Filter, imaging device, and imaging system

Abstract

To provide a filter which does not need alignment between a plurality of cells of the filter and a plurality of pixels of a light reception element in an imaging apparatus which can acquire polarization image information and wavelength image information in one shot.SOLUTION: A filter 10 according to an embodiment comprises a plurality of spectral polarization cells allocated with the reference azimuth of spectral transmission characteristics and polarization transmission characteristics. At least one of the size and shape of the plurality of spectral polarization cells is not uniform.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a filter, an imaging device, and an imaging system. [Background technology]

[0002] In recent years, polarization cameras (or polarization imaging cameras) have been used to measure the polarization characteristics of optical components, thin film products, and biological tissues, and to acquire information about the detailed physical properties of the object being measured based on the polarization characteristics obtained through the measurement. Polarizers with predetermined orientations are incorporated into multiple pixels of the light-receiving element of a polarization camera. Polarization cameras can acquire polarization image information in one shot (or snapshot). Conventionally proposed polarization cameras can acquire images in four polarization directions by acquiring polarization information in four different orientations for each pixel (see, for example, Non-Patent Document 1).

[0003] Although the above-mentioned polarization camera can acquire polarization information as described above, it has been difficult to acquire color images or spectral information because its spectral transmittance characteristics are limited to a certain wavelength band. On the other hand, conventionally proposed spectroscopic cameras (or spectral imaging cameras) can acquire multispectral images by acquiring spectral information for each pixel in a single shot (see, for example, Non-Patent Document 2). However, it has been difficult to acquire polarization information with the above-mentioned spectroscopic cameras. In light of this, imaging technologies have been proposed that can acquire different polarization and spectral characteristics for each pixel and acquire polarization image information and wavelength image information in a single shot (see, for example, Patent Document 1 and Non-Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-040976 [Non-patent literature]

[0005] [Non-Patent Document 1] Shojiro Kawakami, Takayuki Kawashima, Yoshihiko Inoue, Hiroshi Homma, Hisashi Sato, Shinichi Ohta, Kiyoshi Nagashima, and Takafumi Aoki; "Development of a Polarization Imaging Camera Using a Photonic Crystal Polarizer," IEICE Transactions on Electronics, Information and Communication Engineers, Vol. 90, No. 1, pp. 17-24 (2007). [Non-patent document 2] PJ. Lapray, X. Wang, JB. Thomas, P. Gouton; “Multispectral Filter Arrays: Recent Advances and Practical Implementation,” Sensors, Vol.14, pp.21626-21659 (2014). [Non-patent document 3] K. Shinoda. Y. Ohtera, M. Hasegawa; “Snapshot multispectral polarization imaging using a photonic crystal filter array,” Optics Express, Vol.26, pp.15948-15961 (2018). Summary of the Invention [Problem to be solved by the invention]

[0006] In imaging devices capable of acquiring polarization image information and wavelength image information in one shot, such as the devices disclosed in Patent Document 1 and Non-Patent Document 3, a filter is arranged closer to the light incident surface than the light receiving element. This filter has multiple cells, which are arranged in a surface that intersects with the direction of light propagation. Each cell has predetermined polarization and spectral characteristics. The light receiving element has multiple pixels, which are arranged in a light receiving surface that is parallel to the surface. When viewed from the direction of light incidence, each cell has the same shape as the corresponding pixel.

[0007] As described above, when manufacturing an imaging device capable of acquiring polarization image information and wavelength image information in one shot, when mounting a filter on the incident surface side of the light receiving element, it is necessary to align the multiple cells of the filter with the multiple pixels of the light receiving element. Such alignment between the filter and the light receiving element requires precision on the order of μm depending on the size of each cell or pixel, and in practice, a dedicated alignment device has been used. As a result, it has been very difficult to manufacture an imaging device capable of acquiring polarization image information and wavelength image information in one shot.

[0008] The present invention provides an imaging device capable of acquiring polarization image information and wavelength image information in one shot, a filter that does not require alignment between multiple cells of the filter and multiple pixels of a light receiving element, and an imaging device and imaging system that are equipped with this filter and are easy to manufacture. [Means for solving the problem]

[0009] According to this embodiment Imaging device teeth , the reference direction of the polarization transmission characteristics, Spectral transmission characteristics Sex A plurality of assigned spectral polarization cells are provided, and at least one of the sizes and shapes of the plurality of spectral polarization cells is non-uniform. a filter; and a light receiving unit that is disposed opposite the filter and includes a plurality of pixels that receive light emitted from the filter, wherein at least one of the size and shape of the spectral polarization cells that are disposed opposite each of the pixels and from which the light received by each of the pixels is emitted is non-uniform among the plurality of pixels. .

[0010] The above Imaging device In the above, the spectroscopic polarization cell may be composed of a photonic crystal having a grating pitch corresponding to the assigned spectral transmission characteristic and a grating direction corresponding to the reference orientation of the assigned polarization transmission characteristic.

[0012] In the imaging device described above, the range in which the pixel can receive the light emitted from the spectral polarization cell may include a boundary portion between the spectral polarization cells.

[0013] The imaging system according to this embodiment includes the imaging device described above; a calculation device that calculates, for each pixel, spectral information indicating the wavelength band of light acquired by the pixel when light to be measured is incident, and calculates, for each pixel, orientation information indicating the orientation of polarization acquired by the pixel, by irradiating the filter with calibration light that includes at least a wavelength band corresponding to the spectral transmission characteristics assigned to each of the spectral polarization cells, based on calibration information that stores, for each pixel, a correspondence relationship between the wavelength band of light acquired by the pixel, the orientation of polarization acquired by the pixel, and the intensity of light acquired by the pixel; and an output device that outputs the spectral information and orientation information calculated by the calculation device. [Effects of the Invention]

[0014] According to the present invention, in an imaging device capable of acquiring polarization image information and wavelength image information in one shot, it is possible to provide a filter that does not require alignment between multiple cells of the filter and multiple pixels of the light receiving element, and an imaging device and imaging system that are equipped with this filter and are easy to manufacture. [Brief explanation of the drawings]

[0015] [Figure 1] 1A and 1B are a perspective view of a filter according to an embodiment of the present invention and an enlarged perspective view of a region R1 of the filter. [Figure 2] 2 is an enlarged plan view of a region R1 of the filter shown in FIG. [Figure 3] 2 is a diagram for explaining a method for manufacturing the filter shown in FIG. 1, and is an enlarged cross-sectional view of a region R2 shown in FIG. [Figure 4] 2 is a diagram for explaining a method for manufacturing the filter shown in FIG. 1, and is an enlarged cross-sectional view of a region R2 shown in FIG. [Figure 5] 2 is an enlarged cross-sectional view of a region R2 shown in FIG. 1, illustrating a method for manufacturing the filter shown in FIG. 1. FIG. [Figure 6] 1 is a perspective view of an imaging device according to an embodiment of the present invention; [Figure 7] FIG. 7 is a side view of the imaging device shown in FIG. [Figure 8] 8 is an enlarged perspective view of a filter and a light receiving element in a region R3 of the imaging device shown in FIG. 7. [Figure 9] 8 is an enlarged plan view of a filter and a light receiving element in a region R3 of the imaging device shown in FIG. 7. FIG. [Figure 10] 10 is a schematic diagram showing a reference axis of the polarized light transmission characteristic after combining the transmission characteristics of a plurality of cells in each pixel of the light receiving element shown in FIG. [Figure 11] 1 is a block diagram of an imaging system according to an embodiment of the present invention; [Figure 12] 4 is a graph showing spectral information in Example 1. [Figure 13] 10 is a photograph showing polarization information in Example 2, where the left side is polarization information at an orientation of 0° and the right side is polarization information at an orientation of 90°. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] <Filter configuration> As shown in Fig. 1, filter 10 according to an embodiment of the present invention is formed in the shape of a thin plate. Front surface 12a of filter 10 is incident surface 13, which is the surface into which light enters. Back surface 12b of filter 10 is exit surface 14, which is the surface from which the incident light exits. Hereinafter, two directions that are included in incident surface 13 and exit surface 14 and are perpendicular to each other will be referred to as the x-direction and y-direction, and the direction connecting the periphery of incident surface 13 and the periphery of exit surface 14, i.e., the thickness direction of main body 12, will be referred to as the z-direction.

[0018] The filter 10 includes a plurality of spectral polarizing cells 21-1, 21-2, ..., 21-m, where m is the total number of spectral polarizing cells in the filter 10 and is a natural number greater than or equal to 2. In the following, when describing content common to two or more of the plurality of spectral polarizing cells 21-1, 21-2, ..., 21-m, these spectral polarizing cells will be collectively referred to as spectral polarizing cell 21. When viewed along the z direction, the sizes and shapes of the plurality of spectral polarizing cells 21 are partitioned non-uniformly. That is, the size and shape of each spectral polarizing cell 21 are determined randomly.

[0019] The non-uniform sizes and shapes of the multiple spectral-polarization cells 21 can be obtained based on, for example, a method using random numbers or Voronoi division as described below, and are not limited to sizes and shapes obtained by a specific method.

[0020] The multiple spectral polarization cells 21 include spectral polarization cells 21-i (i is a natural number between 1 and m) to which reference orientations of spectral transmission characteristics and polarized light transmission characteristics are assigned. Note that, hereinafter, the wavelength band of light corresponding to the spectral transmission characteristics will be referred to as wavelength band WB(i), and the reference orientation of the polarized light transmission characteristics will be referred to as polarization orientation φ(i).

[0021] The spectropolarization cell 21 of the filter 10 is made of, for example, a photonic crystal 30, and has a substrate 32 and a multilayer film 34. The material of the substrate 32 is, for example, quartz. The multilayer film 34 may be, for example, a laminated film in which niobium pentoxide (NbO) and silicon dioxide (SiO) are alternately stacked in the z direction.

[0022] The photonic crystal 30 constituting the spectral polarization cell 21-i has a lattice pitch d(i) corresponding to the wavelength band WB(i) assigned to the spectral polarization cell 21-i, and a lattice direction corresponding to the polarization direction φ(i) assigned to the spectral polarization cell 21-i. That is, the substrate 32 and the multilayer film 34 have a periodic uneven structure, with the apexes of the convex structures extending parallel to the polarization direction φ(i), and the distance between the apexes of adjacent convex structures is the lattice pitch d(i).

[0023] <Filter manufacturing method> Next, a brief description of a method for manufacturing the filter 10 will be given. As shown in FIG. 3, a quartz substrate 32 is prepared as a base. Although not shown, a mask is prepared having a mask pattern that matches the grating direction and grating pitch d(i) of the spectral polarization cells 21-i, which are partitioned with non-uniform sizes and shapes, as in FIG. 2. This mask is fabricated, for example, by electron beam lithography. A resist (not shown) is applied to the surface 32a of the substrate 32, and the mask pattern is transferred to the resist. The substrate 32 is etched using the pattern-transferred resist as a mask. As shown in FIG. 4, a periodic structure is formed on the substrate 32, having the grating direction and grating pitch d(i) assigned to the spectral polarization cells 21-i.

[0024] 5, first layers 35-1 made of one of Nb2O5 and SiO2 and second layers 35-2 made of the other of Nb2O5 and SiO2 are alternately laminated on the surface 32a of the substrate 32 on which the periodic structure is formed. The thickness and refractive index of each of the first layer 35-1 and the second layer 35-2 are appropriately set according to the wavelength band WB(i) assigned to the spectropolarization cell 21-i. The first layers 35-1 and the second layers 35-2 are alternately laminated so that the total thickness of the laminated film reaches a predetermined value, thereby forming a multilayer film 34 and completing the filter 10 equipped with the photonic crystal 30.

[0025] <Configuration of imaging device> As shown in FIGS. 6 and 7 , an imaging device 100 according to an embodiment of the present invention includes at least the filter 10, a light receiving element (light receiving unit) 110, and a housing that supports elements including the filter 10 and the light receiving element 110. The imaging device 100 is, for example, an imaging camera equipped with the light receiving element 110. The light receiving element 110 is disposed opposite the filter 10 and includes a plurality of pixels 112-1, 112-2, . . . , 112-n that receive light L emitted from the filter 10 in a direction opposite to the z direction. n is the total number of pixels in the light receiving element 110 and is a natural number equal to or greater than 2. Hereinafter, when describing content common to two or more pixels among the plurality of pixels 112-1, 112-2, . . . , 112-n, these pixels will be collectively referred to as pixel 112. The light receiving element 110 is, for example, an image sensor such as a CMOS or a CCD.

[0026] 8 and 9, in the imaging device 100, the size and shape of the pixels 112 of the light receiving element 110 correspond non-uniformly to the size and shape of the spectral polarization cells 21 arranged opposite the pixels 112. In other words, as shown in Fig. 9, the multiple pixels 112 include pixels 112 that correspond to one spectral polarization cell 21 and pixels 112 that correspond to two or more spectral polarization cells 21, and there is not a one-to-one correspondence between the spectral polarization cells 21 of the filter 10 and the pixels 112 of the light receiving element 110.

[0027] 9, the range in which the pixels 112 of the light receiving element 110 can receive light emitted from the spectral polarizing cells 21 includes the boundary portions between the spectral polarizing cells 21. Furthermore, two or more spectral polarizing cells 21 are included in the range in which at least one pixel 112 of the multiple pixels 112 can receive light emitted from the spectral polarizing cells 21.

[0028] 9, when viewed along the z direction, pixel 112-1 is overlapped by two cells 21-1 and 21-2. The wavelength band WR(1) of light acquired by pixel 112-1 is expressed as a synthetic wavelength band (wavelength band) obtained by combining the wavelength band WB(1) assigned to spectral-polarizing cell 21-1 and the wavelength band WB(2) assigned to spectral-polarizing cell 21-2, in accordance with the area ratio between the area of ​​the portion of spectral-polarizing cell 21-1 that overlaps with pixel 112-1 and the area of ​​the portion of spectral-polarizing cell 21-2 that overlaps with pixel 112-1. Similarly, three spectral-polarizing cells 21-1, 21-2, and 21-e overlap pixel 112-c. Therefore, the wavelength band WR(c) of light received by pixel 112-c is expressed as a synthetic wavelength band (wavelength band) obtained by combining the wavelength bands WB(1), WB(2) and the wavelength band WB(e) assigned to spectral polarizing cell 21-e, depending on the area ratio between the area of ​​the portion of spectral polarizing cell 21-1 that overlaps with pixel 112-c, the area of ​​the portion of spectral polarizing cell 21-2 that overlaps with pixel 112-c, and the area of ​​the portion of spectral polarizing cell 21-e that overlaps with pixel 112-c.

[0029] Furthermore, the polarization direction Φ(1) acquired by pixel 112-1 is represented by a composite direction (orientation) obtained by combining the polarization direction φ(1) assigned to spectral-polarizing cell 21-1 and the polarization direction φ(2) assigned to spectral-polarizing cell 21-2, in accordance with the area ratio between the area of ​​the portion of spectral-polarizing cell 21-1 that overlaps with pixel 112-1 and the area of ​​the portion of spectral-polarizing cell 21-2 that overlaps with pixel 112-1. Similarly, the polarization direction Φ(c) received by pixel 112-c is represented by a composite direction (orientation) obtained by combining the polarization directions φ(1), φ(2) and the polarization direction φ(e) assigned to spectral-polarizing cell 21-e, in accordance with the area ratio between the area of ​​the portion of spectral-polarizing cell 21-1 that overlaps with pixel 112-c, the area of ​​the portion of spectral-polarizing cell 21-2 that overlaps with pixel 112-c, and the area of ​​the portion of spectral-polarizing cell 21-e that overlaps with pixel 112-c.

[0030] <Image capture system configuration> 11 , an imaging system 150 according to an embodiment of the present invention includes at least the imaging device 100 described above, a reading device 152, a storage device 155, a calculation device 160, and an output device 170. In the imaging device 100, a filter 10 is disposed facing the light receiving element 110. When the filter 10 is disposed facing the light receiving element 110 without any particular alignment, the polarization direction Φ(j) and the wavelength band WR(j) of light acquired by the pixel 112-j (j is a natural number between 1 and n) of the light receiving element 110 are determined. In the imaging system 150, the polarization direction Φ(j) and the wavelength band WR(j) of light acquired by the pixel 112-j of the light receiving element 110 of the imaging device 100 are first calibrated by actually measuring them.

[0031] In the imaging system 150, the wavelength band WR(j) of light acquired by the pixel 112-j of the light receiving element 110 and the polarization direction Φ C (j), and the light intensity I acquired by pixel 112-j. C The correspondence between the intensity I of the calibration light LC and the wavelength bands WB(1), WB(2), ..., WB(m) assigned to each of the spectropolarization cells 21 of the filter 10 is recorded in the storage device 155 as calibration information. Specifically, first, the calibration light LC is irradiated onto the filter 10. The calibration light LC is light that includes at least the wavelength bands WB(1), WB(2), ..., WB(m) assigned to each of the spectropolarization cells 21 of the filter 10, and also includes the polarization directions φ(1), φ(2), ..., φ(m) assigned to each of the spectropolarization cells 21. The reading device 152 reads the intensity I of the calibration light LC acquired by the pixels 112-j (j = 1 to n) of the light receiving element 110. C The reading device 152 receives the wavelength band WR (j) of the light acquired by the pixel 112-j. The type of wavelength band and the type of direction of the calibration light LC that are known in advance are externally input to the reading device 152. The reading device 152 receives the wavelength band WR (j) of the light acquired by the pixel 112-j. C (j) and polarization direction Φ CThe type of wavelength band and the type of orientation of the externally input calibration light LC are adopted as (j) and recorded in the storage device 155. When measurements are completed using the calibration light LC of multiple types of wavelength bands and multiple types of polarization orientations, the storage device 155 stores the number j of the pixel 112 and the wavelength band WR, which is the wavelength band of the light acquired by that pixel 112-j and is the calibrated wavelength band. C (j), and the orientation Φ, which is the orientation of the polarization acquired by the pixel 112-j and is the calibrated orientation. C (j) and are stored as table data.

[0032] Next, as shown in FIG. 7, when the optical DC to be measured and emitted from the object to be measured (not shown) is irradiated onto the imaging device 100, the reading device 152 calculates the intensity I of the optical DC to be measured acquired by the pixel 112-j (j=1 to n) of the light receiving element 110. D The calculation device 160 receives the light intensity I(j) for each pixel 112 from the reading device 152. D The calculation device 160 receives the information (j) and reads out the calibration information from the storage device 155. Based on the calibration information, the calculation device 160 calculates, for each pixel 112-j, spectral information indicating the wavelength band of light acquired by the pixel 112-j and orientation information indicating the orientation of polarization acquired by the pixel 112-j.

[0033] The output device 170 receives and outputs the spectral information and orientation information calculated by the arithmetic device 160. The output device 170 is, for example, a liquid crystal display. The spectral information may be, for example, an image in which the multiple pixels 112 of the light receiving element 110 correspond to the multiple display elements of the liquid crystal display and the relative intensity of a wavelength band acquired for each pixel 112-j is displayed, or a spectral histogram in which the horizontal axis represents wavelength and the vertical axis represents the integrated value of the light intensity of that wavelength acquired by all the pixels 112; and is not limited to a specific format. Furthermore, the orientation information may be, for example, an image in which the multiple pixels 112 of the light receiving element 110 correspond to the multiple display elements of the liquid crystal display and the relative intensity of the polarized light orientation acquired for each pixel 112-j is converted into an arbitrary grayscale value and displayed, or an orientation histogram in which the horizontal axis represents the orientation angle and the vertical axis represents the integrated value of the light intensity of that orientation acquired by all the pixels 112; and is not limited to a specific format.

[0034] <Design examples and imaging device calibration> For example, the size and shape of the plurality of spectral polarization cells 21 of the filter 10 can be set using the following equations (1) and (2) based on the concept of Voronoi division.

[0035]

number

[0036] In equations (1) and (2), S represents a set of N generating points, and δ represents the Euclidean distance function. S is determined by selecting N random points in the pattern area (i.e., the area formed by multiple spectral-polarization cells 21). A random pattern created by Voronoi tessellation is created by filling Voronoi cells in a lattice pattern with random pitches and angles. N is preferably set to be approximately the same as the number of pixels, between 1 / 10 and 10 times the number of pixels.

[0037] As described above, the size and shape of each spectral polarizing cell 21 in the filter 10 are determined randomly, and two or more spectral polarizing cells 21 are included in the range in which at least one pixel 112 of the multiple pixels 112 can receive light emitted from the spectral polarizing cell 21. However, if an extremely large number of spectral polarizing cells 21 are included in the range in which a certain number of pixels 112 can receive light emitted from the spectral polarizing cell 21, there will be virtually no difference in the wavelength band and polarization direction of the light acquired between the multiple pixels 112. For this reason, it is preferable that the range in which the pixels 112 can receive light emitted from the spectral polarizing cell 21 include approximately the same number of spectral polarizing cells 21 as the number of pixels, for example, between 1 / 10 and 10 times the number of pixels.

[0038] As described above, when the imaging device 100 is calibrated using the imaging system 150, the calibration method is as follows: S s S =[s0s1s2] T For ease of explanation, it is assumed that one pixel 112-j (j is a natural number between 1 and n) among the multiple pixels 112 is irradiated with calibration light LC of a certain wavelength. Stokes parameters and polarization intensity I I =[I 0° I 45° I 90° ] T The relationship between these is expressed by the following equations (3) and (4).

[0039]

number

[0040] In the imaging device 100 and imaging system 150 of this embodiment, multiple spectral polarization cells 21 correspond to at least one pixel 112-j, so the observed signal value at a specific pixel 112 of the light receiving element 110 is expressed by the following equation (5).

[0041]

number

[0042] The above equation (5) assumes that M Voronoi regions (i.e., regions with different wavelength bands and polarization directions of transmitted light) overlap and are mixed in a certain pixel 112 of the light receiving element 110. Furthermore, in equation (5), w represents the mixture ratio of each Voronoi region, q and r represent the spectral transmittance characteristics of TE polarized light and TM polarized light in each Voronoi region, and θ represents the lattice angle, i.e., the orientation φ(i), in each Voronoi region. Rearranging equation (5), the following equations (6) to (9) are obtained.

[0043]

number

[0044] When the filter 10 of this embodiment is attached to a specific position of the light receiving element 110, it is difficult to calculate the accurate k1, k2, 2(θ'+ψ) for the specific pixel 112 from equations (7) to (9). However, by using an imaging device with a filter together with a light source that emits linearly polarized light, k1, k2, 2(θ'+ψ) in equation (6) can be easily determined. The Stokes parameter s normalized by the linear polarization angle α is S s S =[1 cos2α sin2α] T Then, the above equation (6) can be expressed as the following equation (10).

[0045]

number

[0046] Observed signal value g α is a cosine wave with period π and phase 2(θ´+ψ), so according to sampling theory, the observed signal value g αBy measuring at three or more points, the phase 2(θ'+ψ) can be determined. In other words, it seems that the values ​​of the above equations (7) to (9) cannot be obtained unless the spectral transmittance characteristics of TE polarized light, the spectral transmittance characteristics of TM polarized light, and the lattice angle of all Voronoi regions (i.e., spectro-polarization cells 21) corresponding to a specific pixel are obtained. However, by irradiating the imaging device 100 with linearly polarized light of a known orientation, under the condition of equation (10), and changing the polarization orientation of the calibration light LC by at least three angles between 0 and π, the phase 2(θ'+ψ) can be obtained.

[0047] Once the phase 2(θ´+ψ) is calculated as described above, the angle α q The observed signal value g when linearly polarized light is incident αq and angle α r The observed signal value g when the calibration light LC having the polarization direction is incident αr can be seen from the following equations (11) and (12).

[0048]

number

[0049] By substituting the equations (11) and (12) into the above equation (6), the following equation (13) is obtained.

[0050]

number

[0051] As can be seen from the above equation (13), the filter 10 of this embodiment has the same transmission characteristics as when a conventional filter regularly divided into a plurality of cells is mounted on an imaging camera. αq , g αr , α q is determined by measuring the spectral characteristics of the calibration light LC for each of the three polarization directions.

[0052] The filter 10 of this embodiment described above includes a plurality of spectral polarization cells 21-i (i is a natural number from 1 to m) to which wavelength bands WB(i) and polarization directions φ(i) are respectively assigned, and the plurality of spectral polarization cells 21-i are non-uniform in size and shape. According to the filter 10 of this embodiment, when it is mounted on an imaging camera, for example, it is not necessary to align the plurality of pixels 112-j (j is a natural number from 1 to n) of the light receiving element with the plurality of spectral polarization cells 21-i.

[0053] In the filter 10 of this embodiment, the spectral polarization cell 21-i is composed of a photonic crystal having a grating pitch corresponding to the assigned wavelength band WB(i) and a grating direction corresponding to the assigned polarization direction φ(i). According to the filter 10 of this embodiment, the filter 10 having the non-uniform, random pattern described above can be easily manufactured. Furthermore, the filter 10 can be manufactured without changing the materials or processes for each minute region or region corresponding to a pixel 112.

[0054] The imaging device 100 of this embodiment includes the above-described filter 10 and a light receiving element 110 that is disposed opposite the filter 10 and includes a plurality of pixels 112-j that receive light emitted from the filter 10. The size and shape of the pixels 112-j and the size and shape of the spectral polarization cells 21 that are disposed opposite the pixels correspond non-uniformly.

[0055] The imaging device 100 of this embodiment includes the filter 10 described above, and the size and shape of the pixel 112-j and the size and shape of the spectral polarization cell 21 arranged opposite the pixel 112-j correspond non-uniformly. This eliminates the need to align the multiple pixels 112 of the light receiving element with the multiple spectral polarization cells 21 when installing the filter 10 relative to the light receiving element 110. This makes it possible to provide an imaging device 100 that is capable of acquiring polarization image information and wavelength image information in one shot, and that does not require alignment of the multiple spectral polarization cells of the filter 10 with the multiple pixels of the light receiving element. In the imaging device 100 of this embodiment, for example, the range in which pixel 112-j can receive light emitted from the spectral polarization cell 21 may include the boundary between the spectral polarization cells 21, and the above-mentioned effect can be achieved.

[0056] The imaging system 150 of this embodiment is the imaging device 100 described above, and is configured to irradiate the filter 10 with calibration light LC, which is light including at least the wavelength band φ(i) assigned to each spectral polarization cell 21-i, to obtain the wavelength band WR of light acquired by the pixel 112-j. C (j), and the polarization direction Φ acquired by pixel 112-j. C (i) and the light intensity I acquired by pixel 112-j. C The imaging system 150 includes a calculation device 160 that calculates, for each pixel 112, spectral information indicating the wavelength band of light acquired by the pixel 112 when light DC to be measured is incident, based on calibration information in which a correspondence relationship between the filter 10 and (j) is stored for each pixel 112, and calculates orientation information for each pixel 112 indicating the orientation of polarization acquired by the pixel 112, and an output device 170 that outputs the spectral information and orientation information calculated by the calculation device 160. According to the imaging system 150 of this embodiment, various spectral information and orientation information can be obtained in one shot using the imaging device 100 equipped with the filter 10.

[0057] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims.

[0058] For example, in a filter according to the present invention, at least one of the sizes and shapes of the plurality of spectral polarizing cells 21-i may be non-uniform, as long as the same operational effect as that of the filter 10 of this embodiment is obtained. Also, in an imaging device according to the present invention, at least one of the sizes and shapes of the pixels 112 and at least one of the sizes and shapes of the spectral polarizing cells 21 arranged opposite the pixels may be non-uniform, as long as the same operational effect as that of the imaging device 100 of this embodiment is obtained. [Example]

[0059] Next, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0060] Example 1 A photonic crystal having a random structure was prototyped as the filter 10 exemplified in the above-described embodiment, and it was confirmed that the film could be formed without failure. Next, the prototype filter was attached to the front side of the light receiving section of a monochrome camera (model number: ARTCAM150P5, manufactured by ARTRAY) using ultraviolet curing resin, and a color chart was photographed. During the prototype, the multiple spectral polarization cells of the filter were not aligned with the multiple pixels of the light receiving element of the monochrome camera.

[0061] Figure 12 shows the resulting spectrum (spectral information) of 16 colors when the spectropolarimetric image (spectral information, azimuth information) of the color target was restored after capturing the image, and only the RGB components were extracted for color reproduction. In each spectrum in Figure 12, the dashed line represents the spectrum of the original color target, and the solid line represents the reproduced spectrum. As shown in Figure 12, we confirmed that the spectral information of visible light can be restored using a monochrome camera equipped with the prototype filter.

[0062] <Example 2> The LCD screen of a commercially available mobile device was photographed using the same prototype filter and monochrome camera as in Example 1. Fig. 13 shows polarized images (orientation information) restored using polarization orientations of 0° and 90°. Compared to the polarized image with an orientation of 0°, the polarized image with an orientation of 90° was dark overall, confirming that a polarizing plate was installed on the surface of the LCD screen and that the light emitted from the screen was polarized in the orientation of 0°.

[0063] From the above Examples 1 and 2, it was confirmed that the filter, imaging device, and imaging system to which the present invention is applied can obtain good spectral information and azimuth information in one shot without aligning the multiple spectropolarization cells of the filter with the multiple pixels of the light receiving element.

[0064] The above-described embodiment has been described as an imaging device capable of acquiring polarization image information and wavelength image information in one shot, using a filter equipped with multiple spectral polarization cells, each of which is assigned a reference orientation for spectral transmission characteristics and polarization transmission characteristics. However, the principles of the present invention are not limited to the above-described embodiment, and can also be applied to, for example, the following embodiments.

[0065] For example, this can be applied to a case where a filter equipped with multiple polarization cells to which reference orientations of polarization transmission characteristics are assigned is used as an imaging device capable of acquiring polarization image information in one shot, as described in Non-Patent Document 1. In this case, the same effect can be achieved by replacing the spectral polarization cell in the above-mentioned embodiment with a polarization cell.

[0066] For example, the present invention can be applied to a case where a filter equipped with a plurality of spectral cells to which spectral transmittance characteristics are assigned is used as an imaging device capable of acquiring spectral information for each pixel in one shot, as described in Non-Patent Document 2. In this case, the same effect can be achieved by replacing the spectral polarization cell in the above-described embodiment with a spectral cell.

[0067] For example, as described in Patent Document 1, an imaging device capable of acquiring polarization image information and wavelength image information in one shot can be applied to a case in which a filter including a plurality of spectroscopic cells to which spectral transmission characteristics are assigned and a filter including a plurality of polarizing cells to which reference orientations of the polarization transmission characteristics are assigned is used. In this case, the same effect can be achieved by replacing the spectroscopic polarization cells in the above-described embodiments with spectroscopic cells and polarizing cells. Note that in this case, the spectroscopic cells and polarizing cells arranged opposite each other can be made to correspond to each other in terms of at least one of their sizes and shapes in a non-uniform manner, thereby eliminating the need to align the spectroscopic cells and polarizing cells. [Explanation of symbols]

[0068] 10...Filter 100...imaging device 150...imaging system

Claims

1. A filter comprising a plurality of spectral polarization cells to which reference orientations of polarization transmission characteristics and spectral transmission characteristics are assigned, wherein at least one of the sizes and shapes of the plurality of spectral polarization cells is non-uniform; a light receiving section disposed opposite the filter and including a plurality of pixels for receiving light emitted from the filter; Equipped with the spectral polarization cells are arranged to face the respective pixels, and at least one of the size and the shape of the spectral polarization cells from which the light received by the respective pixels is emitted is non-uniform among the plurality of pixels; Imaging device.

2. the spectral polarization cell is configured with a photonic crystal having a grating pitch corresponding to the assigned spectral transmission characteristics and a grating direction corresponding to a reference orientation of the assigned polarization transmission characteristics. The imaging device according to claim 1 .

3. a boundary portion between the spectral polarization cells is included in the range in which the pixel can receive the light emitted from the spectral polarization cell; 3. The imaging device according to claim 1.

4. The imaging device according to claim 1 , a calculation device that calculates, for each pixel, spectral information indicating the wavelength band of light acquired by the pixel when light to be measured is incident, and calculates, for each pixel, orientation information indicating the orientation of polarization acquired by the pixel, by irradiating the filter with calibration light that includes at least a wavelength band corresponding to the spectral transmittance characteristics assigned to each of the spectral polarization cells, based on calibration information that stores, for each pixel, a correspondence relationship between the wavelength band of light acquired by the pixel, the orientation of polarization acquired by the pixel, and the intensity of light acquired by the pixel; and an output device that outputs the spectrum information and the direction information calculated by the arithmetic device; An imaging system comprising:

Images