaging device 100 to set the polarized and non-polarized regions, but the method of setting the polarized and non-polarized regions is not limited to this.

[0173] 21 and 22 are diagrams showing other examples of the setting of the polarized and non-polarized regions. Note that Fig. 22 shows the illumination-side polarizing filter 240 arranged in the front-side illumination device 200F as viewed from the light-emitting side (the front side of the illumination device).

[0174] 21 and 22 show an example in which the degree of polarization is reduced in the peripheral region (region away from the center). That is, the example shows a case in which the degree of polarization in the peripheral region is relatively lower than the degree of polarization in the central region. In particular, the examples shown in FIGS. 21 and 22 show an example in which a polarizing region (region hatched with vertical lines in the figure) is located slightly closer to the image capture device 100 from the center in the polarizing plate that constitutes the illumination-side polarizing filter 240, and non-polarizing regions are located around it.

[0175] In this way, by lowering the degree of polarization on the periphery side more than on the center side, it is possible to efficiently suppress the reflection of the light source while ensuring the amount of light. In other words, by lowering the degree of polarization in areas where the reflection of the light source does not occur or areas where the impact of the reflection of the light source is low, it is possible to efficiently suppress the reflection of the light source while ensuring the amount of light.

[0176] Fig. 23 is a diagram showing another example of the setting of the polarized and non-polarized regions, showing the illumination-side polarizing filter 240 arranged in the front-side illumination device 200F as viewed from the light exit side.

[0177] 23 shows an example in which a polarizing region (the region hatched with vertical lines in the figure) is located in the center of the polarizing plate that constitutes the illumination-side polarizing filter 240, and non-polarizing regions are located around it. In this way, a configuration in which a polarizing region is located in the center can also be used.

[0178] 23, the polarizing region is disposed in the center in both the vertical direction (short direction) and the horizontal direction (longitudinal direction), but it may be disposed in the center in only one of the directions. For example, the polarizing region may be disposed only in the center in the vertical direction and across the entire horizontal direction.

[0179] When it is difficult to identify the area where the light source is reflected because the distance to the subject changes or the surface shape is unstable, it is preferable to set the polarization area with some margin of error.

[0180] In the above modification, the polarized region is an example of the third region, and the non-polarized region is an example of the fourth region. The above modification is also another example of a polarizing plate having different degrees of polarization between the region corresponding to the region where the light source is reflected (first region) and the other region (second region).

[0181] [Other examples of polarizing plate] In the above embodiment, the polarizing plate with partially different degrees of polarization is configured by dividing the area through which light passes into two and changing the degree of polarization, but configuration examples of polarizing plates with partially different degrees of polarization are not limited to this.

[0182] Fig. 24 is a conceptual diagram showing another example of imaging using partially different polarizing plates, in which the polarizing plates constituting the illumination-side polarizing filter 240 are configured with polarizing plates that partially differ in polarization degree.

[0183] The illumination-side polarizing filter 240 shown in Fig. 24 is composed of a polarizing plate having discrete regions with a polarization degree of 0%. The regions with a polarization degree of 0% (non-polarized regions) are composed, for example, of clear regions. In this case, polarizing plates are arranged in the regions to be polarized (regions other than the clear regions). In other words, the polarizing plates are arranged sparsely to form a single polarizing plate as a whole.

[0184] The degree of polarization of the polarizing plate disposed in the polarizing region (polarizing region) is not particularly limited. As an example, a polarizing plate with a polarization degree of 100% (including nearly 100%) is disposed.

[0185] In this way, a polarizing plate having a partially different degree of polarization can be configured to have discrete regions with a polarization degree of 0% (non-polarizing regions).

[0186] For example, in cases where it is difficult to identify the area where the light source is reflected due to changes in the distance to the subject or an unstable surface shape, a polarizing plate having discrete areas with a polarization degree of 0%, such as the polarizing plate of this example, is advantageous. In other words, a polarizing plate having uniformly polarized areas throughout the entire surface is advantageous.

[0187] On the other hand, when the area into which the light source is reflected is predetermined to a certain extent, a polarizing plate having a two-part structure like the polarizing plate of the above embodiment is advantageous, i.e., a polarizing plate having a polarizing area corresponding to the area into which the light source is reflected is advantageous.

[0188] The arrangement of the non-polarizing regions is not particularly limited. A configuration in which they are arranged evenly over the entire surface is preferable. For example, they may be arranged in a striped pattern or a checkered pattern.

[0189] The degree of polarization of the polarizing region does not necessarily have to be 100%. In the above-described embodiments, the region that is set as a non-polarizing region may be configured to polarize light at a predetermined degree of polarization.

[0190] [Image Capture-Side Polarizing Filter] In the above embodiment, the image capture-side polarizing filter 120 is configured with a polarizing plate having a uniform degree of polarization, but the image capture-side polarizing filter 120 can also be configured with polarizing plates having partially different degrees of polarization.

[0191] In the above embodiment, because two illumination devices 200F and 200R are arranged on either side of the image capture device 100, a polarizing plate with a uniform degree of polarization is used for the image capture-side polarizing filter 120. If there is only one illumination device, it is preferable to use a polarizing plate with partially different degrees of polarization for the image capture-side polarizing filter 120 as well.

[0192] Fig. 25 is a conceptual diagram showing an example of imaging using one illumination device. Fig. 25 shows an example in which one imaging unit 20 is equipped with only a front-side illumination device 200F. In this case, the entire imaging area of ​​the imaging device 100 is illuminated by only the front-side illumination device 200F.

[0193] 25, both the illumination-side polarizing filter 240 and the imaging-side polarizing filter 120 are made up of polarizing plates with partially different degrees of polarization. The configuration of the illumination-side polarizing filter 240 is the same as that of the above embodiment.

[0194] The image capture-side polarizing filter 120 in this example is configured as a polarizing plate with a polarization degree of 0% in some areas. The areas with a polarization degree of 0% (non-polarized areas) are, for example, transparent areas. The polarized areas (polarized areas) are set to correspond to the areas in which the light source is reflected. In the image capture device 100, the area in which the light source is reflected is the area on the lighting device side. In the example shown in FIG. 25 , the light incident area is divided into two along the arrangement direction of the image capture device 100 and the lighting device 200F, and the area on the lighting device side is configured as the polarizing area.

[0195] In this way, by using polarizing plates with different degrees of polarization in parts of the image-capturing-side polarizing filter 120, it is possible to ensure a larger amount of light.

[0196] 25, the light incidence area is divided into two along the arrangement direction of the image capture device 100 and the illumination device 200F, and a polarizing area is arranged on the illumination device side. However, the arrangement of the polarizing area and non-polarizing area is not limited to this. Alternatively, a polarizing area may be arranged in the central portion, and a non-polarizing area may be arranged in the peripheral area. In other words, a configuration in which the degree of polarization is lower on the peripheral side than on the central side may be adopted. In this case, a polarizing area may be arranged in the central portion, and a non-polarizing area may be arranged in the peripheral area, on both the image capture device side and the illumination device side.

[0197] Alternatively, the image-capturing-side polarizing filter 120 may be a polarizing plate having discrete non-polarizing regions.

[0198] Furthermore, polarizing plates with partially different degrees of polarization can be configured to be used only on either the illumination side or the imaging side. When used on the illumination side, the change in polarization degree on the captured image is smoother than when used on the imaging side. This reduces brightness unevenness. When used on the imaging side, the size of a specially configured polarizing plate can be made smaller.

[0199] Third Embodiment In this embodiment, the degree of polarization within the imaging field angle is decreased over time, thereby achieving the same effects as those of the imaging systems of the first and second embodiments.

[0200] In this embodiment, the polarizing plate on the illumination side is retracted during exposure, thereby temporarily reducing the degree of polarization within the imaging field angle.

[0201] Fig. 26 is a conceptual diagram of imaging. Fig. 26 shows imaging with one imaging unit.

[0202] 26, in this embodiment, the illumination-side polarizing filter 240 is provided to be slidable. The illumination-side polarizing filter 240 is driven by an actuator (not shown) to slide into and out of the optical path. The driving of the actuator is controlled by the control device 500 (see FIG. 14).

[0203] For example, a polarizing plate (linear polarizing plate) that uniformly transmits light that is linearly polarized in a specific direction with a predetermined degree of polarization is used for the imaging-side polarizing filter 120 and the illumination-side polarizing filter 240. As an example, a polarizing plate that completely polarizes light (including almost completely polarized light) is used.

[0204] The control device 500 drives the illumination-side polarizing filter 240 in synchronization with imaging by the imaging device 100, and retracts the illumination-side polarizing filter 240 from the light-emitting unit 230 during exposure. As the illumination-side polarizing filter 240 retracts from the light-emitting unit 230 during exposure, the degree of polarization within the imaging field of view changes over time. Specifically, the degree of polarization of the illumination light decreases over time. In other words, as the illumination-side polarizing filter 240 retracts from the light-emitting unit 230, the proportion of light that does not pass through the illumination-side polarizing filter 240 increases, and as a result, the degree of polarization of the illumination light decreases (decreases over time).

[0205] By retracting the polarizing plate during exposure, the degree of polarization within the imaging field angle is reduced over time to a degree of polarization of 10% or more and 90% or less.

[0206] In this manner, in this embodiment, the polarizing plate on the illumination side is retracted during exposure, thereby temporarily reducing the degree of polarization within the imaging field of view. This makes it possible to suppress reflections of the light source while ensuring sufficient light intensity, similar to the imaging system of the first embodiment. This also makes it possible to capture high-quality images.

[0207] In this embodiment, the polarizing plate on the illumination side is retracted during exposure, but the polarizing plate on the imaging side may be retracted instead. Also, the polarizing plates on both the illumination side and the imaging side may be retracted.

[0208] Although the present embodiment is configured to retract the polarizing plate during exposure, it may also be configured to insert the polarizing plate during exposure. That is, it may be configured to retract (remove) the polarizing plate at the start of exposure and insert the polarizing plate during exposure.

[0209] Furthermore, when the area where the light source is reflected is predetermined to some extent, it is preferable to configure the polarizing plate to retreat from the area opposite to the area where the light source is reflected, i.e., to retreat from the area where no reflection occurs.

[0210] Furthermore, the polarizing plate does not necessarily have to be completely retracted from the optical path during exposure, and the exposure may be terminated midway through the retraction.

[0211] [Modification] In the above embodiment, the polarizing plate is retracted or inserted during exposure to reduce the degree of polarization within the image capture field over time, but the method for reducing the degree of polarization within the image capture field over time is not limited to this. For example, a multiple exposure technique may be employed to perform imaging with and without a polarizing plate within a single frame to reduce the degree of polarization within the image capture field over time.

[0212] 27A and 27B are conceptual diagrams of imaging by multiple exposure, in which (A) shows imaging with a polarizing plate and (B) shows imaging without a polarizing plate.

[0213] As shown in FIG. 27A, the first imaging (exposure) is performed with the imaging-side polarizing filter 120 and the illumination-side polarizing filter 240 in place (imaging with polarizing plates).

[0214] As shown in Figure 27 (B), the second imaging (exposure) is performed with the imaging-side polarizing filter 120 and the illumination-side polarizing filter 240 removed (removed from the optical path) (imaging without a polarizing plate).

[0215] In this way, by capturing an image with and without a polarizing plate in one frame, the degree of polarization decreases over time.

[0216] In this example, the second imaging (imaging without polarizing plates) is performed by removing the polarizing plates on both the illumination side and the imaging side (by retracting them from the optical path), but it is also possible to remove only one of them. For example, it is also possible to remove only the polarizing plate on the illumination side.

[0217] In addition, in this example, the image is captured by exposing twice within one frame, but it is also possible to capture images with and without a polarizing plate, and then generate an image afterwards using image processing in the same way as multiple exposure (so-called multiple composition).

[0218] Furthermore, the exposure time may be different between imaging with a polarizing plate and imaging without a polarizing plate. The longer the exposure time for imaging with a polarizing plate, the greater the effect of suppressing light source reflection. On the other hand, the longer the exposure time for imaging without a polarizing plate, the more light intensity can be secured.

[0219] The mechanism for inserting and removing the polarizing plate into and from the optical path is not particularly limited. In addition to a configuration in which the polarizing plate is inserted and removed into and from the optical path by linearly sliding it, a configuration in which the polarizing plate is inserted and removed into and from the optical path by rotating it, for example, like a turret, can be employed. On the illumination side, the mechanism for inserting and removing the polarizing plate into and from the optical path, including the actuator that drives it, is an example of a first drive unit. On the imaging side, the mechanism for inserting and removing the polarizing plate into and from the optical path, including the actuator that drives it, is an example of a second drive unit.

[0220] Fourth Embodiment In this embodiment, the degree of polarization within the imaging field angle is reduced in terms of wavelength, thereby achieving the same effects as those of the imaging systems of the first to third embodiments.

[0221] In this embodiment, a polarizing plate that polarizes only light in a specific wavelength range is used to reduce the degree of polarization within the imaging field angle in terms of wavelength.

[0222] FIG. 28 is a conceptual diagram of imaging with one imaging unit.

[0223] In this embodiment, the imaging-side polarizing filter 120 and the illumination-side polarizing filter 240 are configured with polarizing plates that polarize only light in a specific wavelength range λ1. Because the polarizing plate polarizes only light in the specific wavelength range λ1, light in other wavelength ranges is transmitted unpolarized. This type of polarizing plate can be realized, for example, by a polarizing plate configured to absorb only light in the specific wavelength range λ1. In this case, of the light incident on the polarizing plate, only the component in a specific vibration direction (direction of the polarization axis) in the wavelength range λ1 is transmitted, and the rest is absorbed. Light in other wavelength ranges is transmitted unchanged, resulting in partially polarized light overall. In other words, light in the specific wavelength range λ1 is fully polarized, and light in other wavelength ranges is transmitted unpolarized. As a result, the light overall becomes partially polarized light, containing a predetermined proportion of fully polarized light.

[0224] By polarizing light in the same wavelength range on both the illumination side and the imaging side, it is possible to suppress reflections of the light source in that wavelength range, while ensuring sufficient light intensity by transmitting light in other wavelength ranges.

[0225] By using a polarizing plate that polarizes only light in a specific wavelength range, the degree of polarization within the imaging field of view is reduced in terms of wavelength, to a degree of polarization of 10% or more and 90% or less.

[0226] In this manner, in this embodiment, by using a polarizing plate that polarizes only light in a specific wavelength range λ1, the degree of polarization within the imaging field of view is reduced in wavelength. As a result, similar to the imaging system of the first embodiment, it is possible to ensure the amount of light while suppressing the reflection of the light source. This also makes it possible to capture high-quality images.

[0227] In this embodiment, polarizing plates that polarize only light in a specific wavelength range are used on both the illumination side and the imaging side, but a configuration in which only one of them is used may also be used. For example, a configuration in which a polarizing plate is used only on the illumination side may also be used. In this case, for example, a polarizing plate of a normal configuration (a polarizing plate configured to polarize light in the specific wavelength range) can be used on the imaging side.

[0228] The wavelength range to be polarized is not particularly limited and can be appropriately selected depending on the type of light source to be used, the subject, etc.

[0229] [Modification] When the degree of polarization is reduced with wavelength, the polarization characteristics may be changed for each wavelength range. For example, the presence or absence of polarization and the degree of polarization may be changed for each wavelength range. This makes it possible to simultaneously acquire multiple images with different degrees of gloss or shine. By acquiring multiple images with different degrees of gloss or shine, it becomes possible to estimate the surface condition of the subject (e.g., wet, rough, etc.) from the acquired images. Therefore, the control device 500 may be configured to perform image processing to estimate the surface condition from the acquired images.

[0230] [Other Embodiments] [Polarization Axis Setting] It is preferable to arrange the illumination-side polarizing filter 240 and the imaging-side polarizing filter 120 so that their polarization axes are orthogonal to each other, but the desired effect (the effect of suppressing reflection of the light source) can be ensured if their transmission axes are approximately orthogonal to each other. Therefore, the illumination-side polarizing filter 240 and the imaging-side polarizing filter 120 do not necessarily have to have their polarization axes orthogonal to each other, and they can be arranged within a range in which the polarization axes are approximately orthogonal to each other. As an example, the range in which the polarization axes are considered to be approximately orthogonal is 90°±10°.

[0231] [Circular Polarizer] In the above embodiment, polarizers that linearly polarize transmitted light are used as the illumination-side polarizing filter 240 and the imaging-side polarizing filter 120. However, polarizers that circularly polarize light (circular polarizers) may also be used. When using circular polarizers, circular polarizers with the same orientation are used on the illumination side and the imaging side. That is, for example, if a circular polarizer that transmits clockwise circularly polarized light (right-handed circular polarizer) is used on the illumination side, a right-handed circular polarizer is also used on the imaging side. Conversely, if a circular polarizer that transmits counterclockwise circularly polarized light (left-handed circular polarizer) is used on the illumination side, a left-handed circular polarizer is also used on the imaging side. The direction of circular polarization of circularly polarized light is reversed by specular reflection. That is, right-handed circularly polarized light is converted into left-handed circularly polarized light, and left-handed circularly polarized light is converted into right-handed circularly polarized light. Therefore, by using circular polarizers with the same orientation on the illumination side and the imaging side, reflection of the light source due to specular reflection can be suppressed.

[0232] [Imaging System] In the above embodiment, a single imaging system 1 is configured by combining multiple imaging units 20 as a system capable of imaging a wide area at once, but it is sufficient for the imaging system 1 to include at least one imaging unit 20. Furthermore, it is sufficient for one imaging unit 20 to include at least one imaging device and at least one lighting device. Therefore, the imaging system 1 can be configured with at least one imaging device and at least one lighting device.

[0233] Furthermore, when multiple lighting devices are provided for one imaging device, each lighting device may be configured to irradiate the same area with illumination light, or may be configured to irradiate separate areas with illumination light.

[0234] In the above embodiment, the multi-eye imaging device 10 is mounted on the dolly 3 to capture an image of the inner wall surface 2A of the tunnel 2, which is the subject, but the means for moving the multi-eye imaging device 10 is not limited to this. Alternatively, the multi-eye imaging device 10 may be mounted on an unmanned aerial vehicle (a so-called drone) or the like and moved.

[0235] Furthermore, for example, when the imaging system 1 is configured with one imaging device and one lighting device, it may be configured to perform imaging in a so-called handheld manner.

[0236] [Image Capture Unit] In the above embodiment, a so-called interchangeable lens digital camera is used as the image capture device 100, and the image capture unit is configured by attaching the polarizing filter 120 to the image capture lens 110, but the configuration of the image capture unit is not limited to this. For example, the image capture unit can also be configured by using an integrated lens digital camera and attaching a polarizing filter to the image capture lens.

[0237] Furthermore, in the above embodiment, a polarizing filter (polarizing plate) is attached to the imaging lens, but the position of the polarizing filter is not limited to this. It may be placed anywhere along the optical path leading to the imaging element.

[0238] The imaging unit may be configured so that the imaging element can receive polarized light. For example, the imaging unit may be configured so that a polarizing plate (polarizing element) is provided for each pixel (so-called polarization imaging element). In this case, the imaging unit may be configured to include multiple pixels with different polarization directions.

[0239] [Illumination Unit] In the above embodiment, the illumination units 200F and 200R use LEDs as light sources, but the light source used in the illumination units is not limited to this. Other light sources, such as halogen lamps and xenon lamps, can also be used. Furthermore, in addition to line-shaped light sources, point-shaped light sources, planar light sources, etc. can also be used.

[0240] Furthermore, in the above embodiment, the polarizing filter (polarizing plate) 240 is arranged inside the housing of the illumination devices 200F and 200R, but the arrangement position of the polarizing filter is not limited to this.

[0241] FIG. 29 is a diagram showing another example of the arrangement of the polarizing filters.

[0242] Fig. 29 shows an example of a case where polarizing filter 240 is disposed upstream of light emitting unit 230. As shown in Fig. 29, a filter holding frame 260 is provided in a position upstream of light emitting unit 230. Polarizing filter 240 is held by filter holding frame 260 and disposed in a position upstream of light emitting unit 230. Light (illumination light) emitted from light source unit 220 is emitted from light emitting unit 230 via light distribution lens 250, and is irradiated onto the subject via polarizing filter 240.

[0243] Alternatively, the illumination unit may employ an illumination device that has the function of emitting light polarized in a predetermined direction with a predetermined degree of polarization.

[0244] [Imaging Target, etc.] In the above embodiment, an example has been described in which the inner wall surface 2A of a tunnel 2 is imaged for the purpose of image inspection of a tunnel structure, but the imaging target (subject) is not limited to this. It is effective for imaging using illumination. It is particularly effective when extracting feature points from captured images. Therefore, for example, it is effective for generating a panoramic composite image as well as restoring a three-dimensional shape from captured images.

[0245] [Hardware Configuration of Control System] In this embodiment, each process is executed by a computer. The computer may execute these processes using a processor, a program, or a combination thereof. The computer may be a general-purpose computer, a computer for a specific purpose, a system such as a workstation, or other hardware element capable of executing a program.

[0246] The processor may be composed of one or more pieces of hardware, and the type of hardware is not limited. For example, the processor may be composed of hardware such as a programmable logic device such as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), or an FPGA (Field Programmable Gate Array), a dedicated circuit for executing specific processes such as an ASIC (Application Specific Integrated Circuit), a GPU (Graphic Processing Unit), or an NPU (Neural Processing Unit). The processor also has various units or means for executing various processes in this embodiment. The type of hardware may also be a combination of different types of hardware. When multiple pieces of hardware are configured to execute one or more processes of a certain processor, the multiple pieces of hardware may exist in devices physically separated from each other or in the same device. In any of the embodiments, the order of each process performed by the processor is not limited to the order described above and may be changed as appropriate. The hardware may be composed of an electrical circuit (circuitry) combining circuit elements such as semiconductor devices.

[0247] Furthermore, the present embodiment may be implemented by hardware, software, firmware, microcode, or a combination thereof. Software, firmware, and microcode are configured by a program. Furthermore, a program may be, for example, a group of program modules, each function of which may be implemented by a processor configured to execute the respective function. The program may be, for example, a program code and / or multiple code segments stored in one or more non-transitory computer-readable media (e.g., storage media and other storages). The program may be stored in multiple non-transitory computer-readable media that reside in physically separate devices. The program code or code segment may represent a procedure, a function, a subprogram, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. The program code or code segment may be connected to another code segment or a hardware circuit by sending or receiving information, data, arguments, parameters, or memory contents.

[0248] [Combination] The configurations of the above-described embodiments, including modified examples, can be combined as appropriate. For example, a configuration may be adopted in which a polarizing plate with a different polarization degree is used in parts to reduce the polarization degree over time (a combination of the second and third embodiments), or a configuration may be adopted in which a polarizing plate that polarizes only light in a specific wavelength range in only a part of the region is used (a combination of the second and fourth embodiments).

[0249] [Note] In this specification, the terms "same" and "identical" mean not only completely identical but also "almost identical," which includes tolerances allowed in design and manufacturing. In this specification, the term "orthogonal" means not only completely orthogonal but also "almost orthogonal," which includes tolerances allowed in design and manufacturing. In this specification, the term "parallel" means not only completely parallel but also "almost parallel," which includes tolerances allowed in design and manufacturing. In this specification, the term "synchronized" means not only completely synchronized but also a range that is recognized as substantially synchronized (the meaning of "almost synchronized"). In this specification, the term "simultaneous" means not only completely simultaneous but also a range that is recognized as substantially simultaneous (the meaning of "almost simultaneous"). In this specification, the term "constant" means not only completely constant but also a range that is recognized as substantially constant (the meaning of "almost constant"). In this specification, the term "equally spaced" means not only perfectly equal intervals but also a range that is recognized as being substantially equally spaced (meaning "almost equally spaced").

[0250] 1...imaging system 2...tunnel 2A...inner wall surface 3...cart 10...multi-lens imaging device 11...frame 12...base 13...column 14...mounting base 20...imaging unit 21...bracket 22...clamp 100...imaging device 110...imaging lens 111...lens group 112...diaphragm 113...lens drive unit 114...diaphragm drive unit 115...lens operation unit 116...lens microcomputer 120...polarizing filter (imaging side polarizing filter) 130...imaging device main body 131...imaging element 132...mechanical shutter 133...digital signal processing unit 134...storage unit 135...display unit 136...interface unit (I / F unit) 137...camera operation unit 138...camera microcomputer 200F...illumination device (front side illumination device) 200R...illumination device (rear side illumination device) 210...Housing 220...Light source unit 221...LED element 230...Light emitting unit 240...Polarizing filter (lighting side polarizing filter) 250...Light distribution lens 260...Filter holding frame 300...Relay device 500...Control device 511...Processor 511A...Camera control unit 511A1...Imaging control unit 511A2...Captured image acquisition unit 511A3...Captured image display control unit 511A4...Captured image recording control unit 511B...Illumination control unit 511C...Processing target image acquisition unit 511D...Synthesis processing unit 511E...Composite image recording control unit 511F...Composite image display control unit 512...Memory 514...Auxiliary storage device 515...Input device 516...Display device 517...Communication interface (communication I / F) 520...Image database Ax...Axis of multi-eye imaging device IDA1...Image display area IDA2...Image display area IDA3...Image display area IDA4...Image display area IDA5...Image display area

Claims

1. An imaging system comprising: an illumination unit that emits light polarized in a first direction to an imaging area at a first degree of polarization; and an imaging unit that receives light polarized in a second direction from the imaging area at a second degree of polarization, wherein the first direction and the second direction intersect, and at least one of the first degree of polarization and the second degree of polarization is 10% or more and 90% or less.

2. The imaging system of claim 1, wherein the illumination unit comprises a light source and a first polarizing plate that transmits light polarized in the first direction, and the imaging unit comprises an imaging element and a second polarizing plate that transmits light polarized in the second direction.

3. The imaging system according to claim 2, wherein the first polarizing plate is constituted by a polarizing plate having the first polarization degree, and the second polarizing plate is constituted by a polarizing plate having the second polarization degree.

4. The imaging system according to claim 2, wherein at least one of the first polarizing plate and the second polarizing plate is configured with a polarizing plate having partially different degrees of polarization.

5. The imaging system according to claim 4, wherein the polarizing plate having a partially different degree of polarization is a polarizing plate having a partial area with a polarization degree of 0%.

6. The imaging system according to claim 5, wherein the polarizing plate with a partially different degree of polarization is a polarizing plate having discrete regions with a degree of polarization of 0%.

7. The imaging system described in claim 4, wherein the polarizing plate having partially different degrees of polarization is a polarizing plate having different degrees of polarization in a first region corresponding to the region where the light source is reflected and a second region different from the first region, and the degree of polarization in the second region is lower than that in the first region.

8. The imaging system according to claim 7, wherein the degree of polarization of the second region is 0%.

9. The imaging system according to claim 4, wherein at least one of the first polarizing plate and the second polarizing plate has a lower degree of polarization in a fourth region on the periphery than in a third region on the central side.

10. The imaging system according to claim 9, wherein the degree of polarization of the fourth region is 0%.

11. The imaging system according to claim 2, wherein at least one of the first polarizing plate and the second polarizing plate is configured as a polarizing plate that transmits light in a specific wavelength range.

12. The imaging system according to claim 2, further comprising a first drive unit that moves the first polarizing plate in and out of the optical path, and / or a second drive unit that moves the second polarizing plate in and out of the optical path.

13. The imaging system according to claim 12, further comprising a processor, wherein the processor controls the first driving unit and / or the second driving unit to move the first polarizing plate and / or the second polarizing plate out of the optical path during exposure of the imaging unit.

14. The imaging system of claim 12, further comprising a processor that controls the first driving unit and / or the second driving unit and the imaging unit to cause the imaging unit to perform imaging with the first polarizing plate and / or the second polarizing plate inserted into the optical path, and imaging with the first polarizing plate and / or the second polarizing plate retracted from the optical path.

15. An imaging system according to any one of claims 1 to 14, wherein the first direction and the second direction intersect at an angle of 90°±10°.

16. The imaging system according to any one of claims 1 to 14, wherein at least one of the first polarization degree and the second polarization degree is 30% or more and 70% or less.

17. The imaging system according to any one of claims 1 to 14, wherein the first polarization degree and the second polarization degree are 10% or more and 90% or less.

18. An imaging system according to any one of claims 1 to 14, comprising a plurality of illumination units for one imaging unit.

19. An imaging method using an illumination unit that emits light polarized in a first direction to an imaging area at a first polarization degree, and an imaging unit that receives light polarized in a second direction from the imaging area at a second polarization degree, wherein the first direction and the second direction are crossed to suppress reflection of the light source, and imaging is performed with at least one of the first polarization degree and the second polarization degree set to 10% or more and 90% or less.

20. The imaging method according to claim 19, wherein the degree of polarization in the imaging region is reduced spatially, temporally, or wavelength-wise to set at least one of the first degree of polarization and the second degree of polarization to 10% or more and 90% or less.

Images