基于几何细节建模和双向纹理函数的真实感羽毛

根据羽毛具有近似规则的微观几何结构特点,提出了一种基于高精细几何细节建模和双向纹理函数的真实感羽毛建模和绘制算法。算法首先对羽毛进行基于Bezier或Hermite的参数化羽毛建模,进一步建立羽轴和羽枝的曲线管状体细节几何模型并离散网格化获得羽毛的高细节网格模型;最后利用该羽毛模型在不同光照和视线条件下采样的双向纹理函数（BTF）纹理和羽毛内在纹理合成的方法绘制基于BTF的真实感羽毛。     

纤维可控的质感布料三维建模与服装仿真

传统布料和服装动态仿真主要通过网格模型进行模拟,并通过光照、材质和颜色设置进行渲染,布料与服装质感效果通常不能体现.本文提出一种新的基于纤维的质感布料建模与服装仿真算法.首先使用集合球约束粒子扰动的方法模拟纤维轮廓,然后根据纱线加捻的动力学和运动学原理模拟基于纤维的纱线构造方法,接着将纱线经纬编织组织结构与弹簧-质点模型结合起来,构造基于纤维块的织物布料模型,最后通过建立人体混合层次包围盒进行快速碰撞检测,实现由质感布料生成的服装动态仿真.实验结果验证了该方法可靠,有效,生成的布料能体现织物外观纤维级别的细节,对应的服装几何纹理和质感效果得到增强.     

一种基于三角形面片模型的二维纹理贴图方法

对三维几何模型进行纹理贴图，是三维建模软件开发的一项重要内容。本文给出了一种基于三角面片模型的二维纹理贴图算法，该算法允许用户选择模型的贴图范围，自动生成模型的纹理坐标。试验表明，算法是可行的。     

基于调和映射的纹理映射方法

对三维几何模型进行交互式纹理映射,是三维建模软件开发的一项重要内容。该文采用基于调和映射的方法,实现了对一种基于三角面片模型的二维纹理映射算法,该算法允许用户交互选择模型的贴图范围,自动生成模型的纹理坐标,试验表明,该算法是可行的。     

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。     

园林植物数字化仿真算法

植物建模是计算机图形学研究热点之一,提出一种园林植物数字化建模算法。该算法通过园林植物的数字化表示方法以及四个主要步骤实现仿真效果。第一步初始化空间网格结构以及植物的轮廓结构;第二步通过生长范围计算、生长控制、网格能量计算、新的骨架结点更新等步骤生成树木的骨架结构;第三步实现交互剪枝功能,并实现纹理的获取以及三维几何结构的生成;第四步完成最终园林场景的搭建及绘制。该算法可以生成具有简单/复杂轮廓模型的植株。实验结果表明：该算法可以真实地模拟绿篱与立体花坛等园林植物场景。     

带纹理的三维模型简化算法

三维物体的几何造型中,物体通常用三角形网格来描述.随着计算机建模、仿真,虚拟现实与可视化技术的发展,经常会遇到带有纹理的三角形网格模型的简化问题.为此,提出一种带纹理的三角形网格模型简化算法.该算法中综合考虑了模型几何信息以及纹理信息的全局误差,并通过记录每步边折叠操作来消除累计误差,最终生成在形状和纹理上与原始模型最相似的简化模型.     

采用几何模型切分的人脸纹理图像生成算法

为了克服传统的照片图像拼接方法中利用特征线进行不同照片之间公共交界线定位不准确的缺点,提出一种“几何模型切分”的人脸纹理图像生成算法。通过对人脸几何模型进行切分,以切分后模型图片的轮廓作为边界线裁剪相应的人脸照片,实现不同照片之间交界线的准确对接,并采用柱面纹理映射方法将生成的纹理图像映射到特定人脸几何模型上。实验结果表明,采用提出的“几何模型切分”算法生成的人脸纹理图像进行纹理映射可以得到较好的真实感三维人脸模型,是一种生成人脸纹理图像的有效方法。     

基于纹理结构分析的织物疵点检测方法

提出了一种新的基于纹理结构分析的织物疵点检测方法,首先根据规则纹理的特点,利用自相关函数计算纹理基元模板,并通过计算每个纹理基元与基元模板的差来进行疵点区域的增强。然后通过计算纹理图像的局部不平整度来定位疵点,并采用Otsu方法自动获取阈值进行图像分割,从而实现织物疵点的检测。最后通过对不同织物疵点图像检测分割实验证明了算法的有效性和鲁棒性。     

三维离散点采样表面基于全局优化的纹理合成算法

提出了一个直接在三维离散点采样表面上进行基于全局优化的纹理合成算法．算法首先对点模型表面进行基于协方差分析的递归式聚类削分，然后通过对各初始聚类进行优化调整和区域生长，得到更为均匀的计算单元块且使相邻单元块间具有重叠区域．基于所得到的计算单元块和样本纹理，在点模型表面上建立了一个全局的纹理合成能量方程，并采用最大期卑值算法迭代优化求解出一个全局的能量最小值．在全局优化算法中，通过加入的约束条件，进而给出了点模型颜色纹理的修复算法和流引导的可控纹理合成算法．由于点模型表面离散点元的稠密性，通过对离散点元的法向基于纹理合成结果进行相应的扰动，进一步增强了表面纹理的几何粗糙感．实验结果表明，该文的算法在点采样几何表面上有效地保持了生成的纹理结构和视觉效果的连续性和平滑性，得到了令人满意的结果。     

色织物组织计算机设计与分析方法的研究

给出了一种色织物组织计算机设计及分析方法,首先讨论了一般组织、重组织和双层组织的设计方法及其核心算法,接下来给出了配色模纹分析方法、色纱选择及规则织物组织自动生成算法,最后给出了原型系统的设计体系结构。     

The Implementation Methods for Computer Aided Design and Analysis on Color-Woven Fabrics

Methods for computer aided design and analysis on color-woven fabrics are presented. The relation of color pattern, colored warp, colored weft and the model for regular weave texture are given based on their formative principle. Some efficient algorithms are developed to determine the color order of warp and weft threads which yields a given color pattern and regular weave texture. Finally, the design system structure and data process flowing are introduced.     

Decorating surfaces with bidirectional texture functions

We present a system for decorating arbitrary surfaces with bidirectional texture functions (BTF). Our system generates BTFs in two steps. First, we automatically synthesize a BTF over the target surface from a given BTF sample. Then, we let the user interactively paint BTF patches onto the surface such that the painted patches seamlessly integrate with the background patterns. Our system is based on a patch-based texture synthesis approach known as quilting. We present a graphcut algorithm for BTF synthesis on surfaces and the algorithm works well for a wide variety of BTF samples, including those which present problems for existing algorithms. We also describe a graphcut texture painting algorithm for creating new surface imperfections (e.g., dirt, cracks, scratches) from existing imperfections found in input BTF samples. Using these algorithms, we can decorate surfaces with real-world textures that have spatially-variant reflectance, fine-scale geometry details, and surfaces imperfections. A particularly attractive feature of BTF painting is that it allows us to capture imperfections of real materials and paint them onto geometry models. We demonstrate the effectiveness of our system with examples.     

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     

基于小波变换的织物纹理方向检测方法

织物组织结构及参数的正确识别与分析是一项费时而又重要的工作。该文提出了一种运用图像处理技术检测织物纹理方向和识别织物组织的新方法。把小波变换对织物图像信号良好的分解性能与Radon变换对纹理直线的检测特性结合，运用于织物纹理方向的检测分析及织物组织识别中。实验表明该方法能较准确地测定纹理方向等结构参数，检测结果为正确推断与识别织物所属的基本组织类型提供有效依据。     

一种纹理映射新技术的应用研究

传统纹理映射所使用的照片是在特定光照条件下获取的，在虚拟环境中纹理缺少随虚拟光照条件动态变化的真实感。通过分析物体表面细节产生的机理，描述了BRDF和BTF的概念和理论方法，探讨了一种适用于漫反射物体表面细节动态重构的纹理映射新方法，这种方法通过多项式模型合成BTFs图像，可以使映射后的纹理在不同虚拟光照条件下呈现动态变化的效果。     

Edit Propagation on Bidirectional Texture Functions

We propose an efficient method for editing bidirectional texture functions (BTFs) based on edit propagation scheme. In our approach, users specify sparse edits on a certain slice of BTF. An edit propagation scheme is then applied to propagate edits to the whole BTF data. The consistency of the BTF data is maintained by propagating similar edits to points with similar underlying geometry/reflectance. For this purpose, we propose to use view independent features including normals and reflectance features reconstructed from each view to guide the propagation process. We also propose an adaptive sampling scheme for speeding up the propagation process. Since our method needn't any accurate geometry and reflectance information, it allows users to edit complex BTFs with interactive feedback.     

Capturing and rendering geometry details for BTF-mapped surfaces

Bidirectional texture functions, or BTFs, accurately model reflectance variation at a fine (meso-) scale as a function of lighting and viewing direction. BTFs also capture view-dependent visibility variation, also called masking or parallax, but only within surface contours. Mesostructure detail is neglected at silhouettes, so BTF-mapped objects retain the coarse shape of the underlying model. We augment BTF rendering to obtain approximate mesoscale silhouettes. Our new representation, the 4D mesostructure distance function (MDF), tabulates the displacement from a reference frame where a ray first intersects the mesoscale geometry beneath as a function of ray direction and ray position along that reference plane. Given an MDF, the mesostructure silhouette can be rendered with a per-pixel depth peeling process on graphics hardware, while shading and local parallax are handled by the BTF. Our approach allows real-time rendering, handles complex, non-height-field mesostructure, requires that no additional geometry be sent to the rasterizer other than the mesh triangles, is more compact than textured visibility representations used previously, and, for the first time, can be easily measured from physical samples. We also adapt the algorithm to capture detailed shadows cast both by and onto BTF-mapped surfaces. We demonstrate the efficiency of our algorithm on a variety of BTF data, including real data acquired using our BTF–MDF measurement system.     

Synthesis and rendering of bidirectional texture functions on arbitrary surfaces

The bidirectional texture function (BTF) is a 6D function that describes the appearance of a real-world surface as a function of lighting and viewing directions. The BTF can model the fine-scale shadows, occlusions, and specularities caused by surface mesostructures. In this paper, we present algorithms for efficient synthesis of BTFs on arbitrary surfaces and for hardware-accelerated rendering. For both synthesis and rendering, a main challenge is handling the large amount of data in a BTF sample. To addresses this challenge, we approximate the BTF sample by a small number of 4D point appearance functions (PAFs) multiplied by 2D geometry maps. The geometry maps and PAFs lead to efficient synthesis and fast rendering of BTFs on arbitrary surfaces. For synthesis, a surface BTF can be generated by applying a texton-based sysnthesis algorithm to a small set of 2D geometry maps while leaving the companion 4D PAFs untouched. As for rendering, a surface BTF synthesized using geometry maps is well-suited for leveraging the programmable vertex and pixel shaders on the graphics hardware. We present a real-time BTF rendering algorithm that runs at the speed of about 30 frames/second on a mid-level PC with an ATI Radeon 8500 graphics card. We demonstrate the effectiveness of our synthesis and rendering algorithms using both real and synthetic BTF samples.