基于图象的绘制中的纹理编辑

现有的基于图象的绘制 (IBR)系统中 ,只能提供新视点的图象 ,并不具有对场景编辑的功能 .由于 IBR系统的场景模型不同于传统图形学 ,难于直接应用传统图形学中已有的方法进行编辑 .为此提出了一种修改 IBR场景中物体的表面纹理的方法 ,这种方法通过在原始的参考图象上指出编辑区域并给出纹理定义 ,修改各个视点上的纹理 .这种方法不限制编辑区域的形状、尺寸 ,并且考虑了亮度信息 ,适应了环境光照 ,使新纹理与原有场景更好地融合在一起 .实验证明 ,场景的复杂程度并不影响本方法的效果 ,但是由于本方法不能得到场景物体准确的三维数学模型 ,无法用现有图形引擎进行绘制 ,因此无法实现硬件加速 ,不适用于过大的场景     

计算机群体动画中的真实感行为综述

近年来,计算机群体动画在虚拟现实、计算机游戏、在线教育、娱乐和模拟训练等多个领域得到广泛深入的应用。目前群体动画技术中两个关键的研究领域是：1)研究并建立大规模群体运动的仿真模型,即如何实现对群体运动的真实感行为模拟;2）研究群体动画中高质量的可视化效果,即如何将大规模群体运动以三维的方式逼真地展现到虚拟场景中。现在这两个领域的技术研究也得到了一些很好的研究成果。定义了群体运动的概念,并给出了群体动画的引擎框架;对群体运动的真实感行为从其发展历程、模型和关键算法等方面进行了归纳与分析;最后讨论了群体动画真实感行为的发展趋势。     

Deformable models for laparoscopic surgery simulation

This paper introduces a method for handling deformation in interactive, real time computer graphics simulations which involve deformable objects and require a high degree of visual realism. Our proposal, the virtual structure, is a “divide and conquer” approach, which combines a novel physical model with a geometric modelling utilizes the theory of elasticity and Newtonian mechanics, applied by a numerical method, the finite element method. Using different levels of structural resolution for global and local or collision with other objects. The geometric modelling uses the physical structure as a set of control points and produces a fine polygonal mesh generated by a B-spline surface. In order to demonstrate the method we have modelled the gallbladder as a spherical membrane containing liquid, in an interactive simulated environment for laporoscopic cholecystectomy.     

Detail-driven digital hologram generation

Digital holography is a technology with a potential to provide realistic 3D images. However, generation of digital holograms is a computationally demanding task. Thus, the performance is a major concern. We propose a new method that reduces spatial resolution in order to accelerate hologram generation. It employs the propagation between parallel planes for efficient optical field values evaluation and a computer graphics approach for approximating visibility. Our results show that the proposed reduction has only a minimal impact on the visual quality, while the formal computational complexity confirms performance improvement.     

Elimination of artifacts due to occlusion and discretization problems in image space blurring techniques

Traditional computer graphics methods render images that appear sharp at all depths. Adding blur can add realism to a scene, provide a sense of scale, and draw a viewer’s attention to a particular region of a scene. Our image-based blur algorithm needs to distinguish whether a portion of an image is either from a single object or is part of more than one object. This motivates two approaches to identify objects after an image has been rendered. We illustrate how these techniques can be used in conjunction with our image space method to add blur to a scene.     

Visual creation of inhabited 3D environments

The creation of virtual reality applications and 3D environments is a complex task that requires good programming skills and expertise in computer graphics and many other disciplines. The complexity increases when we want to include complex entities such as virtual characters and animate them. In this paper we present a system that assists in the tasks of setting up a 3D scene and configuring several parameters affecting the behavior of virtual entities like objects and autonomous virtual humans. Our application is based on a visual programming paradigm, supported by a semantic representation, an ontology for virtual environments. The ontology allows us to store and organize the components of a 3D scene, together with the knowledge associated with them. It is also used to expose functionalities in the given 3D engine. Based on a formal representation of its components, the proposed architecture provides a scalable VR system. Using this system, non-experts can set up interactive scenarios with minimum effort; no programming skills or advanced knowledge is required.     

A Scalable Approach to Interactive Global Illumination

The addition of global illumination can dramatically increase the realism achievable when rendering virtual environments.In particular with interactive applications we expect the environment to reflect changes in the scenedue to global lighting effects instead of it being just a static backdrop. However, a sufficiently fast and accuratecomputation of global illumination at interactive rates has been difficult even with recent approaches based onrealtime ray tracing. In this paper we present a highly scalable approach to interactive global illumination. It fully recomputes a high‐qualitysolution for each frame and thus offers immediate feedback even for dynamic scenes, achieving more than20 fps for simple scenes. Compared to previous systems we increased the raw performance by a factor of up toeight and removed the bottlenecks that were limiting scalability. The system now scales linearly in quality andavailable computing resources, tested with up to 48 CPUs in a commodity PC‐cluster. Due to its logarithmicscaling property with respect to scene complexity it even supports lighting simulation in complex scenes with morethan 50 million triangles. This scalability allows applications to perform flexible performance trade‐offs. We alsoargue that the realism achievable through interactive global illumination will make it a standard feature of future3D graphics systems once the required computing resources are readily available.     

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。     

A realistic lighting model for computer animators

Because of the problems inherent in modeling the physics of light transmission, all lighting models used in computer graphics are approximations. Each model provides a different balance between image realism, model complexity, and runtime efficiency. A model that balances these factors and is easier than its predecessors for inexperienced animators to use is presented     

A computer graphics course for the two cultures

The subject of computer graphics offers a special educational opportunity for bringing together students from the two cultures of the arts/humanities and of the sciences/technologies. The author describes a computer graphics course with this approach. Several important problems arise because of students' varying backgrounds in programming and their expectations, the lack of suitable texts, and the lack of suitably-oriented computer graphics centers. The course schedule is composed of lectures, discussions of readings, and workshops in a computer graphics facility. The hardware and software basis of the course is flexible. Students complete an assigned initial project, a final project of their choice, and are responsible for documenting their project visually and verbally before the close of the semester. Student performance and evaluation of the course suggest this cross-cultural approach is a valid, worthwhile experiment to introduce the structure and significance of computer graphics imagery and computer graphics display systems.     

Volume graphics

Volume graphics, which employs a volume buffer of voxels for 3D scene representation, is discussed. Volume graphics offers advantages over surface graphics: it is viewpoint independent, insensitive to scene and object complexity, and suitable for the representation of sampled and simulated data sets. Moreover, geometric objects can be mixed with these data sets. Volume graphics supports the visualization of internal structures and lends itself to the realization of block operations, constructive solid geometry modeling, irregular voxel sizes, and hierarchical representation. The problems associated with the volume buffer representation (such as discreteness, memory size, processing time, and loss of geometric representation) are discussed     

Proposals for creative uses of computer graphics in architectural design

Computer graphics are used by architects mainly for presentation purposes. However, the rapid pace of the development of computer technology enables more creative applications. This research proposes the use of dynamically simulated computer graphics as an evaluation tool for architectural design. Since buildings are living entities, whole life cycles of buildings should be dynamically simulated in highly visualised virtual environments to evaluate the future performance of prospective designs. Two areas that seem especially promising for near future (evaluation of user-building interaction and visualisation of environmental factors) are mentioned and some proposals are presented for the future use of dynamic simulations in virtual environments.     

Accelerating molecular dynamics simulations using Graphics Processing Units with CUDA

Molecular dynamics is an important computational tool to simulate and understand biochemical processes at the atomic level. However, accurate simulation of processes such as protein folding requires a large number of both atoms and time steps. This in turn leads to huge runtime requirements. Hence, finding fast solutions is of highest importance to research. In this paper we present a new approach to accelerate molecular dynamics simulations with inexpensive commodity graphics hardware. To derive an efficient mapping onto this type of computer architecture, we have used the new Compute Unified Device Architecture programming interface to implement a new parallel algorithm. Our experimental results show that the graphics card based approach allows speedups of up to factor nineteen compared to the corresponding sequential implementation.     

Dynamic load balancing for parallel polygon rendering

Using parallel processing for visualization speeds up computer graphics rendering of complex data sets. A parallel algorithm designed for polygon scan conversion and rendering is presented which supports fast rendering of highly complex data sets using advanced lighting models. Dedicated graphics rendering engines do not necessarily suit such data sets, although they can support real-time update of moderately complex scenes using simple lighting. Advantages to using a software-based approach include the feasibility of adding special rendering features to the program and the capability of integrating a parallel scientific application with a parallel graphics renderer. A new work decomposition strategy presented, called task adaptive, is based on dynamically partitioning the amount of computational work left at a given time. The algorithm uses a heuristic for dynamic task decomposition in which image space tasks are partitioned without requiring interruption of the partitioned processor. A sophisticated memory referencing strategy lets local memory access graphics data during rendering. This permits implementation of the algorithm on a distributed memory multiprocessor. An in-depth analysis of the overhead costs accompanying parallel processing shows where performance is adequate or could be improved     

1001 Acquisition viewpoints: efficient and versatile view-dependent modeling of real-world scenes

Modeling is a severe bottleneck for computer graphics applications. Manual modeling is time consuming and fails to capture the complexity of real-world scenes. Automated modeling based on acquiring color and depth data is a promising alternative. However, the usual approach of densely sampling the scene from a few viewpoints suffers from long acquisition times, high data redundancy, and lack of robustness, leading to incomplete models. We propose automated modeling based on sampling the scene sparsely from a dense set of viewpoints. We show that the sparse data quickly accumulates to generate models with good scene coverage. The sparse depth is acquired efficiently and robustly, which enables an interactive, operator-in-the-loop acquisition pipeline. We describe a modeling system that implements this approach. The system acquires scenes with complex geometry and complex reflective properties from thousands of viewpoints in minutes. The resulting models are compact and support photorealistic rendering at interactive rates.     

dPVS: an occlusion culling system for massive dynamic environments

A platform-independent occlusion culling library for dynamic environments, dPVS, can benefit such applications as CAD and modeling tools, time-varying simulations, and computer games. Visibility optimization is currently the most effective technique for improving rendering performance in complex 3D environments. The primary reason for this is that during each frame the pixel processing subsystem needs to determine the visibility of each pixel individually. Currently, rendering performance in larger scenes is input sensitive, and most of the processing time is wasted on rendering geometry not visible in the final image. Here we concentrate on real-time visualization using mainstream graphics hardware that has a z-buffer as a de facto standard for hidden surface removal. In an ideal system only the complexity of the geometry actually visible on the screen would significantly impact rendering time - 3D application performance should be output sensitive.     

Simulations of pulse propagation in optical fibers using graphics processor units

Several simple cases of pulse propagation in optical fibers have been simulated using a graphics processor unit. Comparisons with simulations in a computer processor unit are also reported. Speedups from 4 to 36 have been obtained by different numerical methods, reaching a similar accuracy both in computer processor unit and in graphics processor unit, working with double-precision floating point numbers. Best results are achieved in simulations when the number of points in t grid rises. Therefore, the results indicate that graphics processor units could be a good tool to improve numerical simulations of pulse propagation in fibers.     

Simulating the task-level control of human motion: a methodology and framework for implementation

A task-level control framework is proposed for providing feedback control in the simulation of goal-directed human motion. An operational space approach, adapted from the field of robotics, is used for this purpose. This approach is augmented by a significant new extension directed at addressing the control of muscle-driven systems. Task/posture decomposition is intrinsically exploited, allowing human musculoskeletal properties to direct postural behavior during the performance of a task. This paper also describes a simulation architecture for generating musculoskeletal simulations of human characters. The evolving capabilities of the collective environment are directed toward autonomously generating realistic motion control for virtual actors in interactive computer graphics applications, as well as synthesizing the control of human-like motion in robotic systems.     

体视化中LOD技术思想的应用与实现

在真实感图形学研究中,复杂模型的实时绘制与动态显示是研究的热点之一.细节层次是实时图形生成的一项重要技术.细节层次模型是指对同一个场景或场景中的物体,使用具有不同细节的方法得到一组模型,供绘制时使用.建立细节层次模型能很有效地降低数据量和复杂度,实现三维场景的实时处理.针对光线投射绘制算法图像质量高,但是速度较慢的特点,提出将LOD技术思想引入到光线投射算法以改善图像体绘制时的交互性能,该方法为以后在地形可视化、虚拟现实等领域的应用提供了理论依据.     

On‐demand transmission model for remote visualization using image‐based rendering

Interactive distributed visualization is an emerging technology with numerous applications. However, many of the present approaches to interactive distributed visualization have limited performance because they are based on the traditional polygonal processing graphics pipeline. In contrast, image‐based rendering uses multiple images of the scene instead of a three‐dimensional geometrical representation, and so has the key advantage that the final output is independent of the scene complexity and depends on the desired final image resolution. Furthermore, the discrete nature of the light field dataset maps well to a hybrid solution, which can overcome the identified drawbacks. In this paper, we propose an on‐demand solution for efficiently transmitting visualization data to remote users/clients. This is achieved through sending selected parts of the dataset based on the current client viewpoint, and is done instead of downloading a complete replica of the light field dataset to each client, or remotely sending a single rendered view back from a central server to the user each time the user updates their viewing parameters. The on‐demand approach shows stable performance as the number of clients increases because the load on the server and the network traffic are reduced. Furthermore, detailed performance studies show that the proposed scheme outperforms the current solution in terms of interactivity measured in frames per second. Copyright © 2012 John Wiley & Sons, Ltd.