森林场景的钢笔风格化实时绘制技术*

在大型复杂场景绘制关键技术研究项目中,通过把复杂场景绘制与调度技术,如Slicing、MMI、层次图像缓存和基本布告板等大场景实时加速绘制技术的多层次绘制方法,融合到非真实感绘制技术中,以提高系统面对复杂场景的实时绘制能力。最后实现了对森林等大型场景的钢笔画绘制,借助非真实感绘制技术中基于图像空间的生成方法,利用各种不同大小及形状的笔画实现了艺术化森林场景实时交互绘制。提出了植物多层次钢笔风格化渲染算法。     

基于特征跟踪和融合的人脸风格化动画的研究

文中为人脸图片或视频的风格化生成提出一种新方法.首先,通过主动外观模型(AAM)识别人脸的轮廓及五官,记录这些特征点的位置;然后,从现有样图中提取风格化因子,通过几何变形等手段映射到任意一张输入人脸图片上,合成具有样图风格化效果的人脸图片.本方法可以与许多应用结合,如电子贺卡、网上聊天等,可实现自动生成具有表情变化的风格化视频.此方法还有易于训练、速度快、扩展性强等特点.     

GPU上的非侵入式风格化渲染

提出一种基于硬件加速的算法,在实时图形应用中非侵入式地获得各种风格化渲染特效.通过实时地截获OpenGL API函数调用,修改了常规的渲染流程.该算法完全采用硬件加速的方法,在图形处理器中对颜色缓冲区和深度缓冲区进行后处理;同时采用OpenGL绘制语言作为高级绘制语言,从而可以和其他硬件加速算法（如置换式贴图、矩阵调色盘变形等）完全兼容.实验结果表明：文中算法适用于交互式非真实感渲染的应用,可以作为一种风格化渲染的强有力的工具.     

离散时间多智能体系统的一致性

研究了离散时间高维线性系统的一致性问题. 所考虑的系统可视为包含多个个体的多智能体系统, 每个个体的动力学行为与其他个体不同并受其他个体状态的影响. 本文建立了系统具有一致性的若干充分必要条件. 如果一致性函数存在, 文章给出了该函数的显式表达. 文末用一个数值例子说明了所得的理论结果.     

基于物理的烟雾动画

基于物理的烟雾模拟中,需要求解Navier-Stokes偏微分方程组．通过量纲分析,简化了该方程．在求解对流项时采用半拉格朗日方法,为弥补该方法带来的数值耗散,引入了高阶精度紧致格式,在较粗的网格上亦可得到较高精度的导数值．实验结果表明：该算法效果比较真实,速度较快．     

时间上下文的属性限制及一致性分析研究*

首先分析了本体创建的一般过程,定义了一组时间关系的表示函数及通用的时间限制性公理;在此基础上设计一个面向带时间特征的概念属性逻辑关系一致性分析算法;最后,直接针对本体概念的时间属性,设计了一个时间属性值描述的一致性分析算法。实际应用表明,提出的两个算法,既能有效地实现带时间侧面的本体属性的一致性检查,又能针对时间属性本身消除其不一致性。上述算法可应用于带时间上下文的本体创建中分析并检查其一致性。     

构件动态演化内部一致性保证方法

基于构件的软件开发已成为软件开发的主流方法,针对构件式软件动态演化后的一致性保持问题,目前大多数学者主要是从构件式软件的外部一致性角度进行分析和研究。为此,从构件内部的角度出发,提出一种保证构件式软件动态演化构件内部一致性的方法。首先,对构件及其相关模型进行建模,并给出了构件内部类有向图的同态映射关系的判定算法;其次,给出构件式构件动态演化内部一致性的标准,基于进程代数的强模拟理论和图论中的同态映射关系,分别从全局和局部的角度定义了构件式软件动态演化前后构件内部一致性标准的充分条件和必要条件,并对其进行了证明;然后,基于上述工作,给出了构件动态演化内部一致性保证方法的流程;最后,通过案例研究表明该方法的可行性和有效性。     

轮式移动机器人预定时间领导跟随一致性控制

研究了轮式移动机器人的领导跟随一致性问题,提出了预定时间一致性控制算法。首先,在有向图下,为每个跟随者提出一个分布式观测器,使其在预定时间内估计领导者状态。其次,基于观测器和构造的双幂次趋近律、非线性流形,设计了一种新的控制器,使得估计的领导者状态在预定时间内被跟踪。再次,引用了一个切换协议和一个线性流形,以确保在不引起奇异性问题的情况下,控制器在任何初始条件下均能实现预定时间的领导跟随一致性。然后,通过代数图论和李雅普诺夫理论证明系统的预定时间稳定性。最后,通过仿真对比实验验证了所提算法的有效性和优越性。相较于有限时间控制器,所提控制器收敛时间不依赖于初始状态,且收敛效果更好;相较于固定时间控制器,本文控制器收敛时间设定简单,可直接通过单一参数预先设定系统收敛时间。     

基于时间约束Petri网的一致性验证算法

时间约束的一致性验证是保证工作流时间模型正确工作的前提,因而一致性验证的算法的精确度和复杂度关乎整个工作流时间模型的运行效率。文中简要介绍了时间约束一致性定义及约束关系的推理规则,提出了一种简洁有效的时间约束一致性验证算法并分析了算法的时间复杂度。该算法借助于T-组件网和时间约束流图,能有效验证时间约束Petri网中存在的各种时间冲突,以保证工作流时间约束模型的建立及运行等各个阶段的正确性,对业务流程的建立、维护和优化都具有重要的参考意义。     

State‐of‐the‐Art Report on Temporal Coherence for Stylized Animations

Non‐photorealistic rendering (NPR) algorithms allow the creation of images in a variety of styles, ranging from line drawing and pen‐and‐ink to oil painting and watercolour. These algorithms provide greater flexibility, control and automation over traditional drawing and painting. Despite significant progress over the past 15 years, the application of NPR to the generation of stylized animations remains an active area of research. The main challenge of computer‐generated stylized animations is to reproduce the look of traditional drawings and paintings while minimizing distracting flickering and sliding artefacts present in hand‐drawn animations. These goals are inherently conflicting and any attempt to address the temporal coherence of stylized animations is a trade‐off. This state‐of‐the‐art report is motivated by the growing number of methods proposed in recent years and the need for a comprehensive analysis of the trade‐offs they propose. We formalize the problem of temporal coherence in terms of goals and compare existing methods accordingly. We propose an analysis for both line and region stylization methods and discuss initial steps towards their perceptual evaluation. The goal of our report is to help uninformed readers to choose the method that best suits their needs, as well as motivate further research to address the limitations of existing methods.     

Stylized ambient displays of digital media collections

The falling cost of digital cameras and camcorders has encouraged the creation of massive collections of personal digital media. However, once captured, this media is infrequently accessed and often lies dormant on users' PCs. We present a system to breathe life into home digital media collections, drawing upon artistic stylization to create a “Digital Ambient Display” that automatically selects, stylizes and transitions between digital contents in a semantically meaningful sequence. We present a novel algorithm based on multi-label graph cut for segmenting video into temporally coherent region maps. These maps are used to both stylize video into cartoons and paintings, and measure visual similarity between frames for smooth sequence transitions. The system automatically structures the media collection into a hierarchical representation based on visual content and semantics. Graph optimization is applied to adaptively sequence content for display in a coarse-to-fine manner, driven by user attention level (detected in real-time by a webcam). Our system is deployed on embedded hardware in the form of a compact digital photo frame. We demonstrate coherent segmentation and stylization over a variety of home videos and photos. We evaluate our media sequencing algorithm via a small-scale user study, indicating that our adaptive display conveys a more compelling media consumption experience than simple linear “slide-shows”.     

基于时空一致性的非结构化网格时变流场高效体绘制方法

时空一致性是时变流场的重要性质,也是加速时变数据可视化算法的关键.以硬件加速的光线投射算法(HRC)为框架,设计并实现了一种基于时空一致性的非结构化网格时变流场高效体绘制方法.首先提出一种分析非结构化网格单元和顶点数据时间一致性的方法,分别建立单元和顶点数据时间表,以降低绘制过程中的计算开销;然后设计一种单元和顶点数据相分离的GPU纹理结构,并采用一种小巧的单元梯度矩阵来降低显存开销;同时,设计了一种合理的数据调度策略,既能有效地避免绘制停顿,又使显存纹理结构更为紧致、高效.实验结果表明,该方法不仅明显地提高了绘制效率,而且具有更优显存空间利用率,能实现更大网格规模的非结构化网格时变流场数据体绘制.     

Temporal Coherence Methods in Real‐Time Rendering

Nowadays, there is a strong trend towards rendering to higher‐resolution displays and at high frame rates. This development aims at delivering more detail and better accuracy, but it also comes at a significant cost. Although graphics cards continue to evolve with an ever‐increasing amount of computational power, the speed gain is easily counteracted by increasingly complex and sophisticated shading computations. For real‐time applications, the direct consequence is that image resolution and temporal resolution are often the first candidates to bow to the performance constraints (e.g. although full HD is possible, PS3 and XBox often render at lower resolutions). In order to achieve high‐quality rendering at a lower cost, one can exploit temporal coherence (TC). The underlying observation is that a higher resolution and frame rate do not necessarily imply a much higher workload, but a larger amount of redundancy and a higher potential for amortizing rendering over several frames. In this survey, we investigate methods that make use of this principle and provide practical and theoretical advice on how to exploit TC for performance optimization. These methods not only allow incorporating more computationally intensive shading effects into many existing applications, but also offer exciting opportunities for extending high‐end graphics applications to lower‐spec consumer‐level hardware. To this end, we first introduce the notion and main concepts of TC, including an overview of historical methods. We then describe a general approach, image‐space reprojection, with several implementation algorithms that facilitate reusing shading information across adjacent frames. We also discuss data‐reuse quality and performance related to reprojection techniques. Finally, in the second half of this survey, we demonstrate various applications that exploit TC in real‐time rendering.     

Radiosity for dynamic environments

In this paper we present a radiosity algorithm for dynamic scenes with a high level of frame-to-frame coherence. The algorithm is restricted to dynamic environments, where the object's movement is known a priori and the viewpoint is static. Each image is computed as the sum of two images: the base-level image, computed in a pre-process, and the frame-level image computed incrementally at each frame. The computation of the images is based on an importance-driven heuristic approach. The results of the implementation are analysed and discussed. © 1997 John Wiley & Sons, Ltd.     

具有多时间粒度的时态数据库初等关键字、简单范式分解问题研究

一个好的数据库逻辑设计目标是消除数据冗余以及插入、删除和更新异常.对于时态数据库也是如此.提出了时态初等函数依赖、时态初等关键字、时态简单关键字等概念,在此基础上利用具有多时间粒度的时态函数依赖(TFD)约束对时态数据库进行了规范化研究,提出了规范程度高于时态三范式低于时态Boyce-Code范式的时态初等关键字范式(TEKNF)及时态简单范式(TSNF),并研究了时态初等关键字范式和时态简单范式的分解问题,给出了相关分解算法,并对算法的可终止性、正确性进行了证明,对时间复杂度进行了分析.     

High‐Quality Screen‐Space Ambient Occlusion using Temporal Coherence

Ambient occlusion is a cheap but effective approximation of global illumination. Recently, screen‐space ambient occlusion (SSAO) methods, which sample the frame buffer as a discretization of the scene geometry, have become very popular for real‐time rendering. We present temporal SSAO (TSSAO), a new algorithm which exploits temporal coherence to produce high‐quality ambient occlusion in real time. Compared to conventional SSAO, our method reduces both noise as well as blurring artefacts due to strong spatial filtering, faithfully representing fine‐grained geometric structures. Our algorithm caches and reuses previously computed SSAO samples, and adaptively applies more samples and spatial filtering only in regions that do not yet have enough information available from previous frames. The method works well for both static and dynamic scenes.     

基于光线相关性的快速光线投射算法

光线投射算法是一种应用广泛的体绘制技术的基本算法，其存在的主要问题是绘制速度较慢。为了提高光线投射算法的绘制速度，以满足医学图像三维重建的应用需求，在深入研究和比较各种光线投射加速算法的基础上，提出了以接近云算法为核心的、适用于医学图像三维重建的综合性加速算法，并在PC机平台上实现了该算法，在保证图像质量的同时绘制速度提高了一个数量级左右，为医学图像三维重建的实用化提供了有效的手段。