Holographic Stereogram Research Articles

Fast and continuous recording of refreshable holographic stereograms

We present a technique to record refreshable holographic stereograms continuously. We eliminated the translation stage that shifts the recording beams back and forth and replaced it with an uninterrupted transparent belt holding holographic lenses. The belt is driven along a perimeter, shifting the lens laterally in front of a photorefractive screen without reversing direction. The holographic lenses focus the object beam onto holographic pixels and are permanently recorded in a thin photopolymer. The photopolymer material is flexible enough for the lenses to follow the curvature of the belt when it goes around the tensioning rollers. The hogel data are uploaded sequentially onto a spatial light modulator to form the object beam. The rotation of the belt in one single direction allows for a continuous operation and a much faster recording speed than with a translation stage that needs to reverse direction at the end of its travel span.

Speckle reduction method for image-based coherent stereogram generation

We propose a speckle noise reduction method for generation of coherent holographic stereograms. The method employs densely sampled light field (DSLF) of the scene together with depth information acquired for each ray in the captured DSLF. Speckle reduction is achieved based on the ray separation technique where the scene is first described as a superposition of sparse sets of point sources corresponding to separated sets of rays and then the holographic reconstructions corresponding to these sparse sets of point sources are added incoherently (intensity-wise) to obtain the final reconstruction. The proposed method handles the light propagation between the sparse scene points and hologram elements accurately by utilizing ray resampling based on the notion of DSLF. As a result, as demonstrated via numerical simulations, significant speckle suppression is achieved at no cost of sampling related reconstruction artifacts.

有效视角图像切片嵌合法全息体视图的数值重构

有效视角图像切片嵌合法全息体视图的数值重构

全息打印技术研究进展

Holographic printing technique can achieve a true three-dimensional display of the scene well. Based on different sources and different recording methods of interference patterns, holographic printing techniques can be classified as synthetic holographic stereogram printing, computer-generated hologram printing, and wavefront printing. Synthetic holographic stereogram printing can't record the depth information of the three-dimensional scene accurately, so there occurs the vergence-accommodation conflicts during the reconstruction of the hologram. Computer-generated hologram printing can record and reconstruct the depth information of the scene accurately, and solve the vergence-accommodation conflicts. However, the hologram is only a thin transmission hologram which can't be reconstructed by white light. Wavefront printing can not only solve the vergence-accommodation conflicts, but also achieve a thick reflection hologram for white-light reconstruction with good observation effect. Principles of different holographic printing techniques were introduced, then research status of each technique was analyzed. Finally, the advantages and disadvantages of them were discussed to illustrate their own properties.

Method of single-step full parallax synthetic holographic stereogram printing based on effective perspective images' segmentation and mosaicking.

With the principle of ray-tracing and the reversibility of light propagation, a new method of single-step full parallax synthetic holographic stereogram printing based on effective perspective images' segmentation and mosaicking (EPISM) is proposed. The perspective images of the scene are first sampled by a virtual camera and the exposing images, which are called synthetic effective perspective images, are achieved using the algorithm of effective perspective images' segmentation and mosaicking according to the propagation law of light and the viewing frustum effect of human eyes. The hogels are exposed using the synthetic effective perspective images in sequence to form the whole holographic stereogram. The influence of modeling parameters on the reconstructed images are also analyzed, and experimental results have demonstrated that the full parallax holographic stereogram printing with the proposed method could provide good reconstructed images by single-step printing. Moreover, detailed experiments with different holographic element sizes, different scene reconstructed distances, and different imaging planes are also analyzed and implemented.

High-resolution full-parallax computer-generated holographic stereogram created by e-beam technology

A high-resolution computer-generated stereogram for forming full-parallax three-dimensional (3-D) images is proposed. A full-parallax 3-D image is formed from 825 two-dimensional (2-D) projections and can be observed in a wide angular range. The stereogram is a reflective diffractive optical element (DOE) that consists of 50×50 μm2 hogels, where each hogel corresponds to one pixel of the 2-D frames. A phase-type kinoform is computed in every hogel by solving a nonlinear inverse problem. The DOE relief is fabricated using electron-beam technology with pixel size of 0.2×0.2 μm2. The effectiveness of the technology developed is illustrated by photographs and a video of a real DOE under monochromatic light and under white light. The new high-resolution full-parallax stereograms can be used for protecting bank notes, documents, and ID cards against counterfeit.

Full-Parallax Holographic Light-Field 3-D Displays and Interactive 3-D Touch

A light-field 3-D display (LFD) reproduces light rays or wavefront as if there are real objects, and a perfect 3-D display that satisfies all the depth cues in human vision becomes possible. By reproducing both horizontal and vertical parallaxes, i.e., full-parallax, an LFD reconstructs a real or virtual image in 3-D space. A rich 3-D experience can be provided to viewers, and moreover, multiple viewers can share the same reproduced 3-D image. A technology called holographic stereogram (HS) is the integration of ray-based and wavefront-based methods, and has been applied to LFD. Hardcopy HS has already been commercialized. The technology of HS is helpful also for an interactive LFD; a full-parallax LFD using a projector and a holographic screen that modulates the directions of light rays is based on the principle of HS. In this case, accurate registration between the projected image and the holographic screen is necessary, and it is achieved by projecting some test patterns and capturing them with a calibration camera. As a full-parallax LFD can reproduce real images in midair between the screen and viewers, it is possible to realize interactive 3-D touch interface. If a user touches the 3-D real image floating in the air, the reproduced light is scattered by the user’s fingertip. The scattered light is detected by a color image sensor placed behind the holographic screen, and can be employed to detect the user’s touch. In this system, the reproduced 3-D images and the 3-D touch detection are associated with each other, and thus, we do not have to worry about the complicated registration between them. The identification of the user’s interaction is simple, because the color information of the 3-D image can be used for this purpose. Some experimental results of the 3-D touch-sensing display are introduced, and possible applications of this technology are discussed as well.

Метод и устройство для одноэтапной цифровой записи цветных полнопараллаксных голограммных стереограмм

Метод и устройство для одноэтапной цифровой записи цветных полнопараллаксных голограммных стереограмм

High efficient generation of holographic stereograms based on wavefront recording plane

A computer generated holographic stereogram based on the wavefront recording plane (WRP) is presented. A WRP closed to the parallax image plane is introduced to record the complex amplitude in a small region for each point in the parallax image. By using three times of fast Fourier transform (FFT) to execute the Fresnel diffraction calculation between the WRP and the holographic stereogram plane, the object wave contributing to the hologram pattern can be achieved. The computation complexity of the proposed approach is dramatically reduced. The results show that the calculation time can be decreased by more than one order of magnitude.

Light-field and holographic three-dimensional displays [Invited

A perfect three-dimensional (3D) display that satisfies all depth cues in human vision is possible if a light field can be reproduced exactly as it appeared when it emerged from a real object. The light field can be generated based on either light ray or wavefront reconstruction, with the latter known as holography. This paper first provides an overview of the advances of ray-based and wavefront-based 3D display technologies, including integral photography and holography, and the integration of those technologies with digital information systems. Hardcopy displays have already been used in some applications, whereas the electronic display of a light field is under active investigation. Next, a fundamental question in this technology field is addressed: what is the difference between ray-based and wavefront-based methods for light-field 3D displays? In considering this question, it is of particular interest to look at the technology of holographic stereograms. The phase information in holography contributes to the resolution of a reconstructed image, especially for deep 3D images. Moreover, issues facing the electronic display system of light fields are discussed, including the resolution of the spatial light modulator, the computational techniques of holography, and the speckle in holographic images.

Speckle regularization and miniaturization of computer-generated holographic stereograms.

Holographic stereograms produce multiple parallax images that are seen from multiple viewpoints. Because random phase distributions are added to the parallax images to remove areas where images cannot be seen in the viewing area, speckles are generated in the reconstructed images. In this study, virtual viewpoints are inserted between the original viewpoints (real viewpoints) to make the interval of the viewpoints smaller than the pupil diameter of the eyes in order to remove the areas without images. In this case, regular interference patterns appear in the reconstructed images instead of the speckle patterns. The proper phase modulation of the parallax images displayed to the real and virtual viewpoints increases the spatial frequencies of the regular interference patterns on retinas so that the eyes cannot perceive them. The proposed technique was combined with the multiview-based holographic stereogram calculation technique and was experimentally verified.

Layered holographic stereogram based on inverse Fresnel diffraction.

We propose an efficient algorithm using layered holographic stereogram for three-dimensional (3D) computer-generated holograms. The hologram is spatially partitioned into multiple holographic elements (hogels) to provide the occlusion effect and motion parallax by use of multiple viewpoint rendering. Each hogel is calculated with inverse Fresnel diffraction by slicing the viewing frustum according to the depth image. The sliced layers can provide accurate depth cues for reconstruction since the geometric information of the 3D scene is faithfully matched. The algorithm is compatible with computer graphics rendering techniques and robust for holograms with different parameters. When the hogel size equals 1mm, the signal-to-noise ratio of the diffraction calculation is above 39dB with a propagation distance longer than 10mm. Numerical simulations and optical experiments have demonstrated that the proposed method can reconstruct quality 3D images with reduced computational load.

Calculation of angular and spectral selectivity for full-parallax holographic stereograms

In this paper, dependencies of the angular and spectral selectivity on the incidence angle of the reference beam in a scheme for obtaining reflection and transmission holograms are obtained and analyzed. It is shown that for obtaining color holographic stereograms a scheme for obtaining transmission holograms is more suitable. While the angular selectivity of reflection and transmission color holograms is the same, the spectral selectivity of the reflection hologram is much higher at all wavelengths of recording. A method and equipment for one-step digital recording of color full-parallax holographic stereograms with rasterless image are developed. Samples of color full-parallax security holographic stereograms with a “flip-flop” effect in the image were obtained. The quality of the reconstructed image verifies high spectral selectivity for this type of holograms.

用波前平面提高全息体视图成像分辨率

用波前平面提高全息体视图成像分辨率

关于全视差全息体视图成像系统光瞳尺寸的研究

关于全视差全息体视图成像系统光瞳尺寸的研究

Bandwidth compression of full parallax holographic stereogram using nonuniform sampling

A novel nonuniform sampling method for bandwidth compression of full parallax holographic stereograms is presented. The configuration of the holographic stereograms and the angular-frequency characteristics of the holographic element on the holographic plane are investigated. The sampling angular-frequencies are chosen for each hogel according to their spectral distribution. Sampling and decompression process for low-pass and band-pass hogels are both introduced. The decompressed hogels can reconstruct their angular spectral distributions accurately, which demonstrates that the nonuniform sampling is a lossless method. Simulation experiments are carried out to verify the proposed method. The results indicate that the method can reduce the number of samples to 46.26% of that of the traditional uniform sampling method, and the decompressed holographic stereogram can reconstruct full parallax images of a 3D object with high quality.

Natural three-dimensional display with high quality of reconstructed images based on dense sampling

For the light-field display based on holographic functional screen, the number of captured images or projectors is a critical factor. It determines the display quality of the reconstructed three-dimensional (3D) image. With the increase of number, the observed image becomes more consecutive. Here, a novel display method is proposed to realize natural 3D scene with high quality of reconstructed images. To increase the sampling density, a long scanning camera is used to capture 500 images in 40° angle. According to eyes’ positions, the stereo pair view images are generated in real time. A set of active partially pixelated masks are used to direct the views to corresponding eyes. The observer can move freely in the viewing area and experiences real 3D scene. The display effect is equivalent to the holographic stereogram.

Fully computed holographic stereogram based algorithm for computer-generated holograms with accurate depth cues

We propose an algorithm based on fully computed holographic stereogram for calculating full-parallax computer-generated holograms (CGHs) with accurate depth cues. The proposed method integrates point source algorithm and holographic stereogram based algorithm to reconstruct the three-dimensional (3D) scenes. Precise accommodation cue and occlusion effect can be created, and computer graphics rendering techniques can be employed in the CGH generation to enhance the image fidelity. Optical experiments have been performed using a spatial light modulator (SLM) and a fabricated high-resolution hologram, the results show that our proposed algorithm can perform quality reconstructions of 3D scenes with arbitrary depth information.

采用视角切片法提高全息体视图再现视差图像分辨率

采用视角切片法提高全息体视图再现视差图像分辨率

Computer-generated phase-modulated full parallax holographic stereograms without conjugate images

A pure phase-modulated computer-generated hologram (CGH) method is presented to generate a full parallax holographic stereogram. The holographic stereogram plane is divided into several two-dimensional holographic elements (hogels). The spectra of the hogels are rendered from multiview full parallax images of three-dimensional (3-D) objects. The phase-modulated hogel is calculated by iterative Fourier transform algorithms to improve diffraction efficiency and eliminate conjugate images. A gray calibration technique is introduced to generate the accurate intensity modulation of pure phase hogels. The holographic stereogram that we proposed is reconstructed by an optical system based on a phase only spatial light modulator. The experimental results demonstrate that our proposed method can successfully reconstruct parallax images of 3-D objects.