JP2013052180A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of acquiring polarization information from each pixel.SOLUTION: The imaging apparatus 100 in the embodiment includes: an optical sensing cell array (imaging element 110) in which a plurality of optical sensing cells are two-dimensionally arranged along an imaging surface 110a; an imaging lens 109 for forming an image on the imaging surface 110a; a polarization element 106c having and N (N is an integer of not less than 3) polarizers having different polarization transmission axis directions, in which the N polarizers are concentrically arranged, and wherein a boundary of adjacent polarizers is concentric; a shutter 106b for shielding at least one part of light entering to the polarization element 106c or at least one part of light transmitting the polarization element 106c; and a shutter driving part 112 for driving the shutter 106b so as to enter light transmitting the plurality of polarizers having different polarization transmission axis directions of the polarization element 106c into a same optical sensing cell of the optical sensing cell array 110 sequentially during imaging.

Description

  The present invention relates to an imaging apparatus such as a camera that can simultaneously acquire a color image and polarization information.

  Polarization imaging that can acquire information that cannot be obtained with only a luminance image has attracted attention. In order to perform polarization imaging, it is necessary to arrange a polarizer or a polarizing plate in front of the imaging surface of the imaging device. Patent Document 1 discloses an image pickup device in which fine polarizers are arranged at a pitch of about 100 μm, for example. Patent Document 2 discloses an imaging apparatus having a mechanism for rotating a polarizing plate. Patent Document 3 discloses an endoscope that acquires a polarization image by alternately using two polarizing plates having a polarization transmission axis orthogonal to each other.

JP 2007-86720 A US Patent Application Publication No. 2007-79982 JP 2003-47588 A

  According to the prior art described in Patent Document 1, since the polarizer is fixed, the problem of pixel shift does not occur, and a mechanism for rotating the polarizing plate is unnecessary. However, only light that has passed through a polarization transmission axis in a certain direction enters each image. Therefore, in order to acquire polarization information such as the degree of polarization and the polarization phase angle, it is necessary to use signals from a plurality of pixels, resulting in a decrease in resolution.

  According to the prior art described in Patent Document 2, there is a problem of pixel misalignment due to the rotating polarizing plate, and the resolution and SN ratio decrease. Moreover, it is difficult to reduce the size of an apparatus for rotating the polarizing plate.

  According to the prior art described in Patent Document 3, the moving distance of the polarizing plate is large, and it is difficult to reduce the size of the apparatus for changing the position of the polarizing plate.

  Furthermore, at the present time, a camera that simultaneously acquires a color image and polarization information has not been realized.

  SUMMARY An advantage of some aspects of the invention is to provide an imaging apparatus capable of acquiring polarization information from each pixel.

  An imaging apparatus according to the present invention includes a photosensitive cell array in which a plurality of photosensitive cells are two-dimensionally arranged along an imaging surface, a photographing lens that forms an image on the imaging surface, and N (with different polarization transmission axis directions). N is an integer greater than or equal to 3), and the N polarizers are arranged concentrically, and the boundary between adjacent polarizers is concentric, and enters the polarizing element A shutter that shields at least a part of the light to be transmitted or at least a part of the light transmitted through the polarizing element, and light transmitted through a plurality of polarizers having different polarization transmission axis directions of the polarizing element at the same time or at different timings. A shutter driving unit that drives the shutter so as to be incident on the same photosensitive cell of the photosensitive cell array.

  In one embodiment, the shutter driving unit transmits light transmitted through one polarizer of the N polarizers of the polarization element within each charge accumulation period of the photosensitive cell array. In the next charge accumulation period, the shutter is driven so that light transmitted through the other polarizer enters the imaging surface of the photosensitive cell array.

  In one embodiment, the polarizing element includes a transparent portion in which no polarizer is present.

  In one embodiment, the N polarizers include a circular central polarizer and a plurality of ring polarizers arranged around the central polarizer.

  In one embodiment, the polarizing element includes a transparent portion at the center.

  In one embodiment, the N polarizers are four polarizers whose polarization transmission axis directions are different by 45 °.

  In one embodiment, the N polarizers are three polarizers whose polarization transmission axis directions are different by 60 °.

  In one embodiment, the shutter includes a ring-shaped light shielding portion or a circular light shielding portion that shields at least one of the N polarizers of the polarizing element.

  In one embodiment, the shutter driving unit rotates the shutter.

  In some embodiments, the imaging device includes a light source that illuminates the subject with unpolarized light.

  In some embodiments, the imaging device is an endoscope.

  According to the present invention, since light having different polarization principal axes can be incident on each pixel, a high-resolution polarized image can be acquired. In addition, since it is not necessary to arrange fine polarizers in front of individual pixels, it is possible to obtain a color image using a wide band polarizer.

It is a figure which shows the structural example of the imaging device by this invention. It is a figure which shows typically the plane structure and cross-sectional structure of an example of the polarizing element 106c. It is a figure which shows the definition of angle (PSI) I of the polarization plane in polarized light. 3 is a diagram illustrating a configuration example of an imaging surface 110a of the imaging element 110. FIG. It is a figure which shows typically the state by which the polarizers S1-S4 of the polarizing element 106c were shielded by the function of the shutter 106b shown in FIG. It is a figure which shows typically the state by which polarizer S2-S4 of the polarizing element 106c was shielded by the function of the shutter 106b shown in FIG. It is a figure which shows typically the state by which polarizer S1, S3-S4 of the polarizing element 106c was shielded. It is a figure which shows typically the state by which polarizer S1-S2, S4 of the polarizing element 106c was shielded. It is a figure which shows typically the state by which polarizer S1-S3 of the polarizing element 106c was shielded. The position of the polarizer S1 to S4, is a diagram showing the correspondence between the light transmitted through the polarizer (linearly polarized light _{I 0, I 45, I 90} , I 135). 1 is a diagram illustrating a schematic configuration of an imaging apparatus according to an embodiment of the present invention. It is a figure which shows the enlarged view of the front-end | tip part of FIG. It is a figure which shows the structural example of the shutter apparatus 106b in this embodiment. It is a figure which shows the shutter located in front of the polarizing element 106c, the polarization image produced | generated by the image pick-up element 110, and each polarization image transferred to the color polarization image process part from the image pick-up element 110. FIG. It is a figure which shows the other structural example of the shutter apparatus 106b. In the case of using the shutter device of FIG. 11, the shutter is located on the front surface or the back surface of the polarizing element 106 c, the type of polarizer that is transmitted, the data generated and stored by the image sensor 110, and the signal processing. It is a figure which shows a polarization image and the timing diagram of each polarization image transferred to a color polarization image process part.

  FIG. 1 is a diagram illustrating a configuration example of an imaging apparatus according to the present invention.

  The illustrated imaging apparatus includes an imaging element 110 in which a plurality of photosensitive cells are two-dimensionally arranged along an imaging surface, and a photographing lens 109 that forms an image on the imaging surface 110a of the imaging element 110. The photographic lens 109 is schematically described as a single lens in FIG. 1, but is usually an optical system in which a plurality of lenses are combined, and has a known configuration. These configurations may be basically the same as those in the conventional imaging apparatus. The imaging apparatus further includes a polarizing element 106c having N polarizers (N is an integer of 3 or more) having different polarization transmission axis directions, and a shutter 106b that shields at least part of light incident on the polarizing element 106c. Is provided. In the polarizing element 106c, three or more polarizers are arranged concentrically, and the boundary between adjacent polarizers is a concentric circle.

  FIG. 2 is a diagram schematically illustrating a planar configuration and a cross-sectional configuration of an example of the polarizing element 106c. The polarizing element 106c includes a circular transparent portion S0, a ring-shaped first polarizer S1, a ring-shaped second polarizer S2, a ring-shaped third polarizer S3, a ring-shaped fourth polarizer S4, and a ring. It has a transparent part S5. These transparent portions S1, S5 and polarizers S1-S4 are arranged concentrically.

  Since the polarizing element 106c can function as a polarizer in the entire visible light wavelength band (400 nm to 700 nm), it is possible to acquire a color polarization image. The polarizing element 106c can function as a polarizer not only for visible light but also for infrared light. Note that in the case of a polarization mosaic filter in which fine polarizers are arranged on the image sensor 110, the wavelength range that can function as a polarizer is narrow, and it is difficult to acquire a color polarization image.

  The polarization transmission axis directions of the polarizers S1 to S4 in the example of FIG. This angle is a value obtained by dividing 180 ° by 4 which is the number N of polarizers. When the number N of the polarizers is 3, the polarization transmission axis direction of each polarizer may be different by 60 ° (= 180/3). The angle in the polarization transmission axis direction is preferably a value obtained by dividing 180 ° by the number N of polarizers, but is not necessarily limited to such a case.

  FIG. 3 is a diagram showing the definition of the angle ΨI of the polarization plane in the polarized light. An XY coordinate system is set toward the subject. The angle ΨI of the polarization plane is defined as the direction of the angle of turning from the X axis positive direction to the Y axis positive direction with the X axis being 0 °. When the angle ΨI of the polarization plane is increased or decreased, the same polarization state is repeated with a period of 180 °. That is, the function having the polarization plane angle ψI as a variable is a periodic function having a period of 180 °.

  FIG. 4 is a diagram illustrating a configuration example of the imaging surface 110a of the imaging element 110. As shown in FIG. 4, a plurality of photosensitive cells (photodiodes) are regularly arranged in rows and columns on the imaging surface. A color mosaic filter that transmits RGB three types of wavelengths is installed on the front surface of the imaging surface 110a. Each photosensitive cell generates an electrical signal according to the amount of incident light by photoelectric conversion. Thus, as the imaging device 110, a conventional imaging device for luminance images (CCD or CMOS sensor) can be used.

  Since each photosensitive cell of the image sensor 110 corresponds to a pixel, the photosensitive cell array may be referred to as a pixel array. As will be described in detail later, the pixel array of the image sensor 110 transmits the polarizers of the polarizer 106c each composed of N polarizers (N is an integer of 3 or more) having different polarization transmission axis directions. Light enters.

  Reference is again made to FIG. In the configuration example of FIG. 1, the shutter 106b is disposed on the front surface side (light incident surface side) of the polarizing element 106c, but the shutter 106b is disposed between the polarizing element 106c and the photographing lens 109, that is, the back surface of the polarizing element 106c. It may be arranged on the side. When the shutter 106b is disposed on the back side of the polarizing element 106c, the shutter 106b can block at least a part of the light transmitted through the polarizing element 106c, not the light incident on the polarizing element 106c.

  The shutter 106 b is connected to the shutter driving unit 112, and the operation of the shutter 106 b is controlled by the shutter driving unit 112. The shutter driving unit 112 drives the shutter 106b so that light transmitted through a plurality of polarizers having different polarization transmission axis directions in the polarizing element 106c is incident on the imaging element 110 sequentially at the time of imaging. When the polarizing element 106c shown in FIG. 2 is used, the shutter 106b can be operated so that one polarizer is selected from the four types of polarizers S1 to S4 and the polarizers are sequentially switched. The shutter drive unit 112 may be incorporated in the image sensor 110 or the polarizing element 106c, or may be mounted as another component.

FIG. 5A schematically shows a state where the polarizers S1 to S4 of the polarizing element 106c are shielded and the transparent portions S0 and S5 are opened by the action of the shutter 106b shown in FIG. In this case, the light that reaches the imaging surface of the image sensor 110 and contributes to image formation is light (I _R ) that has passed through the transparent portions S0 and S5. When imaging is performed, which of the transparent portions S0 and S5 and the polarizers S1 to S4 is used can be determined by the action of the shutter 106b. For the sake of clarity, FIG. 5 shows the planar configuration of the polarizing element 106c, but the cross-sectional configuration of the light beam (I _R ) transmitted through the polarizer and the imaging device 110. The same applies to FIGS. 5B to 5E described below. A reference image can be taken based on the light transmitted through the transparent portions S0 and S5.

FIG. 5B schematically shows a state where the polarizers S2 to S4 of the polarizing element 106c are shielded and the polarizer S1 and the transparent portions S0 and S5 are opened by the action of the shutter 106b shown in FIG. In this case, light that reaches the imaging surface of the image sensor 110 and contributes to image formation is light that has passed through the polarizer S1 (linearly polarized light I ₁₃₅ ) and light that has passed through the transparent portions S0 and S5 (I _R ).

FIG. 5C schematically shows a state where the polarizers S1 and S3 to S4 of the polarizing element 106c are shielded and the polarizer S2 and the transparent portions S0 and S5 are opened. In this case, the light that reaches the imaging surface of the image sensor 110 and contributes to image formation is light that has been transmitted through the polarizer S2 (linearly polarized light I ₉₀ ) and light that has been transmitted through the transparent portions S0 and S5 (I _R ).

FIG. 5D schematically shows a state where the polarizers S1 to S2 and S4 of the polarizing element 106c are shielded, and the polarizer S3 and the transparent portions S0 and S5 are opened. In this case, the light that reaches the imaging surface of the image sensor 110 and contributes to image formation is light that has passed through the polarizer S3 (linearly polarized light I ₄₅ ) and light that has passed through the transparent portions S0 and S5 (I _R ).

FIG. 5E schematically shows a state where the polarizers S1 to S3 of the polarizing element 106c are shielded and the polarizer S4 and the transparent portions S0 and S5 are opened. In this case, the light that reaches the imaging surface of the image sensor 110 and contributes to image formation is light that has passed through the polarizer S4 (linearly polarized light I ₀ ) and light that has passed through the transparent portions S0 and S5 (I _R ).

In the present embodiment, as described above, imaging is performed in a state where a polarizer having a polarization transmission axis in a specific direction is selected and the transparent portions S0 and S5 are opened. For this reason, non-polarized light (I _R ) transmitted through the transparent portions S0 and S5 also enters the imaging surface of the imaging device 110. As a result, an image in which polarized light and non-polarized light are mixed is obtained. However, since the non-polarized light (I _R ) transmitted through the transparent portions S0 and S5 is acquired as a reference image, it is polarized using the reference image from an image in which polarized light and non-polarized light are mixed. An image only by light, that is, a polarization image can be acquired.

  In addition, in a state where the transparent portions S0 and S5 are shielded by the shutter 106b, light transmitted through any one of the polarizers S1 to S4, that is, polarized light may be incident on the imaging surface of the imaging device. In that case, a polarization image can be acquired without using a reference image. Further, it is not necessary to provide the transparent portions S0 and S5 in the polarizer 106c. For example, one or both of the transparent portions S0 and S5 may be covered with a light shielding member, or another polarizer may be disposed in one or both regions of the transparent portions S0 and S5.

In the present embodiment, by using the polarizing element 106c and the shutter 106b in which a plurality of polarizers having different polarization transmission axes are concentrically arranged, the polarization direction of the polarized light reaching the imaging surface 110a of the imaging element 110 is sequentially changed. It is possible to change. Therefore, for example, when imaging is performed in the state shown in FIG. 5B within a certain charge accumulation period, the polarization direction of polarized light incident on each photosensitive cell is defined by the polarization transmission axis direction of the polarizer S1. If the opening state of the shutter 106b is kept constant during the charge accumulation period, the luminance of linearly polarized light polarized in a certain direction can be obtained for each pixel by subtracting the value of the corresponding pixel in the reference image. Is possible. By synchronizing the switching timing of the charge accumulation period and the switching timing of the opening state of the shutter 106b, it is possible to acquire polarized images of colors having different polarization directions. In other words, according to the above example, it is possible to obtain polarized images (I ₀ , I ₄₅ , I ₉₀ , I ₁₃₅ ) of colors whose directions of polarization transmission axes are different by 45 °. As described above, when only the light transmitted through any one of the polarizers S1 to S4, that is, the polarized light is incident on the imaging surface of the imaging device, the polarization image (I ₀ , I ₄₅ , I ₉₀ , I ₁₃₅ ) need not be subtracted from the value of the corresponding pixel in the reference image.

Note that the entire shutter 106b may be opened during imaging. In that case, the light incident on the polarizing element 106c or the light transmitted through the polarizing element 106c is not shielded by the shutter 106b, and the whole reaches the image sensor 110 and contributes to image formation. At this time, the light transmitted through each of the polarizers S1 to S4 (linearly polarized light I ₀ , I ₄₅ , I ₉₀ , I ₁₃₅ ) and the light transmitted through each of the transparent portions S1 and S5 (I _R ) Will overlap. An image including the polarization information (polarized image) is not obtained, and a relatively bright luminance image with a wide aperture is obtained. Further, the entire polarizers S1 to S4 may be opened, and the transparent portions S1 and S5 may be shielded. At that time, the light (linearly polarized light I ₀ , I ₄₅ , I ₉₀ , I ₁₃₅ ) transmitted through each of the polarizers S1 to S4 overlaps on the imaging surface.

FIG. 6 is a diagram illustrating a correspondence relationship between the positions of the polarizers S1 to S4 and the light (linearly polarized light I ₀ , I ₄₅ , I ₉₀ , I ₁₃₅ ) transmitted through each polarizer. The boundaries of the polarizers S1 to S4 are concentric circles, and the center of the circle is aligned with the center of the photographic lens 109 of FIG. For this reason, the linearly polarized light I ₁₃₅ transmitted through the polarizer S 1 is constituted by light transmitted through the vicinity of the center of the photographing lens 109. On the other hand, the linearly polarized light I _{0 that} has passed through the polarizer S 4 is constituted by light that has passed through the vicinity of the photographing lens 109. In a preferred embodiment, each of the polarizers S1 to S4 has an equal area.

  Hereinafter, embodiments of the imaging apparatus of the present invention will be described in more detail.

  First, referring to FIG. FIG. 7 is a diagram illustrating a schematic configuration of the imaging apparatus according to the present embodiment.

  The imaging apparatus 100 of the present embodiment has a configuration that can be suitably used as an endoscope. As illustrated in FIG. 7, the imaging apparatus 100 includes an imaging unit 101 and an imaging control unit 102 that controls the imaging unit 101. The color polarization image acquired by the imaging unit 101 is sent to the color polarization image processing unit 121 and processed. The color polarization image processed by the color polarization image processing unit 121 is displayed by a display unit 122 such as a flat panel display. The color polarization image processing unit 121 is connected to a color polarization image recording unit 123 that records data of a color polarization image, a polarization degree image frame recording unit 124, and a polarization phase image frame recording unit 125. All or part of the color polarization image processing unit 121, the display unit 122, the color polarization image recording unit 123, the polarization degree image frame recording unit 124, and the polarization phase image frame recording unit 125 may be incorporated in the imaging apparatus 100. Alternatively, another device that is external to the imaging apparatus 100 and connected to the imaging apparatus 100 by wire or wireless may be used. The color polarization image processing unit 121 can be suitably realized by a personal computer or an image processing processor.

  The imaging unit 101 includes a polarizing element 106c having the configuration described with reference to FIGS. 1 to 5D, a shutter device 106b that sequentially selects a specific transmission polarizer from the polarizing element 106c, an imaging element (image sensor) 110, and the like. And a photographing lens 109 for forming an image on the imaging surface of the image sensor 110. The imaging unit 101 includes an illumination lens 107 that irradiates a subject with light from the light source unit 104 for illumination through an optical guide 105. In this embodiment, the subject 114 is irradiated with unpolarized light 115a.

  The photographic lens 109 in the present embodiment has a known configuration, and may actually be a lens unit that includes a plurality of lenses. The photographing lens 109 is driven by a mechanism (not shown), and operations necessary for optical zooming, automatic exposure (AE) and automatic focus (AF) may be performed as necessary.

  The imaging control unit 102 includes a light source unit 104, an imaging element driving unit 108 that drives the imaging element 110, and a shutter driving unit 112 that controls the shutter device 106b to change the light transmission region of the polarizing element 106c. . The image sensor driving unit 108 is constituted by, for example, a driver LSI, and drives the image sensor 110 to read an analog signal from the image sensor 110 and convert it into a digital signal.

The shutter drive unit 112 selectively drives a shutter unit that transmits a portion corresponding to a specific polarizer S1, S2, S3, S4 among different polarizers constituting the polarization element 106c by driving the shutter device 106b. Thus, it becomes possible to capture an image with respect to a predetermined polarization direction. By controlling the data storage timing and data transfer timing of the rotary mechanical shutter and CCD, the polarization images (I ₀ , I ₄₅ , I ₉₀ , I ₁₃₅ ) of different colors whose polarization transmission axis directions are different by 45 ° are acquired. Can do. If the relationship between the direction of the polarization transmission axis and the luminance value is obtained for each pixel by Sin-fitting based on these polarization images, the degree of polarization and the polarization phase can be obtained in units of pixels. The degree of polarization and the polarization phase in pixel units can be expressed as a polarization degree image and a polarization phase image, respectively.

  The color polarization image processing unit 121 includes an image processing unit (image processor), a memory, and an interface (IF) unit. The color polarization image processing unit 121 performs various signal processes necessary for operations such as color tone correction, resolution change, automatic exposure, autofocus, and data compression, and also executes polarization information acquisition processing according to the present invention. The color polarization image processing unit 121 is preferably realized by a combination of hardware such as a known digital signal processor (DSP) and software that executes image processing including polarization information processing according to the present invention. The memory is configured by a DRAM or the like. The memory records image data obtained from the image sensor 110 and temporarily records image data subjected to various types of image processing by the color polarization image processing unit 121. These image data are converted into analog signals and then displayed on the display unit 122, or a color polarization image is recorded on the color polarization image recording medium unit via the interface unit as a digital signal.

  The imaging apparatus 100 according to the present embodiment may include known components such as a viewfinder, a power source (battery), and a flashlight, but a description thereof is omitted because it is not particularly necessary for understanding the present invention.

  FIG. 8 shows an enlarged view of the tip of FIG. The non-polarized light 115 a illuminates the subject 114 through the light guide 105. Non-polarized light 116a, which is reflected light from the subject 114, becomes linearly polarized light polarized in a specific direction by sequentially passing through the opening of the shutter 106b and the polarizing element 106c. This linearly polarized light is imaged on the image sensor 110 by the lens 109.

  Hereinafter, an example of driving the shutter device 106b by the shutter driving unit 112 will be described.

  FIG. 9 shows a configuration example of the shutter device 106b in the present embodiment. The shutter device 106b includes four shutters A1 to D1 having openings for allowing light to enter the polarizers S1 to S4 of the polarizing element 106c and a shutter E1 that opens only the transparent portions S0 and S5. By rotating the shutter device 106b, any one of the five shutters A1 to E1 can be disposed on the front surface of the polarizing element 106c. In the example of FIG. 9, a state in which the second shutter B1 is positioned in front of the polarizing element 106c is schematically shown. When the shutter device 106b rotates in the direction indicated by the dashed arrow in FIG. 9, the third shutter C1 is then placed on the front surface of the polarizing element 106c.

  When the first shutter A1 is disposed in front of the polarizing element 106c, the first shutter A1 allows light to enter the first polarizer S1 of the polarizing element 106c and shields the other polarizers. When the second shutter B1 is disposed in front of the polarizing element 106c, the second shutter B1 causes light to enter the second polarizer S2, and the other polarizers are shielded. When the third shutter C1 is disposed in front of the polarizing element 106c, the third shutter C1 causes light to enter the third polarizer S3, and the other polarizers are shielded. When the fourth shutter D1 is disposed in front of the polarizing element 106c, the fourth shutter D1 allows light to enter the fourth polarizer S4 and shields the other polarizers. The fifth shutter E1 allows light to enter the transparent portions S0 and S5 and shields the polarizer. In this way, when the shutter positioned in front of the polarizing element 106c changes from the first shutter A1 to the fourth shutter D1, the polarization direction of the polarized light that passes through the polarizing element 106c and contributes to imaging rotates in order. I will do it.

FIG. 10 illustrates the polarization image data generated and accumulated by the shutter 106b positioned in front of the polarization element 106c, the image sensor 110, and the data of each polarization image transferred from the image sensor 110 to the color polarization image processing unit. It shows. For example, when the shutter A1 is positioned in front of the polarizing element 106c, linearly polarized light polarized in the direction of 135 ° and light transmitted through the transparent portion are incident on the imaging element 110, and the polarization image I ₁₃₅ and the reference image I _R are obtained. The image data mixed with is accumulated. After the charge accumulation period has elapsed, the data of the polarization image I ₁₃₅ reference image I _R is collected by mixed image is transferred to the outside from the image pickup device 110. By the time the next charge accumulation period starts, the movement of the shutter is completed. In this example, the second shutter B1 is positioned in front of the polarizing element 106c in place of the first shutter A1. Then, the incident and the light transmitted through the linearly polarized light and a transparent portion that is polarized in a direction of 90 ° to the imaging device 110, the reference image I _R and the polarization image I ₉₀ are bets that data of the mixed image are accumulated. This data is transferred to the outside after the charge accumulation period has elapsed. Thus, as shown in FIG. 10, color polarization images are acquired and transferred in order. When the reference image data is subtracted by signal processing from the image data obtained by mixing the polarization image and the reference image, the polarization images I ₀ , I ₄₅ , I ₉₀ , and I ₁₃₅ are obtained.

As described above, the intensity (pixel value or luminance) of light transmitted through four types of polarizers (Ψi = 0 °, 45 °, 90 °, 135 °) having different directions of the polarization transmission axis is represented by I ₀ , I ₄₅ , I ₉₀ , I ₁₃₅ Here, the luminance observed when the rotation angle Ψ of the polarization transmission axis is Ψ _i is defined as I _i . However, “i” is an integer from 1 to N, and “N” is the number of samples.

In this embodiment, since N = 4, i = 1, 2, 3, and 4. According to the present embodiment, with the configuration described above, luminances I ₁ , I ₂ , I ₃ , and I ₄ corresponding to four samples (ψ _i , I _i ) are obtained from each pixel. The relationship between the polarization transmission axis angle Ψ _i and the luminance I _i is generally expressed by a sine function with a period = π (180 °). There are only three unknowns in the sine function with a fixed period: amplitude, phase, and average. By observing at least three luminances I _i at different angles Ψ, one sine function curve is completely determined. The This sine function curve fitting can be performed by a known method.

The observed luminance with respect to Ψ of the polarization main axis of the polarizer unit is expressed by the following equation.

  Note that “polarization information” in this specification means amplitude modulation degree ρ and phase information φ in a sine function curve indicating the dependence of luminance on the polarization principal axis angle. When the three parameters A, B, and C of the sine function are determined for each pixel by the above processing, a polarization degree image indicating the polarization degree ρ in each pixel and a polarization phase image indicating the polarization phase φ in each pixel are obtained. The degree of polarization ρ represents the degree to which the light of the corresponding pixel is polarized, and the polarization phase φ represents the angular position that takes the maximum value of the sine function. The angle of the polarization main axis is the same between 0 ° and 180 ° (π).

The values ρ and φ (0 ≦ φ ≦ π) are calculated by the following (formula 2) and (formula 3), respectively.

  Thus, in this embodiment, by changing the position of the opening of the shutter device, the color polarization information is acquired from all the pixels based on the pixel value of the image formed by the light transmitted through different regions of the polarizing element 106c. be able to.

  The signal output from the image sensor 110 is sent to the color polarization image processing unit 121, processed by the color polarization image processing unit 121, and then stored in the polarization degree image frame recording unit 124 and the polarization phase image frame recording unit 125. The The stored data may be output to the display unit 122. Specifically, the polarization degree image frame storage unit 124 outputs data of the polarization degree image (ρ). The data of the polarization phase image (φ) based on the data of the polarization phase image frame storage unit 125 can be output. In this embodiment, polarization image information can be acquired from a subject and four types of polarization images (polarization degree image ρ and polarization phase image φ) can be output.

  Next, another configuration example of the shutter device 106b will be described with reference to FIG.

  The shutter device 106b shown in FIG. 11 includes a shutter A2 having one polarizer selected from the polarizers S1 to S4 of the polarizing element 106c and an opening for allowing light to enter the transparent parts S0 and S5, and a plurality of polarized lights. The shutters B2, C2, and D2 having openings for allowing light to enter even for the inclusion of the children and the shutter E1 that opens only the transparent portions S0 and S5 are provided. By rotating the shutter device 106b, any one of the five shutters A2, B2, C2, D2, and E1 can be disposed on the front surface of the polarizing element 106c. In the example of FIG. 11, a state in which the shutter B2 is positioned in front of the polarizing element 106c is schematically shown. When the shutter device 106b rotates in the direction indicated by the dashed arrow in FIG. 11, next, the shutter C2 is disposed on the front surface of the polarizing element 106c.

  When the shutter A2 is disposed in front of the polarizing element 106c, the shutter A2 allows light to enter the first polarizer S1 of the polarizing element 106c and shields the other polarizers. In this example as well, each shutter always opens the transparent portions S0 and S5. When the shutter B2 is disposed in front of the polarizing element 106c, the shutter B2 allows light to enter both the first polarizer S1 and the second polarizer S2, and shields the other polarizers. When the shutter C2 is disposed in front of the polarizing element 106c, the shutter C2 causes light to enter all of the first polarizer S1, the second polarizer S2, and the third polarizer S3, and the fourth polarizer S4 is shielded. To do. When the shutter D2 is disposed in front of the polarizing element 106c, the shutter D2 causes light to enter all the polarizers S1 to S4. In this way, when the shutter located in front of the polarizing element 106c changes from the shutter A2 to the shutter D2, the polarization state of the light that transmits through the polarizing element 106c and contributes to imaging changes in order. More specifically, when the shutter A2 is disposed on the front surface or the back surface of the polarizing element 106c, the light transmitted through the polarizing element 106c is linearly polarized light, but when the shutter D2 is disposed on the front surface of the polarizing element 106c. In addition, the light transmitted through the polarizing element 106c is in a state where light polarized in different directions is mixed.

  FIG. 12 shows a shutter positioned in front of the polarizing element 106c, the type of polarizer to be transmitted, data generated and accumulated by the image sensor 110, signal processing, and transfer to a color polarization image processing unit. The data of each polarization image is shown.

When the shutter E1 is positioned in front of the polarizing element 106c, the light transmitted through the transparent portion S0, S5 is incident on the image pickup device 110, the data of the reference image I _R is accumulated. At this time, data stored in the image sensor 110 is referred to as data a. After the charge accumulation period has elapsed, data a is read from the image sensor 110. Data a is not subjected to special processing and is transferred as it is. By the time the next charge accumulation period starts, the movement of the shutter is completed. In this example, the shutter A2 is positioned in front of the polarizing element 106c instead of the shutter E1.

When the shutter A2 is located in front of the polarizing element 106c, and the light incident transmitted through the linearly polarized light and a transparent portion that is polarized in a direction of 135 ° to the image pickup device 110, the polarization image I ₁₃₅ and the reference image I _R The mixed image data is accumulated. At this time, data stored in the image sensor 110 is referred to as data a. After the charge accumulation period has elapsed, the data b of the polarization image I ₁₃₅ reference images I _R and is mixed with the image is read from the image sensor 110. After the charge accumulation period has elapsed, the added data b is read from the image sensor 110. The data b, by subtracting the data a of the reference image I _R, it is possible to obtain a polarized image I _135. By the time the next charge accumulation period starts, the movement of the shutter is completed. In this example, the shutter B2 is positioned in front of the polarizing element 106c instead of the first shutter A2.

Next, when the shutter B2 is positioned in front of the polarizing element 106c, the linearly polarized light polarized in the direction of 135 °, the linearly polarized light polarized in the direction of 90 °, and the light transmitted through the transparent portion are incident on the image sensor 110. In the image sensor 110, the data c obtained by adding the polarization image I ₁₃₅ , the polarization image I _90, and the reference image I _R is generated and stored. After the charge accumulation period has elapsed, the added data c is read from the image sensor 110. By subtracting data b from this data c, a polarization image I ₉₀ can be obtained.

Similarly, the movement of the shutter is completed before the next charge accumulation period starts. This time, the shutter C2 is positioned in front of the polarizing element 106c. Linearly polarized light polarized in each direction of 135 °, 90 °, and 45 ° and light transmitted through the transparent portion are superimposed on the image pickup device 110, and the image pickup device 110 receives polarized images I ₁₃₅ , I ₉₀ , and I _45. And data d in a state where the reference image I _R is mixed are accumulated. The data d is read after the charge accumulation period has elapsed. When the data c is subtracted from the data d by signal processing, a polarization image I ₄₅ is obtained.

Furthermore, the movement of the shutter is completed before the next charge accumulation period starts. This time, the shutter D2 is positioned in front of the polarizing element 106c. Linearly polarized light polarized in each direction of 135 °, 90 °, 45 °, and 0 ° and light transmitted through the transparent portion are superimposed and incident on the image sensor 110. In the image sensor 110, polarized images I ₁₃₅ and I _{90 are} input. , I ₄₅ , I ₀ and the reference image I _R are stored as data e. The data d is read after the charge accumulation period has elapsed. When the data d is subtracted from the data e by signal processing, a polarization image I ₀ is obtained.

In the example shown in FIG. 12, the imaging element 110 is polarized in each direction of 135 °, 90 °, 45 °, and 0 ° during the next charge accumulation period with the shutter D2 positioned in front of the polarizing element 106c. Linearly polarized light and light transmitted through the transparent portion are superimposed and incident. Thus, the image sensor 110 accumulates data f in a state where the polarization images I ₁₃₅ , I ₉₀ , I ₄₅ , I ₀ and the reference image I _R are mixed. The data f is read after the charge accumulation period has elapsed. When the data a is subtracted from the data f by signal processing, an image in which the polarized light transmitted through each of the polarizers S1 to S4 is superimposed is obtained.

  The imaging apparatus of the present invention can be applied to various fields of polarization imaging technology. For example, the imaging device and imaging apparatus of the present invention are useful as key devices for security, medical care, communication, and analysis.

DESCRIPTION OF SYMBOLS 100 Image pick-up device 101 Image pick-up part 102 Image pick-up control part 104 Light source part 105 Light guide 106b Shutter device 106c Polarization element 107 Illumination lens 108 Image pick-up element drive part 109 Shooting lens 110 Image pick-up element 110a Image pick-up surface 112 Shutter drive part 113 Tip part 114 Subject 121 Color Polarization image processing unit 122 Display unit 123 Color polarization image recording unit 124 Polarization degree image frame recording unit 125 Polarization phase image frame recording unit

Claims (10)

A photosensitive cell array in which a plurality of photosensitive cells are two-dimensionally arranged along the imaging surface;
A photographic lens for forming an image on the imaging surface;
A polarizing element having N polarizers (N is an integer of 3 or more) having different polarization transmission axis directions, wherein the N polarizers are arranged concentrically, and boundaries between adjacent polarizers are concentric circles. A polarizing element;
A shutter that shields at least part of the light incident on the polarizing element or at least part of the light transmitted through the polarizing element;
A shutter driver that drives the shutter so that light transmitted through a plurality of polarizers having different polarization transmission axis directions of the polarizing element is incident on the same photosensitive cell of the photosensitive cell array at the same time or at different timings; ,
An imaging apparatus comprising:   The shutter driving unit enters light that has passed through one of the N polarizers of the polarizing element into an imaging surface of the photosensitive cell array during each charge accumulation period of the photosensitive cell array. The imaging apparatus according to claim 1, wherein the shutter is driven so that light transmitted through the other polarizer enters the imaging surface of the photosensitive cell array during a next charge accumulation period.   The imaging device according to claim 1, wherein the polarizing element includes a transparent portion having no polarizer.   The imaging device according to claim 1, wherein the N polarizers include a circular central polarizer and a plurality of ring-shaped polarizers arranged around the central polarizer.   The imaging apparatus according to claim 1, wherein the N polarizers are four polarizers whose polarization transmission axis directions are different by 45 °.   The imaging apparatus according to claim 1, wherein the N polarizers are three polarizers whose polarization transmission axis directions are different by 60 °.   The imaging device according to claim 1, wherein the shutter includes a ring-shaped light shielding portion or a circular light shielding portion that shields at least one of the N polarizers of the polarizing element.   The imaging apparatus according to claim 7, wherein the shutter driving unit rotates the shutter.   The imaging apparatus according to claim 1, further comprising a light source that illuminates a subject with non-polarized light.   The imaging apparatus according to claim 1, which is an endoscope.

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