Enlargement of the viewing zone and size of a reconstructed image in electro-holography using multiple reconstruction lights by eye-tracking.

To solve the problem of the narrow viewing zone in electro-holography, we propose a method using eye-tracking and a property of holography where the viewing zone varies with the angle of the reconstruction light. The method can enlarge the viewing zone without moving the optical elements for higher-order diffracted light removal and high-refresh-rate devices. The size of the reconstructed image is also enlarged using lenses. We conducted an experiment to validate the effectiveness of our method, and the results indicate that the viewing zone was enlarged by 1.44 times and the size of the reconstructed image was enlarged by 1.49 times.

Realistic rendering method for specular reflections with continuous motion parallax in a computer-generated hologram.

A computer-generated hologram (CGH) enables the display of virtual images and videos as well as the communication and storage of holographic data. The point-based method, which is a CGH-calculation method for representing the surface of an object as a set of point-light sources, has not been sufficiently studied in terms of realistic representation. This paper proposes a CGH-calculation method for realistic rendering using ray tracing to be used with a point-based method. Experiments were conducted with an optical system to confirm the effectiveness of the proposed method in terms of hidden-surface removal in mirror images and its implementation on multiple mirror surfaces. The results indicate that the proposed method enabled hidden-surface removal with continuous parallax and reflection on mirror surfaces.

Method of calculating speckle-reduced hologram data using a convergence light wave for a computer-generated hologram.

In a computer-generated hologram, random phases are required for representing object surfaces; however, speckle noise occurs in the random phases. We propose a speckle reduction method for three-dimensional virtual images in electro-holography. The method does not have random phases but instead converges the object light on the observer's viewpoint. Optical experiments demonstrated that the proposed method greatly reduced speckle noise while maintaining a calculation time comparable to that of the conventional method.

Fast calculation method based on hidden region continuity for computer-generated holograms with multiple cameras in a sports scene.

We propose, to the best of our knowledge, the world's first system capable of fast calculating computer-generated holograms (CGHs) from a large-scale outdoor sports scene captured with multiple RGB cameras. In the system, we introduce a fast calculation method focusing on hidden region continuity (HRC) that frequently appears in a point cloud of a 3D sports scene generated from free-viewpoint video technology. The experimental results show that the calculation time of the proposed HRC method is five to 10 times faster than that of the point-based method, which is one of the common CGH calculation methods.

Corneal protective effects of novel tear substitutes containing sodium hyaluronate and dodecahydrosqualene, squalane, in a porcine dry eye model.

To develop a novel tear substitute (TS) containing sodium hyaluronate (SH) and dodecahydrosqualene (DHS, squalane), we improved the prescription of a previously developed TS containing saline, 0.5% SH and 1% castor oil (CO), which had corneal protective effects against 60-min desiccation in a porcine dry eye model and viscosity of 106.8 mPa·S. Fresh porcine eyes were treated with a TS containing saline, 0.1%, 0.25%, 0.3% or 0.5% SH, and 1% CO or 1%, 2.5% or 5% DHS, and TS-treated eyes were desiccated for up to 180 min. The corneal damage was evaluated by the staining score of methylene blue (MB), absorbance of MB extracted from the cornea, the staining density of lissamine green (LG) and histopathology. The viscosities of the examined TS were also measured. A saline/0.5% SH/1% DHS solution had corneal protective effects for 90 min under desiccation and a viscosity of 110.0 mPa·s. A TS with saline, 0.1%, 0.25% or 0.3% SH and 1% or 2.5% DHS did not have better protective effects than a saline/0.5% SH/1% DHS solution, although a saline/0.3% SH/5% DHS solution exhibited greater corneal protection against 180-min desiccation on MB and LG staining and histopathological examination, and its viscosity was 34.5 mPa·s, which was similar to the 29.5 mPa·s of 0.3% SH. The saline/0.3% SH/5% DHS solution is available as a novel 3-hr long-lasting TS containing mucinomimetic and liquid oil components to treat and relieve dry eye symptoms in animals and humans.

Radiometric Calibration for a Multispectral Sensor Onboard RISESAT Microsatellite Based on Lunar Observations.

Radiometric calibration utilizing the Moon as a reference source is termed as lunar calibration. It is a useful method for evaluating the performance of optical sensors onboard satellites orbiting the Earth. Lunar calibration provides sufficient radiometric calibration opportunities without requiring any special equipment, and is suitable for nano/microsatellites. This study applies lunar calibration to a multispectral sensor, Ocean Observation Camera (OOC), on board a microsatellite named Rapid International Scientific Experiment Satellite. Simulating the brightness of the Moon based on the RObotic Lunar Observatory and SELENE/Spectrum Profiler models, sensitivity degradation was proven to be negligible in any of the four spectral bands of the OOC with the sensor temperature correction. A bluing trend in the OOC's sensor sensitivity was revealed, indicating a shorter observation wavelength shows larger irradiance. Comparing the top-of-atmosphere reflectance of Railroad Valley Playa with the Radiometric Calibration Network dataset revealed that the derived calibration parameter from the lunar calibration was valid for correcting the bluing trend in the visible range. Although the lunar and vicarious calibration parameters for the infrared band were unexpectedly inconsistent, lunar calibration could potentially contribute toward estimating the contaminated background radiance in the Earth observation images.

Sensitizer-host-annihilator ternary-cascaded triplet energy landscape for efficient photon upconversion in the solid state.

In this paper, we introduce a new strategy for improving the efficiency of upconversion emissions based on triplet-triplet exciton annihilation (TTA-UC) in the solid state. We designed a ternary blend system consisting of a triplet sensitizer (TS), an exciton-transporting host polymer, and a small amount of an annihilator in which the triplet-state energies of the TS, host, and annihilator decrease in this order. The key idea underpinning this concept involves first transferring the triplet excitons generated by the TS to the host and then to the annihilator, driven by the cascaded triplet energy landscape. Because of the small annihilator blend ratio, the local density of triplet excitons in the annihilator domain is higher than those in conventional binary TS/annihilator systems, which is advantageous for TTA-UC because TTA is a density-dependent bimolecular reaction. We tracked the triplet exciton dynamics in the ternary blend film by transient absorption spectroscopy. Host triplet excitons are generated through triplet energy transfer from the TS following intersystem crossing in the TS. These triplet excitons then diffuse in the host domain and accumulate in the annihilator domain. The accumulated triplet excitons undergo TTA to generate singlet excitons that are higher in energy than the excitation source, resulting in UC emission. Based on the excitation-intensity and blend-ratio dependences of TTA-UC, we found that our concept has a positive impact on accelerating TTA.

Fast calculation method with saccade suppression for a computer-generated hologram based on Fresnel zone plate limitation.

The computer-generated hologram (CGH) is an ideal 3D technology that can satisfy all the physiological factors of the human eye (such as binocular parallax, focus adjustment and convergence etc.) by simulating the recording part of traditional optical holography with a computer. CGH has a lot of advantages such as being able to be used for animation. However, it also has many disadvantages, and one of them is the large amount of calculation. A saccade is one of a very rapid movement of human eye, and also, it is an ability of the eye to quickly and accurately move from one target to another. This is very critical for reading and involves very precise and specific eye movements. Saccades normally happen at a frequency of 2 - 8 times per second in daily life without our being conscious, and their peak angular speed can reach 900 degrees/second. However, saccades can also be initiated by an expected stimulus such as looking from one object to another, and they last from 20 - 200 ms depending on their amplitude. In addition, our visual information is suppressed while saccade occurs. In this paper, to realize the fast calculation of CGHs, a new method is proposed that uses saccades to reduce the amount of CGH calculation without any negative effects on observers viewing CGH reconstruction images. We increased high-speed calculation by at least 4 times through Fresnel zone plate limitation and 4.64 times through saccade suppression.

Fast calculation method for viewpoint movements in computer-generated holograms using a Fourier transform optical system.

Augmented reality (AR) using a holographic head-mounted display has been attracting a great deal of attention. In the AR system, computer-generated holograms (CGHs) are calculated and displayed on an electronic display. However, the time required for making CGHs is very long. Here, we propose a fast calculation method for arbitrary viewpoint movements in holographic AR systems. The calculation uses a Fourier transform optical system to enlarge the visual field of electroholography. In experiments, the generation time of the proposed method was approximately twice as fast as that of the conventional method. Furthermore, the quality of the CGHs generated by our method was sufficiently high.

Wide visual field angle holographic display using compact electro-holographic projectors.

Electro-holography has the problem of having a narrow visual field angle, because the resolution of a spatial light modulator is insufficient for displaying a fringe pattern. To solve this problem, this paper proposes a projector-type electro-holographic compact display that achieves a wide visual field angle by using the combination of an optical system and calculation algorithms. The results of experiments show that the visual field angle is three times larger than that of a normal electro-holographic display. In addition, it is demonstrated that the system has the ability to display 3D reconstructed images with binocular, full-color, high-resolution, and accurate depth presentation.

Lossless compression applying linear predictive coding based on the directionality of interference patterns of a hologram.

This paper proposes lossless linear predictive coding based on the directionality of the interference patterns of a hologram. We approached this study from two aspects. First, to determine the directionality of the interference patterns, we performed differential pulse coding modulation (DPCM), segmenting interference patterns into n blocks and scanning the pixels in eight directions for each block. Then, we determined the direction that had minimum entropy, calculating entropy in each direction, and encoded the difference by DPCM in the determined direction. In the second approach, we attempted linear prediction using the prediction coefficients for the determined direction based on the first process. In this case, the DPCM was utilized only to determine the direction in which to progress prediction about the original pixel. Then, we calculated the difference between the predicted and the original, and encoded it. Through the above procedure, we derived an appropriate compression scheme for the hologram by comparing DPCM with the linear predictive coding. Experimental results showed that the compression rate of 26.7% could be obtained through the first process.

Fast calculation method with foveated rendering for computer-generated holograms using an angle-changeable ray-tracing method.

The computer-generated hologram (CGH) technique is a technique that simulates the recording of holography. Although the CGH technique has a lot of advantages, it also has some disadvantages; one of them is the long calculation time. Much research on the human eye has established that humans see 135° vertically and 160° horizontally, but can see fine detail within an only 5° central circle. Foveated rendering uses this characteristic of the human eye to reduce image resolution in the peripheral area and achieve a high calculation speed. In this paper, a new method for CGH fast calculation with foveated rendering using an angle-changeable ray-tracing method is introduced. The experiments demonstrate the effectiveness and high-speed calculation of this method.

Holographic display method for volume data by volume rendering.

Volume data are widely used in many areas, especially in biomedical science and geology. Visualizing volume data is very important to enable intuitive understanding of 3D structures, making them easier to analyze. However, current visualization technologies for volume data cannot satisfy human requirements. In this study, we propose a holographic display method for volume data by volume rendering. Based on this holographic display method, we can generate holograms for transparent objects and multi-layer objects. In this paper, to increase the speed of calculation, we propose an approximate volume rendering based CGH calculation method with elemental holograms.

HPT: A High Spatial Resolution Multispectral Sensor for Microsatellite Remote Sensing.

Although nano/microsatellites have great potential as remote sensing platforms, the spatial and spectral resolutions of an optical payload instrument are limited. In this study, a high spatial resolution multispectral sensor, the High-Precision Telescope (HPT), was developed for the RISING-2 microsatellite. The HPT has four image sensors: three in the visible region of the spectrum used for the composition of true color images, and a fourth in the near-infrared region, which employs liquid crystal tunable filter (LCTF) technology for wavelength scanning. Band-to-band image registration methods have also been developed for the HPT and implemented in the image processing procedure. The processed images were compared with other satellite images, and proven to be useful in various remote sensing applications. Thus, LCTF technology can be considered an innovative tool that is suitable for future multi/hyperspectral remote sensing by nano/microsatellites.

Holographic display methods for volume data: polygon-based and MIP-based methods.

Volume data are widely used in many areas, especially in biomedical science and geology. However, current visualization technologies of volume data cannot satisfy the visual requirements of humans. In this study, we propose two holographic display methods for volume data. The first method is polygon-based, and the other is maximum intensity projection (MIP)-based. Both methods are able to generate computer generated holograms of volume data. The polygon-based method can obtain various and colorful holograms, while the MIP-based method can be quickly calculated. Both methods can generate holographic animations, which were displayed on an electro-holography device.

Dynamic visual responses of accommodation and vergence to electro-holographic images.

Electro-holography can display images without inducing fatigue and three-dimensional (3D) sickness, i.e., visual discomfort due to viewing a stereoscopic display. Thus, this technology is expected to be applied to 3D media. However, there are no studies that have shown the agreement between the dynamic responses of accommodation and vergence to the reconstructed images of electro-holography and those to the real targets. This paper describes the measurement results of these responses using a developed system that can simultaneously measure the dynamic responses of accommodation and vergence. Moreover, statistical analysis for associating the accommodation and the vergence responses was achieved, and our study confirmed that these responses were in agreement.

Rho kinase inhibitor enables cell-based therapy for corneal endothelial dysfunction.

The corneal endothelium maintains corneal transparency; consequently, its dysfunction causes severe vision loss. Tissue engineering-based therapy, as an alternative to conventional donor corneal transplantation, is anticipated to provide a less invasive and more effective therapeutic modality. We conducted a preclinical study for cell-based therapy in a primate model and demonstrated regeneration of the corneal endothelium following injection of cultured monkey corneal endothelial cells (MCECs) or human CECs (HCECs), in combination with a Rho kinase (ROCK) inhibitor, Y-27632, into the anterior chamber. We also evaluated the safety and efficacy of Good Manufacturing Practice (GMP)-grade HCECs, similar to those planned for use as transplant material for human patients in a clinical trial, and we showed that the corneal endothelium was regenerated without adverse effect. We also showed that CEC engraftment is impaired by limited substrate adhesion, which is due to actomyosin contraction induced by dissociation-induced activation of ROCK/MLC signaling. Inclusion of a ROCK inhibitor improves efficiency of engraftment of CECs and enables cell-based therapy for treating corneal endothelial dysfunction as a clinically relevant therapy.

Fast point-based method of a computer-generated hologram for a triangle-patch model by using a graphics processing unit.

The point-based method and fast-Fourier-transform-based method are commonly used for calculation methods of computer-generation holograms. This paper proposes a novel fast calculation method for a patch model, which uses the point-based method. The method provides a calculation time that is proportional to the number of patches but not to that of the point light sources. This means that the method is suitable for calculating a wide area covered by patches quickly. Experiments using a graphics processing unit indicated that the proposed method is about 8 times or more faster than the ordinary point-based method.

Fast calculation method of computer generated hologram animation for viewpoint parallel shift and rotation using Fourier transform optical system.

Computer generated hologram (CGH) animations can be made by switching many CGHs on an electronic display. Some fast calculation methods for CGH animations have been proposed, but one for viewpoint movement has not been proposed. Therefore, we designed a fast calculation method of CGH animations for viewpoint parallel shifts and rotation. A Fourier transform optical system was adopted to expand the viewing angle. The results of experiments were that the calculation time of our method was over 6 times faster than that of the conventional method. Furthermore, the degradation in CGH animation quality was found to be sufficiently small.

Response of accommodation and vergence to electro-holographic images.

Studies on measuring accommodation and vergence responses of human vision are important to evaluate three-dimensional (3D) display technologies. Electro-holography is expected to be an ideal 3D display. However, there has been little research on measuring responses to it. In this study, the static responses to electro-holographic images with a large visual field and correct stimuli were measured. In addition, responses to real objects were measured for comparison with those to displayed images. There were more subjects than in conventional studies for statistical analysis. The experimental results statistically confirmed the equivalence of the responses to electro-holographic images and those to real objects. Therefore, it was experimentally suggested that electro-holography enables human vision to perform correct accommodation and vergence responses in accordance with the depths.