In this paper, we expand the eyebox size of lens-less holographic near-eye-display (NED) using passive eyebox replication technique that incorporates the spatial light modulator (SLM) and a holographic optical element (HOE). In holographic NEDs, the space-bandwidth product (SBP) of the SLM determines the exit pupil dimensions and corresponding eyebox size. The base eyebox is replicated in horizontal direction by using the horizontal high-order diffractions of the SLM under spherical wave illumination and multiplexed HOE combiner. The HOE combiner is used as a see-through reflective screen for the projected holographic virtual image, and it is fabricated based on two spherical divergent waves recording condition. When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be used for eyebox expansion. When the eyebox size is expanded, the field-of-view (FOV) is not sacrificed; spherical divergence wave illumination alleviates the need for a tradeoff between FOV and eyebox size. Astigmatism distortion introduced during the HOE fabrication was counterbalanced by pre-correcting the target image using a computer-generated, holographic computation algorithm. The experimental results prove that the proposed prototype system is simple and effective to achieve distortion-free reconstruction of 3D virtual image and eyebox extension of lens less holographic NED.
In this paper, color optimization of a full-color holographic stereogram printing system using a single SLM based on iterative exposure is proposed. First, an array of sub-holograms (hogels) is generated effectively within fast computergenerated integral imaging, and fully analyzed phase-modulation for red, green, and blue (RGB) channels of hogel. Then, the generated hogels are recorded into holographic material sequentially where SLM displays the R, G, and B channels of a single hogel via effectual exposure under synchronized control with three electrical shutters for RGB laser illumination to obtain verified color optimization. Numerical simulation and optical reconstructions are implemented.
In this paper, a full-color holographic stereogram (HS) printing system based on effective digital content generation using the inverse-directed propagation (IDP) algorithm is proposed. The digital content is generated effectively within the fast computation based on the IDP algorithm, and an optimized phase-modulation of hogel for red, green, and blue (RGB) channels of computer-generated hologram (CGH). Parallel computing is applied to provide high-resolution hologram data based on the independent hogel property. Finally, the generated hogels are recorded into holographic material sequentially as a volume hologram via fully-automated hogel printing setup using a single spatial-light modulator (SLM) to obtain a full-color HS. Numerical simulation and optical reconstructions demonstrate the simple and effective computation operated in content generation using the proposed IDP-based full-color HS printing system without degrading the image quality of the holograms.
A holographic stereogram printing system is a valuable method to output the natural-view holographic three-dimensional images. Here, the 3D information of the object such as parallax and depth information, are encoded into the elemental holograms, i.e. hogels, and recorded onto the holographic material via the laser illumination of the holographic printing process. However, according to the low resolution of the hogels, the quality of the printed image is reduced. Therefore, in this paper, we propose the real object-based fully automatic high-resolution light field image acquisition system using the one-directional moving camera array and smart motor-driven stage. The proposed high-resolution light field image acquisition system includes interconnected multiple cameras with one-dimensional configuration, the multi-functional smart motor and controller, and the computer-based integration between the cameras and smart motor. After the user inputs the main parameters such as the number of perspectives and distance/rotation between each neighboring perspectives, the multiple cameras capture the high-resolution perspectives of the real object automatically, by shifting and rotating on the smart motor-driven stage, and the captured images are utilized for the hogel generation of the holographic stereogram printing system. Finally, the natural-view holographic three-dimensional visualization of the real-object is outputted on the holographic material through the holographic stereogram printing system. The proposed method verified through the optical experiment, and the experimental results confirmed that the proposed onedimensional moving camera array-based light field image system can be an effective way to acquire the light field images for holographic stereogram printing.
In this paper, a fast and efficient multiple wavefront recording planes method with parallel processing is proposed for enhancing the image quality and generation speed of point cloud-based holograms. The proposed method gives an optimized fixed active area to generate depth-related multiple WRPs to improve the calculation speed and enhance the color uniformity of full-color hologram. In other to parallel processing the ray tracing intermediate plane is created. This method is more effective when the number of depths is smaller, such as the RGB-D image.
KEYWORDS: Holograms, 3D image reconstruction, Image quality, Wavefronts, Computer generated holography, Digital holography, Holography, 3D modeling, Image enhancement, RGB color model
In this paper, a uniform multiple wavefront recording planes (UM-WRPs) method for enhancing the image quality of the RGB-depth (RGB-D) image hologram is proposed. The conventional multiple wavefront recording planes (M-WRPs) based full-color computer-generated hologram (CGH) have color uniformity problem caused by intensity distribution. In order to solve the problem, the proposed method generates depth-related wavefront recording planes (WRPs) to enhance the color uniformity and accelerate hologram generation using a fixed active area. Compared with conventional MWRPs methods, the quality of reconstructed images of this method is improved significantly. The image improvement of the proposed method is confirmed by numerical reconstruction
In this paper, we have implemented a 3D content generation simulator based on integration of phase-only spatial light modulator (SLM) and LabVIEW software to develop a holographic stereogram printer that consists of a coherent laser, a spatial light modulator and X-Y translation stage with stepper motors. This content generation platform provides encoding of directional information extracted from rendered perspective images of real or virtual 3D object. There are mainly three parts related to the implementation for holographic stereogram printer. In the first part, “Digital content generation” phaseonly SLM will be applied to the holographic printer system by loading series of perspective 2D images for each holographic elements (hogel). Regarding this part, phase-only SLM can be converted into an amplitude modulator by adjusting the angles of the polarizer. The second part is “Control system” made in LabVIEW based platform for automatic recording of the holographic stereograms which is synthesized from previous part. The third implementation part is “Optical system” for printing of parallax-related hogels on the holographic plate. To check the performance of the developed approach, numerical simulations and optical experiments are implemented. The hogel images are sequentially exposed using the perspective images to form the whole holographic stereogram on the holographic light sensitive material.
A design and implementation of full-parallax holographic stereogram printer is presented. The holographic stereogram is synthesized using 2D perspective images of the 3D object that are rendered from multiple directions. The perspective images of the 3D scene are firstly captured by a virtual camera and transformed to two-dimensional holographic elements called hogels. The hogels are exposed using the perspective images to form the whole holographic stereogram. After all the hogels are exposed successively, a holographic stereogram can be achieved. Numerical simulation and optical reconstructions are implemented.
KEYWORDS: Clouds, 3D image processing, Cameras, 3D displays, Adaptive optics, 3D modeling, Image quality, Digital micromirror devices, Image resolution, Mirrors
A novel 360-degree integral-floating display based on the real object is proposed. The general procedure of the display system is similar with conventional 360-degree integral-floating displays. Unlike previously presented 360-degree displays, the proposed system displays the 3D image generated from the real object in 360-degree viewing zone. In order to display real object in 360-degree viewing zone, multiple depth camera have been utilized to acquire the depth information around the object. Then, the 3D point cloud representations of the real object are reconstructed according to the acquired depth information. By using a special point cloud registration method, the multiple virtual 3D point cloud representations captured by each depth camera are combined as single synthetic 3D point cloud model, and the elemental image arrays are generated for the newly synthesized 3D point cloud model from the given anamorphic optic system’s angular step. The theory has been verified experimentally, and it shows that the proposed 360-degree integral-floating display can be an excellent way to display real object in the 360-degree viewing zone.
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