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In this paper, a depth-related uniform multiple wavefront recording plane (UM-WRP) method is proposed for enhancing the image quality of point cloud-based holograms. Conventional multiple WRP methods, based on full-color computer-generated holograms, experience a color uniformity problem caused by intensity distributions. To solve this problem, the proposed method generates depth-related WRPs to enhance color uniformity, thereby accelerating hologram generation using a uniform active area. The aim is to calculate depth-related WRPs with designed active area sizes that then propagate to the hologram. Compared with conventional multiple WRP methods, reconstructed images have significantly improved quality, as confirmed by numerical simulations and optical experiments.

RESUMEN

A robust, asymmetric, multidepth, three-dimensional object encryption scheme based on a computer-generated Fresnel hologram in the cascaded fractional Fourier domain is proposed. A layer-based Fresnel transform is used to generate a computer-generated hologram, which is then decomposed into two phase-only masks with a random phase distribution using matrix composition and decomposition methods. Encryption is implemented by using the created phase-only masks in two cascaded fractional Fourier transform domains, and a pair of private keys is generated in the encryption process. The cryptosystem is asymmetric and possesses high resistance against various potential attacks, such as brute-force, chosen-plaintext, known-plaintext, and ciphertext-only attacks. The simulation results and cryptanalysis confirmed the feasibility and effectiveness of the proposed encryption scheme.

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A multiple-camera holographic system using non-uniformly sampled 2D images and compressed point cloud gridding (C-PCG) is suggested. High-quality, digital single-lens reflex cameras are used to acquire the depth and color information from real scenes; these are then virtually reconstructed by the uniform point cloud using a non-uniform sampling method. The C-PCG method is proposed to generate efficient depth grids by classifying groups of object points with the same depth values in the red, green, and blue channels. Holograms are obtained by applying fast Fourier transform diffraction calculations to the grids. Compared to wave-front recording plane methods, the quality of the reconstructed images is substantially better, and the computational complexity is dramatically reduced. The feasibility of our method is confirmed both numerically and optically.

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Recently, computer-generated holograms (CGHs) of real three-dimensional (3D) objects have become widely used to support holographic displays. Here, a multiple-camera holographic system featuring an efficient depth grid is developed to provide the correct depth cue. Multidepth cameras are used to acquire depth and color information from real scenes, and then to virtually reconstruct point cloud models. Arranging the depth cameras in an inward-facing configuration allowed simultaneous capture of objects from different directions, facilitating rendering of the entire surface. The multiple relocated point cloud gridding method is proposed to generate efficient depth grids by classifying groups of object points with the same depth values in the red, green, and blue channels. CGHs are obtained by applying a fast Fourier transform diffraction calculation to the grids. Full-color reconstructed images were obtained flexibly and efficiently. The utility of our method was confirmed both numerically and optically.

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We propose a multi-depth three-dimensional (3D) image cryptosystem by employing the phase retrieval algorithm in the Fresnel and fractional Fourier (Fr-FrF) domains. Encryption was realized by applying the phase retrieval algorithm based on the double-random-phase-encoding architecture in which two encryption keys will be incessantly updated in each iteration loop. The phase-only functions (POFs) are generated in two cascaded Fr-FrF transforms (Fr-FrFT), serving as decryption keys to efficiently reduce the speckle noise and crosstalk between encrypted 3D image depths. The use of Fr-FrFT position parameters and fractional order as decryption keys further extended the key space, enhancing the cryptosystem's security level. Numerical simulations demonstrated the feasibility and robustness of our proposed scheme.

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A mobile three-dimensional image acquisition and reconstruction system using a computer-generated integral imaging technique is proposed. A depth camera connected to the mobile device acquires the color and depth data of a real object simultaneously, and an elemental image array is generated based on the original three-dimensional information for the object, with lens array specifications input into the mobile device. The three-dimensional visualization of the real object is reconstructed on the mobile display through optical or digital reconstruction methods. The proposed system is implemented successfully and the experimental results certify that the system is an effective and interesting method of displaying real three-dimensional content on a mobile device.

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We propose a multiple-3D-object secure information system for encrypting multiple three-dimensional (3D) objects based on the three-step phase shifting method. During the decryption procedure, five phase functions (PFs) are decreased to three PFs, in comparison with our previous method, which implies that one cross beam splitter is utilized to implement the single decryption interference. Moreover, the advantages of the proposed scheme also include: each 3D object can be decrypted discretionarily without decrypting a series of other objects earlier; the quality of the decrypted slice image of each object is high according to the correlation coefficient values, none of which is lower than 0.95; no iterative algorithm is involved. The feasibility of the proposed scheme is demonstrated by computer simulation results.

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A compact wavelength multiplexing technique is proposed and experimentally investigated to improve the efficiency of a full-color holographic diffuser using photopolymer. The exposure responses of a monochromatic hologram and a three wavelength multiplexed hologram recorded in photopolymer film are presented. The time-scheduled exposure energies at wavelengths of 633, 532, and 473 nm were chosen to optimize the uniform diffraction efficiency of the wavelength multiplexed hologram. These three wavelength iterative sequences of exposures are applied to achieve a specific color balance for a multicolor holographic diffuser. The experimental results confirm that the fabrication method is well suited to the manufacture of holographic diffusers for full-color display applications.

RESUMEN

Fast calculation method for a computer-generated cylindrical hologram (CGCH) is proposed. The method consists of two steps: the first step is a calculation of a virtual wave-front recording surface (WRS), which is located between the 3D object and CGCH. In the second step, in order to obtain a CGCH, we execute the diffraction calculation based on the fast Fourier transform (FFT) from the WRS to the CGCH, which are in the same concentric arrangement. The computational complexity is dramatically reduced in comparison with direct integration method. The simulation results confirm that our proposed method is able to improve the computational speed of CGCH.

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We propose a multiple-image encryption (MIE) scheme based on triple interferences for flexibly decrypting high-quality images. Each image is discretionarily deciphered without decrypting a series of other images earlier. Since it does not involve any cascaded encryption orders, the image can be decrypted flexibly by using the novel method. Computer simulation demonstrated that the proposed method's running time is less than approximately 1/4 that of the previous similar MIE method. Moreover, the decrypted image is perfectly correlated with the original image, and due to many phase functions serving as decryption keys, this method is more secure and robust.

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A method for fast computer hologram generation for long-depth objects using double wavefront recording planes (WRPs) and a graphics-processing unit (GPU) is presented. The WRPs are placed between the object and the hologram plane. Each WRP records the wavefront from a section of the object. Double WRPs can provide a shorter calculation time and enhanced reconstructed image quality compared with a single WRP, especially for long-depth objects. The average generation speed of two WRPs is 2.5 times that of one WRP. The correlation efficiency of the reconstructed layer relative to the original is 94% for two WRPs and 88.3% for one WRP at the close depth layer.

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We developed a head-mounted display (HMD) that achieved high levels of color uniformity and optical efficiency. The full-color holographic volume grating (HVG) attached on the specially designed wedge-shaped waveguide HMD system provided a 17° horizontal field of view (FOV). Theoretical analyses showed that the proposed waveguide resolved the problems of thickness and limited FOV. In this system, the HVG was recorded using a special sequential recording process on single photopolymer unit with 633, 532, and 473 nm wavelengths. The results confirm that the designed and fabricated waveguide can be employed in future commercial HMS.

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Viewing-zone control of integral imaging (II) displays using a directional projection and elemental image (EI) resizing method is proposed. Directional projection of EIs with the same size of microlens pitch causes an EI mismatch at the EI plane. In this method, EIs are generated computationally using a newly introduced algorithm: the directional elemental image generation and resizing algorithm considering the directional projection geometry of each pixel as well as an EI resizing method to prevent the EI mismatch. Generated EIs are projected as a collimated projection beam with a predefined directional angle, either horizontally or vertically. The proposed II display system allows reconstruction of a 3D image within a predefined viewing zone that is determined by the directional projection angle.

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This paper presents an analysis of error in parallel two-step phase-shifting method. From the analysis, it is clarified that the maximum bandwidth of the object that this technique can capture is a half bandwidth of recording devices. Also, the recording distance must be two times longer than the conventional method to have a good reconstruction image. The analysis was verified by simulations and experimental results.

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Microenvironmental acidosis is a common feature of inflammatory loci, in which clearance of apoptotic cells is necessary for the resolution of inflammation. Although it is known that a low pH environment affects immune function, its effect on apoptotic cell clearance by macrophages has not been fully investigated. Here, we show that treatment of macrophages with low pH medium resulted in increased expression of stabilin-1 out of several receptors, which are known to be involved in PS-dependent removal of apoptotic cells. Reporter assays showed that the -120/-1 region of the mouse stabilin-1 promoter was a low pH-responsive region and provided evidence that extracellular low pH mediated transcriptional activation of stabilin-1 via Ets-2. Furthermore, extracellular low pH activated JNK, thereby inducing translocation of Ets-2 into the nucleus. When macrophages were preincubated with low pH medium, phagocytosis of phosphatidylserine-exposed red blood cells and phosphatidylserine-coated beads by macrophages was enhanced. Blockade of stabilin-1 in macrophages abolished the enhancement of phagocytic activity by low pH. Thus, our results demonstrate that a low pH microenvironment up-regulates stabilin-1 expression in macrophages, thereby modulating the phagocytic capacity of macrophages, and suggest roles for stabilin-1 and Ets-2 in the maintenance of tissue homeostasis by the immune system.

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The effects of vitamin C, vitamin E and vitamin B12 on the noise-induced acute change in hepatic glycogen content in rats were investigated. The exposure of rats to 95 dB and 110 dB of noise acutely reduced their hepatic glycogens. Vitamin C (ascorbic acid) and vitamin E (alpha-tocopherol) attenuated the noise-induced acute reduction in the hepatic glycogen contents. This result suggests that antioxidants could reduce the change via reactive oxygen species. Vitamin B12 (cobalamin) delayed the noise-induced change, a finding that suggests that vitamin B12 could postpone the acute change via compensating for vitamin B12 deficiency.

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The activities of serum glutamic pyruvic transaminase (GPT), alkaline phosphatase (ALP) and creatine kinase (CK) in rats injected or not with the Chinese medicines, Astragali, Rhodiolae and Ligusticum, were determined after noise exposure. Noise at 95 and 105 dB significantly increased the activities of GPT, ALP and CK, and showed a dependence on the exposure time. The injection of each medicine significantly suppressed the increased enzyme activities by 95 and 105 dB noise.

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Noise is one of the factors that induces critical stress in animals. The contents of glycogen, lactic acid and cholesterol in the liver of noise-stressed rats were analyzed in order to investigate the alleviation of noise-stress-induced physiological damages by traditional medicine using Astragali and Rhodiolae radices. More than 95 dB noise ranging from 2 to 4 kHz reduced the contents of these compounds in the liver of rats not injected with the extract of Astragali or Rhodiolae, but did not change the contents in the liver of rats injected with the Astragali or Rhodiolae extract. These results show that noise induced stress in the rats via a decrease in contents of these compounds in the liver and that Astragali or Rhodiolae maintained the contents of these compounds in the liver of the noise-stressed rats. The results indicate that Astragali or Rhodiolae improved the ability for rats to resist noise stress.

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