一种新的可伸缩小波视频编码方法

提出了一种高度可伸缩的视频编码系统,首先对图象序列进行时间、水平和垂直方面的三维小波分解,并采用改进的集合分区等级树算法（ＳＰＩＨＴ）对小波系数进行量化。在量化过程,对压缩比特流进行排序和重组,以便中根据需要从中抽取某些子集进行译码。本编码方案帧率、空间分辨率和失真水平等的可伸缩性,对于在移动通信信道及ＡＴＭ网中进行视频传输业务是非常有用的。     

基于混合编码和IWT的医学图像近无损压缩

本文对医学图像先采用DPCM预测变换后,再选择IWT(整数小波变换)对其进行分解,对分解后的低频和高频子带分别作无损Huffman编码和有损矢量量化.根据小波分解后系数的分布特征,能量大部分集中在低频部分,对低频进行无损熵编码,对高频采用量化处理,去除人眼不敏感的冗余信息.最后利用处理过的低频和高频系数进行重构获得压缩后的图像.并与传统的离散小波变换压缩编码,JPEG和JPEG2000进行比较,实验结果表明,利用该方法能得到较高的压缩比和较好的压缩效果.     

IFS行扫描分块压缩编码

基于分块自动分形压缩PIFS理论，提出了一种新的行扫描双门限自适应多级分块压缩方法。与普通近距分块压缩方法相比，在基本保证解码质量(PSNR)的前提下，编码时间大幅降低，又压缩比有一定的提高；对于较细致的图像，在压缩比基本不变的情况下能保持较高的解码质量。在此基础上，又提出了一种新的行扫描H－V多级分块方法，与双门限自适应多级分块方法相比，压缩比有一定的提高，而解码质量略有下降。     

基于改进零树小波的红外图像盲水印算法

提出了一种小波域自适应盲水印算法,采用（7,4）汉明码技术进行纠错编码。基于整数小波变换,在中高频区采用不重复零树小波编码,自适应的量化小波系数,将水印嵌入到重要系数上。水印提取过程不需要原始图像的参与。实验结果表明,算法自适应性强,实现速度快,具有较好的不可见性,对常见的JPEG压缩、滤波、加噪、剪切等攻击具有较强的鲁棒性。     

一种利用离散余弦变换频谱图和小波变换图像编码的语音编码算法

语音、图像编码技术是现代数字通信的核心技术,通常是分开进行的,提出了一种利用二维DCT频谱图和小波变换图像编码的语音编码算法.深入分析了算法实现的关键技术——语音信号的二维DCT频谱图,仿真实现了该编码算法,对一段语音的处理结果表明,小波分解系数置零率为83.1941％,压缩后保存能量92.0867％,合成语音达到“优...     

方块编码算法之改进

利用传统方块编码算法编码压缩灰度图像,算法简单、失真率不大,却因为其方法比较固定而导致了其压缩比较小,伸缩度往往不大,在一些情况下不适合被利用来压缩图像。为了改变传统方块编码算法编码压缩灰度图像压缩比之不足,对传统方块编码算法作出改进以提高压缩比。实验证明在对一般图像进行方块编码的时候,改进以后所获得的算法有效。     

基于三维小波变换的视频图像编码研究

本文对视频序列的三维小波变换压缩编码算法进行了研究.与传统方法相比,基于三维小波变换的视频序列压缩算法更能消除帧间的冗余度,获得较高的压缩比,因而是一种很有潜力的编码方法.目前,基于三维小波变换的视频序列压缩编码的具体算法也比较多,本文对其中三种有代表性的算法进行了研究,并分析了这三种算法的优劣,并对其进行了展望.     

基于视觉特性的图像压缩编码

根据图像信号的时域相关和人的视觉特性.提出了一种易于硬件实现的图像空域压缩方法.它充分利用人的视觉分辨特性和图像保真度要求,对图像采用二维亚采样、循环移位和二维内插补偿方法.完成图像信号的压缩编码和解码,对灰度图像(8 bit量化),压缩比达6倍多,恢复图像没有失真.特别是该方法与PCM、DPCM、ADPCM等方法比较.具有信道抗干扰性强,信源编码容易.算法实现简单等特点.     

阈值改进整数小波与LZW算法相结合的水声数据压缩方法

提出一种阈值改进整数小波与基于字典编码的LZW(Lempel-Ziv-Welch)算法相结合的数据压缩方法,该方法旨在减少水声数据传输量的同时尽可能地达到高保真。数据压缩过程中,先对水声数据进行整数小波变换,再对变换后的高频系数采用改进的小波阈值算法和阈值函数进行处理,提高了数据压缩倍数和信噪比,降低了误差。最后通过LZW将处理后的系数进行编码输出,进一步提升压缩效果。文中给出了相应的数据压缩算法流程。实际舰船辐射噪声数据的压缩处理结果表明,该方法能有效提高信号信噪比、减少信号失真并能获得更大的压缩倍数。     

基于小波包分解复杂度可分级的音频编码算法

提出了一种基于小波包分解的复杂度可分级的音频编码算法。该算法对信号进行复杂度可分级的不完全不波包分解,并充分利用人耳的听觉特性和不同子带间小波系数的相关性对系数进行零树编码,不仅可在低码率上获得透明质量的重构信号,而且具有复杂度可分级编,解码和多码率可分级编码的功能,可在具有不同计算能力的计算机上实时实现音频编码的解码。     

Evaluation of the discrete element method (DEM) and of the experimental evidence on concrete behaviour under static 3D compression

The authors successfully employed the discrete element method (DEM) in numerical determinations of the response up to and beyond failure of reinforced concrete structures subjected to impact and impulsive loadings in which tensile fracture, which is reliably predicted by DEM models, often controls the dominant failure modes. However, in impact problems when penetration occurs, the reliability of the approach in predictions of the structural response of the 3D compression zone that develops at the tip of the projectile has not yet been explicitly confirmed. In this context, in view of its complexity, the performance of the method is herein assessed and compared with available experimental results in static tests. By means of numerical simulations, it was previously verified that DEM models do predict, but overestimate, the strength increase observed on concrete cubes subjected to static multiaxial compression in relation with the unconfined strength, for confining (lateral) pressures up to about 20% of the unconfined compressive stress. For higher confining stresses, however, the DEM formulation underestimates the compressive strength increase observed in cubic and cylindrical samples, for the reasons examined in the paper, in which limitations of both the numerical predictions and experimental observations are thoroughly discussed.     

干涉合成孔径声纳海试样机研制与试验

介绍了干涉合成孔径声纳海试样机的研制情况,重点阐述了其中的主要关键技术：实时干涉信号处理技术、高稳定性拖曳体设计以及高幅相一致性基阵设计,并给出了干涉合成孔径声纳的湖试和海试成像结果。结果表明：干涉合成孔径声纳海试样机系统稳定可靠,成功获取了海底的高精度数字高程图,距离分辨率达到2．5cm,方位分辨率达到5cm,高程测量精度约为0．15m。     

An Optimal Lempel Ziv Markov Based Microarray Image Compression Algorithm

In the recent years, microarray technology gained attention for concurrent monitoring of numerous microarray images. It remains a major challenge to process, store and transmit such huge volumes of microarray images. So, image compression techniques are used in the reduction of number of bits so that it can be stored and the images can be shared easily. Various techniques have been proposed in the past with applications in different domains. The current research paper presents a novel image compression technique i.e., optimized Linde–Buzo–Gray (OLBG) with Lempel Ziv Markov Algorithm (LZMA) coding technique called OLBG-LZMA for compressing microarray images without any loss of quality. LBG model is generally used in designing a local optimal codebook for image compression. Codebook construction is treated as an optimization issue and can be resolved with the help of Grey Wolf Optimization (GWO) algorithm. Once the codebook is constructed by LBG-GWO algorithm, LZMA is employed for the compression of index table and raise its compression efficiency additionally. Experiments were performed on high resolution Tissue Microarray (TMA) image dataset of 50 prostate tissue samples collected from prostate cancer patients. The compression performance of the proposed coding esd compared with recently proposed techniques. The simulation results infer that OLBG-LZMA coding achieved a significant compression performance compared to other techniques.     

Effect of lognormal particle size distributions on particle spreading in additive manufacturing

Additive manufacturing (AM) has attracted much attention worldwide in various applications due to its convenience and flexibility to rapidly fabricate products, which is a key advantage compared to the traditional subtractive manufacturing. This discrete element method (DEM) study focusses on the impact of particle polydispersity during the particle spreading process on parameters that affect the quality of the final product, like packing and bed surface roughness. The particle systems include four lognormal particle size distribution (PSD) widths, which are benchmarked against the monodisperse system with the same mean particle diameter. The results reveal that: (i) the solid volume fraction of the initial packed particle bed in the delivery chamber increases then plateaus as the PSD width increases; (ii) regardless of PSD width, the solid volume fraction of the particle bed increases with spreading layer height before compression, but decreases with layer height after compression; (iii) the bed surface roughness increases with PSD width or layer height both before and after the compression of the spreading layer; (iv) the extent of increase in solid volume fraction during compression is correlated with the extent of decrease in bed surface roughness; and (v) the broader PSDs exhibit larger fluctuations of solid volume fraction of the particle bed and bed surface roughness due to greater variability in the arrangement of particles of different sizes. The results here have important implications on the design and operation of particle-based AM systems.     

Realizing fragment spawning and fragment growth in the parallelized Discrete Element Method (DEM) during modelling of comminution

The particle based Discrete Element Method (DEM) can be applied to examine comminution processes. In this study, a DEM framework has been extended to model particle breakage without mass loss. After a breakage event occurs, spherical particles, as often considered in the DEM, are replaced by size reduced spherical fragments. During the following time steps, the fragments grow to their desired sizes, so that the mass loss can be counterbalanced. Previously defined overlaps with adjacent unbroken and broken particles (fragments) as well as walls are allowed. The breakage model has been realized in a parallelized DEM framework because comminution processes are often attributed to large numbers of particles and by parallelization the computational time can be reduced efficiently. An oedometer (one-dimensional compression in axial direction of a confined particle bed) has been modelled to investigate the parallelization efficiency and the influence of the permitted overlaps during the growth process on the growth duration. A simplified roller mill has been considered to examine the applicability of the breakage procedure considering parallelization. The results show that parallelization reduces computational time considerably. The breakage procedure is suitable to model comminution processes involving even densely packed particle systems and is superior to existing approaches.     

基于DWT-SVD的可伸缩图像渐进性水印算法

目的提出基于DWT-SVD的可伸缩图像渐进性水印算法,可用于可伸缩图像的版权保护,对可伸缩图像的安全技术具有重要的意义。方法对载体图像进行三级小波分解,确保能量的集中,减小因攻击对水印信息的影响;对各个小波分解的子带都进行H×H不重复分块,对每个子块进行奇异值分解,并计算第1个奇异值,以便选取合适的嵌入强度,经综合考虑,该算法中嵌入强度选为5;将灰度水印图像进行8个位平面分解,根据重要性降低的次序依次嵌入到载体图像三级小波分解和量化后的重要性排序降低的分辨率子带中。结果压缩比从90~20,随着压缩比的减小,提取灰度水印图像的位平面增加,图像质量不断改善,NC值逐渐增大。当压缩比在70以下时,对最低频子带系数无影响;当压缩比增大至80以上时,对最低频子带信息产生一定的影响,但水印图像依然可以提取。不同攻击和常规的信号处理攻击后各级分辨率均可提取到水印信息,水印质量随着分辨率增加逐渐变好。结论渐进性提取和鲁棒性仿真实验表明该算法能很好地抵抗压缩攻击和剪切攻击,并对常规的信号处理攻击具有很好的鲁棒性。     

Comprehensive numerical modelling of the hot isostatic pressing of Ti-6Al-4V powder: From filling to consolidation

Hot Isostatic Pressing (HIP) is a manufacturing process for production of near-net-shape components, where models based on Finite Element Method (FEM) are generally used for reducing the expensive experimental trials for canister design. Researches up to date implement in the simulation a uniform powder relative density distribution prior HIPping. However, it has been experimentally observed that the powder distribution is inhomogeneous after filling, leading to a non-uniform tool shrinkage. In this study a comprehensive numerical model for HIPping of Ti-6Al-4V powder is developed to improve model prediction by simulating powder filling and pre-consolidation by means of a two-dimensional Discrete Element Method (DEM). Particles’ dimension has been scaled up in order to reduce the computational cost of the analysis. An analytical model has been developed to calculate the relative density distribution from powder particle distribution provided by DEM, which is then passed in information to a three-dimensional FEM implementing the Abouaf and co-workers model for simulating powder densification during HIPping. Results obtained implementing the initial relative density distribution calculated from DEM are compared with those obtained considering a uniform relative density distribution over the powder domain (classic approach) at the beginning of the analysis. Experimental work has been carried out for validating the DEM (filling) and FEM (HIP) model. Comparison between experimental and numerical results shows the ability of the DEM model to represent the powder flow during filling and pre-consolidation, providing also a reliable values of the relative density distribution. It also highlights that taking into account the non-uniform powder distribution inside the canister prior HIP is vital to improve numerical results and produce near-net-shape components.     

A calibration framework for the microparameters of the DEM model using the improved PSO algorithm

The discrete element method (DEM) is commonly used for simulating the mechanical characteristics of rock materials; however, constructing a DEM model requires the specification of a number of microparameters. In this paper, to obtain the microparameters of the DEM model, the improved particle swarm optimization (PSO) calibration method was presented. Based on numerical simulation examples, the new approach is considered valid for calibrating the microparameters of the DEM model. Moreover, it is concluded that different sets of microparameters can be determined when few macroparameters are used, which indicates that the empirical formula between microparameters and macroparameters is not reliable. From the analysis of the numerical simulation results, it is suggested that more macroparameters should be used to calibrate the microparameters of the DEM model, and the corresponding numerical simulation results could be more reliable; otherwise, the generated numerical model may not accurately simulate the mechanical characteristics of rock materials.     

Comparison of two different types of railway ballast in compression and direct shear tests: experimental results and DEM model validation

Railway ballast is an angular and coarse material, which demands careful DEM modelling and validation. Particle shape is often modelled in high accuracy, thus leading to computational expensive DEM models. Whether this effort will increase the DEM model’s overall prediction quality will also vitally depend on the used contact law and the validation process. In general, a DEM model validated using different types of principal experiments can be considered more trustworthy in simulating other load cases. Here, two types of railway ballast are compared and DEM model validation is conducted. Calcite and Kieselkalk are investigated under compression and direct shear test. All experimental data will be made openly accessible to promote further research on this topic. In the experiments, the behaviour of Calcite and Kieselkalk is surprisingly similar in the direct shear test, while clear differences can be seen in the stiffnesses in the compression test. In DEM modelling, simple particle shapes are combined with the Conical Damage Model contact law. For each type of ballast, one set of parameters is found, such that simulation and experimental results are in good accordance. A comparison with the simplified Hertz-Mindlin contact law shows several drawbacks of this model. First, the model cannot be calibrated to meet both compression and shear test results. Second, the similar behaviour in shear testing but differences in compression cannot be reproduced using the Hertz-Mindlin model. For these reasons, the CDM model is considered the better choice for the simulation of railway ballast, if simple particle shapes are used.     

Reversible Data Hiding Based on Run-Level Coding in H.264/AVC Video Streams

This paper presents a reversible data hiding (RDH) method, which is designed by combining histogram modification (HM) with run-level coding in H.264/advanced video coding (AVC). In this scheme, the run-level is changed for embedding data into H.264/AVC video sequences. In order to guarantee the reversibility of the proposed scheme, the last nonzero quantized discrete cosine transform (DCT) coefficients in embeddable 4×4 blocks are shifted by the technology of histogram modification. The proposed scheme is realized after quantization and before entropy coding of H.264/AVC compression standard. Therefore, the embedded information can be correctly extracted at the decoding side. Peak-signal-noise-to-ratio (PSNR) and Structure similarity index (SSIM), embedding payload and bit-rate variation are exploited to measure the performance of the proposed scheme. Experimental results have shown that the proposed scheme leads to less SSIM variation and bit-rate increase.