体绘制技术

可视化技术是继计算、实验两大科学研究方法之后的第三种研究方法,体绘制技术作为可视化技术的一个重要分支,已经取得长足发展。对常用体绘制技术进行了分类,并且指出、分析了各自特点及适用场合,为进一步应用、改进这些技术提供参考。     

Bounded Radiosity – Illumination on General Surfaces and Clusters

Traditionally, Radiosity algorithms have been restricted to scenes made from planar patches. Most algorithms for computing form factors and the subdivision criterion for hierarchical methods implicitly assume planar patches. In this paper, we present a new radiosity algorithm that is solely based on simple geometric information about surface elements, namely their bounding boxes and cone of normals. Using this information allows to compute efficient error bounds that can be used for the subdivision oracle and for computing the energy transfer. Due to the simple interface to geometric objects, our algorithm not only allows for computing illumination on general curved surfaces, but it can also be directly applied to a hieararchy of clusters. Several examples demonstrate the advantages of the new approach.     

Photon Differential Splatting for Rendering Caustics

We present a photon splatting technique which reduces noise and blur in the rendering of caustics. Blurring of illumination edges is an inherent problem in photon splatting, as each photon is unaware of its neighbours when being splatted. This means that the splat size is usually based on heuristics rather than knowledge of the local flux density. We use photon differentials to determine the size and shape of the splats such that we achieve adaptive anisotropic flux density estimation in photon splatting. As compared to previous work that uses photon differentials, we present the first method where no photons or beams or differentials need to be stored in a map. We also present improvements in the theory of photon differentials, which give more accurate results and a faster implementation. Our technique has good potential for GPU acceleration, and we limit the number of parameters requiring user adjustment to an overall smoothing parameter and the number of photons to be traced.     

Rendering gems with aterism or chatoyancy

In this paper we describe an algorithm to render the asterism or chatoyancy effect in gems. This effect is due to light dispersion caused by inclusions consisting of vast numbers of thin fibrous needles. We develop models for distribution of the microfacet directions of the inclusions and of the light dispersion by them. Based on these models we derive an algorithm to render gems with the asterism effect. By introducting a ray distribution map, a new algorithm for tracing dispersed light rays is developed.     

An Incremental Alignment Algorithm for Parallel Volume Rendering

This paper introduces a data distribution scheme and an alignment algorithm for parallel volume rendering. The algorithm performs a single wrap-around shear transformation which requires only a regular inter-processor communication pattern. The alignment can be implemented incrementally consisting of short distance shifts, thus significantly reducing the communication overhead. The alignment process is a non-destructive transformation, consisting of a single non-scaling shear operation. This is a unique feature which provides the basis for the incremental algorithm.     

对光线追踪引起物体边缘走样的研究

分析了光线追踪中造成物体锯齿状边缘的原因，讨论了几种反走样方法。在此基础上设计了一个自适应随机反走样算法，实践证明该算法能有效地消除物体的锯齿状边缘。     

Capturing and Re-Using Rendition Styles for Non-Photorealistic Rendering

Rendering high-quality non-photorealistic images of a given geometric model is often associated with a considerable amount of effort on the part of a user to fine-tune the rendition. In this paper we introduce a method and tools for re-using the user's effort invested in one model for the rendering of other models.
Our method uses templates to describe rendition styles. The paper gives a number of examples of the successful transfer of styles from one model to another.     

Optimal Sample Weights for Hemispherical Integral Quadratures

This paper proposes optimal quadrature rules over the hemisphere for the shading integral. We leverage recent work regarding the theory of quadrature rules over the sphere in order to derive a new theoretical framework for the general case of hemispherical quadrature error analysis. We then apply our framework to the case of the shading integral. We show that our quadrature error theory can be used to derive optimal sample weights (OSW) which account for both the features of the sampling pattern and the bidirectional reflectance distribution function (BRDF). Our method significantly outperforms familiar Quasi Monte Carlo (QMC) and stochastic Monte Carlo techniques. Our results show that the OSW are very effective in compensating for possible irregularities in the sample distribution. This allows, for example, to significantly exceed the regular convergence rate of stochastic Monte Carlo while keeping the exact same sample sets. Another important benefit of our method is that OSW can be applied whatever the sampling points distribution: the sample distribution need not follow a probability density function, which makes our technique much more flexible than QMC or stochastic Monte Carlo solutions. In particular, our theoretical framework allows to easily combine point sets derived from different sampling strategies (e.g. targeted to diffuse and glossy BRDF). In this context, our rendering results show that our approach overcomes MIS (Multiple Importance Sampling) techniques.     

DEMC: A Deep Dual-Encoder Network for Denoising Monte Carlo Rendering

In this paper, we present DEMC, a deep dual-encoder network to remove Monte Carlo noise efficiently while preserving details. Denoising Monte Carlo rendering is different from natural image denoising since inexpensive by-products (feature buffers) can be extracted in the rendering stage. Most of them are noise-free and can provide sufficient details for image reconstruction. However, these feature buffers also contain redundant information. Hence, the main challenge of this topic is how to extract useful information and reconstruct clean images. To address this problem, we propose a novel network structure, dual-encoder network with a feature fusion sub-network, to fuse feature buffers firstly, then encode the fused feature buffers and a noisy image simultaneously, and finally reconstruct a clean image by a decoder network. Compared with the state-of-the-art methods, our model is more robust on a wide range of scenes, and is able to generate satisfactory results in a significantly faster way.     

A Rendering Equation for Specular Transfers and Its Integration into Global Illumination

In this paper, we present a rigorous theoretical formulation of the fundamental problem—indirect illumination from area sources via curved ideal specular surfaces. Intensity and area factors are introduced to clarify this problem and to rectify the radiance from these specular surfaces. They take surface geometry, such as Gaussian curvature, into account. Based on this formulation, an algorithm for integrating ideal specular transfers into global illumination is also presented. This algorithm can deal with curved specular reflectors and transmitters. An implementation is described based on wavefront tracing and progressive radiosity. Sample images generated by this method are presented.     

基于蒙特卡罗整体光照计算的真实感图形绘制系统

提出并实现了一个基于蒙特卡罗整体光照计算的照片真实感图形绘制系统,该系统以蒙特卡罗路径跟踪技术为核心,实现了双向路径跟踪、辐照度缓存和光子图等著名的经典算法并以动态链接库的形式提供给用户,非常便于应用。系统高度模块化、具有良好的可扩展性。     

Optimal Source Selection in Shooting Random Walk Monte Carlo Radiosity

In this paper we study how to optimally select between different sources in shooting random walk Monte Carlo Radiosity. Until now the probability of selecting a source has been made proportional to the importance of that source for the region of interest. We will show here that, whenever the transition probabilities are the Form Factors, this is not optimal, and will consequently give the optimal case. This will correspond to probabilities proportional to the square root of importances, rather than to importances themselves.     

基于OpenGL的三维地形场景绘制及并行方法探讨

三维地形场景的真实感绘制常被应用于一些大规模综合分布仿真系统中.这些仿真系统有时有并行绘制的需求,例如远程显示场景等.而OpenGL作为一种开放式的图形工业标准,利用它可以方便高效地实现三维场景的真实感绘制.本文在分析OpenGL内在特点的基础上,举例说明基于OpenGL的三维地形场景真实感绘制的一般过程,然后讨论基于局域网的OpenGL三维地形场景真实感绘制程序的并行方法.     

一种实现森林场景漫游的几何与图像混合绘制方法*

提出了一种基于粒子系统和Particle System API的景物模拟方法,并采用Line方式取代传统的Point方式渲染粒子,结合纹理映射方法实现了多种喷泉模拟。实验证明用该方法模拟喷泉效果比较真实,速度快,在普通微机上可以得到令人满意的效果。     

采煤塌陷区地形渲染研究

随着煤炭的大量开采,塌陷区逐渐增多,严重地破坏了矿区生态结构,影响了矿区及周边地区人们的生活。因此良好的塌陷区漫游系统成为了治理这些危害的关键。三维地形是可视化系统及虚拟仿真的基本组成部分,也是此次项目至关重要的一部分。针对当前三维地形及其渲染技术的研究现状,该文结合常用图形接口OPENGL,在VC＋＋6.0平台下,运用GIS技术和采煤塌陷区地形数据,对LOD技术和ROAM算法进行研究,更好地实现塌陷区漫游效果。     

提高生成真实感图形速度的研究

图形的真实感是指用计算机生成的图形反映客观世界真实的程度。真实感越强,人们获得的图形信息越完整、愈丰富,用计算机生成真实感图形,实际上就是基于光学物理的光照模型计算场景中景物各表面投射到观察者眼中的光强度大小和色彩分量,并将它转换成图形设备的颜色值,从而确定画面每一象素的颜色,最终生成图形——真实感图形。用计算机生成一幅真实感图形,首先要正确的描述景物几何图形,其次是计算出景物上有关部位各点的光亮度和色彩,这些都有较成熟的算法,但由于采用光线跟综算法,计算量很大.所以如何提高真实感图形生成速度是一个重要问题,本文对此问题进行了分析研究。     

Monte Carlo simulation of X-ray and gamma-ray photon transport on a graphics-processing unit

Graphics-processing units (GPUs) suitable for general-purpose numerical computation are now available with performances in excess of 1 Teraflops, faster by one to two orders of magnitude than conventional desktop CPUs. Monte Carlo particle transport algorithms are ideally suited to parallel processing architectures and so are good candidates for acceleration using a GPU. We have developed a general-purpose code that computes the transport of high energy (>1 keV) photons through arbitrary 3-dimensional geometry models, simulates their physical interactions and performs tallying and variance reduction. We describe a new algorithm, the particle-per-block technique, that provides a good match with the underlying GPU multiprocessor hardware design. Benchmarking against an existing CPU-based simulation running on a single-core of a commodity desktop CPU demonstrates that our code can accurately model X-ray transport, with an approximately 35-fold speed-up factor.     

使用光子映射渲染参与介质

光子映射是近年发展起来的一种新的全局光照算法。本文依据光子映射对实体物体的渲染,将其扩展到对包含参与介质的场景的渲染,为此提出了一个两路的渲染算法。在第一路中,光子从光源发射,并使用光子追踪来构造体光子图;第二路从视点出发向场景中发射光线,使用光线追踪来进行渲染,其中,根据构造好的光子图,用光线步进进行
行递归的辐射估计,得出最终光强。     

一种基于逃逸时间算法的M-集渲染方法

用逃逸时间算法绘制传统的分形集———Mandelbrot集(M-集)和Julia集(J-集)时,常用迭代次数来控制色彩,得到的往往是黑白两色的或缺乏色彩渐变的图形。文章提出了基于逃逸时间算法、利用“距离”来控制色彩变化的M-集渲染方法,这种方法可以同时渲染M-集的外部结构和内部结构。适当选择控制色彩变化的距离函数,还可以得到富有3D效果的分形图形。     

基于机器学习的三维场景高度真实感绘制方法综述

目前,电影、动漫、游戏等产业对真实感绘制的需求越来越高,而三维场景高度真实感绘制通常需要耗费大量的计算时间和存储空间来计算全局光照,如何在保证绘制质量的前提下提升绘制速度依然是图形学领域面临的核心和热点问题之一.数据驱动的机器学习方法开辟了一种新的研究思路,近年来研究者将多种高度真实感绘制方法映射为机器学习问题,从而大...