Imaging apparatus and signal processing apparatus

Abstract

To provide a photographing device and a signal processor capable of obtaining a high-quality reproduced image by effectively utilizing light lost by the use of a linear polarizer.SOLUTION: The imaging device includes a polarization beam splitter that splits incoherent light propagating from an imaging target into two linearly polarized light beams having different polarization states, a first imaging function unit that receives one of the linearly polarized light beams, constitutes a self-interferometer, and collectively images a plurality of holograms having different phase shift amounts from the linearly polarized light beam, and a second imaging function unit that receives the other of the linearly polarized light beams, constitutes a self-interferometer, and collectively images a plurality of holograms having different phase shift amounts from the linearly polarized light beam. The signal processing device adds and averages the two complex amplitude distributions extracted from the hologram to generate a reconstructed image.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging device and a signal processing device, and more particularly to an imaging device and a signal processing device (both of which may be collectively referred to as a "system") used in incoherent digital holography. [Background technology]

[0002] Digital holography is a technology that records three-dimensional information about an object as a hologram, extracts a complex amplitude distribution from the hologram using a signal processing device, and applies numerical reconstruction based on propagation calculations to the complex amplitude distribution to obtain a reconstructed image of the object. In particular, incoherent digital holography utilizes the self-interference of light to capture a hologram of the object using spatially incoherent light sources such as sunlight, LED (Light Emitting Diode) illumination, and fluorescent light, making it possible to obtain three-dimensional information under natural light conditions (Patent Document 1, Non-Patent Document 1). Furthermore, incoherent digital holography has superior spatial frequency characteristics to conventional cameras, making it a powerful technology for capturing high-resolution images.

[0003] Incoherent digital holography uses a phase-shifting method to extract complex amplitude distributions from holograms. Information on the complex amplitude distribution is obtained by capturing multiple holograms with different phase shift amounts and applying arithmetic operations based on the phase-shifting algorithm to these holograms. As shown in Non-Patent Document 1, multiple holograms are typically obtained by capturing multiple holograms sequentially, and information on the complex amplitude distribution is obtained from the holograms by applying a time-division phase-shifting method. However, when capturing multiple holograms sequentially, the subject must remain stationary during the capture, and this method cannot be applied to capturing moving subjects.

[0004] To solve this problem and support the capture of moving images, imaging devices that simultaneously capture multiple holograms have been proposed (Patent Documents 2 and 3). (Hereinafter, such imaging devices may be referred to as "moving image capture devices"). These moving image capture devices utilize the geometric phase obtained by simultaneously transmitting two orthogonal circularly polarized beams of light through a linear polarizer, thereby simultaneously capturing multiple holograms with different phase shift amounts. Applying a phase shift method to these holograms provides a complex amplitude distribution, which can then be used to obtain a complex amplitude distribution for each frame of a moving image, enabling the capture of three-dimensional moving images. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6416270 [Patent Document 2] Patent No. 6245551 [Patent Document 3] Patent No. 7348858 [Non-patent literature]

[0006] [Non-Patent Document 1] Myung K. Kim, "Full color natural light holographic camera", Optics Express, (2013), vol. 21, pp. 9636-9642. Summary of the Invention [Problem to be solved by the invention]

[0007] In order to utilize two orthogonal circularly polarized lights in a video capture device, the polarization state of the light propagating from the subject must be linearly polarized. However, the incoherent light captured by incoherent digital holography is typically unpolarized light, in which the plane of vibration of the light changes randomly. In conventional video capture devices, to capture a hologram of this unpolarized incoherent light, a linear polarizer is used to convert the polarization state of the light being captured from unpolarized to linearly polarized. However, using a linear polarizer in this process halves the light energy. This reduction in light energy reduces the signal-to-noise ratio when capturing a hologram, degrading the quality of the reconstructed image.

[0008] Furthermore, when light propagating from a subject is reflected by specular reflection or total reflection, even if it is incoherent light, it may be linearly polarized or elliptically polarized. If this light is passed through a linear polarizer, depending on the angle of the linear polarizer, most of the reflected light from the subject may be removed, making it impossible to capture it as a hologram.

[0009] Therefore, in view of the above-mentioned problems, an object of the present invention is to provide an imaging device and a signal processing device that can effectively utilize light that would otherwise be lost when using a conventional linear polarizer, and obtain a high-quality reproduced image. [Means for solving the problem]

[0010] In order to solve the above problems, the photographing device according to the present invention comprises: (1) An imaging device comprising: a polarizing beam splitter that splits incoherent light propagating from an object to be imaged into two linearly polarized lights with different polarization states; a first imaging function unit that receives one of the linearly polarized lights, constitutes a self-interferometer, and simultaneously images multiple holograms with different phase shift amounts from the linearly polarized light; and a second imaging function unit that receives the other linearly polarized light, constitutes a self-interferometer, and simultaneously images multiple holograms with different phase shift amounts from the linearly polarized light.

[0011] (2) In the photographing device of (1) above, it is further preferable that the first photographing function unit and the second photographing function unit photograph the hologram with different optical energies.

[0012] (3) In the photographing device of (1) or (2) above, it is preferable that the first photographing function unit and the second photographing function unit further include a bifocal lens, a quarter-wave plate, and a polarizer array imaging element.

[0013] (4) In the photographing device of (1) or (2) above, it is preferable that the first photographing function unit and the second photographing function unit further include a bifocal lens, a quarter-wave plate, a phase grating, an area-divided polarizer, and an image sensor.

[0014] (5) In the imaging device of (3) or (4) above, it is preferable that the bifocal lens and the quarter-wave plate are replaced with a geometric phase lens.

[0015] In order to solve the above problems, a signal processing device according to the present invention comprises: (6) A signal processing device to which two sets of holograms with different phase shift amounts, captured by any of the image capturing devices (1) to (5), are input, the signal processing device including a control unit that applies a phase shift method to each set of holograms to extract a complex amplitude distribution, averages the two complex amplitude distributions, and applies a propagation calculation to the averaged complex amplitude distribution to generate a reconstructed image.

[0016] (7) In the signal processing device of (6) above, it is preferable that the control unit further performs an intensity correction process on at least one of the complex amplitude distributions to unify the light energy when capturing the hologram, and averages the two complex amplitude distributions after the intensity correction process.

[0017] (8) In the signal processing device of (6) or (7) above, it is preferable that the control unit, before the intensity correction process, calculates an average value of each extracted complex amplitude distribution, extracts a phase value from the argument, calculates a difference in the phase values ​​of the two extracted complex amplitude distributions, and adds the phase difference to one of the complex amplitude distributions, thereby performing a phase correction process to unify the initial phases of the two complex amplitude distributions.

[0018] In order to solve the above problems, a signal processing device according to the present invention comprises: (9) A signal processing device that receives as input two sets of multiple holograms with different phase shift amounts, captured by any of the imaging devices described in (1) to (5), the signal processing device comprising: a control unit that adds or averages the two sets of multiple holograms with matching phase shift amounts; applies a phase shift method to the added or averaged holograms to extract a complex amplitude distribution; and applies propagation calculations to the extracted complex amplitude distribution to generate a reconstructed image. [Effects of the Invention]

[0019] The imaging device and signal processing device of the present invention can effectively utilize light that would otherwise be lost when using a conventional linear polarizer, enabling imaging that is independent of the polarization state of light reflected from a subject and reducing noise contained in holograms during imaging, thereby producing high-quality reconstructed images. Furthermore, the present invention can simultaneously capture multiple holograms to obtain complex amplitude distributions, enabling the acquisition of high-quality three-dimensional moving images. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a conceptual diagram of an incoherent digital holography system according to the present invention. [Figure 2] 1 is a diagram illustrating an example of the configuration of a system according to a first embodiment of the present invention. [Figure 3] 10 is a diagram illustrating an example of the configuration of a system according to a second embodiment of the present invention. [Figure 4]10 is a diagram illustrating an example of the configuration of a system according to a third embodiment of the present invention. [Figure 5] 10 is a diagram illustrating an example of the configuration of a system according to a fourth embodiment of the present invention. [Figure 6] 1 is a flowchart illustrating an example of signal processing in the signal processing device of the present invention. [Figure 7] This shows the configuration of the incoherent digital holography system used in the verification experiment. [Figure 8] 10 shows an example of a subject used in a verification experiment. [Figure 9A] 10 is an example of a hologram of a subject photographed by the first photographing function unit. [Figure 9B] 10 is an example of a reconstructed image (focused on object A) reconstructed from a hologram captured by the first imaging function unit. [Figure 9C] 10 is an example of a reconstructed image (focused on object B) reconstructed from a hologram captured by the first imaging function unit. [Figure 10A] 10 is an example of a hologram of a subject photographed by the second photographing function unit. [Figure 10B] 10 is an example of a reconstructed image (focused on object A) reconstructed from a hologram captured by the second imaging function unit. [Figure 10C] This is an example of a reconstructed image (focused on object B) reconstructed from a hologram captured by the second imaging function unit. [Figure 11A] 1 is an example of a reconstructed image (focused on object A) obtained by the present invention. [Figure 11B] 10 is an example of a reconstructed image (focused on object B) obtained by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described below with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals. In the description of each embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0022] Figure 1 is a conceptual diagram of an incoherent digital holography system according to the present invention. System 1 comprises a polarizing beam splitter 10, a first imaging function unit 20, and a second imaging function unit 30, and is composed of an imaging device that captures holograms, and a signal processing device 40 that reconstructs an object from the holograms captured by the imaging device.

[0023] The polarizing beam splitter 10 splits the incoherent light propagating from the subject into two linearly polarized lights, p-polarized and s-polarized, whose polarization states are orthogonal to each other, and propagates each polarized light along a separate optical path. A first image capturing function unit 20 and a second image capturing function unit 30 are disposed on each optical path, respectively.

[0024] The first photographing function unit 20 functions as a self-interferometer of a common optical path using polarized light, and for example, p-polarized light is input, and a plurality of holograms with mutually different amounts of phase shift are photographed at once.

[0025] Similarly, the second photographing function unit 30 also functions as a self-interferometer of a common optical path using polarized light, and for example, s-polarized light is input and multiple holograms with different phase shift amounts are photographed at once. The hologram images photographed by the photographing devices (the first photographing function unit 20 and the second photographing function unit 30) are output to the signal processing device 40.

[0026] The signal processing device 40 may generally be a computer or a server equipped with a control unit, a storage unit, a communication unit, etc. The processing unit of the signal processing device 40 combines multiple holograms captured by the first imaging function unit 20 and the second imaging function unit 30, and generates a reconstructed image by applying propagation calculations to the obtained complex amplitude distribution. The processing of the signal processing device 40 will be described later.

[0027] According to the imaging device and signal processing device of the present invention, by using a polarizing beam splitter 10 instead of a conventional linear polarizer, it is possible to effectively utilize light that would otherwise be lost, thereby enabling imaging that is not dependent on the polarization state of the light reflected from the subject and reducing noise contained in the hologram during imaging, thereby producing a high-quality reproduced image.

[0028] The imaging device of the present invention can be used in various ways. As an example, it can capture holograms using the same exposure time (same light energy) with the first imaging unit 20 and the second imaging unit 30. Therefore, unlike conventional methods where multiple holograms are simultaneously captured using a single imaging element, the present invention can capture two sets of the same holograms. For example, by making the phases and sizes of the holograms captured by the first imaging unit 20 and the second imaging unit 30 identical, adding the two holograms together can obtain a hologram with twice the light intensity of conventional methods. Furthermore, even if the light propagating from the subject is polarized, no light components are removed when generating linearly polarized light. Therefore, adding the holograms from the first imaging unit 20 and the second imaging unit 30 allows for effective use of all the propagating light. Furthermore, adding two sets of holograms captured simultaneously cancels out random noise, enabling noise reduction. Extracting the complex amplitude distribution from the added holograms and applying propagation calculations can produce a high-quality reconstructed image.

[0029] Next, four examples of the imaging function unit constituting the self-interferometer will be described for the embodiment of the imaging device of the present invention. However, the configurations of the first and second imaging function units of the present invention are not limited to these, and any configuration may be used as long as the imaging function unit has the function of simultaneously imaging multiple holograms with different phase shift amounts.

[0030] (First embodiment) 2 shows an example of the configuration of a system according to the first embodiment of the present invention. In this embodiment, the first imaging function unit 20 is composed of a bifocal lens 21, a quarter-wave plate 22, and a polarizer array imaging element 26, and the second imaging function unit 30 is composed of a bifocal lens 31, a quarter-wave plate 32, and a polarizer array imaging element 36.

[0031] The polarizing beam splitter 10 splits the incoherent light propagating from the subject into two linearly polarized lights, p-polarized and s-polarized, whose polarization states are orthogonal to each other. The p-polarized and s-polarized lights propagate in different directions and enter the bifocal lenses 21 and 31, respectively.

[0032] The bifocal lens 21 is a lens with different focal lengths for horizontally polarized light and vertically polarized light. Therefore, the bifocal lens 21 gives phases with different focal lengths to the horizontally polarized component and vertically polarized component of the light wave (the first split light and the second split light). The first split light and the second split light, which are transmitted through the bifocal lens 21 and have different concentrations, are linearly polarized light that is orthogonal to each other and enter the quarter-wave plate 22. Note that the bifocal lens 21 is made of a birefringent optical device, and a birefringent crystal, metasurface, or liquid crystal lens can be used.

[0033] The quarter-wave plate 22 converts the two beams of light (the first split beam and the second split beam) that have passed through the bifocal lens 21 into right-handed and left-handed circularly polarized beams, respectively. The two circularly polarized beams have different focal length phases, which causes a slight optical path difference, resulting in interference.

[0034] The polarizer array imaging element 26 has linear polarizers with transmission axes rotated by 0°, 45°, 90°, and 135° periodically arranged on the pixels, for example, for every four adjacent 2 × 2 pixels. The polarizer array imaging element 26 captures a hologram of the self-interference of the first and second divided lights (right- and left-handed circularly polarized lights). Since two orthogonal circularly polarized lights are incident on each pixel, four different phase shift amounts (0, π / 2, π, and 3π / 2) are imparted based on the geometric phase of the circularly polarized light, depending on the angle of the transmission axis of the polarizer for each pixel mounted on the polarizer array imaging element 26.

[0035] The bifocal lens 31, quarter-wave plate 32, and polarizer array imaging element 36 that constitute the second imaging function unit 30 are the same as the bifocal lens 21, quarter-wave plate 22, and polarizer array imaging element 26, respectively, of the first imaging function unit 20. Therefore, in the second imaging function unit 30, the bifocal lens 31 similarly imparts phases of different focal lengths to the horizontally polarized component and vertically polarized component of the light wave (the first divided light and the second divided light), the quarter-wave plate 32 converts the first divided light and the second divided light into right-handed and left-handed circularly polarized light, respectively, and the polarizer array imaging element 36 captures a hologram of the self-interference of the first divided light and the second divided light (right-handed and left-handed circularly polarized light).

[0036] The images captured by the polarizer array image pickup elements 26 and 36 of the first and second imaging function units 20 and 30 are transferred to a signal processing device 40 .

[0037] The signal processing device 40 may store images captured by the polarizer array image capture elements 26 and 36 in a storage unit as needed. The processing unit of the signal processing device 40 performs demosaicing processing on each captured image to obtain four holograms with phase shift amounts of 0, π / 2, π, and 3π / 2. From the four holograms with phase shift amounts of 0, π / 2, π, and 3π / 2, a complex amplitude distribution of the object on each optical path is extracted using, for example, a phase shift method, and a propagation calculation or the like is further performed from the complex amplitude distribution to generate a reconstructed image of the object. The processing in the signal processing device 40 will be described in detail later.

[0038] (Second embodiment) 3 shows an example of the configuration of a system according to a second embodiment of the present invention. In this embodiment, the first imaging function unit 20 is composed of a geometric phase lens 23 and a polarizer array imaging element 26, and the second imaging function unit 30 is composed of a geometric phase lens 33 and a polarizer array imaging element 36. In the configuration of FIG. 3, the bifocal lenses 21 and 31 and the quarter-wave plates 22 and 32 of FIG. 2 are replaced with geometric phase lenses 23 and 33.

[0039] The function of the polarizing beam splitter 10 is the same as in the first embodiment, splitting incoherent light propagating from a subject into two linearly polarized lights: p-polarized light and s-polarized light. The p-polarized light and s-polarized light propagate in different directions and enter the first and second imaging function units, respectively.

[0040] The geometric phase lenses 23 and 33 convert the incident linearly polarized light into orthogonal circularly polarized light with different focal lengths and polarization states of left and right rotation. In other words, the geometric phase lenses 23 and 33 combine the functions of a bifocal lens and a quarter-wave plate, and compared to the configuration shown in Figure 2, the number of optical elements constituting the optical system can be reduced. The geometric phase lenses 23 and 33 can be fabricated using metasurface or polarization holography technology.

[0041] Thereafter, as in the first embodiment, a hologram of self-interference between the first and second split light beams (right- and left-handed circularly polarized light) is captured by the polarizer array image capturing elements 26 and 36. The images captured by the polarizer array image capturing elements 26 and 36 of the first and second imaging function units 20 and 30, respectively, are transferred to the signal processing device 40.

[0042] As in the first embodiment, signal processing device 40 performs demosaicing on the captured image to generate four holograms with phase shift amounts of 0, π / 2, π, and 3π / 2. Signal processing device 40 extracts complex amplitude distributions from these holograms and further performs propagation calculations to generate a reconstructed image of the subject.

[0043] (Third embodiment) FIG. 4 shows an example of the configuration of a system according to a third embodiment of the present invention. In this embodiment, the first imaging function unit 20 is composed of a bifocal lens 21, a quarter-wave plate 22, a phase grating 24, an area-divided polarizer 25, and an image sensor 27, and the second imaging function unit 30 is composed of a bifocal lens 31, a quarter-wave plate 32, a phase grating 34, an area-divided polarizer 35, and an image sensor 37. In the configuration shown in FIG. 4, phase gratings 24 and 34, area-divided polarizers 25 and 35, and image sensors 27 and 37 are used instead of the polarizer array image sensors 26 and 36 shown in FIG. 2. The imaging function unit of this embodiment configures an optical system based on a self-interferometer with a common optical path, but splits light waves in multiple directions along the way to simultaneously generate multiple holograms with different phase shift amounts.

[0044] As in the embodiment shown in FIG. 1, the polarizing beam splitter 10 splits incoherent light propagating from a subject into two linearly polarized light beams: p-polarized light and s-polarized light. The p-polarized light and s-polarized light beams propagate in different directions and enter the first and second imaging function units (bifocal lenses 21 and 31), respectively. The bifocal lenses 21 and 31 impart phases of different focal lengths to the horizontally polarized and vertically polarized light components of the light wave (first and second split light beams). The quarter-wave plates 22 and 32 convert the two light beams (first and second split light beams) that have passed through the bifocal lenses 21 and 31 into right- and left-handed circularly polarized light beams, respectively.

[0045] The phase gratings 24 and 34 are phase-modulating diffractive optical elements with a periodic microstructure, and have the function of generating three or four beams of light of the same quality as the incident light. For example, the phase gratings 24 and 34, which have two types of phase objects (objects that change only the phase of light) arranged in a checkerboard pattern, split the first and second split beams, which are left-handed and right-handed circularly polarized light, into four directions, and each beam is incident on a respective region of the region-dividing polarizers 25 and 35.

[0046] The area-divided polarizers 25 and 35 are composed of three or four linear polarizers with different transmission axes. The light split by the phase gratings 24 and 34 passes through the area-divided polarizers 25 and 35, obtaining different phase shifts. For example, the area-divided polarizers 25 and 35 can be composed of four types (four regions) of linear polarizers with transmission axes of 0°, 45°, 90°, and 135°. When the first and second split light beams split in four directions are incident on each region, the area-divided polarizers 25 and 35 impart different phase differences to the first and second split light beams in each region. As a result, different phase shifts of 0, π / 2, π, and 3π / 2 [rad] are imparted to each pair of linearly polarized light beams in each region, depending on the angle of the transmission axis of the linear polarizer.

[0047] Then, according to the geometric phase of the circularly polarized light, multiple holograms with different phase shift amounts are formed in different regions on the imaging surfaces of the image sensors 27 and 37. The image sensors 27 and 37 can simultaneously acquire multiple holograms with different phase shift amounts in a single image capture.

[0048] In this embodiment, the signal processing device 40 obtains multiple holograms required for applying the phase-shifting method by trimming holograms from images obtained by the image sensors 27 and 37. The signal processing device 40 extracts complex amplitude distributions from these holograms and then performs propagation calculations and the like to generate a reconstructed image of the subject.

[0049] (Fourth embodiment) Fig. 5 shows an example of the configuration of a system according to a fourth embodiment of the present invention. In this embodiment, the first photographing function unit 20 is composed of a geometric phase lens 23, a phase grating 24, an area-divided polarizer 25, and an image sensor 27, and the second photographing function unit 30 is composed of a geometric phase lens 33, a phase grating 34, an area-divided polarizer 35, and an image sensor 37. In the configuration of Fig. 5, the bifocal lenses 21 and 31 and quarter-wave plates 22 and 32 in Fig. 4 are replaced with geometric phase lenses 23 and 33. The photographing function unit of this embodiment also splits light waves in multiple directions along the way to simultaneously generate multiple holograms with different phase shift amounts.

[0050] The function of the polarizing beam splitter 10 is the same as in the other embodiments, splitting incoherent light propagating from a subject into two linearly polarized lights, p-polarized light and s-polarized light, which propagate in different directions and enter the first and second imaging function units, respectively.

[0051] The geometric phase lenses 23 and 33 convert the incident linearly polarized light into circularly polarized light having different focal lengths and orthogonal left-handed and right-handed polarization states.

[0052] The subsequent process is the same as in the third embodiment shown in Fig. 4, except that the phase gratings 24, 34 split the first and second split light beams, which are left-handed and right-handed circularly polarized, into three or four directions and cause each beam to enter a corresponding region of the area-divided polarizer 25, 35. The area-divided polarizers 25, 35 impart different phase differences to the first and second split light beams for each region, thereby forming multiple holograms with different phase shift amounts on the imaging surface of the image sensor 27, 37. The image sensor 27, 37 can simultaneously acquire multiple holograms with different phase shift amounts with a single image capture.

[0053] The signal processing device 40 obtains multiple holograms by trimming holograms from the images obtained by the image sensors 27 and 37. The signal processing device 40 extracts complex amplitude distributions from these holograms, and then performs propagation calculations and the like to generate a reconstructed image of the subject.

[0054] Although the above embodiment shows a configuration example using the minimum necessary optical elements for capturing a self-interference hologram, a wavelength filter may be introduced to improve image quality, or an additional lens may be introduced to control the angle of view and resolution and reduce aberration. Furthermore, the imaging element may be a monochrome one or a color one with a Bayer array.

[0055] Next, a process for generating a reconstructed image from a hologram captured by the image capturing device will be described. Fig. 6 is a flowchart of the process performed by the signal processing device 40.

[0056] Step S1: The control unit of the signal processing device 40 acquires holograms obtained from the p-polarized light and s-polarized light of incoherent light from the subject. Specifically, the signal processing device 40 acquires images captured by the first imaging function unit 20 and the second imaging function unit 30 from the imaging device of any of the first to fourth embodiments described above. In the case of the imaging devices of the first and second embodiments (FIGS. 2 and 3), image demosaicing is performed to acquire four holograms with different phase shift amounts from the image of one polarizer array imaging element 26, 36. In the case of the imaging devices of the third and fourth embodiments (FIGS. 4 and 5), multiple holograms separated from each other are generated on the imaging screen of the imaging elements 27, 37, so each hologram is trimmed to acquire multiple holograms with different phase shift amounts from the image of one imaging element 27, 37. Note that the signal processing device 40 may store the images captured by the imaging device or the acquired holograms in a storage unit as needed.

[0057] Step S2: The control unit of the signal processing device 40 extracts complex amplitude distributions O1 and O2 for each optical path from the acquired hologram. For example, a phase shift method can be used to extract the complex amplitude distributions. The intensity distributions of four holograms with phase shift amounts of 0, π / 2, π, and 3π / 2 are denoted as I0, I π / 2 , I π , I 3π / 2 Then, information on the complex amplitude distributions O1 and O2 of the object on each optical path can be obtained by the following equation (1).

[0058]

number

[0059] Step S3: The control unit of the signal processing device 40 corrects the shift in the initial phase (phase on the imaging screen) of the complex amplitude distributions O1 and O2. Even if the holograms are generated from s-polarized and p-polarized light separated from the same incoherent light, a phase difference may occur between the hologram and complex amplitude distribution obtained through each optical path (first image capture unit 20 and second image capture unit 30). To align the initial phases of the complex amplitude distributions O1 and O2 obtained through each optical path, the control unit calculates the average value of the xy plane (complex amplitude of each pixel) of each complex amplitude distribution O1 and O2, calculates the deflection angle, and extracts the phase value (average phase value). The control unit calculates the difference between the extracted phase value of the complex amplitude distribution O1 of the first image capture unit 20 and the phase value of the complex amplitude distribution O2 of the second image capture unit 30, and adds this phase difference to one of the complex amplitude distributions (adds it to the complex amplitude of all pixels) so as to reduce the shift in the initial phase. In this way, a phase correction process is performed to unify the phase after passing through the first imaging function unit 20 and the phase after passing through the second imaging function unit 30, thereby matching the initial phases of the complex amplitude distributions O1 and O2. Note that application of the process of step S3 is not essential, but applying this process increases the noise reduction effect.

[0060] Step S4: The control unit of the signal processing device 40 corrects the difference in light energy between the complex amplitude distributions O1 and O2. The holograms captured by the first and second imaging units 20 and 30 have different physical light energies due to differences in the exposure times of the respective imaging elements. Note that, as described below, the light energy during exposure may be intentionally made different between the first and second imaging units 20 and 30 for high dynamic range synthesis. Methods for making the light energy different include making the aperture settings different during imaging and making the exposure times different during imaging. However, because making the aperture settings different affects the resolution of the hologram, making the exposure times different is preferable. The difference in light energy during exposure causes differences in amplitude intensity between the complex amplitude distributions O1 and O2. Therefore, the amplitude intensity of one or both of the complex amplitude distributions O1 and O2 is adjusted to correct the difference in light energy (to unify the light energies). For example, if the optical energy of one complex amplitude distribution is twice that of the other, the amplitude intensity of one complex amplitude distribution is doubled. Alternatively, the physical optical energies of the two complex amplitude distributions may be unified by multiplying each complex amplitude distribution by the reciprocal of the exposure time of the imaging element. Note that the intensity correction process for unifying the optical energies of the two complex amplitude distributions can be omitted if the optical energies used when capturing the hologram are the same.

[0061] Step S5: The control unit of the signal processing device 40 averages the complex amplitude distributions O1 and O2 corrected to have equal optical energy in step S4. In this way, a single complex amplitude distribution O1 is obtained by averaging the complex amplitude distributions O1 and O2. m Get.

[0062] Step S6: The control unit of the signal processing device 40 calculates the averaged complex amplitude distribution O m A propagation calculation is applied to generate a reconstructed image. For example, propagation calculations based on the angular spectrum method or Fresnel diffraction can be applied to generate an image of an object at any distance. When using the angular spectrum method, the complex amplitude distribution U of light that has propagated over a propagation distance z is mis obtained by the following equation (2).

[0063]

number

[0064] Here, FT[…] and FT -1 […] are the Fourier transform operator and the inverse Fourier transform operator, respectively. u and v are variables in the spatial frequency coordinate system. λ is the central wavelength of the light source. By setting the propagation distance z to the focal plane of the object, the complex amplitude distribution U m A reconstructed image is obtained as follows.

[0065] (Modification of the flowchart) When the above-mentioned process of unifying the initial phase is not applied, the complex amplitude distributions O1 and O2 are not averaged, but the four holograms I0, I1 acquired by each imaging function unit are averaged. π / 2 , I π , I 3π / 2 That is, after acquiring the holograms in step S1, the control unit of the signal processing device 40 integrates (arithmetically averages) holograms with the same phase shift amount to obtain four holograms I m0 , I mπ / 2 , I mπ , I m3π / 2 The phase shift method of equation (1) may be applied to these four holograms that have been averaged. The optical energy of the holograms may be unified as appropriate. This processing procedure also generates the above-mentioned single complex amplitude distribution O m After this, the process of generating a reconstructed image in step S6 can be carried out.

[0066] By performing such processing, the signal processing device 40 of the present invention can reduce noise contained in the hologram when it is captured, and can obtain a high-quality reproduced image.

[0067] (Example and verification of effects) The incoherent digital hologram imaging device shown in FIG. 7 was set up, and imaging simulations were performed to verify the effects of the invention.

[0068] The optical system of the imaging device in FIG. 7 has the same basic configuration as the imaging device of the first embodiment (FIG. 2), and is composed of a polarizing beam splitter 10, a first imaging function unit 20 (bifocal lens 21, quarter-wave plate 22, polarizer array imaging element 26), and a second imaging function unit 30 (bifocal lens 31, quarter-wave plate 32, polarizer array imaging element 36). Furthermore, the optical system in FIG. 7 uses a lens 12 to adjust the magnification of the reproduced image, and also applies a wavelength filter 11 to narrow the wavelength width of the light source and improve image quality. The specifications and placement distances of the optical elements that make up the first imaging function unit 20 and the second imaging function unit 30 of this optical system are the same.

[0069] The subjects were two objects A and B, placed on different planes in the depth direction, as shown in Figure 8. The size of each object was 520 μm × 455 μm, and they were placed 10 mm apart in the depth direction. The brightness of the reflected light from object A was set to 1, and the brightness of the reflected light from object B was set to 0.002.

[0070] The distance from object A to lens 12 in the hologram imaging device was 250 mm, the distance from lens 12 to bifocal lenses 21 and 31 was 50 mm, and the distance from bifocal lenses 21 and 31 to polarizer array imaging elements 26 and 36 was 350 mm. Bifocal lenses 21 and 31 had a focal length of 300 mm for one split light and an infinite focal length for the other split light. The two polarizer array imaging elements 26 and 36 were assumed to have a pixel pitch of 6.5 μm, 512 × 512 pixels, and 12-bit gradation. The center wavelength of wavelength filter 11 was 633 nm, with a wavelength width of 1 nm.

[0071] FIG. 9A shows an example of a hologram (one of multiple holograms) captured by the first imaging function unit 20. This simulation shows an example of an overexposed image captured by the polarizer array imaging element 26 of the first imaging function unit 20, resulting in overexposure of part of the hologram and loss of information about the subject's interference fringes. FIGS. 9B and 9C show reconstructed images at the focal planes of objects A and B, respectively, obtained by calculating the complex amplitude distribution of this hologram using the phase shift method and applying propagation calculations. In FIG. 9C, the image of object B can be seen, but in FIG. 9B, the image of object A cannot be seen because information about the subject's interference fringes has been overexposed and lost.

[0072] FIG. 10A shows an example of a hologram (one of multiple holograms) captured by the second imaging function unit 30. This example captures a hologram with an exposure time 1 / 1000 of that of the first imaging function unit 20. Contrary to the results captured by the first imaging function unit 20, the hologram of object A was captured without overexposure, but the hologram of object B is underexposed and appears blacked out. FIGS. 10B and 10C show reconstructed images at the focal plane of objects A and B obtained by calculating the complex amplitude distribution of this hologram using the phase shift method and applying propagation calculations. In FIG. 10B, the image of object A can be seen, but in FIG. 10C, the image of object B cannot be seen because the information on the interference fringes of object B has been lost due to blacked out.

[0073] 9B and 10C are issues faced by conventional incoherent digital hologram recording devices. With conventional incoherent hologram recording devices, if the exposure setting of the imaging element is inappropriate when recording a hologram, blown-out highlights due to overexposure or crushed shadows due to underexposure can occur, resulting in a partial loss of hologram signal and partial loss of the reconstructed image of the subject, significantly degrading the quality of the reconstructed image.

[0074] The present invention can solve this problem by integrating the holograms captured by the first imaging function unit 20 and the second imaging function unit 30. The phase shift method is applied to each of the holograms in FIG. 9A and FIG. 10A to extract complex amplitude distributions. The initial phases of the two obtained complex amplitude distributions are unified, and the amplitude of the complex amplitude distribution obtained from the hologram in FIG. 10A is multiplied by 1000. The two complex amplitude distributions, corrected to have equal optical energy, are averaged to obtain an integrated complex amplitude distribution O. m Finally, the integrated complex amplitude distribution O m A propagation calculation is applied to generate a reconstructed image.

[0075] 11A and 11B show the reconstructed images at the respective in-focus positions of object A and object B, obtained from the integrated complex amplitude distribution Om. Unlike the reconstruction results obtained from a single polarizer array image sensor (FIGS. 9B and 10C), the reconstructed images in FIGS. 11A and 11B show the in-focus images of object A and object B, indicating that the images of the subjects were correctly obtained.

[0076] As described above, by applying the present invention, high dynamic range synthesis hologram imaging becomes possible, and imaging of higher quality than that achieved by conventional incoherent digital hologram imaging devices is possible.

[0077] A computer can be suitably used to function as the above-described signal processing device 40, and such a computer can be realized by storing a program describing the processing contents of the signal processing device 40 in a storage unit of the computer and having the central processing unit (CPU) of the computer read and execute the program. The program can be recorded on a computer-readable recording medium.

[0078] Although the above-described embodiments have been described as typical examples, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications or alterations are possible without departing from the scope of the claims. For example, the functions included in each block, step, etc. described in the embodiments can be rearranged so as not to be logically inconsistent, and multiple constituent blocks, steps, etc. can be combined or divided into one. [Explanation of symbols]

[0079] 1 System 10 Polarizing Beam Splitter 11 Wavelength filter 12 Lenses 20 First imaging function unit 30 Second imaging function unit 21,31 Bifocal lenses 22,32 1 / 4 wave plate 23,33 Geometric phase lens 24,34 phase grating 25,35 region-splitting polarizer 26,36 Polarizer array image sensor 27,37 Image sensor 40 Signal Processing Device

Claims

1. A polarizing beam splitter that splits the incoherent light propagating from the subject into two linearly polarized lights with different polarization states, a first photographing function unit that receives one of the linearly polarized lights, constitutes a self-interferometer, and photographs a plurality of holograms with different phase shift amounts from the linearly polarized light at the same time; a second photographing function unit configured to receive the other linearly polarized light and to form a self-interferometer, and to simultaneously photograph a plurality of holograms having different phase shift amounts from the linearly polarized light; An imaging device comprising:

2. 2. The imaging device according to claim 1, The imaging device, wherein the first imaging function unit and the second imaging function unit image a hologram using different optical energies.

3. 2. The imaging device according to claim 1, 10. An imaging device, wherein the first imaging function unit and the second imaging function unit each include a bifocal lens, a quarter-wave plate, and a polarizer array imaging element.

4. 2. The imaging device according to claim 1, An imaging device, characterized in that the first imaging function unit and the second imaging function unit each include a bifocal lens, a quarter-wave plate, a phase grating, an area-dividing polarizer, and an imaging element.

5. 5. The imaging device according to claim 3, An imaging device, characterized in that the bifocal lens and the quarter-wave plate are replaced with a geometric phase lens.

6. 5. A signal processing device to which two sets of multiple holograms having different phase shift amounts, which are captured by the imaging device according to claim 1, are input, A phase shift method is applied to each set of multiple holograms to extract a complex amplitude distribution; averaging the two complex amplitude distributions; generating a reconstructed image by applying a propagation calculation to the averaged complex amplitude distribution; A signal processing device comprising a control unit.

7. 7. The signal processing device according to claim 6, the control unit performs intensity correction processing for unifying light energy at the time of capturing a hologram on at least one of the complex amplitude distributions; A signal processing device characterized in that the two complex amplitude distributions are averaged after the intensity correction processing.

8. 8. The signal processing device according to claim 7, the control unit further performs, before the intensity correction process, a phase correction process to unify the initial phases of the two complex amplitude distributions by calculating an average value of each of the extracted complex amplitude distributions, extracting a phase value from the argument thereof, calculating a difference in the phase values ​​of the two extracted complex amplitude distributions, and adding the phase difference to one of the complex amplitude distributions.

9. 5. A signal processing device to which two sets of multiple holograms having different phase shift amounts, which are captured by the imaging device according to claim 1, are input, Adding or averaging two sets of holograms having the same phase shift amount, A phase shift method is applied to the summed or averaged hologram to extract a complex amplitude distribution; generating a reconstructed image by applying a propagation calculation to the extracted complex amplitude distribution; A signal processing device comprising a control unit.

Images