基于局部最小生成树的点模型快速无损压缩算法

点模型数据往往非常庞大,需要对这些数据高效压缩以方便进行存储和网络传输.提出了一个高效快速的点模型无损压缩算法.首先将点模型表面切分成多个小面块;以每个块为单位,生成最小生成树并按宽度优先顺序对树形结构进行编码,同时沿树形结构预测.最后,将预测值与真实值分解成符号位、指数和尾数3个部分,分别做差并在各自的上下文中用算数编码压缩.算法在压缩时间和压缩率两项指标上超过以往的点模型无损压缩算法.可以作为点模型压缩算法的一个有益补充,用来对精度要求高的工程数据进行压缩.     

基于点的三维模型压缩技术研究进展

基于点的图形学是近年来的一个研究热点,但由于基于点的模型(点模型)数据往往非常庞大,为便于存储和网络传输,有效地对这些数据进行压缩非常重要.总结了点模型的压缩流程,并给出了点模型压缩算法的分类原则;然后以单分辨率算法和渐进算法为主线,详细介绍了点模型压缩的最新研究进展,分析比较了相应的关键技术;最后对该领域未来的发展提出了一些研究建议.     

基于点的计算机图形学研究与进展

基于点的图形学是计算机图形学中一个新的研究领域,它为解决大量三维采样数据的快速绘制处理提供了一条新的途径.从点模型数字几何处理流程出发,详细分析了点模型数字几何处理流程各阶段新的进展,并对相应的     

大规模点模型的实时高质量绘制

提出了一个针对大规模点模型的实时高质量绘制算法．该算法采用距离相关的自适应绘制策略,在不损失绘制质量的前提下简化了计算．在预处理阶段,对点模型进行剖分,为每一分片分别建立层次结构,并序列化为线性二叉树保存．绘制时,首先根据每片的包围盒和法向等信息进行快速视域裁剪与背面剔除．对于可见的分片,依据它与视点的距离和视线方向,选择恰当的细节层次,直接取出线性二叉树中对应的点几何数据,自适应地选择最合适的绘制模式对其进行绘制．为了减少存储空间的消耗,该文提出了一种面向保留模式图形硬件加速的点模型压缩和解压缩算法,压缩比例达到8：1．作者在可编程图形硬件中实现了该文算法,在普通微机上实现了百万数量级点模型的实时高质量绘制。     

基于点的图形绘制技术

基于点的图形绘制技术是实现高度复杂场景实时绘制的新的有效方法,也可以对顶点数达数百万数量级的采样法表示的物体模型进行实时交互绘制,它具有基于图象绘制方式的绘制速度和基于几何绘制方式的绘制质量、灵活性和内存需求。论文介绍了基于点绘制技术的原理、工作流程,分析和比较了几种有代表性的点绘制方法,探讨了点绘制的关键技术,并对今后研究和发展的方向进行了展望。     

精度可控的字典全局相似性点云压缩

为了控制三维点云数据的压缩精度,通过对点云空间划分建立字典结构,提出一种压缩精度可控的全局相似性点云压缩方法.首先对点云进行均匀空间划分并离散表示;然后建立一个字典,作为表示该离散数据的一组基以及一套用词条索引表示的数据结构;最后通过对字典中相似词条合并实现字典压缩,并通过无损编码实现索引压缩.实验结果表明,在普通PC机环境下对ModelNet和Farman数据集中的2组点云数据,该方法均能进行任意指定精度的压缩.     

适于点绘制的图形表示方法的研究

在基于点的图形绘制技术中,作为绘制基本元素的点不是数学上无意义的点,它有位置、形状、大小等属性,如何基于点有效地表示图形将影响图形绘制的效果。论文研究了基于点的图形表示方法——单纯基于点的表示、圆球表示和表面足迹表示,重点讨论了足迹表示法的关键问题——足迹大小的求解,提出了一种基于协方差分析的表面足迹的求解方法,结果表明这种方法是有效的。     

基于Surfel点云数据的压缩算法*

针对点云数据局部集中的特点,使用差值预测对点云数据进行预测处理;在预测的同时,根据IEEE754浮点数标准,简化浮点数的尾数,使用3.5 Byte来表示一个浮点数,以提高压缩效果;然后对预测数据中连续重复的字节使用该字节加该字节重复的次数的方式存储;最后对经过以上处理的数据使用一阶自适应算术编码进行压缩。最终得到的程序在压缩比和内存占用两个方面远优于WinRAR、WinZip压缩软件。     

适于点绘制的层次多分辨率建模方法的研究

在基于点的图形绘制技术中,需要记录大量的场景采样点,如何有效地组织这些数据是实现快速高效绘制的关键问题之一。论文研究了适于点绘制的有效数据组织——层次多分辨率建模,分析了三种常用的模型结构及其构建算法,讨论了模型结构中的层次细节选择方案,提出了一种层次细节的顺序选择方法,实验证明这些方法是有效的。     

自适应分割的视频点云多模式帧间编码方法

基于视频的点云压缩(Video based point cloud compression, V-PCC)为压缩动态点云提供了高效的解决方案,但V-PCC从三维到二维的投影使得三维帧间运动的相关性被破坏,降低了帧间编码性能.针对这一问题,提出一种基于V-PCC改进的自适应分割的视频点云多模式帧间编码方法,并依此设计了一种新型动态点云帧间编码框架.首先,为实现更精准的块预测,提出区域自适应分割的块匹配方法以寻找最佳匹配块;其次,为进一步提高帧间编码性能,提出基于联合属性率失真优化(Rate distortion optimization, RDO)的多模式帧间编码方法,以更好地提高预测精度和降低码率消耗.实验结果表明,提出的改进算法相较于V-PCC实现了-22.57%的BD-BR (Bjontegaard delta bit rate)增益.该算法特别适用于视频监控和视频会议等帧间变化不大的动态点云场景.     

A motion compression/reconstruction method based on max t-norm composite fuzzy relational equations

A motion compression/reconstruction method based on max t-norm composite fuzzy relational equations (MCF) is proposed, where into intra-pictures (I-pictures) and predictive-pictures (P-pictures) of the original motion are compressed by uniform and non-uniform coders, respectively. The non-uniform coders of the proposed method can preserve edge information of P-pictures on the compressed image. To perform an effective compression/reconstruction of the P-pictures, a design method of non-uniform coders is proposed based on an overlap level of fuzzy sets and a fuzzy equalization. An experiment using 10 P-pictures confirms that the root mean square error of the reconstructed images obtained by the proposed non-uniform coders is decreased to 89.4% of that one of the uniform coders under the condition that compression rate (the ratio between the file size of compressed image and original one) is 0.0057. Two test motions (‘Tennis’ and ‘Woman’, 100 frames) are compressed and reconstructed by the proposed MCF.     

Improving the fingerprint verification performance of set partitioning coders at low bit rates

Multimedia Tools and Applications - Wavelet transform combined with the set partitioning coders (SPC) are the most widely used fingerprint image compression approach. Many different SPC coders have...     

改进的嵌入式小波在航天图像压缩上的应用

JPEG2000是基于小波变换的图像压缩技术,它不像传统的压缩技术,JPEG2000的良好的压缩效果取决于选取好的小波.嵌入式零树小波编码算法是基于小波变换的一种图像压缩方法,也是有相对不错的压缩效果。对此研究将以嵌入式零树小波为基础,改进其算法,实现在航天项目上的快速高效的压缩图像。     

Context‐Based Coding of Adaptive Multiresolution Meshes

Multiresolution meshes provide an efficient and structured representation of geometric objects. To increase the mesh resolution only at vital parts of the object, adaptive refinement is widely used. We propose a lossless compression scheme for these adaptive structures that exploits the parent–child relationships inherent to the mesh hierarchy. We use the rules that correspond to the adaptive refinement scheme and store bits only where some freedom of choice is left, leading to compact codes that are free of redundancy. Moreover, we extend the coder to sequences of meshes with varying refinement. The connectivity compression ratio of our method exceeds that of state‐of‐the‐art coders by a factor of 2–7. For efficient compression of vertex positions we adapt popular wavelet‐based coding schemes to the adaptive triangular and quadrangular cases to demonstrate the compatibility with our method. Akin to state‐of‐the‐art coders, we use a zerotree to encode the resulting coefficients. Using improved context modelling we enhanced the zerotree compression, cutting the overall geometry data rate by 7% below those of the successful Progressive Geometry Compression. More importantly, by exploiting the existing refinement structure we achieve compression factors that are four times greater than those of coders which can handle irregular meshes.     

点集模型的直接可见性测试与基于视点的绘制

点集模型作为一种新兴的三维几何形体表示形式,近年来备受关注.本文运用点集法向计算与凸包构建等技术,对原始点集模型进行直接可视性计算,并利用可见性计算的结果对点集模型进行基于视点的绘制.算法首先对原始模型进行基于视点的精简,剔除大部分不可见点;再对精简后的模型进行球面对称变换,并构建变换后点集的凸包,进而提取出可见点集;最后运用真实感图形绘制技术实现可见点集的快速绘制.实验证明,本文算法能够快速地计算点集模型中采样点的可见性.该算法可应用于点集模型基于视点的绘制与曲面重建,以及点集模型的阴影绘制等领域.     

Performance analysis of hybrid coders in multi-constraints pruned environment

Multimedia Tools and Applications - Advance Video Coder (H.264/AVC) and High-Efficiency Video (H.265/HEVC) coders are fast developing video compression standards, provides high compression and...     

Design of integrated multimedia compression and encryption systems

Two approaches for integrating encryption with multimedia compression systems are studied in this research, i.e., selective encryption and modified entropy coders with multiple statistical models. First, we examine the limitations of selective encryption using cryptanalysis, and provide examples that use selective encryption successfully. Two rules to determine whether selective encryption is suitable for a compression system are concluded. Next, we propose another approach that turns entropy coders into encryption ciphers using multiple statistical models. Two specific encryption schemes are obtained by applying this approach to the Huffman coder and the QM coder. It is shown that security is achieved without sacrificing the compression performance and the computational speed. This modified entropy coding methodology can be applied to most modern compressed audio/video such as MPEG audio, MPEG video, and JPEG/JPEG2000 images.     

Using difference intervals for time-varying isosurface visualization

We present a novel approach to out-of-core time-varying isosurface visualization. We attempt to interactively visualize time-varying datasets which are too large to fit into main memory using a technique which is dramatically different from existing algorithms. Inspired by video encoding techniques, we examine the data differences between time steps to extract isosurface information. We exploit span space extraction techniques to retrieve operations necessary to update isosurface geometry from neighboring time steps. Because only the changes between time steps need to be retrieved from disk, I/O bandwidth requirements are minimized. We apply temporal compression to further reduce disk access and employ a point-based previewing technique that is refined in idle interaction cycles. Our experiments on computational simulation data indicate that this method is an extremely viable solution to large time-varying isosurface visualization. Our work advances the state-of-the-art by enabling all isosurfaces to be represented by a compact set of operations.     

基于人眼视觉系统的自适应小波图像编码算法

本文提出了一种基于自适应小波分解与人眼视觉系统的低比特率图像压缩编码算法,该算法具有以下特点：（1）以子带能量为判别标准,能够根据图像内容进行自适应形式的小波分解;（2）建立了人眼视觉系统的掩蔽模型,并据此给出了全新的小波系数自适应量化策略.仿真实验表明：本文算法是一种高效的图像压缩算法,不仅其压缩效果明显优于JPEG2000、EZW、FWP等小波域图像压缩算法（特别是低比特率下）,而且可广泛适用于不同特征的数字图像.     

XML compression techniques: A survey and comparison

XML has been acknowledged as the defacto standard for data representation and exchange over the World Wide Web. Being self describing grants XML its great flexibility and wide acceptance but on the other hand it is the cause of its main drawback that of being huge in size. The huge document size means that the amount of information that has to be transmitted, processed, stored, and queried is often larger than that of other data formats. Several XML compression techniques has been introduced to deal with these problems.In this paper, we provide a complete survey over the state-of-the-art of XML compression techniques. In addition, we present an extensive experimental study of the available implementations of these techniques. We report the behavior of nine XML compressors using a large corpus of XML documents which covers the different natures and scales of XML documents. In addition to assessing and comparing the performance characteristics of the evaluated XML compression tools, the study also tries to assess the effectiveness and practicality of using these tools in the real world. Finally, we provide some guidelines and recommendations which are useful for helping developers and users for making an effective decision towards selecting the most suitable XML compression tool for their needs.