Multispectral camera

Abstract

This makes it easier to design filters when setting steep cutoff characteristics, suppresses the degradation of spatial resolution and the occurrence of crosstalk between channels, and makes the device more compact. The dichroic prism 10a and N (N is an integer of 2 or more) imaging plates 11a and the like are provided, and the dichroic prism 10a generates N different spectral characteristics D for wavelength components contained in an incident light beam 2. (1) (λ)~D (N) The nth (n is an integer between 1 and N) of the N imaging plates is a set of M n Type (M n is 2 or moreM n (an integer less than or equal to) are arranged at the corresponding pixels, and in the n-th imaging plate, M n The mth filter (m is 1 or more) n (an integer less than or equal to T m (n) (λ), D (n) (λ)T m (n) (λ) has different spectral properties for different ordered pairs (m,n).

Description

[Technical Field]

[0001] The present invention relates to a camera, and more particularly to a multispectral camera having four or more different spectral sensitivity characteristics. [Background technology]

[0002] In digital cameras, single-chip imaging is often used as an imaging method for compactly capturing images having a plurality of different spectral sensitivity characteristics. Single-chip imaging uses an imaging plate on which multiple types of filters that transmit specific wavelength bands such as R, G, and B are arranged in a specific pattern for each pixel on the imaging sensor, making it possible to capture color images using a multispectral camera with multiple different spectral sensitivity characteristics using a compact device.

[0003] In such single-chip imaging, known cameras include a four-wavelength multispectral camera in which each pixel in a 2x2 pixel block has a different spectral characteristic, and a multispectral camera for multiple wavelengths exceeding four wavelengths, which has a pixel block consisting of more than 2x2 pixels (for example, 3x3 pixels) and in which filters (mosaic filters) with multiple types of spectral characteristics are arranged in each pixel that makes up this pixel block (see Patent Document 1 below).

[0004] Furthermore, even within single-chip imaging, a structure known as the Bayer array is widely used, which has a structure in which pixel blocks consisting of 2 pixels vertically and 2 pixels horizontally are repeatedly arranged, with each pixel block having a green filter on the two diagonal pixels and a blue filter and a red filter on the remaining two pixels, making it compatible with human visual sensitivity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-201317 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a multispectral camera using a single-chip imaging system, the period of the repeating structure increases as the number of types of filters increases, resulting in a decrease in spatial resolution. Furthermore, single-chip imaging requires the placement of tiny filters with different characteristics for each pixel, making it difficult to design individual filters, such as filters with steep cutoff characteristics. In particular, when a dye filter is used, a light passband of unwanted wavelengths may be formed adjacent to the outside of the desired wavelength band, which may cause crosstalk between channels.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a multispectral camera that allows for easy filter design in cases such as when setting a steep cutoff characteristic, can suppress a decrease in spatial resolution and the occurrence of crosstalk between channels, and can be made compact compared to the number of spectral distributions (number of spectral wavelength bands) obtained. [Means for solving the problem]

[0008] The multispectral camera of the present invention includes: a dichroic prism or a dichroic mirror; imaging plates disposed at predetermined positions facing N (N is an integer of 2 or more) light exit portions of the dichroic prism or the dichroic mirror, The dichroic prism or the dichroic mirror has the N different spectral characteristics D (1) (λ)~D (N) (λ) into N light rays, each multiplied by The n-th (n is an integer between 1 and N) imaging plate among the N imaging plates has M n Type (Mn is an integer equal to or greater than 2), a filter is disposed on the corresponding pixel; In the n-th imaging plate, n The mth filter (m is 1 or more) n The spectral transmittance of a filter (an integer less than or equal to T m (n) (λ), D (n) (λ)T m (n) (λ) is characterized by having different spectral properties for different ordered pairs (m,n).

[0009] The N different spectral characteristics D (1) (λ)~D (N) It is preferable that (λ) corresponds to the band of each of the three primary colors, and that in each of the imaging plates, each of the filters is configured to have spectral transmission characteristics that divide the band of the corresponding primary color among the three primary colors into multiple wavelength bands.

[0010] Each of the imaging plates is n The structure is formed by repeatedly arranging blocks in which different types of filters are arranged on pixels in a predetermined order, The dichroic prism or the dichroic mirror is n It is preferable that the filters are configured to have comb-shaped spectral characteristics so that, when viewed from the side of each imaging plate, the band of each of the types of filters is divided into two wavelength bands, one on the long wavelength side and one on the short wavelength side, and the filter passes the wavelength band related to the imaging of that imaging plate while blocking the remaining wavelength bands. In this case, it is preferable that each of the imaging plates has a structure in which blocks, each of which has three primary color filters arranged on pixels in a Bayer array, are repeatedly arranged.

[0011] an intermediate optical filter is provided between the dichroic prism or the dichroic mirror and each of the image plates; The intermediate optical filter preferably has spectral characteristics that block a specific wavelength band that causes crosstalk between channels, from among the pass bands of the dichroic prism, the dichroic mirror, or the filter of the imaging plate. In this case, it is preferable that a dye filter is used as the filter of the dichroic prism or the dichroic mirror, or the imaging plate, and that the specific wavelength band is a light pass band of unwanted wavelengths formed adjacent to the outside of the desired wavelength band. [Effects of the Invention]

[0012] According to the multispectral camera of the present invention, a dichroic prism or a dichroic mirror is used to generate N different spectral characteristics D (1) (λ)~D (N) The image sensor receives each of the N decomposed light rays, and the image sensor receives M n Type (M n is an integer equal to or greater than 2) are arranged on the corresponding pixels. That is, in the n-th imaging plate, n The mth filter (m is 1 or more) n The spectral transmittance of a filter (an integer less than or equal to T m (n) (λ), D (n) (λ)T m (n) (λ) has different spectral properties for different ordered pairs (m,n), M1+M2+…+M N It is possible to capture images of the subject image information carried by the light beams having different spectral characteristics.

[0013] When using only a single-chip imaging sensor to capture images of light rays with different spectral characteristics, the more filters there are, the longer the repetition period of each filter becomes, resulting in a decrease in spatial resolution. Furthermore, placing tiny filters with different characteristics for each pixel makes individual filter design more difficult, making it difficult to create filters with steep cutoff characteristics. This problem is particularly pronounced in multispectral cameras that use more than four wavelengths.

[0014] In the multispectral camera of the present invention, M1+M2+...+M N Among the processes for splitting light beams having different spectral characteristics, the process for splitting into N light beams having different spectral characteristics is performed by a dichroic prism or a dichroic mirror, and the number of types of spectral characteristics split by a filter on each image plate is M. n Only one is allowed. Therefore, even when applied to a multispectral camera for multiple wavelengths (more than four wavelengths), the filter repetition period on each imaging plate can be prevented from becoming too large, preventing a decrease in spatial resolution.In addition, by preventing the filter size from becoming too small, the design of individual filters can be made easier, making it easier to create filters with steep cutoff characteristics.

[0015] Furthermore, particularly when a dye filter is used, a light pass band of unwanted wavelengths may be formed adjacent to the outside of the desired wavelength band, which may result in crosstalk between channels. However, in the multispectral camera of the present invention, the filter characteristics on the dichroic prism or dichroic mirror side make it easy to block even narrow unwanted light pass bands, thereby reducing crosstalk between channels. Note that the filters on each image sensor result in M1+M2+...+M NSince the process of splitting the light into rays with different spectral characteristics is also performed, the optical path length can be shortened compared to the number of types of spectral characteristics, making it possible to make the device more compact and lighter in weight. [Brief explanation of the drawings]

[0016] [Figure 1] 1A to 1D are schematic diagrams showing the configuration of a multispectral camera according to a first embodiment of the present invention ((A) shows the overall configuration, and (B), (C), and (D) show the filter arrays of each imaging plate). [Figure 2] 1 is a graph showing Example 1 in which four bandpass filters (wavelength bands are T1(n)(λ) to T4(n)(λ)) with different passing wavelength bands are arranged within each pass band of the filter characteristic D(n)(λ) of a dichroic prism in a multispectral camera according to a first embodiment of the present invention (the horizontal direction indicates wavelength λ, and the vertical direction indicates spectral characteristics D(n)(λ) and Tm(n)(λ)). [Figure 3] 10 is a graph showing Example 2 in which four bandpass filters (wavelength bands are T1(n)(λ) to T4(n)(λ)) with different passing wavelength bands are arranged within each pass band of the filter characteristic D(n)(λ) of a dichroic prism in the multispectral camera according to the first embodiment of the present invention (the horizontal direction indicates wavelength λ, and the vertical direction indicates spectral characteristics D(n)(λ) and Tm(n)(λ)). [Figure 4] 10 is a graph showing Example 3 in which four bandpass filters (wavelength bands are T1(n)(λ) to T4(n)(λ)) with different passing wavelength bands are arranged within each pass band of the filter characteristic D(n)(λ) of a dichroic prism in the multispectral camera according to the first embodiment of the present invention (the horizontal direction represents wavelength λ, and the vertical direction represents spectral characteristics D(n)(λ) and Tm(n)(λ)). [Figure 5] 1 is a graph showing an example of the spectral characteristics obtained as a combination of the spectral characteristics of a dichroic prism and the spectral transmittance characteristics of the filters provided on each imaging plate in a multispectral camera according to the first embodiment of the present invention (the horizontal direction indicates wavelength λ, and the vertical direction indicates the spectral characteristics D(n)(λ)Tm(n)(λ)). [Figure 6] 10A and 10B are schematic diagrams showing the configuration of a multispectral camera according to a second embodiment of the present invention ((A) shows the overall configuration, and (B), (C), and (D) show the filter arrays of each imaging plate). [Figure 7] 10A and 10B are schematic diagrams showing the configuration of a multispectral camera according to a third embodiment of the present invention ((A) shows the overall configuration, and (B) and (C) show the filter arrays of each imaging plate). [Figure 8] 10 is a graph showing an example of the relationship between the spectral characteristics of a dichroic prism and the spectral transmittance characteristics of the filters provided on each imaging plate in a multispectral camera according to a third embodiment of the present invention (the horizontal direction indicates wavelength λ, and the vertical direction indicates spectral characteristics D(n)(λ), Tm(λ)). [Figure 9] 10 is a graph showing an example of the spectral characteristics obtained as a combination of the spectral characteristics of the dichroic prism and the spectral transmittance characteristics of the filters provided on each imaging plate in a multispectral camera according to a third embodiment of the present invention (the horizontal direction indicates wavelength λ, and the vertical direction indicates the spectral characteristics D(n)(λ)Tm(n)(λ)). DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, a specific configuration of a multispectral camera according to an embodiment of the present invention will be described with reference to the drawings. (First embodiment) In the multispectral camera 1a according to the first embodiment and the multispectral camera 1b according to the second embodiment described below, the incident light ray 2a is separated into R, G, and B wavelength bands by the dichroic prism 10a, and each of the wavelength bands is separated into four mutually different wavelength bands by the filters of the imaging plates 11a, 12a, and 13a. First, Fig. 1A shows the overall configuration of a multispectral camera according to the first embodiment. As shown in Fig. 1A, a multispectral camera 1a according to this embodiment is composed of a dichroic prism 10a, a first imaging plate 11a, a second imaging plate 12a, a third imaging plate 13a, and an imaging lens 14a.

[0018] An incident light beam 2a carrying subject information passes through the imaging lens 14a and enters the light-incident end face 10ap of the dichroic prism 10a. At each of the prism junctions (wavelength band separation sections) 10aa and 10ab of the dichroic prism 10a, the light is subjected to wavelength band separation by transmission / reflection into long-wavelength and short-wavelength sides with a predetermined wavelength as the boundary. Ultimately, the light is split into three light beams: a first light beam 3a, a second light beam 4a, and a third light beam 5a. The first light beam 3a is totally reflected at the prism junction 10aa, and the third light beam 5a is totally reflected at the light-incident end face 10ap, and directed toward the corresponding imaging plates 11a and 13a. It is also possible to use a dichroic mirror in place of the dichroic prism 10a.

[0019] The optical distance (hereinafter referred to as the optical path length) from the second principal point 15a (point P) of the imaging lens 14a to point Q where the optical axis intersects with the first imaging plate 11a, the optical path length from the second principal point 15a (point P) to point R where the optical axis intersects with the second imaging plate 12a, and the optical path length from the second principal point 15a (point P) to point S where the optical axis intersects with the third imaging plate 13a are basically all the same length, but each optical path length may be adjusted to appropriately focus each wavelength band, taking into account the chromatic aberration of the imaging lens 14a. Here, the spectral characteristics on the path from the imaging lens 14a to the nth imaging plate (hereinafter, the spectral characteristics of the dichroic prism) are defined as D (n) The following description will be given assuming that (λ) is the wavelength of the incident light ray 2a.

[0020] The spectral characteristics of the dichroic prism 10a are shown in Figs. 2 (Example 1), 3 (Example 2), and 4 (Example 3). (1) (λ), D (2) (λ) and D (3) It is denoted by (λ). Spectral characteristic D of the dichroic prism in Figure 2 (1) (λ), D (2) (λ) and D (3)(λ) are the long-pass filter, the band-pass filter, and the short-pass filter, respectively.

[0021] Next, the structure and function of the imaging plates (first imaging plate 11a to third imaging plate 13a) will be described. Each of these imaging plates 11a to 13a is configured as an area sensor, but may be configured as a line sensor instead of an area sensor.

[0022] The first imaging plate 11a receives the first split light 3a and converts it into an electrical signal. The first imaging plate 11a is equipped with optical filters R1 (111) to R4 (114), and as shown in FIG. 1B, four pixels to which these four types of optical filters are attached are repeatedly arranged in a tiled pattern. The spectral transmission characteristics of R1 (111) to R4 (114) are respectively defined as T1 (1) (λ) to T4 (1) Let (λ). Similarly, the second imaging plate 12a receives the second split light 4a and converts it into an electrical signal. The second imaging plate 12a is provided with optical filters G1 (121) to G4 (124), and as shown in FIG. 1C, four pixels to which these four types of optical filters are attached are repeatedly arranged in a tiled pattern. The spectral transmission characteristics of G1 (121) to G4 (124) are respectively defined as T1 (2) (λ) to T4 (2) Let (λ). Similarly, the third imaging plate 13a receives the third split light 5a and converts it into an electrical signal. The third imaging plate 13a is provided with optical filters B1 (131) to B4 (134), and as shown in FIG. 1(D), four pixels to which these four types of optical filters are attached are repeatedly arranged in a tiled pattern. The spectral transmittance characteristics of B1 (131) to B4 (134) are respectively defined as T1 (3) (λ) to T4 (3) Let (λ).

[0023] Each of the optical filters R1 (111) to R4 (114), G1 (121) to G4 (124), and B1 (131) to B4 (134) may be an interference filter (such as a Fabry-Perot filter) or a color filter colored with a dye or the like.

[0024] Spectral transmission characteristics T1 (1) (λ) to T4 (1) (λ), T1 (2) (λ) to T4 (2) (λ), and T1 (3) (λ) to T4 (3) Examples 1 to 3 relating to (λ) are shown in FIGS. The spectral transmittance characteristics of Example 1 are shown in Figure 2, which are spectral transmittance characteristics T1 (1) (λ) to T4 (1) (λ) is the long-pass filter characteristic D of the dichroic prism 10a. (1) The spectral transmittance characteristics T1 corresponding to the four bandpass filters with different pass wavelength bands are arranged within the pass band of (λ). (2) (λ) to T4 (2) (λ) is the bandpass filter characteristic D of the dichroic prism 10a. (2) (λ), and the spectral transmittance characteristics T1 (3) (λ) to T4 (3) (λ) is the short-pass filter characteristic D of the dichroic prism 10a. (3) It is placed within the passband of (λ).

[0025] The spectral transmittance characteristics of Example 2 are shown in Figure 3, which are spectral transmittance characteristics T1 (1) (λ) to T4 (1) (λ) is the bandpass filter characteristic D on the long wavelength side of the dichroic prism 10a. (1) The spectral transmittance characteristics T1 corresponding to the four bandpass filters with different pass wavelength bands are arranged within the pass band of (λ). (2) (λ) to T4(2) (λ) is the bandpass filter characteristic D at the center of the dichroic prism 10a. (2) (λ), and the spectral transmittance characteristics T1 (3) (λ) to T4 (3) (λ) is the bandpass filter characteristic D of the short wavelength side of the dichroic prism 10a. (3) It is placed within the passband of (λ).

[0026] The spectral transmittance characteristics of Example 3 are shown in the upper part of Figure 4. First, the spectral transmittance characteristics T1 corresponding to one short-pass filter, two band-pass filters with different pass wavelength bands, and one long-pass filter are shown. (1) (λ) to T4 (1) (λ) is the bandpass filter characteristic D on the long wavelength side of the dichroic prism 10a. (1) As shown in the middle of Figure 4, the spectral transmittance characteristics T1 corresponding to one short-pass filter, two band-pass filters with different pass wavelength bands, and one long-pass filter are (2) (λ) to T4 (2) (λ) is the bandpass filter characteristic D at the center of the dichroic prism 10a. (2) (λ) is arranged so that at least a part of it falls within the passband. Furthermore, as shown in the bottom of Figure 4, the spectral transmittance characteristics T1 corresponding to one short-pass filter, two band-pass filters with different pass wavelength bands, and one long-pass filter are (3) (λ) to T4 (3) (λ) is the bandpass filter characteristic D of the short wavelength side of the dichroic prism 10a. (3) The arrangement is such that at least a portion of (λ) falls within the passband.

[0027] The overall spectral characteristics achieved by the dichroic prism 10a and the optical filters 111 to 114, 121 to 124, and 131 to 134 on the imaging plates 11a to 13a are D (n) (λ)T m (n)(λ), and in each of the examples (Examples 1 to 3) shown in FIGS. 2 to 4, different ordered pairs (n, m) have different spectral characteristics D (n) (λ)T m (n) (λ). In the above Examples 1 to 3, as shown in FIG. 5, the D (1) (λ)T1 (1) (λ), D (1) (λ)T2 (1) (λ), D (1) (λ)T3 (1) (λ), D (1) (λ)T4 (1) (λ), D (2) (λ)T1 (2) (λ), D (2) (λ)T2 (2) (λ), D (2) (λ)T3 (2) (λ), D (2) (λ)T4 (2) (λ), D (3) (λ)T1 (3) (λ), D (3) (λ)T2 (3) (λ), D (3) (λ)T3 (3) (λ), D (3) (λ)T4 (3) In other words, the multispectral camera 1a according to this embodiment enables multispectral imaging in 12 wavelength bands. As described above, the multispectral camera 1a according to this embodiment captures images using 12 pass bands, but the process of splitting the 12 light beams with different spectral characteristics into three light beams (corresponding to R, G, and B) with different spectral characteristics is performed by the dichroic prism 10a. This prevents the filter repetition period on each of the imaging plates 11a, 12a, and 13a from becoming too large, thereby preventing a decrease in spatial resolution. In addition, by preventing the filter size from becoming too small, the design of each filter becomes easier, making it easier to create filters with steep cutoff characteristics.

[0028] Furthermore, particularly when a dye filter is used, a light pass band of unwanted wavelengths may be formed adjacent to the outside of the desired wavelength band, which may result in crosstalk between channels. However, in the multispectral camera 1a of this embodiment, by adjusting the filter characteristics on the dichroic prism 10a side, it is possible to easily block the passage of light in the unwanted light pass band, even if it is narrow, thereby reducing crosstalk between channels. In addition, the filters of the imaging plates 11a, 12a, and 13a are used to n Since the process of splitting the light into rays with different spectral characteristics is also performed, the optical path length can be shortened compared to the number of types of spectral characteristics, making it possible to make the device more compact and lighter in weight.

[0029] (Second embodiment) FIG. 6(A) shows the overall configuration of a multispectral camera 1b according to the second embodiment. As shown in Fig. 6(A), the multispectral camera 1b includes the same configuration as the multispectral camera 1a according to the first embodiment shown in Fig. 1(A), but also includes intermediate optical filters 21, 22, and 23 inserted between the exit end faces 10aq, 10ar, and 10as of the dichroic prism 10a and the corresponding imaging plates 11a, 12a, and 13a. The configuration other than the intermediate optical filters 21, 22, and 23 is the same as that of the multispectral camera 1a according to the first embodiment, and corresponding components are denoted by the same reference numerals, and detailed descriptions thereof will be omitted to avoid redundancy. Note that Figs. 6(B), 6(C), and 6(D) also have the same configuration as Figs. 1(B), 1(C), and 1(D), respectively. By inserting the intermediate optical filters 21, 22, and 23, the spectral characteristic D of the dichroic prism 10a is (1) (λ), D (2) (λ) and D (3) It is possible to adjust all or part of (λ). For example, the spectral characteristics D shown in Fig. 2 (1) (λ), D(2) (λ) and D (3) In the dichroic prism 10a configured to have a spectral characteristic D (λ), an intermediate optical filter 21 functioning as a short-pass filter is inserted so as to face the exit end face 10aq from which the first split light 3a directed toward the first imaging plate 11a is emitted, and an intermediate optical filter 23 functioning as a long-pass filter is inserted so as to face the exit end face 10as from which the third split light 5a directed toward the third imaging plate 13a is emitted. As shown in FIGS. 3 and 4, by inserting the intermediate optical filter 21 functioning as a short-pass filter, the spectral characteristic D (1) (λ), D (2) (λ) and D (3) (λ) can be bandpass filtered.

[0030] The intermediate optical filters 21, 22, and 23 may be interference filters (Fabry-Perot filters, etc.) or color filters colored with a dye or the like. In the configuration of the multispectral camera 1b according to this embodiment, the spectral transmittance characteristics of the intermediate optical filters 21 to 23 are appropriately set, thereby achieving the spectral characteristic D (n) (λ)T m (n) It is possible to easily reduce the crosstalk occurring between different ordered pairs (n, m) of (λ). The multispectral camera 1b according to this embodiment can achieve the following effects in addition to the effects of the multispectral camera 1a according to the first embodiment. In other words, if crosstalk occurs between channels in the spectral characteristics obtained by multiplying the spectral characteristics of the dichroic prism 10a and the spectral characteristics of the filters on the imaging plates 11a, 12a, and 13a, the crosstalk can be significantly reduced by selectively blocking the passage of light in specific wavelength bands that cause this crosstalk using the intermediate optical filters 21, 22, and 23.

[0031] (Third embodiment) In the multispectral camera 1c according to the third embodiment, the filters of the imaging plates 11b and 12b are configured to separate the light into the R, G, and B wavelength bands, while the dichroic prism 10b is configured to separate the light into a second light beam (3b) having spectral characteristics that block the shorter wavelengths of the R, G, and B wavelength bands, and a first light beam (4b) having spectral characteristics that block the longer wavelengths of the R, G, and B wavelength bands. FIG. 7A shows the overall configuration of a multispectral camera 1c according to the third embodiment. As shown in FIG. 7(A), in a multispectral camera 1c, an incident light ray 2b that has passed through an imaging lens 14b enters a dichroic prism 10b and is split into a first split light ray 3b (transmitted light) and a second split light ray 4b (reflected light) at a prism junction (wavelength band separation section) 10ba in the dichroic prism 10b. The first split light beam 3b is guided to a first imaging plate 11b (point on the optical axis is T), and the second split light beam 4b is guided to a second imaging plate 12b (point on the optical axis is U). Note that, among the components of this embodiment, components corresponding to the components of the multispectral camera 1a according to the first embodiment are represented by the same numbers with the addition of the symbol b (instead of the symbol a). The imaging plates 11b and 12b arranged on the exit side of the dichroic prism 10b are both Bayer array sensors with similar spectral sensitivity characteristics. That is, as shown in Figures 7(B) and 7(C), four pixels, each fitted with filters of the three primary colors R, G, and B, are arranged repeatedly in a tiled pattern in a Bayer array.

[0032] Here, if the spectral transmission characteristics of the R, G, and B optical filters on the first imaging plate 11b are T1(λ), ​​T2(λ), and T3(λ), respectively, and the spectral transmission characteristics of the R, G, and B optical filters on the second imaging plate 12b are also T1(λ), ​​T2(λ), and T3(λ), respectively, the spectral transmission characteristics T1(λ), ​​T2(λ), and T3(λ) are expressed, for example, as shown in Figure 8. That is, the upper part of Figure 8 shows the spectral transmission characteristics T1(λ), ​​T2(λ), and T3(λ) of the R, G, and B optical filters of the first imaging plate 11b, and the lower part of Figure 8 shows the spectral transmission characteristics T1(λ), ​​T2(λ), and T3(λ) of the R, G, and B optical filters of the second imaging plate 12b, and the graphs in the upper and lower parts show that each optical filter has similar spectral transmission characteristics.

[0033] Here, the spectral characteristics of the path from the incident light ray 2b to the first split light ray 3b in the dichroic prism 10b are defined as D (1) (λ), the spectral characteristics of the path from the incident light ray 2b to the second split light ray 4b are D (2) (λ), as shown in Figure 7, D (1) (λ) is designed to transmit the longer wavelengths of the pass wavelength bands of T1(λ), ​​T2(λ), and T3(λ), while D (2) (λ) has a comb-like spectral characteristic so as to transmit the shorter wavelength side of each of the pass wavelength bands of T1(λ), ​​T2(λ), and T3(λ).

[0034] With this configuration, the spectral characteristic D of the dichroic prism 10b (n) (λ) and the spectral characteristics T of the filters on the image plates 11b and 12b. m (λ), the overall spectral response is D (n) (λ)T m (λ). In the multispectral camera 1c of this embodiment, as shown in FIG. 9, D (1) (λ)T1(λ), ​​D (2) (λ)T1(λ), ​​D (1) (λ)T2(λ), D (2) (λ)T2(λ), D (1) (λ)T3(λ), and D (2) The bandpass filter characteristic is formed in the order of (λ)T3(λ). That is, the multispectral camera 1c according to this embodiment is configured to perform multispectral imaging for six wavelength bands, and can achieve the same effects as those achieved by the multispectral camera 1a according to the first embodiment.

[0035] (Modifications) The multispectral camera of the present invention is not limited to the above-described embodiments, and various other modifications are possible. For example, in each of the above-described embodiments, a dichroic mirror can be used instead of the dichroic prism. In addition, the dichroic prism in each of the above-described embodiments has three or two different spectral characteristics D (1) (λ)~D (3) The optical fiber is configured to decompose the light into three or two rays each multiplied by (λ), but it can also be configured to decompose the light into multiple rays each multiplied by multiple other spectral characteristics. Furthermore, in each of the above-described embodiments, each imaging plate has four or three types of filters with different spectral transmittance characteristics, but it may also have multiple other types of filters with different spectral transmittance characteristics.

[0036] In the above-described embodiments, each imaging plate has a structure in which blocks in which multiple types of filters are arranged on pixels in a predetermined order are repeatedly arranged, but the order of the filters in each block may be different for each block, and the filter arrangement may be random. Furthermore, the filter arrangement in each block is not limited to the Bayer arrangement, as a matter of course.

[0037] The intermediate optical filters used in the second embodiment may have the same spectral characteristics or may have different spectral characteristics. Also, multiple intermediate optical filters may be inserted into the optical path of the separated light. In the above-described embodiment, the dichroic prism used is a Philips type or a type in which a pair of right-angle prisms are combined to form a square cross section, but it is of course possible to use other types of dichroic prisms, such as a cross dichroic prism. [Explanation of symbols]

[0038] 1a, 1b, 1c Multispectral camera 2a,2b incident ray 3a, 3b First Spectroscopy 4a, 4b Second Spectroscopy 5a The Third Spectroscopy 10a, 10b Dichroic prism 11a, 11b First imaging plate 12a, 12b Second imaging plate 13a Third imaging plate 14a, 14b Imaging lenses 15a, 15b 2nd principal point 111,112,113,114,121,122,123,124,131,132,133,134 Optical filters 21, 22, 23 Intermediate optical filters

Claims

1. a dichroic prism or a dichroic mirror; imaging plates disposed at predetermined positions facing N (N is an integer of 2 or more) light exit portions of the dichroic prism or the dichroic mirror, The dichroic prism or the dichroic mirror generates the N different spectral characteristics D (１) (λ) to D (Ｎ) (λ) into the N light rays, each multiplied by The n-th (n is an integer of 1 to N) imaging plate among the N imaging plates has M ｎ Type (M ｎ a filter (where n is an integer equal to or greater than 2) is disposed on the corresponding pixel; In the n-th imaging plate, ｎ The mth filter (m is 1 or more) of the types of filters ｎ The spectral transmittance of the filter (an integer below) is T ｍ (ｎ) (λ), D (ｎ) (λ)T ｍ (ｎ) (λ) is a multispectral camera characterized by having different spectral characteristics for different ordered pairs (m, n).

2. The N different spectral characteristics D (１) (λ) to D (Ｎ) 2. The multispectral camera according to claim 1, wherein (λ) corresponds to a band of each of the three primary colors, and each of the filters on each of the imaging plates is configured to have spectral transmission characteristics that divide the band of a corresponding primary color among the three primary colors into a plurality of wavelength bands.

3. Each of the imaging plates is ｎ The structure is formed by repeatedly arranging blocks in which different types of filters are arranged on pixels in a predetermined order, The dichroic prism or the dichroic mirror is ｎ 2. The multispectral camera according to claim 1, wherein the filter is configured to have comb-shaped spectral characteristics so that, when viewed from the side of each imaging plate, the band of each of the filters is divided into two wavelength bands, one on the long wavelength side and one on the short wavelength side, and the filter passes the wavelength band related to the imaging of that imaging plate while blocking the remaining wavelength bands.

4. 4. The multispectral camera according to claim 3, wherein each of the imaging plates has a structure in which blocks in which three primary color filters are arranged on pixels in a Bayer array are repeatedly arranged.

5. an intermediate optical filter is provided between the dichroic prism or the dichroic mirror and each of the image plates; 2. The multispectral camera according to claim 1, wherein the intermediate optical filter has spectral characteristics that block a specific wavelength band that causes crosstalk between channels, from among the pass bands of the dichroic prism, the dichroic mirror, or the filter of the imaging plate.

6. 6. The multispectral camera according to claim 5, wherein a dye filter is used as a filter for the dichroic prism, the dichroic mirror, or the imaging plate, and the specific wavelength band is a light pass band of unwanted wavelengths formed adjacent to the outside of a desired wavelength band.

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