JP7795758B2 - Filter, imaging device, and imaging system - Google Patents

Description

The present invention relates to a filter, an imaging device, and an imaging system.

In recent years, polarization cameras (or polarization imaging cameras) have been used to measure the polarization properties of optical components, thin film products, and biological tissues, and to obtain detailed information about the physical properties of the objects being measured based on the polarization properties 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 obtain polarization image information in a single shot (or snapshot). Previously proposed polarization cameras can obtain images in four polarization directions, for example, by obtaining polarization information in four different orientations for each pixel (see, for example, Non-Patent Document 1).

The polarization camera described above can acquire polarization information as described above, but because the spectral transmittance characteristics are limited to a certain wavelength band, it has been difficult to obtain color images or spectral information. Meanwhile, previously 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 technology has been proposed that acquires different polarization and spectral characteristics for each pixel, making it possible to acquire polarization image information and wavelength image information in a single shot (see, for example, Patent Document 1 and Non-Patent Document 3).

Japanese Patent Application Laid-Open No. 2018-040976

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). P-J. Lapray, X. Wang, J-B. Thomas, P. Gouton; “Multispectral Filter Arrays: Recent Advances and Practical Implementation,” Sensors, Vol.14, pp.21626-21659 (2014). K. Shinoda. Y. Ohtera, M. Hasegawa; “Snapshot multispectral polarization imaging using a photonic crystal filter array,” Optics Express, Vol.26, pp.15948-15961 (2018).

In imaging devices capable of acquiring polarization image information and wavelength image information in a single shot, including those disclosed in the above-mentioned Patent Document 1 and Non-Patent Document 3, a filter is placed on the light incident surface side of the light receiving element. This filter has multiple cells, which are arranged within 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 within a light receiving surface that is parallel to the aforementioned surface. When viewed from the direction of light incidence, each cell has the same shape as the corresponding pixel.

As described above, when manufacturing an imaging device capable of acquiring polarization image information and wavelength image information in a single shot, mounting a filter on the incident surface side of the light receiving element required alignment between the filter's multiple cells and the light receiving element's multiple pixels. Aligning the filter and light receiving element requires precision on the order of microns depending on the size of each cell or pixel, and in practice, dedicated alignment equipment was used. This made it extremely difficult to manufacture an imaging device capable of acquiring polarization image information and wavelength image information in a single shot.

The present invention provides an imaging device capable of acquiring polarization image information and wavelength image information in a single shot, a filter that does not require alignment between the filter's multiple cells and the light-receiving element's multiple pixels, and an imaging device and imaging system that are equipped with this filter and are easy to manufacture.

The imaging device of this embodiment comprises a filter having a plurality of spectral polarizing cells to which reference orientations and spectral transmittance characteristics of polarization transmission characteristics are assigned, and at least one of the sizes and shapes of the plurality of spectral polarizing cells is non-uniform; and a light receiving unit arranged opposite the filter and having a plurality of pixels that receive light emitted from the filter, wherein at least one of the sizes and shapes of the spectral polarizing cells arranged opposite each of the pixels and from which light received by each of the pixels is emitted is non-uniform among the plurality of pixels .

In the above-described imaging device , 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 a reference orientation of the assigned polarization transmission characteristic.

In the above-mentioned imaging device, the range in which the pixel can receive light emitted from the spectral polarization cell may include the boundary between the spectral polarization cells.

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 orientation information indicating the orientation of polarization acquired by the pixel, by irradiating the filter with calibration light that includes at least the wavelength band corresponding to the spectral transmittance characteristics assigned to each of the spectral polarization cells, based on calibration information stored for each pixel that describes the correspondence 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.

The present invention provides an imaging device capable of acquiring polarization image information and wavelength image information in a single shot, a filter that does not require alignment between the multiple cells of the filter and the 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.

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. FIG. 2 is an enlarged plan view of a region R1 of the filter shown in FIG. 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. 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. 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. 1 is a perspective view of an imaging device according to an embodiment of the present invention; FIG. 7 is a side view of the imaging device shown in FIG. 6 . FIG. 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. 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. 10 is a schematic diagram showing a reference axis of the polarized light transmission characteristic after combining the transmission characteristics of multiple cells in each pixel of the light receiving element shown in FIG. 9 . 1 is a block diagram of an imaging system according to an embodiment of the present invention; 1 is a graph showing spectral information in Example 1. 10 is a photograph showing polarization information in Example 2, the left side being polarization information at an orientation of 0°, and the right side being polarization information at an orientation of 90°.

Embodiments of the present invention will be described below with reference to the drawings.

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

The filter 10 includes a plurality of spectral polarizing cells 21-1, 21-2, ..., 21-m. m is the total number of spectral polarizing cells in the filter 10 and is a natural number greater than or equal to 2. Below, 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 non-uniformly partitioned. In other words, the size and shape of each spectral polarizing cell 21 is determined randomly.

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

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 for spectral transmittance characteristics and polarized light transmittance characteristics are assigned. Hereinafter, the wavelength band of light corresponding to the spectral transmittance characteristics will be referred to as wavelength band WB(i), and the reference orientation for the polarized light transmittance characteristics will be referred to as polarization orientation φ(i).

The spectropolarization cell 21 of the filter 10 is formed 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 (Nb ₂ O ₅ ) and silicon dioxide (SiO ₂ ) are alternately stacked in the z direction.

The photonic crystal 30 that constitutes the spectral polarization cell 21-i has a lattice pitch d(i) that corresponds to the wavelength band WB(i) assigned to the spectral polarization cell 21-i, and a lattice direction that corresponds to the polarization direction φ(i) assigned to the spectral polarization cell 21-i. In other words, the substrate 32 and multilayer film 34 have a periodic uneven structure, with the peaks of the convex structures extending parallel to the polarization direction φ(i), and the distance between the peaks of adjacent convex structures is the lattice pitch d(i).

<Filter manufacturing method>
Next, a brief description of a manufacturing method for 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.

5, first layers 35-1 made of one of Nb ₂ O ₅ and SiO ₂ and second layers 35-2 made of the other of Nb ₂ O ₅ and SiO ₂ 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 layers 35-1 and second layers 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 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.

<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 described above, 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 arranged 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 CCD.

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

As shown in Figure 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.

For example, as shown in Figure 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 pixel 112-1 and the area of the portion of spectral polarizing cell 21-2 that overlaps 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 the light received by pixel 112-c is expressed as a synthetic wavelength band (wavelength band) obtained by combining the wavelength bands WB(1) and WB(2) with 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.

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) and Φ(2) with 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.

<Configuration of imaging system>
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, the filter 10 is disposed facing the light receiving element 110, and 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.

In the imaging system 150, the correspondence between the wavelength band WR(j) of light acquired by the pixel 112-j of the light receiving element 110, the polarization direction Φ _C (j) acquired by the pixel 112-j, and the light intensity I _C (j) acquired by the pixel 112-j is recorded as calibration information in the storage device 155. Specifically, first, 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 spectroscopic polarization cell 21 of the filter 10, and also includes the polarization directions φ(1), φ(2), ..., φ(m) assigned to each spectroscopic polarization cell 21. The reader 152 receives the intensity I _C (j) of the calibration light LC acquired by the pixel 112-j (j = 1 to n) of the light receiving element 110 for each pixel. The type of wavelength band and the type of orientation of the calibration light LC that are known in advance are externally input to the reading device 152. The reading device 152 adopts the type of wavelength band and the type of orientation of the externally input calibration light LC as the wavelength band WR _C (j) and polarization orientation Φ _C (j) of the light acquired by the pixel 112-j, and records them in the storage device 155. When measurements are completed using calibration light LC of light of multiple types of wavelength bands and multiple types of polarization orientations, the storage device 155 stores, as table data, the number j of the pixel 112, the wavelength band WR _C (j) of the light acquired by that pixel 112-j, which is the calibrated wavelength band, and the orientation Φ _C (j) of the polarization orientation acquired by that pixel 112-j.

7 , when light DC to be measured that is emitted from a measurement object (not shown) is irradiated onto the imaging device 100, the reading device 152 receives the intensity I D (j) of the light DC to be measured that is acquired by the pixels 112-j (j = 1 to n) of the light receiving element 110 for each pixel 112. The arithmetic device 160 receives the information on the light intensity _{I D (} j) for each pixel 112 from the reading device 152, and reads out calibration information from the storage device 155. Based on the calibration information, the arithmetic device 160 calculates, for each pixel 112-j, spectral information indicating the wavelength band of the light acquired by the pixel 112-j and orientation information indicating the orientation of polarization acquired by the pixel 112-j.

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

<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.

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 spectropolarization 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 between 1/10 and 10 times the number of pixels, and is approximately the same as the number of pixels.

As mentioned 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 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. Therefore, it is preferable that the range in which pixels 112 can receive light emitted from the spectral polarizing cell 21 includes spectral polarizing cells 21 that are approximately the same as the number of pixels, for example, between 1/10 and 10 times the number of pixels.

Furthermore, as described above, when calibrating the imaging device 100 using the imaging system 150, the calibration method is as follows. The Stokes parameter s _S incident on the filter is set as s _S = [s ₀ s ₁ s ₂ ] ^T. For ease of explanation, it is assumed that calibration light LC of a certain wavelength is irradiated onto one pixel 112-j (j is a natural number greater than or equal to 1 and less than or equal to n) of the multiple pixels 112. The relationship between the Stokes parameter and the polarization intensity I _I = [I _0° I _45° I _90° ] ^T is expressed by the following equations (3) and (4).

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).

Equation (5) above assumes that M Voronoi regions (i.e., regions with different wavelength bands and polarization directions of transmitted light) overlap and are mixed in a 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.

When the filter 10 of this embodiment is adhered to a specific position on the light receiving element 110, it is difficult to calculate accurate k ₁ , k ₂ , 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, k ₁ , k ₂ , 2(θ' + ψ) in equation (6) can be easily determined. If the Stokes parameter s _S normalized for linearly polarized light at an angle α is s _S = [1 cos2α sin2α] ^T , then the above equation (6) can be expressed as the following equation (10):

Because the observed signal value g _α is a cosine wave with a period π and a phase 2(θ'+ψ), sampling theory dictates that the phase 2(θ'+ψ) can be determined by measuring the observed signal value g _α at three or more points at an angle α between 0 and π. In other words, it would appear that the values of the above equations (7)-(9) cannot be determined 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., the spectroscopic polarization cells 21) corresponding to a particular pixel are determined. However, by irradiating the imaging device 100 with linearly polarized light of a known orientation, under the condition of equation (10), and measuring the spectral characteristics for each pixel 112 while 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 determined.

Once the phase 2(θ'+ψ) has been determined as described above, the observed signal value _gαq when linearly polarized light is incident at an angle _αq and the observed signal value _gαr when calibration light LC having a polarization direction of angle _αr is incident can be determined by the following equations (11) and (12).

Substituting equations (11) and (12) into equation (6) above, we obtain equation (13) below.

As can be seen from the above formula (13), the filter 10 of this embodiment has the same transmission characteristics as when a conventional filter regularly divided into multiple cells is mounted on an imaging camera. That is, g _αq , g _αr , and _αq are determined by measuring the spectral characteristics of the calibration light LC for each of the three types of polarization orientations.

The filter 10 of this embodiment described above includes multiple spectral polarization cells 21-i (i is a natural number from 1 to m), each assigned a wavelength band WB(i) and a polarization direction φ(i), and the multiple spectral polarization cells 21-i are non-uniform in size and shape. When installing the filter 10 of this embodiment in an imaging camera, for example, it is not necessary to align the multiple pixels 112-j (j is a natural number from 1 to n) of the light receiving element with the multiple spectral polarization cells 21-i.

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). The filter 10 of this embodiment makes it easy to manufacture a filter 10 having the non-uniform, random pattern described above. Furthermore, the filter 10 can be manufactured without changing materials or processes for each minute region or region corresponding to a pixel 112.

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 do not uniformly correspond to the size and shape of the spectral polarization cells 21 disposed opposite the pixels.

The imaging device 100 of this embodiment includes the filter 10 described above. Because 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, aligning the multiple pixels 112 of the light receiving element with the multiple spectral polarization cells 21 is not necessary when placing the filter 10 on the light receiving element 110. This makes it possible to provide an imaging device 100 that can acquire polarization image information and wavelength image information in a single shot, and does not require aligning 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, thereby achieving the above-described effect.

The imaging system 150 of this embodiment includes the imaging device 100 described above, and a calculation device 160 that calculates, when light DC to be measured is incident, spectral information indicating the wavelength band of light acquired by the pixel 112 and orientation information indicating the orientation of the polarization acquired by the pixel 112, based on calibration information stored for each pixel 112 that describes a correspondence between the wavelength band WR _C (j) of light acquired by the pixel 112-j, the orientation Φ _C (i) of polarization acquired by the pixel 112-j, and the intensity I _C (j) of light acquired by the pixel 112-j, by irradiating the filter 10 with calibration light LC that includes at least the wavelength band φ(i) assigned to each spectropolarization cell 21-i. The calculation device 160 calculates, for each pixel 112, spectral information indicating the wavelength band of light acquired by the pixel 112 and orientation information indicating the orientation of the polarization acquired by the pixel 112, based on calibration information stored for each 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.

The above describes in detail preferred embodiments of the present invention, but the present invention is not limited to the above-described embodiments. Various modifications and variations of the present invention are possible within the scope of the gist of the present invention as set forth in the claims.

For example, in the filter according to the present invention, as long as the same functional effects as those of the filter 10 of this embodiment are obtained, at least one of the sizes and shapes of the multiple spectral polarizing cells 21-i may be non-uniform. Also, in the imaging device according to the present invention, as long as the same functional effects as those of the imaging device 100 of this embodiment are obtained, 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 those pixels may be non-uniform.

Next, examples of the present invention will be described. Note that the present invention is not limited to the following examples.

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.

Figure 12 shows the resulting 16-color spectrum (spectral information) when the spectropolarimetric image (spectral information, azimuth information) was restored after capturing a color chart, 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 chart, and the solid line represents the reproduced color 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.

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 darker 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°.

From Examples 1 and 2 above, it was confirmed that the filter, imaging device, and imaging system to which the present invention is applied can obtain excellent spectral information and azimuth information in one shot without aligning the filter's multiple spectral polarization cells with the light-receiving element's multiple pixels.

The above-described embodiment describes an imaging device capable of acquiring polarization image information and wavelength image information in a single shot, using a filter equipped with multiple spectral polarization cells, each 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 the following embodiments, for example:

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

For example, this can be applied to an imaging device capable of acquiring spectral information for each pixel in a single shot, as described in Non-Patent Document 2, which uses a filter equipped with multiple spectral cells with assigned spectral transmission characteristics. In this case, the same effect can be achieved by replacing the spectral polarization cell in the above-mentioned embodiment with a spectral cell.

For example, as described in Patent Document 1, this invention can also be applied to an imaging device capable of acquiring polarization image information and wavelength image information in a single shot, which uses a filter equipped with multiple spectroscopic cells to which spectral transmission characteristics are assigned, and multiple polarizing cells to which reference orientations for the polarization transmission characteristics are assigned. In this case, the same effect can be achieved by replacing the spectroscopic polarizing cells in the above-described embodiment with spectroscopic cells and polarizing cells. Note that in this case, by making the size and/or shape of the spectroscopic cells and polarizing cells arranged opposite each other non-uniformly corresponding to each other, it is also possible to achieve the effect of eliminating the need to align the spectroscopic cells and polarizing cells.

10... Filter 100... Image capture device 150... Image capture system

Claims (4)

a filter including 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 opposite to the pixels , and at least one of the size and the shape of the spectral polarization cells from which the light received by the pixels is emitted is non-uniform among the pixels;
Imaging device. 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 . 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 . 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: