用于图象压缩的子波变换的算法结构

在图象信号的传输过程中，为了降低比特率，必须进行图象压缩。数字图象压缩中的一种重要技术是子带编码。子波变换由于其在空间频率的良好局部化性能，特别适合于子带编码。本文从一有限长子波变换的算法结构出发，利用矩阵Ｋｒｏｎｅｃｋｅｒ积的性质提出了一种用于图象压缩的二维有限长离散子波变换的算法结构，并且给出了设计快速子波变换算法的方法。     

Image Data Compression using Zonal Sampling and Piecewise-Linear Transforms

In this paper, image data compression methods based on sample selection in the piecewise-linear transform domain will be presented. The image is subjected to a 2-dimensional piecewise-linear transformation and some coefficients will be selected using threshold method and a proposed zonal sampling method. In the proposed zonal sampling method all samples outside the selected zone will be discarded completely (no zeros are replaced). The inverse transformation in this case will have a dimension equal to that of the selected zone. Thus the number of computations needed for the inverse transformation is reduced. The Peak Signal-to-Noise Ratio (PSNR) is used as a measure of quality of the reconstructed images. Comparisons of the compression ability using piecewise-linear transforms and some selected orthogonal transforms such as Walsh and cosine transforms are given. The results obtained by using the proposed zonal sampling method show that the piecewise-linear transforms have a better performance than the orthogonal transforms.     

ISITRA: A generalized way of signal decomposition and reconstruction

A new generalized way of signal decomposition and reconstruction entitled ISITRA is proposed. It is similar to the 2-channel filter bank scheme. In ISITRA, all the filters are obtained from a real vector. ISITRA allows decomposition of a signal into (1) an approximation and a detail, (2) two details and (3) two approximations. The latter two cases are not generally possible in the filter bank scheme. The choice of filter coefficients in ISITRA is much simpler and more arbitrary compared to that in the existing schemes. This allows one to find better filter coefficients for different applications. One can straight achieve an image compression ratio of 8:1 without doing any coding by modifying the range of pixel values in the decomposed components. One can also find a better set of decomposition and reconstruction filters than the commonly used Daubechies' wavelet filters of length 4. ISITRA is simpler and computationally marginally better than even the computationally efficient polyphase filter bank scheme.     

基于小波变换的三维医学图象压缩技术的研究

满足诊断要求的医学影像无失真压缩编码技术的研究是图象压缩编码研究的新领域,也是ＰＡＣＳ系统和远程医疗诊断系统研究的热点之一。该文正是以ＣＴ,ＭＲＩ等医疗成像设备在临床应用时一次检查产生的人体某一部位的多帧断层图象组为对象,取目前编码领域最具潜力的小波变换技术,并将小波变换由二维推广至三维,同时将二维工邓列图象组视为三维图象而开展的医学影像编码技术研究。实验结果表明,在经临床医师确认的失真门限附近,     

基于可逆整数小波变换的遥感图像的无损压缩

针对遥感数据的特点，将可逆整数小波引入遥感图像压缩领域，与SPIHT编码相结合，试验选用了几种可逆整数小波对几幅遥感图像和标准测试图像进行图像无损压缩试验，结果与JPEG2000相比都所有提高。     

Current state and future directions of multirate filter banks and their applications

This paper provides an overview of the basic concepts, current state and future directions of uniform and nonuniform multirate filter banks and their applications. Research in the areas of multidimensional filter banks, and wavelet transforms, as a direct extension to the topic is still proceeding at a rapid rate. Different design techniques and algorithms that are currently of interest are investigated from hardware complexity and reconstructed signals' quality points of view. Important similarities and differences between different filters categories are noted, which lead to a discussion of important issues that need to be resolved. Distortions and quantization effects present in the filter banks are reviewed and some solutions for controlling different types of distortions are introduced. The problem of designing QMF banks that can provide good frequency resolution while allowing for exact or near perfect reconstruction of the signal is quite challenging, because so many dissimilar types of distortion must be minimized and/or eliminated in the same design context. Recently, the perfect reconstruction cosine-modulated filter bank and filter banks with block sampling have emerged as an attractive choice of filter bank with respect to implementation complexities and design cost. New trends and future directions including selective multirate filter banks, filter banks with nonuniform decimation ratio, filter banks with discrete coefficients, multidimensional filter banks, nonlinear filter banks and data dependent decompositions are presented. Finally, some selected applications of multirate filter banks are described; namely transmultiplexers, speech and image coding, analog voice privacy systems and wavelets based signal and image compression.     

A subband coding approach to control under limited data rates and message losses

For the design of networked control systems, we employ a subband coding technique to efficiently use the available data rate. Such coding schemes have widely been used in signal processing for data compression. We take an approach suitable from the control perspective in that frequency characteristics of a controller are directly used. In particular, we propose a three-step design procedure for the overall controller having the following features: On the coder side, it uses a controller consisting of a filter bank whose outputs are subband signals of the control input. On the decoder side is another filter bank for reconstruction of the subband signals. This decoder is capable to account for random message losses that occur in communication and is designed via an H^∞-type method. For the quantizers in the coder, an efficient bit allocation scheme is also developed.     

一种小波变换域彩色图像压缩编码方案

提出了一种基于人眼视觉特性与局部相关的小波域彩色图像编码方案．该方案以嵌入零树小波（EZW）编码思想为基础,通过建立可逆彩色空间变换,丢弃部分高频细节子带、单独编码最低频子带、高频子带自适应EZW编码及多关联预测算术编码等措施,实现彩色图像的自适应压缩编码．实验结果表明,文中算法具有较好的压缩效果和较强的通用性．     

基于三角网格模型多分辨分解的图像压缩

构造了图像的三角网格模型.基于三角网格模型的多分辨分解,提出了一个新的图像压 缩方法.通过图像的三角网格模型的多分辨分解、压缩与重构,实现了图像的多分辨解、压缩与重 构.构造了一个在小波图像压缩中未曾使用过的小波滤波器组,该小波滤波器组算法具有O(n)运 行时间.实验表明,该方法能获得较好的图像压缩性能.     

基于整数小波变换和子带比特平面编码的图象压缩算法

在分析图象整数小波变换的基础上 ,提出了基于子带比特平面编码的压缩算法 .该算法将整数小波系数按子带分为若干比特平面 ,称之为子带比特平面 ,并采用简单高效的率失真优化算法确定子带比特平面的编码顺序 ,且这一顺序与图象无关 .按此顺序对子带比特平面进行自适应 MQ算术编码 ,便得到嵌入式压缩码流 .该算法可以从无损到有损 ,以任意倍率或质量进行图象压缩 ,压缩效率达到了浮点 EZW算法和 JPEG2 0 0 0整数小波编码方案的水平 ,而速度远快于这两者的速度 .该算法还具有复杂度低 ,占用内存少的优点 .     

基于自适应提升小波变换的图像压缩算法

提出了一种自适应提升小波变换算法,该算法是根据待分析信号的局部特点,自适应的选择更新器,自适应更新器的选择,主要是保持图像边缘不被平滑,防止出现大的小波系数。为确保系统的稳定性,又提出了采用先更新后预测的提升结构。在此结构中,预测过程不影响更新过程,这也为自适应算法的重构提供了有利条件,由于稳定性高、高频系数小以及能够完全重构,使得此方法有利于压缩性能的提高。通过实验证明了该算法的有效性。     

基于内容的嵌入零树小波图像编码算法

提出了一种基于内容的嵌入零树小波图像编码算法 ,该算法以 EZW编码方案为基础 ,但能够充分依据人眼视觉掩蔽特性自适应确定高频子带系数的扫描顺序 ,从而有效克服 EZW算法低比特率下图像边缘及纹理处复原质量不理想的弱点 .对比实验表明 :本文算法的图像复原质量明显优于 EZW等算法     

一种用于图像编码的双正交插值小波

针对CDF-9／7小波滤波器系数是无理数的缺点,利用小波滤波器的精确重构条件,构造一类仅用一个自由参数表达的双正交插值小波。通过调整自由参数构造一种具有最佳编码增益和二进制（形如k／2^n,t,n∈Z的数）系数的插值小波。实验表明其图像压缩性能与CDF-9／7小波相当,小波变换的计算效率提高50％以上。     

整型小波变换应用于遥感图像无损压缩

基于“提升”(Lifting)算法实现整型小波变换(IWT),然后将图像变换到小波域,用零树编码 和算术编码相结合的方式对图像进行无损压缩,并针对遥感图像波段之间的相关性进行了谱间预 测。最后进行了一些相关实验,实验证明将IWT应用于遥感图像无损压缩是有效的。     

智能交通系统中图像融合与压缩技术

针对智能交通系统信息采集的需要,提出基于小波分析的图像融合和零树编码的小波图像压缩算法,利用小波变换将红外和可见光图像进行融合,利用各子带小波系数对图像恢复的重要程度和人眼的视觉特性对融合图像进行压缩,算法的实际应用提高了所采集的交通信息的完整性、统一性和容错性,并改善了智能交通系统的服务质量。     

面向遥感影像的JPEG2000优化压缩算法

在常规的JPEG2000压缩框架下,提出一种面向遥感影像的JPEG2000优化压缩算法,对遥感图像整体处理传输耗时进行分段处理,在EBCOT编码中合并编码通道扫描过程及编码过程,实现对遥感图像编/解码过程用时的优化,在小波变换后清除高频子带小波系数中非重要的背景信息,并缩减相对重要信息的处理过程,从而缩短了与压缩比和图像大小密切相关的传输时间。实验结果表明,该算法在几乎不影响遥感图像质量的情况下可以显著提高遥感图像整体压缩、传输和重构的效率,缩短其处理耗时。     

Rotation and gray scale transform invariant texture identificationusing wavelet decomposition and hidden Markov model

In this correspondence, we have presented a rotation and gray scale transform invariant texture recognition scheme using the combination of quadrature mirror filter (QMF) bank and hidden Markov model (HMM). In the first stage, the QMF bank is used as the wavelet transform to decompose the texture image into subbands. The gray scale transform invariant features derived from the statistics based on first-order distribution of gray levels are then extracted from each subband image. In the second stage, the sequence of subbands is modeled as a hidden Markov model (HMM), and one HMM is designed for each class of textures. The HMM is used to exploit the dependence among these subbands, and is able to capture the trend of changes caused by rotation. During recognition, the unknown texture is matched against all the models. The best matched model identifies the texture class. Up to 93.33% classification accuracy is reported     

快速傅立叶变换的图像数据压缩算法

当今图像数据信息的海量化,使得图像压缩编码应用显得尤为重要,图像压缩的分类方法很多,限失真编码以其压缩比高而得到广泛应用。常见的限失真编码主要采用余弦变换,K-L变换,小波变换等。该文另辟蹊径采用快速傅里叶变换,及霍夫曼编码方式对标准lena图像数据进行限失真压缩编码压缩,得到了较好的压缩效果。     

Wavelet domain-based video noise reduction using temporal discrete cosine transform and hierarchically adapted thresholding

A novel spatio-temporal filter for video denoising, which operates entirely in the wavelet domain, is proposed. For effective noise reduction, the spatial and temporal redundancies that exist in the wavelet domain representation of a video signal are exploited. First, a 2D discrete wavelet transform is applied to the input noisy frames. This is followed by a discrete cosine transform (DCT), which is applied to the temporal subband coefficients to minimise the redundancy among the consecutive frames. The DCT transformed, noise-free coefficients in the different wavelet domain subbands for the original image sequence are modelled using a prior having a generalised Gaussian distribution. On the basis of this prior, filtering of the noisy wavelet coefficients in each subband is carried out using a new, low-complexity wavelet shrinkage method, which utilises the correlation that exists between subsequent resolution levels. Experimental results show that the proposed scheme outperforms several state-of-the-art spatio-temporal filters in terms of both the peak signal-to-noise ratio and the visual quality     

A new approach to design triplet halfband filter banks based on balanced-uncertainty optimization

This paper presents a novel approach to design a class of triplet halfband filter banks (THFB) based on optimized time–frequency localization. First, an Euler–Frobenius polynomial (EFP) is introduced to design a class of halfband polynomial. The vanishing moments and perfect reconstruction conditions are imposed on EFP to obtain maximally flat halfband filter. The resultant halfband filter is optimized using a balanced-uncertainty (BU) metric in order to have balance between time and frequency spread. Next, this optimized halfband filter is used in three-step lifting scheme to obtain analysis and synthesis wavelet filters which have balance between time and frequency localization. The proposed method provides three degrees of freedom that results in flexible design of filter bank. It is observed that the proposed filter bank gives more regularity and better frequency selectivity as compared to existing filter banks. These designed filters are then used for human chromosome image compression application. The performance of the designed filter bank is compared in terms of PSNR using different bit-rates with well-known existing filter banks in order to validate the experimental results.