一种改进的块匹配准则

块匹配算法是视频图像编码的核心技术。通过块匹配算法得到当前块和匹配块之间的残差和运动矢量,并对它们进行编码,从而大大提高了编码效率。在分析常用块匹配准则的基础上,提出一种改进的准则用于视频编码中的运动估计。相对于原始像素灰度值计算均方误差,同时在该准则中加入了一个反映灰度值变化符号的惩罚项。仿真实验表明该准则是有效的。     

基于拉普拉斯分布模型的快速DCT算法

为提高编码效率,通过分析残差系数在空域和DCT域均符合拉普拉斯分布后,提出一种快速DCT算法.该算法能够在DCT之前对每个量化DCT系数进行零值预判而节省DCT计算.通过头肩序列的实验表明新算法在不降低图像质量的条件下,其整体运算复杂度优于常规算法.     

一种优于SAD的匹配准则及其快速算法

本文根据运动估计后的残差图像DCT交流系数的统计分布规律，推导出了一种块匹配运动估计的匹配准则，并针对该匹配准则需要较多乘法运算的缺点，设计了快速算法以减少计算量。实验结果表明对有亮度变化的帧，该匹配准则可以取得比SAD匹配准则更好的图像质量，同时快速算法可以减少约80％的乘法计算量。     

基于H.264的子带DCT快速算法

DCT快速算法是H.264编码的关键问题之一。该文根据H.264中44块残差系数的分布特征及DCT系数的能量分布特性,提出一种基于DCT系数子带划分的子带DCT快速算法。该算法在DCT和量化前预判出为零的DCT系数,节省了这些系数的DCT和量化计算开销,提高编码效率。该文提出了划分DCT系数子带的判断标准,预判出子带中量化后为零的DCT系数后,仅计算非零的DCT系数,相应地也减少量化(Q),反DCT(IDCT),反量化(IQ)的计算。实验结果表明,该文算法在保持图像质量和码率的同时,极大地节省了DCT, Q,IQ,IDCT的计算量,提高了H.264的编码效率。     

基于H.264误差漂移补偿的鲁棒性视频水印算法

针对现有基于H.264的视频水印算法存在误差漂移的问题,在分析了误差漂移产生原因的基础上,提出了一种抑制误差漂移的鲁棒性视频水印新算法.通过调制H.264编码中Ⅰ帧量化后的4 ×4 DCT系数来实现水印的嵌入,并对帧内预测量化后满足特定条件的DCT子块的最后一行、列进行补偿和对帧间预测进行补偿,有效地抑制了帧内、帧间误差漂移.另外,该算法结合CAVLC编码来调制量化后的DCT残差系数,使整体码流变动较小,并且算法能够根据不同视频序列自适应地调节嵌入容量及嵌入位置,具有较好的灵活性和鲁棒性.在水印提取过程中,不需要原始视频的参与,即可实现盲提取.仿真实验结果表明,该算法在具有良好不可见性的前提下,对压缩码率影响较小,能够较好地抵抗噪声、帧剪切、重编码等攻击.     

一种提高H.261编码性能的实现方法

研究表明采用最小均方误差或绝对误差准则的块匹配运动估值算法对H.261编码器来说不是最好的。本文提出了一种改进的块匹配运动估值算法。它所采用的准则不仅考虑了预测误差能量的大小,还考虑了运动矢量信息以及帧间预测误差的编码比特数目的多少.实验结果表明新的准则能够显著地改善H.261的编码性能。     

一种基于H．264的有效运动估计算法

运动估计算法是实时视频编解码技术的研究重点，高精度的匹配和补偿可以减少预测误差，提高视频图像的压缩效果．为降低在视频编码标准H．264中运动估计的高计算复杂度问题，提出了采用一种基于节点模型的可变形块匹配运动估计算法来搜索最佳运动矢量．该算法充分利用了H．264运动矢量的的统计特性和相关性，并采用基于像素差值分类的运动估计匹配准则．实验表明，在编码性能损失很小的条件下，该算法有效降低了视频压缩编码中运动估计的运算复杂度．     

基于变换域Wyner-Ziv视频编码的有效重建算法

为了减少分布式视频编码系统重建值与真实值之间误差,提出了基于变换域Wyner-Ziv视频编码最小均方误差(MMSE)重建的一种有效重建算法.该算法充分利用视频帧间相关性,对MMSE重建算法积分区间做出调整,当边信处于解码值对应量化区间之内时,在量化区闻内利用MMSE重建;当边信息处于解码值对应量化区间之外时,对量化区间做出调整,在改进后的区间利用MMSE重建.实验结果表明,与最佳重建最小均方误差重建算法相比,该算法可以有效提高解码视频的平均PSNR.     

一种应用于指纹识别系统的指纹图像压缩算法

针对应用于指纹识别系统中指纹图像的压缩编码问题,提出了一种改进的基于四叉树分类的网格编码量化(QTCQ)的指纹图像压缩算法.该算法对小波变换后的高频系数采用2×2的DCT变换进一步集中能量,并对变换后的系数进行系数重排以使得高频子带内的重要系数集中于相应子带的低频位置,再通过基于四叉树的网格编码量化进行量化编码.仿真结果表明,该算法比WSQ和JPEG2000等均具有更好的压缩性能.     

第二代Curvelet变换域的信息隐藏方法

提出了一种基于第二代Curvelet变换的信息隐藏方法。该方法以数字图像作为掩体介质,根据Curvelet子带内各向异性尺度关系选择部分系数,并对其实部和虚部分别进行量化嵌入。引入了误差控制编码以减少误码,在提取秘密信息时不需要参考原掩体介质,实现了密文的盲提取。与DCT域Jsteg算法和小波域量化索引调制算法进行比较,结果表明,提出的算法具有较高图像质量和更大的嵌入容量。     

Computation reduction for standard-based video encoders based on the energy preservation property of DCT

Based on the energy preservation property of DCT, an optimization technique for motion estimation (ME), DCT, and quantization for standard-based video encoders is developed. First, a stopping criterion for ME is proposed to reduce the number of checking points in finding the motion vectors, and save the computations. The advantage of introducing such a stopping criterion lies in its adaptability to the quantization parameter and applicability to various fast ME algorithms. Then, the DCT and quantization are jointly optimized by tracing the remaining signal energy and removing unnecessary calculations in the process of DCT and quantization. A pruned 2-D DCT based on Huang's fast DCT algorithm is presented to demonstrate the superiority of this algorithm to the full DCT and an existing all-zero block detection method. Although proved to be computationally efficient, the algorithms introduce no obvious quality loss.     

一种基于DSP的块等级预判DCT算法

本文提出一种基于块等级预判的DCT算法,并讨论了该算法的块等级预判准则以及在DSP上实现了DCT的快速实现方法,该方法在基于DSP的视频编码中取得了良好效果。     

Novel Efficient De-blocking Method for Highly Compressed Images

Due to coarse quantization, block-based discrete cosine transform（BDCT） compression methods usually suffer from visible blocking artifacts at the block boundaries. A novel efficient deblocking method in DCT domain is proposed. A specific criterion for edge detection is given, one-dimensional DCT is applied on each row of the adjacent blocks and the shifted block in smooth region, and the transform coefficients of the shifted block are modified by weighting the average of three coefficients of the block. Mean square difference of slope criterion is used to judge the efficiency of the proposed algorithm. Simulation results show that the new method not only obtains satisfactory image quality, but also maintains high frequency information.     

Dynamic colour table: A novel S‐box for cryptographic applications

In cryptography, S‐boxes play an important role in symmetric ciphers. S‐boxes are used for substitution process to enable diffusion in encryption and decryption of the messages. In most of the conventional and modern symmetric ciphers, the S‐boxes are of static in nature. It will never depend or vary with respect to the message or the key, but dynamic S‐boxes are more resistant to linear and differential attacks when compared with the static S‐boxes. In this paper, we propose the design of a new dynamic colour table (DCT) that can be used as S‐box in symmetric ciphers and it depends upon a master key K . The same key can be used for encryption and decryption in symmetric ciphers. Dynamic colour table is a 64×4 table, having 256 entries. Each column of DCT has 64 unique values. The input to generate the DCT is 160 bit master key K . We have also developed a sub‐key generation algorithm for generating the sub keys and 4 seeds from the master key of 160 bits. These 4 seeds are used to generate the random values in DCT. Dynamic colour table uses the alpha red green blue (ARGB) colour model concept for each entry. Our DCT is so lightweight in nature. Our new DCT have a wide range of applications such as it can be used as S‐boxes in symmetric ciphers or it can be used as pseudorandom number generators. Finally, we show an implementation and the simulated results of DCT. The simulated results are used to analyse the strength of our DCT. The different criterions to verify that DCT has the characteristic of good S‐box are nonlinearity, strong avalanche criterion, bit Independence criterion, differential approximation probability, and linear approximation probability. The performance is measured in terms of time complexity and security. The results show that our DCT is cryptographically stronger to use in various symmetric encryption algorithms.     

Fast algorithm for computing discrete cosine transform

An efficient method for computing the discrete cosine transform (DCT) is proposed. Based on direct decomposition of the DCT, the recursive properties of the DCT for an even length input sequence is derived, which is a generalization of the radix 2 DCT algorithm. Based on the recursive property, a new DCT algorithm for an even length sequence is obtained. The proposed algorithm is very structural and requires fewer computations when compared with others. The regular structure of the proposed algorithm is suitable for fast parallel algorithm and VLSI implementation     

用超长指令实现DCT的新算法

本文介绍一种新的DCT计算方法,它以现有的DCT快速算法为基础,利用超长指令的并行特征来提高DCT计算的性能.仿真结果表明:该方法的运算速度比普通的DCT计算方法提高73%,即便同快速算法相比,也可以提高24%的运算速度.     

离散余弦变换的改进的算术傅立叶变换算法

离散余弦变换(DCT)是数字图像处理等许多领域的重要数学工具.本文通过一种新的傅立叶分析技术——算术傅立叶变换(AFT)来计算DCT.本文对偶函数的AFT进行了改进.改进的AFT算法不但把AFT所需样本点数减少了一半,从而使所需加法计算量减少了一半,更重要的是它建立起AFT和DCT的直接联系,因而提供了适合用于计算DCT的AFT算法.本文推导了用改进的AFT计算DCT的算法并对算法进行了简要的分析.这种算法的乘法量仅为O(N),并且具有公式一致,结构简单,易于并行,适合VLSI设计等特点,为DCT的快速计算开辟了新的途径.     

一种新的静止图象压缩编码算法

本文提出了一种新的静止图象压缩编码算法,即VQ+DPCM+DCT算法,并与JPEG标准的基本系统进行了比较。实验结果表明,新算法的压缩比有较大提高。