一种改进的基于几何和纹理混合简化的快速绘制算法

文中对离视点较近的物体采用几何简化技术,对于距离较远的物体用纹理表示方法,在视点发生变化时,能进行几何－纹理相互转换。转换时,通过对纹理投影面后的几何插值,生成退化几何,实现几何－纹理间的光滑过渡。该算法的一个特点是结合了几何和纹理细节层次的思想,最后通过图例说明了所提出方法的有效性。     

Detail-generating geometry completion for point-sampled geometry

In this paper, we present a novel method for detail-generating geometry completion over point-sampled geometry. The main idea consists of converting the context-based geometry completion into the detail-based texture completion on the surface. According to the influence region of boundary points surrounding a hole, a smooth patch covering the hole is first constructed using radial base functions. By applying region-growing clustering to the patch, the patching units for further completion with geometry details is then produced, and using the trilateral filtering operator formulated by us, the geometry-detail texture of each sample point on the input geometry is determined. The geometry details on the smooth completed patch are finally generated by optimizing a constrained global texture energy function on the point-sampled surfaces. Experimental results demonstrate that the method can achieve efficient completed patches that not only conform with their boundaries, but also contain the plausible 3D surface details.     

A unified method for appearance and geometry completion of point set surfaces

This paper presents a novel approach for appearance and geometry completion over point-sampled geometry. Based on the result of surface clustering and a given texture sample, we define a global texture energy function on the point set surface for direct texture synthesis. The color texture completion is performed by minimizing a constrained global energy using the existing surface texture on the surface as the input texture sample. We convert the problem of context-based geometry completion into a task of texture completion on the surface. The geometric detail is then peeled and converted into a piece of signed gray-scale texture on the base surface of the point set surface. We fill the holes on the base surface by smoothed extrapolation and the geometric details over these patches are reconstructed by a process of gray-scale texture completion. Experiments show that our method is flexible, efficient and easy to implement. It provides a practical texture synthesis and geometry completion tool for 3D point set surfaces.     

Scale‐aware Structure‐Preserving Texture Filtering

This paper presents a novel method to enhance the performance of structure‐preserving image and texture filtering. With conventional edge‐aware filters, it is often challenging to handle images of high complexity where features of multiple scales coexist. In particular, it is not always easy to find the right balance between removing unimportant details and protecting important features when they come in multiple sizes, shapes, and contrasts. Unlike previous approaches, we address this issue from the perspective of adaptive kernel scales. Relying on patch‐based statistics, our method identifies texture from structure and also finds an optimal per‐pixel smoothing scale. We show that the proposed mechanism helps achieve enhanced image/texture filtering performance in terms of protecting the prominent geometric structures in the image, such as edges and corners, and keeping them sharp even after significant smoothing of the original signal.     

基于球面参数化的点模型渐变

为了获得光滑自然的点模型渐变效果,基于球面参数化,提出了一种鲁棒的渐变算法。该算法首先对源和目标模型进行球面参数化,使得参数化后的模型嵌入到单位球面上;然后在球面上自适应地对齐模型间的相应特征点,并将球面映射到矩形参数域上,基于该域建立模型间各采样点的对应关系;接着在渐变过程中,采用拉普拉斯算子计算出中间点模型的几何位置,以保持模型的细节;最后利用移动最小二乘曲面进行动态上采样,以消除中间模型的裂缝。实验结果表明,该算法具有良好匹配的采样点对应和光滑的渐变过程。     

一种无接缝纹理映射算法

针对基于图像三维重构得到的三维形状的纹理映射算法通常存在接缝现象的问题,提出一种无接缝纹理映射算法。该算法通过建立三维网格顶点和视点之间的马尔可夫随机场模型,利用重心坐标权重插值进行颜色填充,构造出一个无接缝的纹理图像。实验结果表明,马尔可夫随机场模型可以在保证纹理图像质量的同时最小化接缝现象,在此基础上的权重颜色插值方法能够完全消除接缝现象。     

基于结构的纹理合成

提出一种纹理合成算法，首先将经验模型分解(EMD)算法引入到纹理合成领域，对样本图像的纹理结构进行提取；然后应用分片采样算法和Markov随机场(MRF)模型生成输出纹理的结构，对于结构之间的空白区域，采用距离变换方法分片提取其不规则的形状并进行填充。实验结果表明，该算法不仅简单、快速、合成质量高，而且具有广泛的适用性。     

基于三角块的曲面纹理合成

根据曲面网格上的切向矢量场,采用广度优先搜索策略从样本纹理空间中为每个三角面片映射纹理面片,直至完全覆盖整个网格．在搜索和映射过程中,首先使网格上相邻三角面片的纹理有最小的匹配误差;然后对相邻的三角面片纹理使用图的分割方法拼接纹理,得到曲面上连续的合成纹理;最后压缩存储合成的三角面片纹理．该算法适用于多种类型的样本纹理和任意的三角化曲面．     

Interactive modeling of complex geometric details based on empirical mode decomposition for multi-scale 3D shapes

In this paper we develop an interactive modeling system for complex geometric details transformation based on empirical mode decomposition (EMD) on multi-scale 3D shapes. Given two models, we aim to transfer geometric details from one model to another one in an interactive manner. Taking full advantages of the multi-scale representation computed via EMD, different-scale geometric details can be transferred individually or in a concerted way, which makes our algorithm much more flexible than cut-and-paste and cloning based methods in transferring geometry details. In this process, the target surface with new transferred details could be generated by a mesh reconstruction method widely used in Laplacian surface editing. With the original positions of target surface serving as the soft constraints, the overall shape of the target model will be fully preserved. Our method can also support real-time continuous details transfer. Compared with state-of-the-art algorithms, our method provides an easier-to-use modeling tool and produces varied modeling results. We demonstrate the effectiveness of our modeling tool with various applications, such as detail transfer and enrichment, model reuse and recreation, and detail recovery for shape completion.     

螺旋线轨迹在纹理合成算法中的应用

本文在MRF模型和已有块拼贴算法的基础上,根据纹理的邻域相关性以及匹配点的位置分布在上次合成匹配点邻域的概率较大这一特点,直接选取前一匹配块的相邻块为待选最佳匹配块,使算法能够快速地采样到最优匹配块,并能较好的保持合成纹理的邻域相关性;同时,采用螺旋顺序逐块合成纹理,能够加强对合成过程的约束,克服了合成过程中不连续区域的出现。本文算法较好的维持了样本图的结构特征,在保证纹理合成质量的同时,能够有效的减少算法的计算量。     

Texture Synthesis From Photographs

The goal of texture synthesis is to generate an arbitrarily large high‐quality texture from a small input sample. Generally, it is assumed that the input image is given as a flat, square piece of texture, thus it has to be carefully prepared from a picture taken under ideal conditions. Instead we would like to extract the input texture from any surface from within an arbitrary photograph. This introduces several challenges: Only parts of the photograph are covered with the texture of interest, perspective and scene geometry introduce distortions, and the texture is non‐uniformly sampled during the capture process. This breaks many of the assumptions used for synthesis. In this paper we combine a simple novel user interface with a generic per‐pixel synthesis algorithm to achieve high‐quality synthesis from a photograph. Our interface lets the user locally describe the geometry supporting the textures by combining rational Bézier patches. These are particularly well suited to describe curved surfaces under projection. Further, we extend per‐pixel synthesis to account for arbitrary texture sparsity and distortion, both in the input image and in the synthesis output. Applications range from synthesizing textures directly from photographs to high‐quality texture completion.     

基于结构的纹理合成

提出一个简单有效的基于样图的纹理合成新方法．现有纹理合成算法仅考虑两块待匹配块之间对应元素的颜色差别作为评价相似性的量度，对于一些纹理图象，找到的不一定是最相似的匹配块，因此合成后，没有得到令人满意的效果．为此，提出一个新的纹理合成算法，不仅考虑了两个匹配块之问的颜色相似性，还充分考虑了结构的差别，把结构的相似性作为匹配块之间相似性量度的重要因素之一．具体作法是：从样本图象产生一个基于结构的新的特征映射，降低结构上不连续的程度，从而获得比较理想的合成结果．     

基于拉普拉斯算子的三角网格模型的平滑与压缩算法

三角网格模型被广泛应用于各个领域并迅速发展,为了既保留网格模型的局部几何特征,又在平滑去噪的同时能够较好地保持边缘、纹理等细节信息,提出一种基于拉普拉斯算子的偏微分方程平滑方法,可以得到较好的去噪效果;为了更加方便三维数据的传输与操作,采用了一种在拉普拉斯算子的基础上,对三角网格模型进行特征分解进而进行光谱压缩的方法,可以实现对模型的压缩.     

Space-Optimized Texture Maps

Texture mapping is a common operation to increase the realism of three‐dimensional meshes at low cost. We propose a new texture optimization algorithm based on the reduction of the physical space allotted to the texture image. Our algorithm optimizes the use of texture space by computing a warping function for the image and new texture coordinates. Neither the mesh geometry nor its connectivity are modified by the optimization. Our method uniformly distributes frequency content of the image in the spatial domain. In other words, the image is stretched in high frequency areas, whereas low frequency regions are shrunk. We also take into account distortions introduced by the mapping onto the model geometry in this process. The resulting image can be resampled at lower rate while preserving its original details. The unwarping is performed by the texture mapping function. Hence, the space‐optimized texture is stored as‐is in texture memory and is fully supported by current graphics hardware. We present several examples showing that our method significantly decreases texture memory usage without noticeable loss in visual quality.     

Multiscaled Texture Synthesis Using Multisized Pixel Neighborhoods

Most recent efforts in texture synthesis have focused on using local statistics - that is, selecting and stitching the textures from an input texture sample on the basis of a local color match to enforce textural features either pixel by pixel or patch by patch. A novel texture synthesis method produces high-quality results by introducing a multiscaled texture similarity measurement. Compared with other multiscaled methods, this approach focuses on measuring texture properties at different scales ranging from local to global using an adaptive similarity metric that accounts for texture variations across different image regions     

基于运行时纹理合成的纹理画刷

纹理画刷是一种交互式纹理生成工具,能够在用户控制下生成所需要的纹理.本文提出了一种基于运行时纹理合成的纹理画刷实现算法.纹理合成采用逐块合成的方式,每次将整个样本图以选定的位移放置到合成图中,然后用Graph Cut来决定最终的输出区域.在预处理过程中计算得到两个相同样本图间的最佳切合位移集合,在合成过程中,贴块位移搜索范围限定在由此集合及用户控制所决定的一个很小的范围内,使合成速度达到实时.另外通过对"孤立块"采取"虚拟贴块法"选取贴块位移,较好地保持了画刷所生成纹理的一致性.实验结果表明该纹理画刷的纹理生成速度满足与用户交互的需求,且生成纹理的质量高.     

一种改进的人脸纹理映射方法

识别人脸图像优化问题,由于人脸纹理映射时容易出现的纹理扭曲和畸变现象,影响图像的真实性,提出一种改进的纹理图像映射方法。根据人脸特征点信息,利用特征块匹配法配准正侧面人脸图像,并使用加权平滑算法和金字塔方法对图像进行双重融合实现图像的平滑过渡;然后利用一种特殊的定位方法来计算三维人脸模型上顶点对应的纹理坐标;最后根据纹理坐标将纹理图像映射到三维特定人脸模型表面上,可得到具有真实感的三维人脸模型。实验结果表明,纹理合成方法简捷有效,纹理映射结果生动逼真,有效的避免了纹理图像的扭曲和畸变现象,具有较高的鲁棒性。     

基于摄影原理的三维纹理重建技术研究

讨论的是基于摄影原理的三维物体表面纹理的重建技术.该技术从国内外研究现状和主要不足出发,对三维物体表面纹理的采集和映射方法进行研究和改进,提出了较为合理的算法.纹理采集过程中分析了回转工作台的结构、纹理采集的原则并建立相关的坐标系;根据拍照和投影变换的原理建立三个坐标系对应点间的关系、推导出坐标变换关系式和转换矩阵;对模型表面微小面片法向量进行均匀化处理;通过计算面片的法向量与纹理采集方向向量的位置关系确定其最佳纹理,最后通过多角度映射达到三维物体表面纹理重建的目的.     

Just‐in‐Time Texture Synthesis

Texture bombing is a texture synthesis approach that saves memory by stopping short of assembling the output texture from the arrangement of input texture patches; instead, the arrangement is used directly at run time to texture surfaces. However, several problems remain in need of better solutions. One problem is improving texture diversification. A second problem is that mipmapping cannot be used because texel data is not stored explicitly. The lack of an appropriate level‐of‐detail (LoD) scheme results in severe minification artefacts. We present a just‐in‐time texturing method that addresses these two problems. Texture diversification is achieved by modelling a texture patch as an umbrella, a versatile hybrid 3‐D geometry and texture structure with parameterized appearance. The LoD is adapted continuously with a hierarchical algorithm that acts directly on the arrangement map. Results show that our method can model and render the diversity present in nature with only small texture memory requirements.     

防止纹理扭曲的模型简化算法

文章分析了多边形模型简化过程中纹理扭曲的产生原因,指出纹理扭曲是由于简化导致模型表面几何方向变化和纹理方向变化不一致造成的,并据此提出了一个根据几何和纹理方向变化来度量纹理扭曲的简化算法。该算法可以有效防止简化模型上纹理扭曲的发生,自动快速生成在几何和纹理特征上都保持得较好的简化模型。