Modeling and visualization of knitwear

Visualization and modeling of textile materials has already been investigated in detail in the computer graphics literature. Most of the work, however, concentrates on woven fabrics. We present a novel approach to the modeling and rendering of knitwear. After the topological specification of a knitting pattern a subdivision into basic elements is done. The yarn microstructure within basic elements is approximated by volume data sets. The repetitive structure of knitted fabrics allows an efficient rendering technique. Resulting images are given that demonstrate the feasibility of our approach     

Image-Based Modeling of the Human Eye

Rendering realistic organic materials is a challenging issue. The human eye is an important part of nonverbal communication which, consequently, requires specific modeling and rendering techniques to enhance the realism of virtual characters. We propose an image-based method for estimating both iris morphology and scattering features in order to generate convincing images of virtual eyes. In this regard, we develop a technique to unrefract iris photographs. We model the morphology of the human iris as an irregular multilayered tissue. We then approximate the scattering features of the captured iris. Finally, we propose a real-time rendering technique based on the subsurface texture mapping representation and introduce a precomputed refraction function as well as a caustic function, which accounts for the light interactions at the corneal interface.     

Light scattering from filaments

Photorealistic visualization of a huge number of individual filaments like in the case of hair, fur, or knitwear is a challenging task: Explicit rendering approaches for simulating radiance transfer at a filament get totally impracticable with respect to rendering performance and it is also not obvious how to derive efficient scattering functions for different levels of (geometric) abstraction or how to deal with very complex scattering mechanisms. We present a novel uniform formalism for light scattering from filaments in terms of radiance, which we call the bidirectional fiber scattering distribution function (BFSDF). We show that previous specialized approaches, which have been developed in the context of hair rendering, can be seen as instances of the BFSDF. Similar to the role of the BSSRDF for surface scattering functions, the BFSDF can be seen as a general approach for light scattering from filaments, which is suitable for deriving approximations in a canonic and systematic way. For the frequent cases of distant light sources and observers, we deduce an efficient far field approximation (bidirectional curve scattering distribution function, BCSDF). We show that on the basis of the BFSDF, parameters for common rendering techniques can be estimated in a non-ad-hoc, but physically-based way     

机织物组织图的数学描述与3维几何建模

目的 织物组织结构的3维几何模型是进行机织物的3维外观模拟和性能预测的基础。提出直接由组织结构参数建立机织物3维几何模型的方法。方法 根据构成机织物组织交织规律的浮长序列、交叉数、飞数、经纬纱循环数等参数,建立单层织物的组织图矩阵生成的数学公式;结合组织图矩阵和织物中纱线的屈曲模型,采用直线和余弦曲线分段函数建立组织矩阵中组织点间纱线路径的数学公式,并基于椭圆截面模型实现机织物的3维模拟;通过对经、纬纱的X或Y坐标函数中引入修正因子,实现纱线路径的扭曲变形。结果 实现不同组织类别、不同结构参数、不同纱线截面及基于均匀分布的纱线扭曲等条件下单层机织物的3维几何结构模拟,仿真效果较好。结论 本文方法将组织图矩阵生成和织物结构3维建模两个过程结合,快速生成单层机织物的3维几何模型。通过实时更改结构参数,实现不同结构织物的模拟,而且可以模拟经、纬纱平面外扭曲现象。     

Decoupled Shading for Real‐time Heterogeneous Volume Illumination

Existing real‐time volume rendering techniques which support global illumination are limited in modeling distinct realistic appearances for classified volume data, which is a desired capability in many fields of study for illustration and education. Directly extending the emission‐absorption volume integral with heterogeneous material shading becomes unaffordable for real‐time applications because the high‐frequency view‐dependent global lighting needs to be evaluated per sample along the volume integral. In this paper, we present a decoupled shading algorithm for multi‐material volume rendering that separates global incident lighting evaluation from per‐sample material shading under multiple light sources. We show how the incident lighting calculation can be optimized through a sparse volume integration method. The quality, performance and usefulness of our new multi‐material volume rendering method is demonstrated through several examples.     

An Algorithmic Reflectance and Transmittance Model for Plant Tissue

Recent developments in rendering have provided very realistic images. However, these images rarely show organic objects. We believe that one of the main difficulties of rendering these objects realistically is the lack of reflectance and transmittance models oriented to organic materials. In this paper an algorithmic reflectance and transmittance model for plant tissue oriented to computer graphics applications is presented. The model accounts for the three components of light propagation in plant tissues, namely surface reflectance, subsurface reflectance and transmittance, and mechanisms of light absorption by pigments present in these tissues. The model design is based on the available biological information, and it is controlled by a small number of biologically meaningful parameters. Its formulation, based on standard Monte Carlo techniques, guarantees its easy incorporation into most rendering systems. The spectral curves of reflectance and transmittance computed by the model are compared with measured curves from actual experiments.     

基于图像的点云建模及其真实感绘制

从视觉凸壳的理论出发,提出了一种基于图像的真实物体的点云建模和绘制方法。在建模方面,首先从不同视点采集目标物体的图像,然后对采样图像所形成的视觉凸壳进行均匀的点采样。同时,利用等间隔索引表来组织每幅采样图像的轮廓边,从而提高了建模效率。在绘制方面,首先分析目标物体在各种不同光照条件下的图像,并得到点云模型的离散反射属性,然后通过优化的插值方法实现真实感的绘制效果。实验表明,该方法的建模速度快,绘制结果具有很强的真实感。     

Computer-Generated Graphite Pencil Rendering of 3D Polygonal Models

Researchers in non-photorealistic rendering have investigated the display of three-dimensional worlds using various display models. In particular, recent work has focused on the modeling of traditional artistic media and styles such as pen-and-ink illustration and watercolor painting. By providing 3D rendering systems that use these alternative display models users can generate traditional illustration renderings of their three-dimensional worlds. In this paper we present our graphite pencil 3D renderer. We have broken the problem of simulating pencil drawing down into four fundamental parts: (1) simulating the drawing materials (graphite pencil and drawing paper, blenders and kneaded eraser), (2) modeling the drawing primitives (individual pencil strokes and mark-making to create tones and textures), (3) simulating the basic rendering techniques used by artists and illustrators familiar with pencil rendering, and (4) modeling the control of the drawing composition. Each part builds upon the others and is essential to developing the framework for higher-level rendering methods and tools. In this paper we present parts 2, 3, and 4 of our research. We present non-photorealistic graphite pencil rendering methods for outlining and shading. We also present the control of drawing steps from preparatory sketches to finished rendering results. We demonstrate the capabilities of our approach with a variety of images generated from 3D models.     

Fast generation method of 3D scene in Chinese landscape painting

The three-dimensional (3D) modeling of Chinese landscape painting is of great significance for the digital protection of cultural heritage and the production of virtual reality content. A fast modeling method to create 3D landscape scenes for traditional Chinese painting is proposed in this paper, based on integrated terrain modeling and the water flow rendering algorithm. A height map generation algorithm based on auxiliary lines is first proposed to carry out fast modeling from a simple two-dimensional contour to create a 3D mountain model. A realistic flow simulation that fits the topography is then undertaken, based on a flow chart which is calculated using the particle force in the normal grid of topography, and the theory of smoothing particle hydrodynamics. Finally, a stylistic scene that conforms to the artistic concept of traditional Chinese painting is acquired by optimizing the parameters. The interactive modeling platform of the integrated algorithm is tested in this study, and compared with existing research. Results show the method can achieve real-time rendering and realistic rendering to rapidly generate a 3D scene model consistent with a traditional painting scene, and provide support for the follow up development of virtual reality applications.

     

Interactive Fibre Structure Visualization of the Heart

The heart consists of densely packed muscle fibres. The orientation of these fibres can be acquired by using Diffusion Tensor Imaging (DTI) ex vivo. A good way to visualize the fibre structure in a cross section of the heart is by showing short line segments originating from the cross section and aligned with the local direction of the fibres. If the line segments are placed dense enough, one can see how the fibre orientations change. However, generation of the line segments takes time and thus the user has to wait for new geometry to be generated when the plane defining the cross section is changed. We present a new direct rendering method for the visualization of the 3D vector field in a 2D user‐definable cross section of a heart. On the intersection of the plane with the vector field, the full 3D vectors are rendered as 3D line segments with a local ray casting approach. No preprocessing of the data is needed and no geometry is generated. This technique allows a fast inspection of the data to identify interesting areas where further analysis is necessary (e.g. quantification or generation of streamlines). We also show how the technique is generalized to other glyph shapes than line segments by implementing ellipsoids.     

基于物理的海浪场景的真实感建模与绘制

提出一种基于物理的海浪场景的真实感建模与绘制算法.基于平滑粒子流体动力学模型.首先提出一种压力状态方程以取代传统的理想气体状态方程,从而在保证系统稳定性的同时,最大程度地保证液体的体积守恒;为了实现对水面浪花飞溅和泡沫的模拟,提出自适应的表面张力模型,通过制定3类流体粒子状态的转化规则,实现了飞溅粒子和主水体之间的无缝连接;并采用GPU图形硬件加速技术大大地提高了整个过程计算效率.最终绘制出海浪行进、翻卷、破碎及拍岸等真实感较强的动态效果.     

流-固交互及可变形体破裂的真实感模拟

为了模拟流体与动态环境的相互作用,提出一种流-固交互及可变形体破裂的真实感建模与绘制的算法.该算法使用光滑粒子流体动力学(SPH)与有限单元法(FEM)分别对流体与变形固体进行建模;再根据流-固交互作用的特点,给出一种快速分离液体表面粒子与固体表面网格的交互方法,并采用虚节点的流-固耦合模型模拟了液-固相互作用力.文中算法可用于多个流-固交互破裂的现象,如水管崩裂、水冲堤坝等.     

高度复杂植物场景的构造和真实感绘制

绘制高度真实感的自然场景是计算机图形学研究领域的一个富有挑战性的难题,植物对象比如草地和树木是虚拟自然场景的重要组成部分,植物类繁多,形态各异,复杂的结构使其无论在造形、存储还是在绘制上都存在相当的困难,为了解决这个难题,根据植在特点,分别采用多边形,纹元和体纹理作为工餐来构成了不同的植物,并且分别给出了不同植物场景的简单构造方法,绘制的结果证明了这些构造和绘制方法是有效可行的。     

A Volumetric Approach to Predictive Rendering of Fabrics

Efficient physically accurate modeling and rendering of woven cloth at a yarn level is an inherently complicated task due to the underlying geometrical and optical complexity. In this paper, a novel and general approach to physically accurate cloth rendering is presented. By using a statistical volumetric model approximating the distribution of yarn fibers, a prohibitively costly explicit geometrical representation is avoided. As a result, accurate rendering of even large pieces of fabrics containing orders of magnitudes more fibers becomes practical without sacrifying much generality compared to fiber‐based techniques. By employing the concept of local visibility and introducing the effective fiber density, limitations of existing volumetric approaches regarding self‐shadowing and fiber density estimation are greatly reduced.     

PERIS: A programming environment for realistic image synthesis

A computer graphics system called PERIS is described. It offers two levels of user interfaces to serve both as a testbed to facilitate further research work and as a pragmatic system for CAD/CAM applications. Flexibility of the system is achieved by providing tools of solid modeling, surface modeling and procedural model representations for physical environment modeling and by including interfaces of immediate display, scan line rendering, ray tracing and two-way ray tracing for realistic image synthesis. A linear octree data structure is established to support the modeling and rendering processes, greatly reducing the computations involved. Meanwhile, we also introduce a new illumination model which unifies most of the existing models on a theoretical basis. An improved Cook-Torrance model is then derived. By examining the merits and limitations of the classic ray tracing methods, we propose a new rendering technique of two-way ray tracing that allows more accurate simulation of light propagation in the environment.     

基于GPU编程的真实感水面模拟绘制

提出基于GPU编程的真实感水面的优化实时渲染算法。介绍了各种水面渲染需要使用到的图形,数学处理技术。通过固定的顶点流实现了水波建模,凹凸映射贴图和纹理混合,水面的反射和折射等多种特效,并使用可编程流水线的补色渲染完成最后的水面绘制。实验证明该方法可以很好地模拟真实水面的渲染要求,可以满足3D游戏和动画中对水面渲染的需要。     

Solid texture synthesis for heterogeneous translucent materials

We present a method to synthesize solid textures from heterogeneous translucent materials that have a complex pattern and subsurface scattering effect. A solid texture provides consistent texture throughout the volume, so that it can be used to model the texture on an arbitrary geometry. However, solid texture synthesis requires a huge amount of time to generate the volume. Moreover, a synthesized solid texture acquires only the color information from an input exemplar. Therefore, it has been difficult to render the appearance of a translucent object realistically without additional appearance data. In this paper, we introduce a new search method to accelerate synthesizing of solid textures. This method decomposes the candidates in an exemplar into several subgroups and searches for the best similar neighborhood in each decomposed subgroup. We also apply subsurface scattering effects to the shell layer of a synthesized object for realistic rendering of a translucent solid texture. Experimental results show that our rendering method can produce realistic rendering results for various heterogeneous translucent objects. It can also represent cross-sections of an object realistically without reconstructing the texture and surface geometry.     

RenderMan: pursuing the future of graphics

RenderMan, a powerful, consistent, yet simple 3-D interface that can adequately describe the most common rendering techniques and provides expandability for future growth is described. The RenderMan interface partitions the process of generating realistic images into two distinct areas, modeling and rendering. RenderMan's features are briefly outlined, and the RenderMan Shading language and interface bytestream protocol are examined. Hardware independence and the acceptance of RenderMan are discussed     

球面全景图漫游算法研究

基于图像的绘制技术不仅可以弥补传统基于几何绘制技术的不足。而且能给出更丰富的图像显示。基于实际应用出发,提出并实现了一种球面全景图的漫游算法。通过重投影球面全景图的可视部分到视平面上,可以生成虚拟场景在不同视线方向上的透视视图。针对直接使用重投影不能满足实时绘制的问题,提出了基于查找表的优化策略。     

Acquisition, Synthesis, and Rendering of Bidirectional Texture Functions

One of the main challenges in computer graphics is still the realistic rendering of complex materials such as fabric or skin. The difficulty arises from the complex meso structure and reflectance behavior defining the unique look‐and‐feel of a material. A wide class of such realistic materials can be described as 2D‐texture under varying light‐ and view direction, namely, the Bidirectional Texture Function (BTF). Since an easy and general method for modeling BTFs is not available, current research concentrates on image‐based methods, which rely on measured BTFs (acquired real‐world data) in combination with appropriate synthesis methods. Recent results have shown that this approach greatly improves the visual quality of rendered surfaces and therefore the quality of applications such as virtual prototyping. This state‐of‐the‐art report (STAR) will present the techniques for the main tasks involved in producing photo‐realistic renderings using measured BTFs in details.