Computer-generated hologram data generator and program

Abstract

To provide a computer-generated hologram data generator and a program for generating CGH data in which object light and conjugate light are completely separated by using object light that proceeds in a range of a discretionary direction, without being limited by an object light calculation method.SOLUTION: A computer-generated hologram data generator comprises: an object light calculation unit including an object three-dimensional information recording unit for recording three-dimensional information of an object for generating hologram data, a calculation method selection unit for selecting an object light calculation method in accordance with the format of the three-dimensional information, a frequency band limiting unit for limiting the range in which object light proceeds by the frequency band of the object light, and a propagation calculation unit for calculating the distribution of the object light on the hologram surface on the basis of the limited frequency band; a reference light calculation unit for setting the incidence angle of reference light in accordance with the limited frequency band and calculating reference light; and an interference fringe calculation unit for calculating an interference between the calculated object light and the calculated reference light and generating computer-generated hologram data.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a computer-generated hologram data generating device and a program for generating hologram data on a computer. [Background technology]

[0002] Holography technology has long been known, which uses the interference and diffraction of light to record and reconstruct three-dimensional information about an object. In the recording process, interference fringes generated by interfering with light emitted from an object (object light) and light with known properties (reference light) are recorded on a recording medium. The medium on which interference fringes are recorded is called a hologram. In the reconstruction process, light identical to the object light can be reconstructed by diffracting light identical to the reference light incident on the hologram. When recording and reconstructing the intensity information of interference fringes on a recording medium, conjugate light, which is the object light with an inverted phase, is also reconstructed at the same time. Conjugate light is different from the original object light, and is therefore generally unnecessary light. Also, a computer generated hologram (CGH) technology is known, which generates hologram data by calculating the process of interference between object light and reference light by a computer. In CGH, the spread of object light is restricted so that conjugate light does not overlap with the object light. Patent Document 1 describes a half zone plate method in which the spread of light waves generated from each point of an object regarded as a point cloud is restricted to only half the direction with respect to the hologram, and each light wave is added on the hologram surface to generate CGH data. Patent Document 2 reports a half zone plate method that is expanded to a polygon-based object light calculation method that can perform calculations faster than point cloud-based methods even for complex objects by regarding the object as a polygon. Non-Patent Document 1 reports a spatial frequency filtering method that can separate conjugate light regardless of the object light calculation method by calculating light waves on only one side with the incident angle of the reference light as a boundary. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4369639 [Patent Document 2] Patent No. 6285327 [Non-patent literature]

[0004] [Non-Patent Document 1] Yuji Sakamoto, "Removal of conjugate images from computer-generated holograms using spatial frequency filtering," Journal of the Institute of Image Information and Television Engineers, vol.59, No.4, 588-591 (2005) Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in order to generate CGH data in which the object light and the conjugate light do not overlap, it is necessary to limit the spread of light waves when calculating the object light. Conventionally, the calculation method of the object light to which the half zone plate method can be applied was limited to point group and polygon-based methods. In addition, the spatial frequency filtering method can be applied without being limited to the calculation method of the object light, but high-order diffracted light is not taken into consideration, and the object light and the conjugate light are not completely separated. Furthermore, the range of the direction in which the object light used for calculation travels is limited, such as only the upper or lower half direction with respect to the hologram in the half zone plate method, and only the upper or lower half direction with the incident angle of the reference light as a boundary in the spatial frequency filtering method.

[0006] Therefore, an object of the present invention is to provide a computer-generated hologram data generation device and program that generates CGH data in which the object light and the conjugate light are completely separated, using object light traveling in a range of any direction, without being limited by the calculation method of the object light. [Means for solving the problem]

[0007] (1) The computer-generated hologram data generation device of the present invention comprises an object three-dimensional information recording unit which records three-dimensional information of an object for generating hologram data; an object light calculation unit including: an object three-dimensional information recording unit which records three-dimensional information of an object for generating hologram data; a calculation method selection unit which selects a calculation method of an object light in accordance with a format of the three-dimensional information; a frequency band limiting unit which limits the range of the direction in which the object light travels by the frequency band of the object light; and a propagation calculation unit which calculates the distribution of the object light on a hologram surface based on the limited frequency band; a reference light calculation unit which sets the angle of incidence of a reference light in accordance with the frequency band limited by the frequency band limiting unit and calculates the reference light; and an interference fringe calculation unit which calculates the interference between the object light calculated by the object light calculation unit and the reference light calculated by the reference light calculation unit, and generates computer-generated hologram data.

[0008] According to (1) above, CGH data in which the object light and the conjugate light are completely separated can be generated using object light traveling in a range of any direction, without being limited by the calculation method of the object light.

[0009] (2) In the computer-generated hologram data generation device described in (1), the object light calculation unit further includes a depth position setting unit that sets a depth position between the object and the hologram surface in the observer's line of sight, and the depth position setting unit inverts the frequency components of the frequency band of the object light when the depth position between the object and the hologram surface is inverted.

[0010] According to (2) above, CGH data in which the object light and the conjugate light are completely separated can be generated using object light traveling in a range of any direction, without being limited by the calculation method of the object light.

[0011] (3) In the computer-generated hologram data generating apparatus according to (1) or (2), the frequency band limiting section limits the frequency band of the object light to a bandwidth equal to or less than a maximum frequency at which aliasing does not occur.

[0012] According to (3) above, CGH data in which the object light and the conjugate light are completely separated can be generated using object light traveling in a range of any direction, without being limited by the calculation method of the object light.

[0013] (4) In the computer-generated hologram data generation device described in (1) or (2), when calculating the distribution of the object light on the hologram surface based on the limited frequency band, the propagation calculation unit does not calculate components outside the frequency band.

[0014] According to (4) above, it is possible to reduce data volume and speed up calculations.

[0015] (5) A program of the present invention causes a computer to function as the computer-generated hologram data generating device according to (1).

[0016] According to (5) above, the same effect as that of (1) above can be achieved. Effect of the Invention

[0017] According to the present invention, CGH data in which the object light and the conjugate light are completely separated can be generated using the object light traveling in a range of any direction, without being limited by the method of calculating the object light. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a diagram showing an example of a functional block configuration of a computer-generated hologram data generation device according to an embodiment. [Diagram 2] FIG. 13 is a diagram showing an example of a bandwidth in the absence of a conjugate light separation process. [Diagram 3] FIG. 1 is a diagram showing an example of band limiting using a conventional half zone plate method. [Figure 4] FIG. 1 is a diagram showing an example of band limiting using a conventional frequency filtering method. [Diagram 5] 11 is a diagram illustrating an example of band limitation by a frequency band limiting unit; FIG. [Figure 6] 10 is a flowchart illustrating a generation process of a computer-generated hologram data generation device. [Figure 7] FIG. 13 is a diagram showing an example of a simulation of the reproduction of a hologram generated by a computer-generated hologram data generating device. [Figure 8A] FIG. 13 is a diagram showing an example of a simulation result of frequency components of object light when no conjugate light separation process is performed. [Figure 8B] FIG. 13 is a diagram showing an example of a simulation result of frequency components of object light in the computer-generated hologram data generating device. [Figure 9A] FIG. 13 is a diagram showing an example of a simulation result of a reconstructed image of a hologram when no process for separating conjugate light is performed. [Figure 9B] FIG. 13 is a diagram showing an example of a simulation result of a reconstructed image of a hologram produced by a computer-generated hologram data generating device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] <One embodiment> Hereinafter, a computer-generated hologram data generating device according to an embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of a functional block configuration of a computer-generated hologram data generation device 1 according to an embodiment. 1, computer-generated hologram data generation device 1 is, for example, an information processing device (computer) or the like, and has object three-dimensional information recording unit 10, object light calculation unit 11, reference light calculation unit 12, interference fringe calculation unit 13, and CGH data recording unit 14. In addition, object light calculation unit 11 has calculation method selection unit 110, frequency band limiting unit 111, depth position setting unit 112, and propagation calculation unit 113.

[0020] Computer-generated hologram data generation device 1 includes a processor (not shown), such as a CPU, to realize the operations of the functional blocks in Fig. 1. Computer-generated hologram data generation device 1 also includes auxiliary storage devices (not shown), such as a Read Only Memory (ROM), Solid State Drive (SSD), or Hard Disk Drive (HDD), that store various control programs, and a main storage device (not shown), such as a Random Access Memory (RAM) for storing data temporarily required for the processor to execute a program.

[0021] In computer-generated hologram data generation device 1, the arithmetic processing device reads the OS and application software from the auxiliary storage device, and performs arithmetic processing based on the OS and application software while expanding the read OS and application software into the main storage device. Based on the results of this calculation, computer-generated hologram data generation device 1 controls each piece of hardware. In this way, the processing by the functional blocks in Fig. 1 is realized. In other words, computer-generated hologram data generation device 1 can be realized by the cooperation of hardware and software.

[0022] The object 3D information recording unit 10 is, for example, an SSD or HDD. The object 3D information recording unit 10 records 3D information of the object for generating computer-generated hologram data. The 3D information of the object is not restricted in format, and may be, for example, point cloud data, 3D model data, RGB data with depth, light field data, or the like.

[0023] The object light calculation unit 11 is a functional unit that calculates the distribution of the object light on the hologram surface using the three-dimensional information of the object in the object three-dimensional information recording unit 10, and has a calculation method selection unit 110, a frequency band limiting unit 111, a depth position setting unit 112, and a propagation calculation unit 113.

[0024] The calculation method selection unit 110 selects one of the known object light calculation methods according to the format of the three-dimensional information of the object, for example. Although various calculation methods have been proposed according to the three-dimensional information of the object, the effect of the present invention is the same regardless of the selected object light calculation method.

[0025] The frequency band limiting section 111 limits the range of the traveling direction of the object light by the frequency band of the object light. For simplicity, the operation of the frequency band limiting section 111 will be described below in one-dimensional space, but the same applies to the case of two-dimensional space. Specifically, for example, when a light wave of wavelength λ is sampled in the spatial domain with a sampling pitch d, the maximum frequency at which aliasing does not occur is λ / 2d, and the maximum bandwidth of the light wave in the frequency domain u is λ / d. Furthermore, since it is a discrete signal in the spatial domain, it becomes periodic every λ / d in the frequency domain. Each frequency component in the frequency domain is an amplitude component for each direction in which the object light travels. Therefore, frequency band limiting unit 111 can limit the range of the direction in which the object light travels by limiting the band of the object light in the frequency domain.

[0026] Here, the band limit in the present invention will be described in terms of the bandwidth in the frequency domain in the process from generation to reconstruction of the hologram. If the object light is O and the reference light is R, when a hologram is generated using the intensity information of the interference fringes, the hologram is OR. * +O * R, where "*" indicates a complex conjugate. When reconstructing a hologram, the reconstruction light is expressed as O|R| 2 +O * R 2 where the first term is the object light, and the second term is the light corresponding to the conjugate light.

[0027] FIG. 2 is a diagram showing an example of a bandwidth when no conjugate light separation process is performed. In FIG. 2, the object light is shown by a thick solid line and a thick dashed line, and the conjugate light is shown by a thin solid line and a thin dashed line. In the object light, the signal shown by the thick solid line centered on frequency 0 corresponds to the first-order diffracted light, and the signals shown by the thick dashed lines on both ends correspond to ±2nd order light. In the conjugate light, the signal shown by the thin solid line centered on frequency 0 corresponds to the first-order diffracted light, and the signals shown by the thin dashed lines on both ends correspond to ±2nd order light. As shown in FIG. 2, the light wave attenuates as it becomes higher in order. Also, as shown in the first row of FIG. 2, the object light O is a light wave having an arbitrary frequency component, and the conjugate light O of the object light is * is a light wave with the frequency components of the object light O inverted. As shown in the second row of FIG. 2, the reference light R is incident at an angle of θ R The object beam O and the conjugate beam O are plane waves. * R * , multiplying by R gives the object light O and conjugate light O in frequency space. * are respectively -sinθ R , +sinθ R As shown in the third row of Fig. 2, the hologram shifts in the OR * and O * R, and the reconstructed light is +sinθ R It has shifted. Without the conjugate light separation process, as shown in the fourth row of Fig. 2, the object light O and the conjugate light O are separated within the range of ±λ / 2d, which is the viewing area of ​​the reconstruction light. * Therefore, it is not possible to separate the object beam from the conjugate beam.

[0028] FIG. 3 is a diagram showing an example of band limiting using a conventional half zone plate method. In FIG. 3, a frequency band lower than the center is used for each period λ / d on the u axis of the object light O. In other words, the conjugate light O * In the half zone plate method, the incident angle of the reference light R is 0°. As shown in the fourth row of Fig. 3, the reconstructed light of the CGH generated by the half zone plate method is divided into object light O and conjugate light O with frequency 0 as the boundary.* The directions of motion are separated.

[0029] FIG. 4 is a diagram showing an example of band limitation by a conventional frequency filtering method. In FIG. 4, the incident angle θ R In the frequency filtering method, the reconstructed light is composed of the object light O and the conjugate light O, as shown in the fourth row of Fig. 4. * There are ranges where the object light O and the conjugate light O do not overlap, but there are also ranges where the higher frequency components overlap. * cannot be completely separated.

[0030] 5 is a diagram showing an example of band limitation by the frequency band limiting unit 111. In FIG. 5, the band for calculating the object light is set to [u 1 :u 2 ]. Note that the bandwidth [u 1 :u 2 ] is in the range of λ / 2d or less, the frequency band limiting unit 111 1 , u 2 can be set arbitrarily. The bandwidth of the object light is [u 1 :u 2 ], the reference light calculation unit 12, which will be described later, determines the incidence angle θ R =-sin -1 (u 1 ), or θ R =-sin -1 (u 2 ) as the reference light, the object light O and the conjugate light O are aligned in the viewing zone as shown in the fourth row of Fig. 5. * It is possible to completely separate the high-order frequency components from the high-order frequency components. R =-sin -1 (u 2 ) is incident as a reference light. In addition, the bandwidth [u 1 :u 2 When the width of the ray bundle is made smaller than λ / 2d, the viewing zone becomes narrow.

[0031] The depth position setting unit 112 sets the position of the object and the hologram plane in the depth direction on the line of sight of the observer. As is well known, when the positional relationship between the object and the hologram plane is inverted, the frequency component of the object light is inverted. That is, depending on the depth direction position of the object set with respect to the hologram plane (for example, whether it is a position closer to the observer or a position farther away from the observer), the propagation calculation unit 113 described later sets the range of the band limit to [u 1 :u 2 ] or [-u 2 :-u 1 By setting in this way, the propagation calculation unit 113 described later can calculate the object light O and the conjugate light O even if there are objects in front of and behind the hologram surface. * and can be separated.

[0032] The propagation calculation unit 113 calculates the distribution of the object light on the hologram surface based on the frequency band set and limited by the frequency band limiting unit 111 and the depth position setting unit 112. Any known method can be used as the method for calculating the object light, but hereinafter, the propagation calculation unit 113 will be described for calculating the propagation of the band-limited object light using the angular spectrum propagation method. Specifically, for example, in the real space domain of xyz, the light wave distribution on the z=0 plane is expressed as g 1 (x,y;0), z=z 12 The light wave distribution on a plane is g 2 (x,y;z 12 ), then according to the angular spectrum theory, g 2 (x,y;z 12 ) is expressed as follows: g 2 (x,y;z 12 )=F -1 [F[g 1 (x,y;0)]·H(u,v;z 12 )] (A) Here, F[] and F -1 [] indicate Fourier transform and inverse Fourier transform, respectively. Also, u and v indicate coordinates in frequency space. Also, H(u,v;z 12 ) is called the propagation transfer function and is expressed as follows:

number

[0033] The reference light calculation unit 12 calculates the incident angle θ of the reference light R according to the frequency band set by the frequency band limiting unit 111 of the object light calculation unit 11. R and calculate the reference light R. The reference light calculation unit 12 calculates the reference light as a plane wave, but may also calculate it as a spherical wave. However, if the reference light is a spherical wave, it has a larger bandwidth than a plane wave, so the band of the object light must be further restricted according to the band of the spherical wave, otherwise the object light and the conjugate light will overlap.

[0034] An interference fringe calculation unit 13 calculates the interference between the object light calculated by the object light calculation unit 11 and the reference light calculated by the reference light calculation unit 12, and generates CGH data.

[0035] The CGH data recording unit 14 is, for example, an SSD or HDD, and records the CGH data calculated by the interference fringe calculation unit 13 .

[0036] <Generation process of computer-generated hologram data generation device 1> Next, the flow of the generation process of computer-generated hologram data generation device 1 will be described with reference to FIG. FIG. 6 is a flowchart illustrating the generation process of computer-generated hologram data generation device 1.

[0037] In step S1, the object light calculation unit 11 reads out the three-dimensional information of the object from the object three-dimensional information recording unit 10.

[0038] In step S2, the calculation method selection unit 110 selects a calculation method for the object light according to the format of the three-dimensional information read in step S1.

[0039] In step S3, the frequency band limiting section 111 limits the frequency band of the object light within the range of the traveling direction of the object light.

[0040] In step S4, the depth position setting unit 112 sets the position in the depth direction between the object and the hologram surface on the viewer's line of sight.

[0041] In step S5, the propagation calculation unit 113 calculates the distribution of the object light on the hologram surface based on the limited frequency bands set in steps S3 and S4.

[0042] In step S6, the reference light calculation unit 12 sets the incident angle of the reference light in accordance with the frequency band set in step S3, and calculates the reference light.

[0043] In step S7, the interference fringe calculation unit 13 calculates the interference between the object light calculated in step S5 and the reference light calculated in step S6.

[0044] In step S8, the interference fringe calculation unit 13 generates the interference calculated in step S7 as CGH data, and records the generated CGH data in the CGH data recording unit .

[0045] <Actual experimental results> Next, we will explain the experimental results of hologram reconstruction using computer-generated hologram data generation device 1. As experimental results, reconstruction of a hologram generated by computer-generated hologram data generation device 1 is simulated on a computer, and compared with reconstruction of a hologram without conjugate light separation processing. FIG. 7 is a diagram showing an example of a simulation of the reproduction of a hologram generated by computer-generated hologram data generation device 1. In FIG. 7, the number of pixels of both the computer-generated hologram (CGH) and the object is 16384×16384, the pixel pitch is 1 μm, and the number of gradations is 8 bits. The object is a two-dimensional plane, and the distance between the CGH and the object is 10 mm. An image of a mandrill is placed on the two-dimensional plane that serves as the object. The object light was calculated with the amplitude on the object plane being the pixel value and the phase being random. The angular spectrum propagation method was used for the propagation calculation. The reference light has a wavelength of 532 nm, and the incident angle is sin -1 The beam was a plane wave of (λ / 4d)°. The distance between the CGH and the observer was 100 mm. The size of the observer's pupil was 3 mm, the size of the eyeball was 24 mm, and the image formed on the retina by the lens of the observer's eye was the reconstructed image. The observation position was 0 mm on both the x-axis and y-axis, and the gaze point was the position of the object.

[0046] Fig. 8A is a diagram showing an example of a simulation result of the frequency components of object beam O when no conjugate beam separation process is performed. Fig. 8B is a diagram showing an example of a simulation result of the frequency components of object beam O in computer-generated hologram data generation device 1. In Figs. 8A and 8B, the vertical axis is the v axis (corresponding to the y axis) and the horizontal axis is the u axis (corresponding to the x axis). As shown in Figure 8A, when there is no conjugate light separation process, there is a signal over the entire uv space. On the other hand, as shown in Figure 8B, the object light generated by computer-generated hologram data generation device 1 has a signal in a horizontal band-like portion because the propagation in the y-axis direction is restricted. In Figure 8B, the frequency bandwidth of the object light generated by computer-generated hologram data generation device 1 is restricted to half, and in this case, the frequency band [v 1 :v 2] was restricted to [-λ / 4d: λ / 4d].

[0047] Fig. 9A is a diagram showing an example of a simulation result of a reconstructed image of a hologram when no process for separating conjugate light is performed, and Fig. 9B is a diagram showing an example of a simulation result of a reconstructed image of a hologram performed by computer-generated hologram data generation device 1. As shown in Figure 9A, in the reconstructed image of a hologram without the process of separating the conjugate light, the conjugate light is perceived as blurred when the object light is focused on, because the conjugate light is reproduced in front of the object light. On the other hand, as shown in Figure 9B, in the reconstructed image of a hologram, the mandrill is clearly perceived because the object light and the conjugate light are separated.

[0048] As described above, one embodiment of the computer-generated hologram data generation device 1 is capable of generating CGH data in which the object light and the conjugate light are completely separated, using object light traveling in a range of any direction, without being limited by the calculation method of the object light. Furthermore, when calculating the propagation of object light by determining the amplitude components of the spectrum, computer-generated hologram data generation device 1 does not need to calculate components that are removed by band limiting, which makes it possible to reduce the amount of three-dimensional information data of the object, thereby reducing data volume and speeding up calculations.

[0049] One embodiment has been described above, but computer-generated hologram data generation device 1 is not limited to the above embodiment, and includes modifications and improvements within the scope of achieving the object.

[0050] <Modification> In the embodiment described above, computer-generated hologram data generation device 1 sets the position in the depth direction between the object and the hologram surface on the viewer's line of sight in depth position setting section 112, but the present invention is not limited to this. For example, in the case where the positional relationship between the object and the hologram surface when the frequency band is limited by frequency band limiting section 111 does not change, computer-generated hologram data generation device 1 may omit the function of depth position setting section 112.

[0051] Each function included in computer-generated hologram data generation device 1 in one embodiment can be realized by hardware, software, or a combination of these. Here, being realized by software means being realized by a computer reading and executing a program.

[0052] The program can be stored and provided to the computer using various types of non-transitory computer readable media. The non-transitory computer readable media includes various types of tangible storage media. Examples of the non-transitory computer readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs). The program may also be provided to the computer by various types of transitory computer readable media. Examples of the transitory computer readable media include electrical signals, optical signals, and electromagnetic waves. The transitory computer readable media can provide the program to the computer via wired communication paths such as electric wires and optical fibers, or wireless communication paths.

[0053] In addition, the steps of writing a program to be recorded on a recording medium include not only processes that are performed chronologically according to the order, but also processes that are not necessarily performed chronologically but are executed in parallel or individually. [Explanation of symbols]

[0054] 1. Computer-generated hologram data generator 10 Object 3D information recording section 11 Object beam calculation section 110 Calculation method selection section 111 Frequency band limiting section 112 Depth position setting section 113 Propagation Calculation Section 12 Reference light calculation section 13 Interference fringe calculation section 14 CGH Data Recording Section

Claims

1. an object three-dimensional information recording unit that records three-dimensional information of an object for generating hologram data; an object light calculation unit including: a calculation method selection unit that selects a calculation method for the object light in accordance with a format of the three-dimensional information; a frequency band limiting unit that limits a range of a direction in which the object light travels by a frequency band of the object light; and a propagation calculation unit that calculates a distribution of the object light on a hologram surface based on the limited frequency band; a reference light calculation unit that sets an incident angle of a reference light in accordance with the frequency band limited by the frequency band limiting unit and calculates the reference light; an interference fringe calculation unit that calculates interference between the object light calculated by the object light calculation unit and the reference light calculated by the reference light calculation unit, and generates data for a computer-generated hologram; A computer-generated hologram data generating device comprising:

2. the object light calculation unit further includes a depth position setting unit that sets a depth position between the object and the hologram surface on a line of sight of an observer, 2. The computer-generated hologram data generating device according to claim 1, wherein the depth position setting section inverts frequency components of the frequency band of the object light when the depth position between the object and the hologram surface is inverted.

3. 3. The computer-generated hologram data generating device according to claim 1, wherein the frequency band limiting section limits the frequency band of the object light to a bandwidth equal to or smaller than a maximum frequency at which aliasing does not occur.

4. 3. The computer-generated hologram data generating device according to claim 1, wherein the propagation calculation unit, when calculating the distribution of the object light on the hologram surface based on the limited frequency band, does not calculate components outside the frequency band.

5. A program for causing a computer to function as the computer-generated hologram data generating apparatus according to claim 1.

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