High rate compression of CAD meshes based on subdivision inversion

In this paper we present a new framework, based on subdivision surface approximation, for efficient compression and coding of 3D models represented by polygonal meshes. Our algorithm fits the input 3D model with a piecewise smooth subdivision surface represented by a coarse control polyhedron, near optimal in terms of control points number and connectivity. Our algorithm, which remains independent of the connectivity of the input mesh, is particularly suited for meshes issued from mechanical or cad parts. The found subdivision control polyhedron is much more compact than the original mesh and visually represents the same shape after several subdivision steps, without artifacts or cracks, like traditional lossy compression schemes. This control polyhedron is then encoded specifically to give the final compressed stream. Experiments conducted on several cad models have proven the coherency and the efficiency of our algorithm, compared with existing methods.     

Scalable intraband wavelet‐based coding scheme for irregular meshes

This paper describes a novel scalable 3D triangular mesh coding method based on wavelet transform and successive approximation quantization. The algorithm efficiently exploits the intracorrelations between wavelet coefficients independently in each subband. Non‐significant wavelet coefficients are clustered, in a per bit‐plane manner, by using an octree‐based approach. An hierarchical bitstream is then generated allowing to gradually decode the 3D mesh at the desired quality or resolution representation. Our proposal can be executed on arbitrary topology meshes by using irregular wavelet decomposition. Objective and subjective quality evaluation on representative 3D meshes shows that the proposed codec provides competitive compression results when compared to the state‐of‐the‐art. Furthermore, it fits well to applications that require fast interactive handling of highly detailed 3D meshes, over networks with limited and/or variable bandwidth.     

基于小波变换的三维网格感兴趣区域编码

在实际应用中,用户可能只对三维网格的部分区域感兴趣,希望该区域能够快速、高质量地解码,而对非感兴趣区则要求一般,以便节省网络带宽和存储.目前还未见三维网格感兴趣区编码的相关工作发表.本文提出一种基于网格小波变换的三维感兴趣区的编码方法,提出了两种感兴趣区优先编码策略和四种编码模型,以及建立感兴趣区域掩模的快速方法.实验结果表明,本文方法有效地实现了三维网格的感兴趣区域编码,较好地满足了用户浏览的交互性和个性化的要求.     

Rate-distortion-optimized predictive compression of dynamic 3D mesh sequences

Compression of computer graphics data such as static and dynamic 3D meshes has received significant attention in recent years, since new applications require transmission over channels and storage on media with limited capacity. This includes pure graphics applications (virtual reality, games) as well as 3DTV and free viewpoint video. Efficient compression algorithms have been developed first for static 3D meshes, and later for dynamic 3D meshes and animations. Standard formats are available for instance in MPEG-4 3D mesh compression for static meshes, and Interpolator Compression for the animation part. For some important types of 3D objects, e.g. human head or body models, facial and body animation parameters have been introduced. Recent results for compression of general dynamic meshes have shown that the statistical dependencies within a mesh sequence can be exploited well by predictive coding approaches. Coders introduced so far use experimentally determined or heuristic thresholds for tuning the algorithms. In video coding, rate-distortion (RD) optimization is often used to avoid fixed thresholds and to select the optimum prediction mode. We applied these ideas and present here an RD-optimized dynamic 3D mesh coder. It includes different prediction modes as well as an RD cost computation that controls the mode selection across all possible spatial partitions of a mesh to find the clustering structure together with the associated prediction modes. The general coding structure is derived from statistical analysis of mesh sequences and exploits temporal as well as spatial mesh dependencies. To evaluate the coding efficiency of the developed coder, comparative coding results for mesh sequences at different resolutions were carried out.     

View-dependent 3-D mesh coding by rate allocation with the image rendering-based distortion measures

Low-bandwidth transmission of synthetic digital content to the end user device in the form of a scene of 3-D meshes requires efficient compression of the mesh geometry. For applications in which the meshes are observed from a single viewpoint, this work explores the use of the image rendering-based distortion measures in rate allocation to their surface regions for view-dependent mesh geometry compression. It is experimentally demonstrated that the image rendering-based distortion measures yield far superior performance (the quality of the rendered image of the reconstructed scene from a viewpoint at a given rate) in optimal rate allocation than other previously proposed distortion measures. A fast rate allocation method is also proposed for use with the image rendering-based measures for real-time or interactive applications. Not only does this method have significantly lower complexity than the optimal rate allocation method due to the rendering of the images of the reconstructed meshes at only judiciously selected rate–distortion operating points, but also its coding performance is just as competitive. Further complexity reduction in rate allocation, through rendering of only the coded regions of the meshes, is also investigated.     

Bi-directional 2-D mesh representation for video object rendering,editing and superresolution in the presence of occlusion

In this paper, we propose a new bi-directional 2-D mesh representation of video objects, which utilizes forward and backward reference frames (keyframes). This framework extends the previous uni-directional mesh representation to enable efficient rendering, editing, and superresolution of video objects in the presence of occlusion by allowing bi-directional texture mapping as in MPEG B-frames. The video object of interest is tracked between two successive keyframes (which can be automatically or interactively selected) both in forward and backward directions. Keyframes provide the texture of the video object, whereas its motion is modeled by forward and backward 2-D meshes. In addition, we employ “validity maps”, associated with each 2-D mesh, which allow selective texture mapping from the keyframes. Experimental results for efficient video object editing and object-based video resolution enhancement in the presence of self-occlusion are presented to demonstrate the effectiveness of the proposed representation.     

肝脏三维重建中模型平滑和网格细化方法

针对力触觉再现系统对三维模型真实性和准确性的要求,在基于二维医学图像重构肝脏三维模型的过程中,提出了一种基于B样条拟合曲线的模型平滑方法和基于最邻近点搜索插值的模型网格细化方法。前者是以最初获得的轮廓点为控制顶点,拟合出平滑的B样条曲线并重新采样,以此实现对模型的平滑操作。后者是在每一次连线构造三角形面片过程中,取两点之间的几何中心作为插值点,以此实现三维网格模型的细化。实验表明,这两种算法能够有效提高肝脏三维模型的重建效果,增强力触觉再现系统的真实性。     

Technologies for 3D mesh compression: A survey

Three-dimensional (3D) meshes have been widely used in graphic applications for the representation of 3D objects. They often require a huge amount of data for storage and/or transmission in the raw data format. Since most applications demand compact storage, fast transmission, and efficient processing of 3D meshes, many algorithms have been proposed to compress 3D meshes efficiently since early 1990s. In this survey paper, we examine 3D mesh compression technologies developed over the last decade, with the main focus on triangular mesh compression technologies. In this effort, we classify various algorithms into classes, describe main ideas behind each class, and compare the advantages and shortcomings of the algorithms in each class. Finally, we address some trends in the 3D mesh compression technology development.     

直角坐标系下非均匀FDTD网格生成系统

基于非均匀FDTD网格的电磁场模拟是一种解决诸多实际电磁场问题的通用、有效方法.本文介绍了在直角坐标系下非均匀FDTD网格图形生成系统,可以快速、高效地产生1D、2D、3D FDTD网格,展现物体的几何图形,还可以动态地、可视化地得到检查、调节和修改.作为检验,本文以一实际结构为例,产生并显示了其网格图形.     

三维网格客观质量评价

随着三维网格在数字游戏、影视动画、虚拟现实等领域的广泛应用,针对三维网格的处理方法也越来越多,包括压缩、简化、嵌入水印和去噪等,这些处理技术均不可避免地导致三维网格的失真.如何更好地评估三维网格的视觉质量成为目前亟需解决的问题.回顾了近20年来发展起来的三维网格的客观质量评价方法.介绍了这一领域常用评价方法的技术指标以...     

Hierarchical representation and coding of surfaces using 3-Dpolygon meshes

This paper presents a novel procedure for the representation and coding of three-dimensional (3-D) surfaces using hierarchical adaptive triangulation. The proposed procedure is based on pyramidal analysis using the quincunx sampling minimum variance interpolation (QMVINT) filters. These are reduced pyramids with quincunx sampling applied to the parametric representation of the surface, chosen so as to minimize the variance of the interpolation error, and thus, when combined with the appropriate encoding of the coefficients, optimize the compression of the mesh information transmitted. At the same time, it produces a hierarchy of meshes based on quincunx sampling where coarse meshes are as similar to their finer versions as possible. This is very much desirable in progressive transmission. Depending on its interpolation error and the available bitrate, each filtered sample is a candidate for becoming a vertex of the mesh. The result is a progressive sequence of meshes consisting of more triangles wherever large variations exist and fewer in uniform regions. Complete correspondence between triangles at each level is identified, resulting in an efficient hierarchical representation of the mesh. The algorithm can be also used for the triangulation of a specific region of interest. Experimental results demonstrate that the proposed scheme provides an improvement in quality (MSE) by a factor of two when compared with other well known adaptive triangulation schemes.     

Image-based rendering and 3D modeling: A complete framework

Multi-viewpoint synthesis of video data is a key technology for the integration of video and 3D graphics, as necessary for telepresence and augmented-reality applications. This paper describes a number of important techniques which can be employed to accomplish that goal. The techniques presented are based on the analysis of 2D images acquired by two or more cameras. To determine depth information of single objects present in the scene, it is necessary to perform segmentation and disparity estimation. It is shown, how these analysis tools can benefit from each other. For viewpoint synthesis, techniques with different levels of tradeoff between complexity and degrees of freedom are presented. The first approach is disparity-controlled view interpolation, which is capable of generating intermediate views along the interocular axis between two adjacent cameras. The second is the recently introduced incomplete 3D technique, which in a first step extracts the texture of the visible surface of a video object acquired with multiple cameras, and then performs disparity-compensated projection from the surface onto a view plane. In the third and most complex approach, a 3D model of the object is generated, which can be represented by a 3D wire grid. For synthesis, this model can be rotated to arbitrary orientations, and original texture is mapped onto the surface to obtain an arbitrary view of the processed object. The result of this rendering procedure is a virtual image with very natural appearance.     

Two-dimensional mesh-based mosaic representation for manipulationof video objects with occlusion

We present a two-dimensional (2-D) mesh-based mosaic representation, consisting of an object mesh and a mosaic mesh for each frame and a final mosaic image, for video objects with mildly deformable motion in the presence of self and/or object-to-object (external) occlusion. Unlike classical mosaic representations where successive frames are registered using global motion models, we map the uncovered regions in the successive frames onto the mosaic reference frame using local affine models, i.e., those of the neighboring mesh patches. The proposed method to compute this mosaic representation is tightly coupled with an occlusion adaptive 2-D mesh tracking procedure, which consist of propagating the object mesh frame to frame, and updating of both object and mosaic meshes to optimize texture mapping from the mosaic to each instance of the object. The proposed representation has been applied to video object rendering and editing, including self transfiguration, synthetic transfiguration, and 2-D augmented reality in the presence of self and/or external occlusion. We also provide an algorithm to determine the minimum number of still views needed to reconstruct a replacement mosaic which is needed for synthetic transfiguration. Experimental results are provided to demonstrate both the 2-D mesh-based mosaic synthesis and two different video object editing applications on real video sequences.     

Object-based coding of stereoscopic and 3D image sequences

The author begins by discussing what object based coding is and goes on to consider the structure of object based stereoscopic coders. Different techniques for object-based stereoscopic image sequence coding are reviewed. These techniques basically differ in the way they define models and estimate model parameters. We review the various models used for representing motion and structure. Then we review segmentation techniques, and discuss coding of object parameters and image synthesis     

3D shape from focus using LULU operators and discrete pulse transform in the presence of noise

3D shape recovery is an interesting and challenging area of research. Recovering the depth information of an object from a sequence of 2D images with varying focus is known as shape from focus. Focus value of an image carries information about the object and shape from focus is a method which depends on different focused value images. It reconstructs the shape/surface/depth of an object based on the different focused values of the object. These different focused valued images should be captured from the same angle. Calculating the shape of the object from different images with different focused values can be done by applying sharpness detection methods to maximize and detect the focused values. In this paper, we propose new 3D shape recovery techniques based on LULU operators and discrete pulse transform. LULU operators are nonlinear rank selector operators that are efficient with low complexity. They hold consistent separation, total variation and shape preservation properties. Discrete pulse transform is a transform that decomposes image into pulses. Therefore selection of right pulses, give sharpest focus values. The proposed techniques provide better result than traditional techniques in a noisy environment.     

Dynamically restricted codebook-based vector quantisation scheme for mesh geometry compression

The transmission and storage of large amounts of vertex geometry data are required for rendering geometrically detailed 3D models. To alleviate bandwidth requirements, vector quantisation (VQ) is an effective lossy vertex data compression technique for triangular meshes. This paper presents a novel vertex encoding algorithm using the dynamically restricted codebook-based vector quantisation (DRCVQ). In DRCVQ, a parameter is used to control the encoding quality to get the desired compression rate in a range with only one codebook, instead of using different levels of codebooks to get different compression rate. During the encoding process, the indexes of the preceding encoded residual vectors which have high correlation with the current input vector are prestored in a FIFO so that both the codevector searching range and bit rate are averagely reduced. The proposed scheme also incorporates a very effective Laplacian smooth operator. Simulation results show that for various size of mesh models, DRCVQ can reduce PSNR degradation of about 2.5–6 dB at 10 bits per vertex comparative to the conventional vertex encoding method with stationary codebooks and, DRCVQ with arithmetic coding of codevector indexes and Laplacian smoothener can outperform the state-of-art Wavemesh for non-smooth meshes while performing slightly worse for smooth meshes. In addition, we use MPS as codevector search acceleration scheme so that the compression scheme is real-time.     

Object-based analysis-synthesis coding (OBASC) based on the sourcemodel of moving flexible 3-D objects

This correspondence investigates object-based analysis-synthesis coding (OBASC) for the encoding of moving images at very low data rates. According to the source model, each moving object of an image is described and encoded by three parameter sets defining its motion, shape, and surface color. The parameter sets of each object are obtained by model-based image analysis. They are coded by an object-dependent parameter coding. Using the coded parameter sets, an image can be synthesized by model-based image synthesis. Here, OBASC based on the source model of "moving flexible 3-D objects with 3-D motion" (F3D) is introduced. The efficiency of this source model F3D is compared to the efficiency of OBASC based on the source model of "moving rigid 3-D objects with 3-D motion" (R3D). Compared to R3D, F3D requires the additional transmission of flexible-shape parameters. Therefore, the source model F3D is only applied in those areas of the image which cannot be described by the source model R3D. The new source model F3D reduces the bit rate from 64 to 56 kb/s, providing the same picture quality measured by the SNR of the encoded color parameters.     

From stereoscopic images to semi-regular meshes

The pipeline to get the semi-regular mesh of a specific physical object is long and fastidious: physical acquisition (creating a dense point cloud), cleaning/meshing (creating an irregular triangle mesh), and semi-regular remeshing. Moreover, these three stages are generally independent, and processed successively by different tools. To overcome this issue, we propose in this paper a new framework to design semi-regular meshes directly from stereoscopic images. Our semi-regular reconstruction technique first creates a base mesh by using a feature-preserving sampling on the stereoscopic images. Afterwards, this base mesh is passed to a coarse-to-fine meshing process to get the semi-regular mesh of the original surface. Experimental results prove the reliability and the accuracy of our approach in terms of shape fidelity, compactness, but also runtime, since many steps have been parallelized on the GPU.