大规模立体显示墙系统的构建

从硬件选择、几何校正、边缘融合、颜色校正和软件环境等5方面系统地研究了构建大规模立体显示墙系统的关键技术.采用并行绘制技术和基于计算机视觉的自动校正,由Linux集群驱动多台普通投影仪拼接成一个统一的高分辨率、大规模的被动立体显示系统.     

监视器产品专题——大屏幕拼接墙 小图像拼出大世界

大屏幕投影拼接墙是由多台投影机、多个投影屏及图像控制器构成的大屏幕显示系统，一般用于一个画面的超大屏幕显示或特技显示以及多个画面的多窗口显示。每个投影单元只显示整个图像的一个部分，全部投影单元加在一起就构成了一幅完整的大画面，现在让我们一起来走近大屏幕拼接墙，体验小图像是如何拼接出了一个大世界。[编者按]     

多投影仪无缝拼接显示中的颜色校正技术比较研究

基于多投影仪的无缝拼接显示是对图形、图像、视频等进行大范围、高分辨率显示的一种有效实现方式。多投影仪无缝拼接显示的一个关键是解决颜色失调问题,而现有的颜色失调原因的分析结果可归纳为投影仪输出颜色的变化特性和投影屏幕与投影环境的影响两个方面。近年来,为解决该问题已提出了多种颜色校正技术,而根据解决颜色失调问题的原理和实现方法的不同,这些技术可分为基于边缘融合的校正技术、基于单一投影光源的校正技术和基于颜色/亮度输出匹配的校正技术3类,并对这3类技术在无缝拼接显示效果、可维护性和可扩展性等方面的优缺点进行了较详细分析,该领域下一步的研究将会朝着兼顾不同投影机类型、不同形状和反射特性的投影屏幕和考虑运动中观察者的实时颜色校正方向发展。     

多投影仪Alpha融合的后期Gamma校正

大屏幕投影的应用中往往使用多台投影仪拼接,投影图像之间的融合程度,历来是评价拼接效果的重要标准.在分析传统Alpha融合拼接技术基础上,对投影仪投射阶段亮度非线性变化的校正进行了分析,并对Gamma校正方法在投影仪拼接中的使用作了探索.     

面向多投影显示墙的画面校正技术

多投影显示墙是缓解对超高分辨率显示屏幕不断增长的需求与单台显示设备分辨率有限性之间矛盾的有效手段,但目前还缺乏规范化的模式和方法以支持高精度、高可靠性的画面校正.提出一种颜色校正方案以解决上述问题.首先介绍多投影显示墙画面校正中存在的主要问题和现有的解决方法;在此基础上,给出了多投影显示墙的画面校正流程和几何校正方法;然后讨论了多投影显示墙画面校正结果的评价标准,提出了投影仪的广义颜色模型和基于搜索技术的视觉无缝方法.该方案使用数码相机实现了高精度的视觉无缝画面校正,从而提高了构造多投影显示墙的效率并降低了维护成本.校正结果在多种类型的投影墙系统中得到验证和应用,对指导多投影显示墙的搭建和维护具有较高的理论与实践价值.     

一种实用的多投影仪显示墙色彩校正方法

针对多投影仪显示墙系统色彩不均匀性的问题,提出一种快速、实用的独立于几何校正结果的色彩校正方法。该方法利用细分网格变形技术将现有针对平面投影屏幕的色彩校正方法推广到适应任意光滑曲面投影屏幕,同时利用加权最小二乘曲线拟合思想降低色彩测量数据量。实际进行色彩校正时,采用可编程图形处理单元(GPU)的像素着色器对投影图像的每个像素进行实时校正计算,并在实际多投影仪显示墙系统中验证了方法的有效性。     

一种基于视频捕获的多投影显示系统

随着科学技术的高速发展以及信息量的急速膨胀,具有多个输出画面的多通道计算机系统得到了广泛应用。多显示器/拼接单元系统无法生成大尺寸高分辨率的无缝画面,多投影显示系统可克服这类系统的不足。提出一种基于视频捕获的多投影显示系统,它将多通道的画面显示与画面生成相分离,从而避免显示系统对画面生成系统的影响。该系统针对VGA模拟视频信号输入,给出基于三维查找表的颜色校正技术;针对非参数化成像模型的投影仪,给出多投影系统颜色校正的三阶段模型及其求解方法;针对工程实际,设计了基于自由曲面变形的交互式网格编辑工具进行多投影系统的几何校正。实验结果表明本系统及其关键技术切实有效,适用于构建投影数量中等规模的显示系统。     

多投影显示墙的全局颜色校正

画面校正是实现无缝多投影显示墙系统的关键环节,针对此,提出了一种基于参数估计和统计思想的全局颜色校正方法.首先根据采样点的粗略分布建立亮度响应曲线的经验参数模型,并通过采样数据来确定该曲线的参数;然后依据亮度响应曲线,引入统计算法来调整投影仪输入,从而实现视觉上无缝的多投影拼接显示.最后在2×2和3×5多投影显示墙上进行了该算法的可行性和效果测试.结果表明,该算法比现有颜色校正算法的画面质量更好,亮度更高.     

多投影显示墙画面校正技术综述

由投影仪阵列组成的多投影显示墙是目前实现高性能、低成本大型绘制平台的首选解决方案。为了保证多投影显示墙画面的完整性,需要通过一定的方法来预补偿由于投影仪特性差异造成的画面几何扭曲与色彩不均衡。结合实际研究工作,从多投影显示墙存在的问题、几何变换矩阵求取、颜色模型估计和全局颜色校正等几个方面对多投影显示墙画面校正的研究情况进行综述, 讨论了存在的问题和进一步的发展方向。     

多投影显示墙的几何校正

随着大屏幕拼接技术的日益发展,多投影显示墙的几何校正成为备受关注的研究课题．在分析多投影显示墙几何校正中关键技术的基础上,提出了一种健壮的校正图案,并通过处理数码相机拍摄的该图案信息,提出一种高精度的平面幕几何校正算法;然后根据双目视觉的立体显示原理,将上述平面幕校正方案推广到立体平面幕系统,给出一种新颖的立体平面幕几何校正方法．     

Building and using a scalable display wall system

Princeton's scalable display wall project explores building and using a large-format display with commodity components. The prototype system has been operational since March 1998. Our goal is to construct a collaborative space that fully exploits a large-format display system with immersive sound and natural user interfaces. Our prototype system is built with low-cost commodity components: a cluster of PCs, PC graphics accelerators, consumer video and sound equipment, and portable presentation projectors. This approach has the advantages of low cost and of tracking technology well, as high-volume commodity components typically have better price-performance ratios and improve at faster rates than special-purpose hardware. We report our early experiences in building and using the display wall system. In particular, we describe our approach to research challenges in several specific research areas, including seamless tiling, parallel rendering, parallel data visualization, parallel MPEG decoding, layered multiresolution video input, multichannel immersive sound, user interfaces, application tools, and content creation     

一种高度并行的多任务并行绘制系统结构

随着计算机图形技术的实用化，需要构造更逼真、更精细的三维复杂场景，其数据规模日益膨胀，加上对场景的实时交互的要求也越来越高，人们对多屏幕高分辨率显示的需求与日俱增，迫切需要一种针对大规模复杂场景的多任务并行图形绘制系统。本文介绍了一种适用于大规模复杂场景的高度并行的多任务多屏幕并行图形绘制系统的体系结构，支持图形任务的并行化处理和多屏幕显示。该系统结构将几何计算任务与图形绘制任务相分离，分剐进行并行化处理，在计算节点按绘制对象类型对任务进行分类以便于并行计算和任务分配，在绘制节点对各个小块屏幕图形进行并行合成。实验测试结果表明，该系统结构对多任务具有较好的并行效率和可扩展性，能够充分利用系统的并行计算资源，达到较好的绘制效果。     

Registration techniques for using imperfect and partially calibrated devices in planar multi-projector displays

Multi-projector displays today are automatically registered, both geometrically and photometrically, using cameras. Existing registration techniques assume pre-calibrated projectors and cameras that are devoid of imperfections such as lens distortion. In practice, however, these devices are usually imperfect and uncalibrated. Registration of each of these devices is often more challenging than the multi-projector display registration itself. To make tiled projection-based displays accessible to a layman user we should allow the use of uncalibrated inexpensive devices that are prone to imperfections. In this paper, we make two important advances in this direction. First, we present a new geometric registration technique that can achieve geometric alignment {\em in the presence of severe projector lens distortion} using a relatively inexpensive low-resolution camera. This is achieved via a closed-form model that relates the projectors to cameras, in planar multi-projector displays, using rational Bezier patches. This enables us to geometrically calibrate a 3000 x 2500 resolution planar multi-projector display made of 3 x 3 array of nine severely distorted projectors using a low resolution (640 x 480) VGA camera. Second, we present a photometric self-calibration technique for a projector-camera pair. This allows us to photometrically calibrate the same display made of nine projectors using a photometrically uncalibrated camera. To the best of our knowledge, this is the first work that allows geometrically imperfect projectors and photometrically uncalibrated cameras in calibrating multi-projector displays.     

Automatic Registration of Multi‐Projector Domes Using a Single Uncalibrated Camera

In this paper we present a novel technique for easily calibrating multiple casually aligned projectors on spherical domes using a single uncalibrated camera. Using the prior knowledge of the display surface being a dome, we can estimate the camera intrinsic and extrinsic parameters and the projector to display surface correspondences automatically using a set of images. These images include the image of the dome itself and a projected pattern from each projector. Using these correspondences we can register images from the multiple projectors on the dome. Further, we can register displays which are not entirely visible in a single camera view using multiple pan and tilted views of an uncalibrated camera making our method suitable for displays of different size and resolution. We can register images from any arbitrary viewpoint making it appropriate for a single head‐tracked user in a 3D visualization system. Also, we can use several cartographic mapping techniques to register images in a manner that is appropriate for multi‐user visualization. Domes are known to produce a tremendous sense of immersion and presence in visualization systems. Yet, till date, there exists no easy way to register multiple projectors on a dome to create a high‐resolution realistic visualizations. To the best of our knowledge, this is the first method that can achieve accurate geometric registration of multiple projectors on a dome simply and automatically using a single uncalibrated camera.     

GPU rendering for tiled multi-projector autostereoscopic display based on chromium

In this paper, a GPU-based high-resolution multiview rendering approach (HRMVRA) is presented and incorporated into Chromium, and then a tiled multi-projector autostereoscopic display system (TMPADS) based on HRMVRA is constructed to provide an immersing 3D perception and a compelling sense of presence without the need of glasses for viewers. HRMVRA renders the multiview images in real time in only one pass, though the traditional multiview rendering approaches based on Chromium render the multiviews in multiple passes. The hardware of the autostereoscopic display system consists of a front-projection screen that covers an area of 360×160 square centimeters, twenty four projectors and thirteen computers connected with the gigabit Ethernet. TMPADS is well scalable since both the resolution and the number of the rendered views are configurable. It is shown by the experiments that HRMVRA has more than five times performance of the traditional high-resolution multiview parallax rendering based on Chromium. Most existing single-view OpenGL applications (e.g., some games like Quake III) can run directly on TMPADS without any source-code modification or re-compiling.     

协同分布式图形硬件的混合并行体绘制

由于一般的共享存储并行机缺乏图形硬件,其上产生的3维科学计算数据,无法采用硬件加速的并行体绘制来就地进行数据可视化。为此基于本地并行机和分布式图形工作站,给出了一种混合并行绘制模型。该模型的工作原理是先将源数据存留在并行机,然后通过并行机的多处理器发布远程绘制命令流,进而通过操控工作站的图形硬件完成绘制;后期图像合成在并行机上执行,以发挥共享存储通信优势。通过负载平衡优化,并行绘制流水线有效实现了绘制、合成与显示的重叠。实验结果显示,该方法能以1024×1024图像分辨率,交互绘制并行机上的大规模数据场。     

一种基于半边折叠的多分辨率模型构造方法*

虚拟现实的真实感限时图形生成中加速技术十分关键, 细节层次模型(LOD)在实时绘制复杂场景中得到了广泛应用。提出了一种基于半边折叠的多分辨率模型构造方法,该算法能够快速简单并有效地减少模型的多边形数,同时将简化记录紧致地存储在隐含着多分辨率模型的单分辨率模型中,减少了存储空间,并能实现快速地提取及显示。     

数据分布型sort-first并行图形绘制系统的研究与实现

sort-first体系结构常用来构建高性能并行图形绘制系统，基于immediate-mode的数据集中型Sort-first系统，对网络带宽高度依赖，网络带宽和归属计算易成为系统瓶颈,提出了一个基于retain-mode的数据分布型并行绘制系统，工作原理是将几何数据分布于绘制结点，并利用帧间相似性动态调整绘制结点上的数据分布以适应视角的改变，有效地降低了数据分布所需的传输开销，系统利用Cell结构来控制并行粒度，实验结果显示能以相对较低的并行开销实现高分辨率显示和并行加速。