二代小波在MPEG-4任意形状图象变换编码中的应用

本文研究了二代小波在MPEG－4任意形状图像（即VOP）变换编码中的应用。与一代小波相比,二代小波具有能对任意尺寸图像变换的能力,以及压缩与解码算法相似、计算效率高等特点。文中采用了两种方法：一种是对VOP做适当的延再进行交换;一种则是在修改提升算法的基础上,获得一种无须延拓的形状自适应变换方法。实验结果表明,与一代小波相比,基于二代小波的形状自适应变换方法在MPEG－4任意形状图像变换编码中具有更好的压缩性能。     

基于二代小波变换的图像目标编码方法

研究了二代小波用于任意形状图像目标变换编码的可行性。文中采用一种需要对目标作适当的延拓后再作变换的方法,另一种则在修改二代小波提升算法的基础上获得一种不需延拓的形状自适应变换方法。实验结果表明,这二种方法与Katata使用的一代小波的方法相比,有更好的压缩性能。     

小波变换和算术编码在MPEG 4中的应用

给出了MPEG－4中基于小波变换的静态纹理编码,包括最低频带和高频子带的自适应算术编码的算法和仿真实验结果。     

一种面向对象的视频分割算法

该文讨论面向对象编码的视频分割算法。由于数学形态学工具能够很好地处理诸如大小、形状、对比度和连通性等对图像分割非常重要的特征,这种技术常用来对图像进行帧内分割,得到一些具有某种相似性的区域。然后利用运动信息进行区域合并。为了实现区域合并,该文提出一种新方法来判定局部运动。设计了一个分割细化步骤,对区域边界点进行再判决,可以得到更好的结果。实验结果表明,该文提出的方法对于平稳背景和运动背景中的视频对象分割都是有效的。     

一种基于灰度连续区域分割的视频对象分割方法

针对目前许多分割方法中分割边界不精确、计算复杂和缓存帧多等问题，提出了一种结合空间区域分割和运动象素检测的自动分割方法：先将当前视频帧分割为不同的灰度连续区域，再利用二次帧差确定视频图像中的运动象素，然后按一定的规则确定哪些灰度连续区域属于运动区域，从而有效地从静止的复杂背景中分割出运动对象区域。实验结果表明这种分割方法计算简单、分割边界比较精确。     

一种彩色视频图像序列的三维小波变换编码方法

该文给出了一种基于三维小波变换的彩色视频图像序列的编码方法。先将彩色视频图像序列的RGB(红绿蓝)色彩表示转换成YCbCr(亮度色度色度)表示,再将表示帧序的t坐标代换成z坐标,可将其看成是三维空间中的体。将其分成子块后,仿照二维图像小波变换的方法,对每个亮度色度分量做三维小波变换。变换后的各亮度色度分量的能量主要集中于低频波段,这些波段对该视频图像序列的视觉效果影响最大。将不同分量的各个不同波段按不同的精度量化并进行熵编码,可以达到去除帧内和帧间冗余,压缩数据的目的。试验表明,使用本方法可以达到较好的压缩效果。此方法较直观,速度也比较快。     

基于小波变换的图像分割技术研究

图像分割是一种重要的图像分析技术.近年来,对图像分割的研究一直是图像技术研究中的热点和焦点.介绍一种基于小波变换的图像分割方法,该方法先对图像的灰度直方图进行小波多尺度变换,然后从较大的尺度系数到较小的尺度系数逐步定位出灰度阈值.实验结果表明,该方法具有较好的抗噪声性能.     

一种基于小波的数字水印技术研究

论文的数字水印算法是通过小波多分辨率分解在容噪性较强的逼近子图上嵌入数字水印，并且采用预滤波的方式获取最佳嵌入位置使得该算法的抗滤波性能大大增强。实验证明，该算法的安全性较好，可以抗各种攻击，包括压缩、滤波、剪切等一该算法还利用BMP格式文件头隐藏水印信息，加快了水印的检测和提取速度．     

面向对象的小波变换软件包设计

本文介绍了小波变换软件包WYUWave的设计.该软件包实现了小波变换的常见基本函数,包括卷积,一维、二维小波正反变换,一维、二维小波包正反变换,各种正交小波滤波器、双正交滤波器设计,小波函数、尺度函数计算,多分辨率分析等功能.该软件包的设计基于C/C++环境,分为三层,其中第二、第三层的设计为面向对象设计,同时兼顾到使用和扩展的方便性及移植的灵活性.最后给了两个例子说明在具体的应用中如何利用WYUWave软件包进行应用开发及扩展设计.     

MPEG—4的验证模型及其图象分割技术

即将诞生的ＭＰＥＧ－４，除了其高压缩率外，主要特点是对音视频数据采用基于内容的操作存取及传输，文中阐述了ＭＰＥＧ－４的基于内容的特点，灵活及可扩展的结构形式和有效的开发方式－验证模型法。最后简要介绍实现ＭＰＥＧ－４的关键技术之一的图象分割。     

Morphological shape representation for very low bit-rate video coding

Region-based coding schemes are among the most promising compression techniques for very low bit-rate applications. They consist of image segmentation, contour and texture coding. This paper deals with the use of the geodesic skeleton as a morphological tool for contour coding of segmented image sequences. In the geodesic case, already coded and known regions are taken into account for the coding of contours of unknown regions. A new technique is presented for the entropy coding of the coordinates of the skeleton points exploiting their special spatial distribution. Furthermore, a fast algorithm for the reconstruction of the skeleton points is given based on hierarchical queues. In the case of numerous isolated contour arcs (for example error coding in a motion prediction loop), the geodesic skeleton proofs higher efficiency than traditional methods. Results at very low bit-rates are presented and compared to standard methods confirming the validity of the chosen approach.     

Postprocessing for very low bit-rate video compression

This paper presents a novel postprocessing algorithm developed specifically for very low bit-rate MC-DCT video coders operating at low spatial resolution, postprocessing is intricate in this situation because the low sampling rate (as compared to the image feature size) makes it very easy to overfilter, producing excessive blurring. The proposed algorithm uses pixel-by-pixel processing to identify and reduce both blocking artifacts and mosquito noise while attempting to preserve the sharpness and naturalness of the reconstructed video signal and minimize the system complexity. Experimental results show that the algorithm successfully reduces artifacts in a 16 kb/s scene-adaptive coder for video signals sampled at 80x112 pixels per frame and 5-10 frames/s. Furthermore, the portability of the proposed algorithm to other block-DCT based compression systems is shown by applying it, without modification, to successfully post-process a JPEG-compressed image.     

Motion compensation for very low bit-rate video

A combination of spatial transformation and image segmentation is used to compensate for non-uniform intensity changes in moving scenes. The method efficiently tracks movements such that the motion vectors alone can be employed to represent a moving object with complex motion. Using fast transformation and interpolation algorithms, it is shown that while the compression efficiency of the presented method is far superior to that of the conventional full search block-matching motion estimation, its computational complexity is still affordable.     

Spatio-temporal segmentation of image sequences for object-oriented low bit-rate image coding

This paper describes a new method of segmentation of time-varying image sequences whose goal is object-oriented image coding. The segmentation represents a partition of each frame of the sequence into a set of regions which are homogeneous with regard to motion criterion. The region borders correspond to spatial contours of objects in the frame. Each spatio-temporal region is characterized by its temporal component, which is a model-dependent vector of motion parameters, and a structural component representing the polygonal approximation of the spatial contour of the region.

The construction of spatio-temporal segmentation includes two phases: the initialization step and temporal tracking. The initialization step is based on the spatial segmentation of the first frame of the sequence. Then homogeneous spatial regions are merged through motion estimation in accordance with a motion-based criterion. The temporal tracking consists of the projection of the segmentation along the time axis, and its adjustment. Special attention is paid to the processing of occlusions.

A predictive coding scheme is proposed which is based on the temporal coherence of the segmentation. This scheme is promising for a low bit-rate image compression.

The results for teleconference and TV sequences show the high visual quality of reconstructed only by prediction images. Moreover, the bit-rates for motion coding are very low: from 0.002 to 0.007 bit/pixel for teleconference sequence and from 0.004 to 0.021 bit/pixel for complex TV sequence. A scheme for encoding of the structural information is proposed which requires 0.083 – 0.17 bit per pixel depending on the content of the sequence.     

MPEG4视频压缩编码技术及应用

MPEG4是国际标准组织制定的多媒体通信的标准，文中概述了MPEG4的背景，MPEG4与MPEG1，MPEG2的主要区别以及MPEG4的主要技术。最后，展望了MPEG4的应用前景。     

Motion-compensated wavelet transform coder for very low bit-rate visual telephony

This paper proposes a new motion-compensated wavelet transform video coder for very low bit-rate visual telephony. The proposed coder sequentially employs: (1) selective motion estimation on the wavelet transform domain, (2) motion-compensated prediction (MCP) of wavelet coefficients, and (3) selective entropy-constrained vector quantization (ECVQ) of the resultant MCP errors. The selective schemes in motion estimation and in quantization, which efficiently exploit the characteristic of image sequences in a visual telephony, considerably reduce the computational burden. The coder also employs a tree structure encoding to represent efficiently which blocks were encoded. In addition, in order to reduce the number of ECVQ codebooks and the image dependency of their performance, we introduce a preprocessing of signals which normalizes input vectors of ECVQ. Simulation results show that our video coder provides good PSNR (peak-to-peak signal-to-noise ratio) performance and efficient rate control.     

Motion vector replensihment for low bit-rate video coding

A low bit-rate video codec based on motion vector replenishment is described. Motion vectors are used to update pictures at full frame rate. In addition, part of each frame is conditionally updated with a strip of interframe video data. The video data fill the remaining channel capacity not used for motion vectors. Thus under most conditions, each frame is fully updated by motion vectors and partially with interframe video data. This method has a comparable compression efficiency with that of the frame dropping method, but does not introduce any picture ‘jerkiness’. Finally the application of the proposed method to packet video networks is examined.     

基于小波变换图像压缩芯片的实现

简述了图像压缩中小波变换的几种方法,介绍了国内外小波芯片现状,提出了在设计小波算法和芯片时需要解决的问题,最后探讨了小波芯片未来的发展机遇。     

小波变换在图像压缩过程中的作用

介绍图像压缩原理,分析小波变换用于图像压缩的一般步骤,基于多分辨分析的理论基础,重点与详细的说明了小波变换在图像压缩中的数学计算过程所起到的作用,并用MATLAB给予模拟演示.     

Shape adaptive wavelet transform for magnetic resonance images coding

Region-based coding is an important feature in today's image coding techniques as it follows different regions of the image that will be encoded at different bit rates and hence at different qualities rather than encoding the entire image with a single quality constraints. This article proposes an algorithm for the region-based coding of the brain magnetic resonance images in which the brain part will be encoded with more number of bits than the background. This method employs Shape Adaptive Discrete Wavelet Transform, which can transform the regions of interest and the background on the images independently and the coefficients can be encoded by using the SPIHT coding at different levels. This algorithm was compared with the existing wavelet-based coding techniques and a better PSNR was achieved for the same bit rate by reconstructing the region of interest with high quality than the background.