Visual perception of Fourier rainbow holographic display

The rainbow hologram provides views of reconstruction with rainbow color within a large viewing zone. In our recent paper, a Fourier rainbow holographic display using diffraction grating and a white‐light LED source was introduced. In this technique, the rainbow effect is realized by the dispersion of white‐light source on diffraction grating, while the slit is implemented numerically by reducing the demands of the space‐bandwidth product of the display. This paper presents a novel analysis on the visual perception of the Fourier rainbow holographic display using Wigner distribution. The view‐dependent appearance of the image, including multispectral field of view and viewing zone, is investigated considering the observer and the display parameters. The resolution of the holographic view is also investigated. For this, a new quantitative assessment for image blur is introduced using Wigner distribution analysis. The analysis is supported with numerical simulations and experimentally captured optical reconstructions for the holograms of the computer model and real object generated with different slit size, reconstruction distance, and different observation conditions.     

Distortion Compensation of Reconstructed Hologram Image in Digital Holographic Display Based on Viewing Window

A holographic display based on a viewing window enables the converging of a reconstruction wave into a viewing window by means of an optical system. Accordingly, a user can observe a reconstructed hologram image, even with a small diffraction angle. It is very difficult to manufacture an optical system with no aberrations; thus, it is inevitable that a certain amount of wave aberrations will exist. A viewing‐window‐based holographic display, therefore, always includes distortions in an image reconstructed from a hologram pattern. Compensating the distortions of a reconstructed image is a very important technical issue because it can dramatically improve the performance when reconstructing a digital three‐dimensional content image from a hologram pattern. We therefore propose a method for suppressing image distortion by measuring and compensating the wave aberration calculated from a Zernike polynomial, which can represent arbitrary wave aberrations. Through our experimental configuration using only numerical calculations, our proposed method decreased the reconstructed image distortion by more than 28%.     

全息立体显示视角增强方法研究

介绍了全息立体成像的工作原理,通过与其他立体成像技术比较,说明全息立体显示能形成真三维再现像,具有可以提供全部物理景深的优势。从改善全息立体像观察视角出发,阐述了4种增强视角的方法,介绍了这些方法的原理,并对这些方法做了比较分析。     

Look, no glasses [3D display system]

Three-dimensional display systems generally require the user to wear special glasses. The author describes a research programme-aimed at providing a high-quality spectacle-free look into the third dimension. It is based on the Twin-LCD display concept developed by the Imaging Technology Department at Sharp Laboratories of Europe. The author describes how the Twin-LCD system works. It is based on two thin-film transistor (TFT) LCDs whose images are superimposed by a half-mirrored beam-combiner. The input optical arrangement creates two laterally displaced images at the nominal observer position. If an observer places an eye in a window, then an image from one of the LCDs can be seen. Each LCD panel displays one of the stereo pair images and so the observer sees the 3D image without the need for any special glasses     

计算全息三维实时显示的研究进展

计算全息三维实时显示是目前国际光学领域的研究热点之一。综述了计算全息三维显示技术研究的现状。从计算全息三维显示的原理出发,简介了全息图计算的复杂度、再现像尺寸与视场角等参数的关系以及影响再现图像质量的主要因素。分析了各种获得高质量、大图像和宽视场角的全息三维实时显示技术方案,指出了其中存在的关键问题,并对全息三维实时显示的未来进行了展望。     

高分辨率多视点动态全息3D显示

提出了一种高分辨率多视点动态全息3D显示方法,观看视点位置变化时,观看者能够看到连续变化的3D效果。在进行全息图计算时,首先根据针孔阵列投影模型,渲染3D动画中每一帧3D模型的光场图像序列;然后从已渲染的多组光场图像序列中抽取对应视角信息的光场图像进行融合,得到融合后的动态光场图像序列;在进行全息图编码时,以动态光场图像序列中的一帧图像作为物光振幅,以来自于针孔的发散球面波的相位作为物光相位,引入平面参考光进行编码,得到一个单元全息图。由于每个单元全息图的计算是相互独立的,因此在计算过程中使用并行加速计算,实现了尺寸为32 mm×32 mm、分辨率为100000 pixel×100000 pixel的高分辨率全息图,其光场图像融合和全息编码的时间仅需27 min。光学再现结果证明了该方法的可行性。所提出的高分辨率多视点动态全息3D显示方法在全息包装和3D广告等领域具有广泛的应用前景。     

An Updatable Holographic Display for 3D Visualization

Among the various methods to produce three-dimensional (3D) images, holography occupies a special niche. Indeed, holograms provide highly realistic 3D images with a large viewing angle capability without the need for special eyewear. Such characteristics make them valuable tools for a wide range of applications such as medical, industrial, military, and entertainment imaging. To be suitable for an updatable holographic display, a material needs to have a high diffraction efficiency, fast writing time, hours of image persistence, capability for rapid erasure, and the potential for large display area—a combination of properties that has not been realized before.      

计算全息图的快速生成技术

传统的2D显示设备只能提供平面图像显示,无法使观看者获得身临其境的观看体验。为了使人们更真实地认识客观世界,显示技术从2D向3D发展已成为了一种趋势。全息3D显示能为人眼提供3D物体全部的深度信息,因而被视作3D显示中最具发展潜力的技术之一。然而,3D物体的全息图计算量巨大,导致计算速度缓慢。为了能够实现实时动态的全息3D显示,计算全息图的快速生成技术受到了很多研究者的关注。本文首先基于标量衍射理论介绍了全息3D显示技术的基本原理,然后根据3D物体的数学描述形式分别介绍了基于点元法、面元法和分层法的三类计算全息图的快速生成方法,并概述了硬件加速法和深度学习法在全息图快速计算中的应用,最后对各类方法进行了总结和展望。      

嵌入式设备立体图像显示技术研究

便携式裸眼3D设备屏幕规格众多,在基于嵌入式系统多规格小尺寸液晶屏的便携式设备上实现立体显示效果,需在嵌入式系统支持下对立体图像进行缩放和插值处理,满足左右眼图像的准确观看。文章对安卓操作系统中3D图像处理进行研究,应用安卓提供的函数获取屏幕物理像素和图像实际分辨率,并根据二者的参数使用失真度小的线性缩放技术和列插值融合方法完成左右格式3D视频和图像的立体播放。在多规格普通2D液晶屏的便携式设备上进行了验证得到正确显示。     

Reducing speckle artifacts in digital holography through programmable filtration

We propose a speckle reduction technique in electronic holographic display systems, where digital micro‐mirror array devices are used as spatial light modulators. By adopting a programmable filtration in a general 4‐f optic configuration, it is shown that the signal spectrum components in the frequency domain of a viewing‐window‐based holographic display system can be selectively filtered. Compared to the widely utilized single‐sideband filtration techniques in electronic holographic display systems, our proposed programmable filtration can be utilized to effectively reduce the speckles in the reconstruction of point‐cloud‐based computer‐generated holograms. Experimental results are presented to verify our proposed concept.     

裸眼立体显示液晶屏的光学结构及设计

裸眼立体显示液晶屏以液晶像素作为立体视图的载体，使用特殊的光学元件改变显示器和人眼的成像系统来获取立体视觉效果。狭缝背光照明的裸眼立体显示液晶屏的光学结构包括狭缝照明板、液晶盒及背光组件。设计了可以完成面光源照明和线光源照明相互转换的可控光栅，研究了一种行之有效的立体显示液晶屏的装配方法——动态装配法，利用装配组件的工作特性产生莫尔条纹，完成立体显示液晶屏的精密装配。研制的裸眼立体显示液晶屏可以方便地在2D和3D显示模式之间转换。     

裸眼立体显示器系统结构研究

裸眼立体显示器是不需要佩带助视眼镜的立体显示设备．它使用特殊的光学元件改变显示器和人眼的成像系统。文章讨论基于狭缝背光照明的液晶立体显示器的原理及其组成结构。利用通用的TFT LCD液晶显示器作为图像显示部件，通过科学设计符合立体显示照明原理的照明板部件．与液晶盒精密装配在一起组成裸眼立体显示屏，配合电路系统和显示软件完成裸眼立体显示器的系统结构设计。     

Stereo imaging quality evaluation in a full-color three-dimensional display system

To evaluate the light field display system with a liquid crystal display (LCD) and a holographic functional screen (HFS), the voxel theory based on the ray tracing is used. By analyzing the voxels defined by the cases of corresponding pixels overlapping completely and partially in the image space, the resolution characteristics of the system are discussed. The theoretical model is verified in the reconstruction experiment of a resolution target and compared with the calculation result of the presented system. Finally, we give an optimization method for the display image quality.     

平行式红外双目立体系统各参数合理效益取值

为解决当前夜间辅助驾驶仪平面显示的弊端以及在合理效益下获得丰富的立体层次感,文中从平行式红外双目夜视系统出发分析对比了红外双目系统和人眼立体感知的最小可分辨距离,结合人眼立体感知机理以及从影像分层角度分析观看立体影像时兼具宽阔的视场张角、丰富的立体层次感时所满足的条件,对红外双目立体系统合理效益条件下的各参数关系进行推导。最后根据推导结果,计算分析3种不同规格显示屏所对应的水平像素数的合理效益取值,并选择5组不同水平像素数的红外立体图像对进行实验验证。结果表明:根据推导结果搭建的红外夜视系统在让观察者获得较大视场张角的同时还兼顾效益。     

基于FFS架构实现宽窄视角切换

基于公共场合隐私保护的需求,宽窄视角可切换的液晶显示技术有着迫切的市场需求。现有宽窄视角切换技术不但增加了显示装置的厚度与成本,而且降低了原本宽视角模式下的显示效果。本文研究了一种基于负性液晶FFS模式的宽窄视角切换技术,它通过在彩色滤光片一侧形成高预倾角配向(40°～60°),在同侧第三电极施加弱电场时,液晶分子离轴方向具有较大相位延迟,形成大视角观看时的暗态漏光与对比度下降,实现窄视角显示模式。而同侧第三电极施加强垂直电场时,大的预倾角液晶分子因负介电各项异性使得倾角降低,可减少暗态漏光和提升对比度,实现宽视角显示模式。验证结果表明:宽视角模式时,其上下左右视角均可达到85°以上;而窄视角模式时,左右视角仅为40°,且具有较好的对称性。本技术结构简单,驱动灵活,在防窥显示领域具有很好的应用前景。     

基于渐变线光源的高亮度集成成像3D显示

为了解决观看视角与亮度的相互制约关系,设计了一种基于渐变线光源的集成成像3D显示器,通过设置渐变线光源中每列线光源的宽度,优化微图像阵列中每列图像元的成像光路,建立了3D成像模型,通过几何光学推导了观看视角以及亮度的计算公式;研制了基于渐变线光源的集成成像3D显示实验装置,通过实验验证了可以在保持观看视角的前提下将3D图像的亮度提高为传统集成成像3D显示的4.5倍。     

计算全息三维显示的数据压缩编码技术

全息三维显示能够重建真实场景的光场,提供全部的深度感,成为真三维显示的最佳解决方案之一。计算全息三维显示只需要知道物光波的数学描述,可以灵活地控制波前,显示出虚拟的三维物体。但是,巨大的数据量和计算量阻碍了计算全息三维显示的实用化。文中提出了计算全息三维显示中多个环节的数据压缩编码技术,包括三维物体的稀疏采样、全息三维视频压缩编码的优选和参数优化、全息图分形压缩算法,有效地压缩了数据量,并利用GPU的并行运算能力实现了全息图的快速计算。     

3-D Mobile Display Based on MoirÉ-Free Dual Directional Backlight and Driving Scheme for Image Crosstalk Reduction

A novel micro-grooved structure of lightguides and a sequential driving scheme of light sources were demonstrated in achieving comparable image qualities of 3-D displays to that of 2-D displays. The modified distribution of micro-grooves not only locates viewing cones for respective eyes but also suppresses the moire pattern, which might occur when a periodic micro-grooved structure and a color filter are superimposed. The configuration of lightguides for a 1.8-in liquid crystal display (LCD) panel can yield acceptable 3-D perceptions at the viewing distance of 7-23 cm and the brightness uniformity of greater than 83%. In addition, the driving scheme of light sources in synchronization with parallax images can project images to the viewer's respective eyes sequentially. With the refreshing sub-frame rate of 190 Hz and double displaying parallax images, the image crosstalk of 3-D perceptions can be efficiently reduced for an LC response time of 7.0 ms.     

透反液晶显示器

透反液晶显示器兼有透射式和反射式显示器的优点,功耗低,环境光适应性强,是目前比较活跃的平板显示技术研究方向,文章介绍了金属开孔半透层透反液晶显示器、双盒厚ECB透反液晶显示器、采用图像增强反射器的透反液晶显示器、双伽玛驱动方法透反液晶显示器、双液晶模式透反液晶显示器和空间混色与时间混色结合的透反液晶显示器等,介绍了它们各自的优点和缺点。目前色彩平衡、图像亮度、视角、生产成本等是透反液晶显示器研究需要解决的主要问题。     

基于FPGA的裸眼3D图像显示系统的设计与实现

裸眼3D技术是无需佩戴任何助视设备即可观看到立体影像的新型光电显示技术。针对裸眼3D像素重配关键技术的研究,设计一种基于FPGA的裸眼3D图像显示系统,根据裸眼3D亚屏幕分区特点,使用硬件描述语言设计从SD卡中读取左右格式立体对图像数据、像素重配及裸眼3D LCD显示驱动等逻辑代码,完成左、右眼视图数据分割,并在裸眼3D LCD亚屏幕上进行像素重配。系统调试运行结果表明3D图像数据亚屏幕重配的硬件逻辑算法是正确的。