细节高度复杂表面模型的视点相关渐进传输

针对细节高度复杂模型的特点,提出一种视点相关的渐进传输方法.根据人的视觉特征,算法将模型表示为多分辨率的四边形参数面片和表面法向细节纹理.该算法利用法向映射提高传输和绘制的效率,然后随着视点的变化动态细化和传输当前视点下轮廓部分的参数面片信息,从而最大限度地减少了模型传输时面片的数量.参数面片的结构规则,面片之间关联性低,因此能够按任意顺序高效地传输,从而实现真正的视点相关传输,并可以采用有效的编码方法对其结构和几何信息进行压缩.实验结果表明了该算法的有效性,特别适合于表面细节复杂的表面模型的交互传输和绘制.     

Perception-motivated multiresolution rendering on sole-cube maps

This paper presents a novel GPU-based multiresolution rendering on sole-cube maps (SCMs), which is a variant of geometry images built upon spherical parameterization. Given spherical parametrization of a manifold mesh, the sphere domain is gnomonically projected to a closed cube, which constitutes the 6-chart sole-cube maps. A quadtree structure of SCMs and normal map atlas are then constructed by using the regular re-sampling. Then, by packing the quadtree nodes into the SCMs texture atlas, a new parallel multiresolution rendering is processed on the latest GPU in two rendering passes: the multiresolution node selection in fragment shader; the triangulation in vertex shader followed by the node culling operation in geometry shader. The proposed approach generates adaptive mesh surfaces dynamically, and can be fully implemented in GPU parallelization. The proposed scheme alleviates the computing load of multiresolution mesh refinement on CPU, and our GPU-based multiresolution rendering is demonstrated with a variety of examples. Our user study confirmed that the visual quality of the SCMs multiresolution rendering, in comparison with the meshes/geometry images rendering, is also highly efficient especially for complex models in large-scale virtual environment.     

Global Texture Mapping for Dynamic Objects

We propose a novel framework to generate a global texture atlas for a deforming geometry. Our approach distinguishes from prior arts in two aspects. First, instead of generating a texture map for each timestamp to color a dynamic scene, our framework reconstructs a global texture atlas that can be consistently mapped to a deforming object. Second, our approach is based on a single RGB‐D camera, without the need of a multiple‐camera setup surrounding a scene. In our framework, the input is a 3D template model with an RGB‐D image sequence, and geometric warping fields are found using a state‐of‐the‐art non‐rigid registration method [GXW*15] to align the template mesh to noisy and incomplete input depth images. With these warping fields, our multi‐scale approach for texture coordinate optimization generates a sharp and clear texture atlas that is consistent with multiple color observations over time. Our approach is accelerated by graphical hardware and provides a handy configuration to capture a dynamic geometry along with a clean texture atlas. We demonstrate our approach with practical scenarios, particularly human performance capture. We also show that our approach is resilient on misalignment issues caused by imperfect estimation of warping fields and inaccurate camera parameters.     

Distribution Update of Deformable Patches for Texture Synthesis on the Free Surface of Fluids

We propose an approach for temporally coherent patch‐based texture synthesis on the free surface of fluids. Our approach is applied as a post‐process, using the surface and velocity field from any fluid simulator. We apply the texture from the exemplar through multiple local mesh patches fitted to the surface and mapped to the exemplar. Our patches are constructed from the fluid free surface by taking a subsection of the free surface mesh. As such, they are initially very well adapted to the fluid's surface, and can later deform according to the free surface velocity field, allowing a greater ability to represent surface motion than rigid or 2D grid‐based patches. From one frame to the next, the patch centers and surrounding patch vertices are advected according to the velocity field. We seek to maintain a Poisson disk distribution of patches, and following advection, the Poisson disk criterion determines where to add new patches and which patches should e flagged for removal. The removal considers the local number of patches: in regions containing too many patches, we accelerate the temporal removal. This reduces the number of patches while still meeting the Poisson disk criterion. Reducing areas with too many patches speeds up the computation and avoids patch‐blending artifacts. The final step of our approach creates the overall texture in an atlas where each texel is computed from the patches using a contrast‐preserving blending function. Our tests show that the approach works well on free surfaces undergoing significant deformation and topological changes. Furthermore, we show that our approach provides good results for many fluid simulation scenarios, and with many texture exemplars. We also confirm that the optical flow from the resulting texture matches the fluid velocity field. Overall, our approach compares favorably against recent work in this area.     

Geometric signal compression

Compression of mesh attributes becomes a challenging problem due to the great need for efficient storage and fast transmission. This paper presents a novel geometric signal compression framework for all mesh attributes, including position coordinates, normal, color, texture, etc. Within this framework, mesh attributes are regarded as geometric signals defined on mesh surfaces. A planar parameterization algorithm is first proposed to map 3D meshes to 2D parametric meshes. Geometric signals are then transformed into 2D signals, which are sampled into 2D regular signals using an adaptive sampling method. The JPEG2000 standard for still image compression is employed to effectively encode these regular signals into compact bit-streams with high rate/distortion ratios. Experimental results demonstrate the great application potentials of this framework.     

Adaptive online transmission of 3-D TexMesh using scale-space and visual perception analysis

Efficient online visualization of three-dimensional (3-D) mesh, mapped with photo realistic texture, is essential for a variety of applications such as museum exhibits and medical images. In these applications synthetic texture or color per vertex loses authenticity and resolution. An image-based view dependent approach requires too much overhead to generate a 360/spl deg/ display for online applications. We propose using a mesh simplification algorithm based on scale-space analysis of the feature point distribution, combined with an associated visual perception analysis of the surface texture, to address the needs of adaptive online transmission of high quality 3-D objects. The premise of the proposed textured mesh (TexMesh)simplification, taking the human visual system into consideration, is the following: given limited bandwidth, texture quality in low feature density surfaces can be reduced, without significantly affecting human perception. The advantage of allocating higher bandwidth, and thus higher quality, to dense feature density surfaces, is to improve the overall visual fidelity. Statistics on feature point distribution and their associated texture fragments are gathered during preprocessing. Online transmission is based on these statistics,which can be retrieved in constant time. Using an initial estimated bandwidth,a scaled mesh is first transmitted. Starting from a default texture quality,we apply an efficient Harmonic Time Compensation Algorithm based on the current bandwidth and a time limit, to adaptively adjust the texture quality of the next fragment to be transmitted. Properties of the algorithm are proved. Experimental results show the usefulness of our approach.     

Visual saliency guided textured model simplification

Mesh geometry can be used to model both object shape and details. If texture maps are involved, it is common to let mesh geometry mainly model object shapes and let the texture maps model the most object details, optimising data size and complexity of an object. To support efficient object rendering and transmission, model simplification can be applied to reduce the modelling data. However, existing methods do not well consider how object features are jointly represented by mesh geometry and texture maps, having problems in identifying and preserving important features for simplified objects. To address this, we propose a visual saliency detection method for simplifying textured 3D models. We produce good simplification results by jointly processing mesh geometry and texture map to produce a unified saliency map for identifying visually important object features. Results show that our method offers a better object rendering quality than existing methods.     

Internet环境三维流式传输算法研究

nternet/Intranet环境的网络带宽和传输速率成为实现协同CAD的瓶颈,针对协同CAD的实时数据传输问题,本文提出了三维流式传输技术,这种新的实时数据传输方法是与视点相关的,将三维几何数据分段、连续地进行传输,可以有效地缩短启动延时,本文具体地研究了相关的实现算法,并通过实验结果证明三维流式传输可以明显地缩短启动延时,能够较好地满足协同CAD的应用需要。     

Implementation of 3D mesh streaming and compression techniques in NVEs

In this paper, we present a framework that integrates three‐dimensional (3D) mesh streaming and compression techniques and algorithms into our EVE‐II networked virtual environments (NVEs) platform, in order to offer support for large‐scale environments as well as highly complex world geometry. This framework allows the partial and progressive transmission of 3D worlds as well as of separate meshes, achieving reduced waiting times for the end‐user and improved network utilization. We also present a 3D mesh compression method focused on network communication, which is designed to support progressive mesh transmission, offering a fast and effective means of reducing the storage and transmission needs for geometrical data. This method is integrated in the above framework and utilizes prediction to achieve efficient lossy compression of 3D geometry. Copyright © 2006 John Wiley & Sons, Ltd.     

Wavelet-based multiresolution analysis of irregular surface meshes

We extend Lounsbery's multiresolution analysis wavelet-based theory for triangular 3D meshes, which can only be applied to regularly subdivided meshes and thus involves a remeshing of the existing 3D data. Based on a new irregular subdivision scheme, the proposed algorithm can be applied directly to irregular meshes, which can be very interesting when one wants to keep the connectivity and geometry of the processed mesh completely unchanged. This is very convenient in CAD (computer-assisted design), when the mesh has attributes such as texture and color information, or when the 3D mesh is used for simulations, and where a different connectivity could lead to simulation errors. The algorithm faces an inverse problem for which a solution is proposed. For each level of resolution, the simplification is processed in order to keep the mesh as regular as possible. In addition, a geometric criterion is used to keep the geometry of the approximations as close as possible to the original mesh. Several examples on various reference meshes are shown to prove the efficiency of our proposal.     

Cutting and Pasting Irregularly Shaped Patches for Texture Synthesis

This paper proposes a patch‐based texture synthesis approach that cuts and stitches irregularly shaped texture patches to generate new texture images with minimized visual discontinuity. It works well on a wide range of textures. A semiautomatic algorithm is developed to obtain the irregularly shaped patches. To synthesize strictly structured textures, a regular pasting method is proposed to identify the texture structures and subsequently position the irregularly shaped patches according to the identified structures. The results and comparisons with related work are given.     

Tessellated Shading Streaming

Presenting high‐fidelity 3D content on compact portable devices with low computational power is challenging. Smartphones, tablets and head‐mounted displays (HMDs) suffer from thermal and battery‐life constraints and thus cannot match the render quality of desktop PCs and laptops. Streaming rendering enables to show high‐quality content but can suffer from potentially high latency. We propose an approach to efficiently capture shading samples in object space and packing them into a texture. Streaming this texture to the client, we support temporal frame up‐sampling with high fidelity, low latency and high mobility. We introduce two novel sample distribution strategies and a novel triangle representation in the shading atlas space. Since such a system requires dynamic parallelism, we propose an implementation exploiting the power of hardware‐accelerated tessellation stages. Our approach allows fast de‐coding and rendering of extrapolated views on a client device by using hardware‐accelerated interpolation between shading samples and a set of potentially visible geometry. A comparison to existing shading methods shows that our sample distributions allow better client shading quality than previous atlas streaming approaches and outperforms image‐based methods in all relevant aspects.     

Image‐Based Surface Compression

We present a generic framework for compression of densely sampled three‐dimensional (3D) surfaces in order to satisfy the increasing demand for storing large amounts of 3D content. We decompose a given surface into patches that are parameterized as elevation maps over planar domains and resampled on regular grids. The resulting shaped images are encoded using a state‐of‐the‐art wavelet image coder. We show that our method is not only applicable to mesh‐ and point‐based geometry, but also outperforms current surface encoders for both primitives.     

Method of Direct Texture Synthesis on Arbitrary Surfaces

A direct texture synthesis method on arbitrary surfaces is proposed in this paper. The idea is to recursively map triangles on surface to texture space until the surface is completely mapped. First, the surface is simplified and a tangential vector field is created over the simplified mesh. Then, mapping process searches for the most optimal texture coordinates in texture sample for each triangle, and the textures of neighboring triangles are blended on the mesh. All synthesized texture triangles are compressed to an atlas. Finally, the simplified mesh is subdivided to approach the initial surface. The algorithm has several advantages over former methods: it synthesizes texture on surface without local parameterization; it does not need partitioning surface to patches; and it does not need a particular texture sample. The results demonstrate that the new algorithm is applicable to a wide variety of texture samples and any triangulated surfaces.     

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.     

Perceptually Optimized 3-D Transmission Over Wireless Networks

Many protocols optimized to transmissions over wireless networks have been proposed. However, one issue that has not been looked into is considering human perception in deciding a transmission strategy for three-dimensional (3D) objects. Several factors, such as the number of vertices and the resolution of texture, can affect the display quality of 3D objects. When the resources of a graphics system are not sufficient to render the ideal image, degradation is inevitable. It is therefore important to study how individual factors affect the overall quality, and how the degradation can be controlled given limited bandwidth resources and possibility of data loss. In this paper, the essential factors determining the display quality are reviewed. We provide an overview of our research on designing a 3D perceptual quality metric integrating two important ones, resolution of texture and resolution of mesh, that control the transmission bandwidth requirements. A review of robust mesh transmission considering packet loss is presented, followed by a discussion of the difference of existing literature with our problem and approach. We then suggest alternative strategies for packet transmission of both 3D texture and mesh. These strategies are then compared with respect to preserving 3D perceptual quality under packet loss     

JPEG2000图像编码综述

随着科学技术的不断发展,为保证图像的实时数据传输,传统的JPEG标准开始不能满足实际应用的需要,新一代静止图像压缩JPEG2000应运而生。通过阐述JPEG2000图像压缩编解码的原理,并与传统的JPEG标准比较,分析JPEG2000的优点和存在的不足,为提高获取图像数据的实时传输性能提供理论依据。     

JPEG2000图像无线传输统计性能分析与误码保护研究

JPEG2000标准是最新的图像压缩标准．首先分析了JPEG2000标准中的抗误码方法，进而提出了一个分析模型来预测在无线信道上传输的JPEG2000编码图像重建质量，并通过仿真加以验证．此分析模型可用来在无线基站上为JPEG2000编码图像的传输设计高效的非均匀误码保护方案．基于该分析模型，定义了一个效用函数来在图像重建质量和传输开销之间进行折中。以决定采用何种非均匀误码保护方案。达到最佳的传输质量．