运用局部纹理映射加速曲面纹理合成

基于样图的纹理合成方法能够在网格曲面上合成高质量纹理,但合成速度有待进一步提高,对此提出一种运用局部纹理映射加速曲面纹理合成的算法.首先以三角形法向量、切向矢量与纹理尺度为约束,将三角网格曲面分割为一系列映射区与合成区;然后用基于块的平面纹理合成方法生成大面积样图,用调和映射方法对映射区进行纹理映射;最后采用基于三角块的合成方法生成合成区纹理.实验结果表明,该算法对一般的随机性纹理与半结构性纹理具有很高的合成质量,能够控制纹理方向与尺度的变化.由于大部分三角形的纹理通过局部纹理映射得到,仅需要合成少数三角形的纹理,纹理合成过程得到大幅度地加速.     

随意图像纹理映射的补偿方法

基于局部摄影测量学的随意图像纹理映射是一种新的三维模型纹理映射方法,但其存在由局部纹理缺失引 起的纹理失真问题。提出一种纹理映射的补偿方法,即在局部摄影测量学和约束参数纹理映射方法的基础上,根据随 意图像与模型的关系确定纹理缺失区域,采用刚体转动惯量极小值测定方法和镜像方法寻找模型待映射范围内的对 称面,用对称点的纹理信息对纹理缺失区域进行纹理映射补偿。实验结果表明,对于有局部对称面的三维模型,补足 了缺失的纹理,消除了纹理拉伸失真现象。     

适用于曲面的纹理映射方法研究

作为纹理映射技术应用于规则和不规则曲面的3种算法,即球面整体纹理映射算法、球面局部纹理映射算法以及投影映射算法在纹理映射的研究中具有重要的意义。该文通过两种球面纹理映射算法进行比较,从球面纹理不变形准则出发,分析了这两种算法的优缺点,并且采用基于调和映射的方法,实现了可应用于不规则曲面映射的投影映射方法。     

环形物体的两步纹理映射算法

鉴于现有的两步纹理映射技术对环形物体表面的纹理映射均不适用,为此提出了一种两步纹理映射方法,用于解决环形物体的纹理映射问题。该算法选择圆环表面为中介曲面,首先运用面积等比约束方法将两块相同类型的纹理分别映射到圆环的上下两侧表面,并通过对纹理拼接区域进行插值预处理来消除纹理接缝;然后采用中介表面法向法将圆环表面的纹理进一步映射至物体表面。实验结果表明,该算法可将平面纹理映射至多种环形物体表面,不仅纹理形变小,且保持连续,能够较好地满足虚拟现实与真实感绘制对环形物体表面的纹理映射要求。     

基于两步法的交互式纹理映射研究

两步纹理映射方法将映射过程分解为S映射与O映射两步进行.针对两步纹理映射方法研究中复杂物体表面纹理映射时出现的变形问题,采用B样条曲面代替简单的中间映射媒介,用它近似地包裹在三维物体的外表面,将纹理通过某种方式映射到曲面上实现参数化.基于两步映射方法提出了一种交互式纹理映射的算法.该算法允许用户交互选择贴图范围,通过控制B样条曲面实现对映射效果的调整.实验结果表明,该算法可显著提高纹理映射质量,纹理贴图效果良好.     

地形纹理映射方法研究

三维真实感地形的生成一直是计算机图形学领域中关注的焦点,而地形纹理映射是实现它的一个不可或缺的要素。采用不同的纹理映射方法会导致地形渲染的帧频率、真实感以及对系统资源需求等特性显著不同,因而如何选择适合的纹理映射方法使得地形渲染效果最佳是开发人员必须面对问题。该文参考了各方面的研究和应用成果,针对不同的应用领域提出了真实图片法、多纹理过渡法和多纹理计算法这三种不同地形纹理映射方法,并对它们各自的优点、缺点和适用范围进行了详尽的论述。     

中心扩散法局部区域纹理映射

为更好地实现对三维模型局部细节的描写,提出一种中心扩散局部区域纹理映射方法.该方法以初始种子面为中心,采用广度优先搜索方法扩散确定待映射区域,保证待映射区域获得更好的圆度.在实现根据初始种子面的位置变化改变映射区域位置的同时,可始终保证纹理图像中心与纹理映射区域中心的对应,避免了纹理图像中心在纹理映射区域的中心偏移问题.实验结果表明了该方法的可行性.     

三维空间任意平面上的双向纹理映射

本文分析了传统的纹理映射方法的不足之处,提出了一种通用的双向纹理映射方法,并结合Z缓冲器算法给出了一个实用的纹理映射算法。     

PNG复杂曲面纹理映射的仿真方法

随着PNG图片越来越广泛的应用,所以研究复杂曲面纹理映射的方法有着重要的意义.为了在保持低存储量,小计算量的同时,针对PNG图片的复杂曲面自动纹理映射的变形,根据纹理扰动的缺点.提出了一种改进的复杂曲面纹理映射的方法,通过利用解二次椭圆偏微分方程,来得到任意曲面到平面的共形映射.方法不但可以自动分配纹理坐标到复杂的没有起伏的曲面,而且可以有效地克服复杂曲面的自动纹理映射的变形.避免纹理扰动,很好地解决了纹理的自动映射.     

纹理映射与光照处理关系研究及应用

纹理映射和光照处理在实际应用中往往被分别计算结果。而在定光源模型下,基于仿射变换的纹理映射和Gouraud明暗处理以及Phong明暗处理在原理上却是一致的。光照处理可以使用纹理映射的方法实现,而且这种方式能更方便地将纹理映射、光照处理以及基于干扰函数的凸凹映射以纹理融合的方式合并为一次纹理映射,从而能加快计算速度。文中提出一种纹理映射与光照模型综合处理方法,该方法在不使用任何图形支持库下,而用软引擎实现真实感三维地貌显示系统,取得了理想的效果。     

Adaptive scale filtering: a general method for obtaining shape fromtexture

Introduces adaptive scale filtering, a general method for deriving shape from texture under perspective projection without recourse to prior segmentation of the image into geometric texture elements (texels), and without thresholding of filtered images. If texels on a given surface can be identified in an image then the orientation of that surface can be obtained. However, there is no general characterization of texels for arbitrary textures. Furthermore, even if the size and shape of texels on the surface is invariant with regard to position, perspective projection ensures that the size and shape of the corresponding image texels vary by orders of magnitude. Commencing with an initial set F_O of identical image filters, adaptive scale filtering iteratively derives a set F_N which contains a unique filter for each image position. Each element of F_N is tuned to the three-dimensional structure of the surface; that is, all image filters in F_N back-project to an identical shape and size on the surface. Thus image texels of various sizes, but associated with a single spatial scale on the surface, can be identified in different parts of the image. When combined with conventional shape from texture methods, edges derived using F_N provide accurate estimates of surface orientation. Results for planar surfaces are presented     

毛发的结构造型方法

人物的绘制是当今计算机图形学中的一项重要任务,特别吸引人的是头发的生成技术.头发生成技术的难点在于其精细的形状和庞大的数量.文章针对头发提出了弯曲纹元和三维纹理体的概念,并给出了它们的数学表达式以及对不同发型的描述方法.弯曲纹元和三维纹理体是一般三维纹理的结构.带三维纹理的景物是由弯曲纹元和三维纹理体构成的,三维纹理体可再分成多个弯曲纹元,因而指明了三维纹理空间的结构,并解决了三维纹理曲面的造型问题.文章通过不同例子表明了结构造型方法在描述头发中的应用价值.     

Bilinear Accelerated Filter Approximation

Our method approximates exact texture filtering for arbitrary scales and translations of an image while taking into account the performance characteristics of modern GPUs. Our algorithm is fast because it accesses textures with a high degree of spatial locality. Using bilinear samples guarantees that the texels we read are in a regular pattern and that we use a hardware accelerated path. We control the texel weights by manipulating the u, v parameters of each sample and the blend factor between the samples. Our method is similar in quality to Cardinality‐Constrained Texture Filtering [ MS13 ] but runs two times faster.     

纹理元提取与纹理合成的自由参数估计

该文分析了常见的两类纹理:随机性纹理与结构性纹理的特性,针对其不同的统计特征,采用两种方法提取纹理元。对随机性纹理采用变尺度窗口特征跟踪的方法提取纹理元;对结构性纹理,利用其具备较为明显的边界特性,采用基于图像分割的方法提取纹理元。为避免图像噪声和自然边界不连续造成的提取误差,使用Bayes分类进行二次精细分割加以修正。实验证明,该文提出的方法对两类纹理元有较好的提取效果,同时可以用来估计纹理合成时的自由参数。     

Parameterization‐Aware MIP‐Mapping

We present a method of generating mipmaps that takes into account the distortions due to the parameterization of a surface. Existing algorithms for generating mipmaps assume that the texture is isometrically mapped to the surface and ignore the actual surface parameterization. Our method correctly downsamples warped textures by assigning texels weights proportional to their area on a surface. We also provide a least‐squares approach to filtering over these warped domains that takes into account the postfilter used by the GPU. Our method improves texture filtering for most models but only modifies mipmap generation, requires no modification of art assets or rasterization algorithms, and does not affect run‐time performance.     

Unicube for dynamic environment mapping

Cube mapping is widely used in many graphics applications due to the availability of hardware support. However, it does not sample the spherical surface evenly. Recently, a uniform spherical mapping, isocube mapping, was proposed. It exploits the six-face structure used in cube mapping and samples the spherical surface evenly. Unfortunately, some texels in isocube mapping are not rectilinear. This nonrectilinear property may degrade the filtering quality. This paper proposes a novel spherical mapping, namely unicube mapping. It has the advantages of cube mapping (exploitation of hardware and rectilinear structure) and isocube mapping (evenly sampling pattern). In the implementation, unicube mapping uses a simple function to modify the lookup vector before the conventional cube map lookup process. Hence, unicube mapping fully exploits the cube map hardware for real-time filtering and lookup. More importantly, its rectilinear partition structure allows a direct and real-time acquisition of the texture environment. This property facilitates dynamic environment mapping in a real time manner.     

Contour‐based polygonal ambient occlusion using a single‐depth texture

We present a novel approximation of a global illumination technique called contour‐based polygonal ambient occlusion, an approach that darkens by only using a depth texture as screen‐space ambient occlusion without additional information such as a normal buffer. We introduce a discrete level structure to calculate the amount of occlusion by using the contour level, an integer value derived from the depth difference of neighboring texels. We use the uniform sampling to define the positions of the neighboring texels in the depth texture. Our method does not depend on geometric complexity because our method works in screen space and works well for both static and dynamic scenes without any precomputation. Copyright © 2013 John Wiley & Sons, Ltd.     

基于形状骨架图匹配的文物碎片自动重组方法

为了有效解决文物碎片自动重组中由于断裂部位受损造成几何信息丢失,采用传统几何驱动方法容易失效的问题,本文提出一种基于形状骨架图匹配的文物碎片自动重组方法,将碎片匹配问题转化为碎片表面纹饰中非完整纹元的互补匹配问题.首先,通过提取文物碎片表面特征线得到碎片表面的纹饰信息;然后根据完整纹元的特征确定非完整纹元互补匹配的约束条件,采用视觉骨架剪枝的方法提取完全位于断裂部位的非完整纹元的形状骨架图,基于形状骨架图语法及匹配约束条件判定非完整纹元是否互补匹配;接着,将碎片上非完整纹元的顺序作为上层约束条件,采用基于带剪枝深度优先的搜索方法搜索匹配碎片;最后,以邻接碎片上非完整纹元间公共弦的端点作为邻接约束点,采用最小二乘法计算刚体变换参数得到碎片的初始位置,并采用迭代最近点方法将邻接碎片精确对齐.实验结果表明,该方法能够有效解决断裂部位存在缺损文物碎片的自动重组问题.     

A Geometrical Based Method for Highly Complex Structured Textures Generation

Conventional 2D or 3D texturing methods do not permit an efficient simulation of highly complex structured textures like fire, fur, cotton, etc. More recent techniques, using specific kinds of 3D textures, such as hypertextures or texels based on volume rendering algorithms, are more interesting, for the simulation of such special types of textures. Unfortunately, these techniques remain still restricted because either they need a functional modelling of the object, as it is the case of hypertextures, or they are strictly limited to one specific kind of texture, as it is the case of texels. In this paper we present a new approach for applying a wide range of very different types of highly complex structured textures (fur, fire, water drops, cotton, fume, …) on every kind of objects. This method is particularly based on the geometrical information given by a geometrical model (as the polyhedral or CSG modelling). Like hypertextures or texels, our method uses the volume density rendering, but it isfree of the serious above mentioned restrictions of these methods. In addition, it allows an easy and very intuitive control of the global geometrical shape of generated textures. Its manipulation is simple evenfor a novice user.     

Periodic pattern of texture analysis and synthesis based on texels distribution

Recently, sample-based texture synthesis techniques have drawn significant attention from researchers. These existing approaches mainly use the Markov Random Field (MRF) or texture features as texture model to analyze the local properties of sample textures. Indeed, human perception is sensitive to structure and periodicity. In this paper, we perform texture synthesis by taking into account the distribution of texels. Given a sample texture, the analysis procedure consists in segmenting texture into individual texels, and detecting each texel in order to analyze their neighborhood relationships by constructing connectivity. Then the synthesis process consists in reproducing a new large texture directly on a user-specified canvas by recomposing segmented texels, which synthesizes two-dimensional texel arrangements based on the previously constructed neighborhood relationships of texels. Results show that the proposed method is successful in generating textures visually indistinguishable to the sample textures. Moreover, the method especially deals with the near-regular textures, which well preserves underlying structural regularity.