摘要
随着虚拟现实技术的日趋成熟,三维光场显示(3D-LFD)逐渐成为研究和产业的焦点,其能够为观众带来无需外部辅助设备的真实立体观看体验。尽管3D-LFD技术展现出广阔的应用前景,但在实际应用中仍面临众多技术难题。视点密度是影响3D-LFD还原度的关键因素。为了提升视点密度,传统方法通常需要增加信息总量,这会使得系统复杂度加大。为此,提出了一种视点密度随观看视角渐变的3D-LFD。该方法在不增加显示面板像素总量的前提下,结合用户的观看习惯和显示深度,为中心观看区域提供所需的密集视点,同时适当降低边缘观看区域的视点数。设计了一种主光线密度渐变的复合透镜阵列(GDLA),能够实现视点密度从视区中心到两侧渐变的分布。结合与视点分布匹配的光场采集与编码方法后,实现了观看视角为100°,视点密度由中心到两侧从2.5个/(°)到1个/(°)渐变的三维光场显示。
Objective As technology progresses,especially with the maturation of virtual reality,three-dimensional(3D)light field display(LFD)emerges as a focal point in both scientific research and industry.This technology enables users to view lifelike 3D scenes without any external devices,offering a unique immersive visual experience.In 3D-LFD,the parameters such as viewing angle,spatial resolution,and viewpoint density are essential in assessing the 3D image quality.Moreover,viewpoint density,indicative of the density in constructing 3D scenes,is a critical metric for evaluating the fidelity of 3D-LFD,directly influencing the realism and accuracy of the reconstructed scenes.Recently,our research group has been dedicated to enhancing viewpoint density and a method based on spatial multiplexing for increasing viewpoint density has been proposed,utilizing 64 projectors to capture information of 3D objects from different angles,and then reproducing the spatial information of these objects through a holographic screen in front of the projectors.This method successfully creates a large-scale,true-color,real-time 3D display system with a viewpoint density of 1.42/(°).However,existing methods often face a common challenge:an increase in the total volume of information.In traditional 3DLFD systems,enhancing viewpoint density typically requires more data transmission and processing,leading to increased system complexity and higher demands on computational and bandwidth resources.Furthermore,traditional 3D display technologies have an inherent contradiction:under a fixed volume of information,there is a trade-off among viewing angle,viewpoint density,and spatial resolution.In other words,simply increasing viewpoint density might reduce the viewing angle or spatial resolution.We hope that our strategy and work will be helpful for the design of large-angle 3D-LFDs and the optimization of viewpoint density.Methods Firstly,the impact of viewpoint density on the image quality of 3D-LFD is analyzed.Black and white striped patterns with identical spatial frequencies are used as test images,and computational simulations are employed to reconstruct them on the same depth plane,determining the central and peripheral viewpoint densities and fitting the relationship curve between viewing angle and viewpoint density.Subsequently,a novel lens is designed to realize the optical path distribution outlined in the relationship curve.Unlike traditional single lenses,the designed lens structure needs to be able to modulate the light emitted from pixels non-uniformly and also meet the distribution requirements of viewpoint density.This design must satisfy three conditions:1)a viewing angle of 100°with a lens period of 1.12 mm;2)the root mean square radius of the optical diffuse spot on the liquid crystal display(LCD)surface should be less than the size of its sub-pixels(62.5μm);3)the main light density distribution of the pixels after modulation by the lens should be consistent with the required viewpoint density curve distribution.Finally,to reconstruct a natural and smooth 3D scene,multi-view information of the scene must be collected and recorded.Using a virtual camera array with off-axis pickup,digital sampling of the direction and intensity of the target virtual 3D object is conducted.By deriving the formula for the propagation of light rays in the 3D-LFD system,the mathematical mapping relationship between the sub-pixels and the designed viewpoints can be calculated.This allows for determining the sub-pixel positions in the synthesized image loaded on the LCD corresponding to the parallax image seen by an observer at a certain position,thereby calculating the arrangement of sub-pixels in the lens unit.Results and Discussions To validate the feasibility of the proposed method,related simulations and optical experiments are conducted.The display system is composed of an LCD panel and the designed compound lens array with gradual main light density(GDLA).The LCD is used to load encoded images containing 3D information,and after modulation by the GDLA,3D images are constructed in space,forming the viewpoint distribution that is dense in the center and gradually sparser towards the edges(Fig.12).With a viewing angle of 100°and an off-screen depth of 300 mm,the simulation results of the 3D light field are compared between traditional and proposed methods(Fig.13).The proposed GDLA,while suppressing aberrations,also achieves a distribution of viewpoint density that is dense in the middle and gradually sparser towards the edges.Therefore,the structural similarity(SSIM)value of the edge viewing area 3D image is lower than that of the traditional viewpoint density uniformity(TVDU).But because GDLA achieves a higher viewpoint density in the central region,the SSIM value of 3D image in the central viewing area is 0.954,which is higher than that of the traditional method.The GDLA optimizes the viewpoint density,effectively enhancing the density in critical areas and improving the quality of 3D images(Fig.14).Further,an experimental optical display system is set up,achieving a high-definition 3D-LFD with a display size of 65 inches(1 inch≈2.54 cm),a viewing angle of 100°,and a display depth of 300 mm with a gradual viewpoint density(Fig.15).This system holds significant potential for applications in medical education and auxiliary medical diagnosis.Conclusions Considering the inherent trade-offs among the number of viewpoints,viewing angle,and depth range,we propose a large-angle 3D-LFD with gradual viewpoint density.The primary objective of this system is to increase the viewing angle and optimize the viewpoint distribution.It is capable of displaying clear 3D images with smooth parallax and correct geometric occlusions across the entire visible range of 100°.The core optical control structure,GDLA,plays a pivotal role.It optimizes the distribution of viewpoints,ensuring a concentration of more effective viewpoint information in the middle of the viewing area.Additionally,to suppress aberrations and further improve image quality,the lens is designed with a specific composite structure.Compared with traditional 3D displays,this system is characterized by a dense distribution of viewpoint information in the middle of the viewing area and a gradually decreasing viewpoint density towards the sides.This design not only significantly enhances the clear maximum offscreen depth in the middle of the viewing area but also increases the viewing angle of the system.In experimental verification,the high-performance 3D-LDF system is obtained with the viewing angle of 100°.The 3D scene captured at a 0°viewing angle has a clear focus depth of up to 300 mm.From a commercial perspective,this prototype has the potential for mass production and exhibits good stability in most situations.We firmly believe that this 3D-LFD system has a broad application prospect in the future,especially in fields such as aviation simulation,industrial design,architectural design,and multimedia educational presentations.
作者
张庭毓
高鑫
于迅博
温旭东
何金泓
张钊赫
颜玢玢
桑新柱
Zhang Tingyu;Gao Xin;Yu Xunbo;Wen Xudong;He Jinhong;Zhang Zhaohe;Yan Binbin;Sang Xinzhu(School of Electronic Engineering,Beijing University of Posts and Telecommunications,Beijing 100876,China)
出处
《中国激光》
北大核心
2025年第2期233-243,共11页
Chinese Journal of Lasers
基金
国家自然科学基金(62175015,61905019,62075016)。
关键词
几何光学
光场
主光线
视点密度
像差
geometric optics
light field
main light
viewpoint density
aberration
