基于DCT量化系数重组的JPEG图像加密算法

整个加密算法分两个过程,首先在DCT变换之前对原始图像进行以8×8图像块为单位的统一图像置乱,使图像整体视觉效果上杂乱无章.其次,DCT变换量化系数之后,将相邻两个8×8系数块的低频系数组成一个新块,高频系数组成一个新块,分别进行块内的系数置乱,在改变原始图像频率成分的同时,可以减少改变零游程结构带来的加密对JPEG图像压缩影响,而且8×8系数块内的非零系数个数发生了变化,可以有效抵御统计非零系数个数攻击.     

图像内区域复制粘贴篡改鉴定

区域复制粘贴篡改检测算法是以图像块匹配为基础的,然而传统的匹配算法计算量大,匹配速度慢,效率低下.针对现有的图像内区域复制粘贴检测算法计算量大,时间复杂度高的问题提出一种有效快速的检测与定位篡改区域算法.首先利用小波变换获取图像低频区域,然后对得到的图像低频部分进行分割,然后对分割后得到的每个图像块进行DCT变换,通过特征向量排序缩小匹配空间,最后通过经验阈值进行真伪鉴定,实验结果表明该算法过程中除掉图像冗余,减少检测块数,降低了时间复杂度,提高了检测效率.     

一种基于H．264标准的视频水印方案

本方案采用量化DCT系数和最低有效位匹配的方式进行水印提取.通过每个4×4整数DCT变换块中的量化DC系数来确定是否嵌入水印.最低有效位是指量化AC系数的幅度之和所在编号的最低住,最低有效位匹配基于水印信息和该编号来实现,根据水印比特修改少量的量化AC系数使水印比特和子块编号相匹配.实验结果表明,所提出的水印算法有效且具有盲检功能.另外.本算法也不复杂,可用于实时应用.     

基于S-PCNN与DDCT相结合的多传感器图像融合

基于简化脉冲耦合神经网络(S-PCNN)与方向离散余弦变换(DDCT)提出一种有效的多传感器图像融合算法。首先将输入图像分为不重叠的方块,并对每个图像块进行8个模的方向DCT变换,得到8方向的模系数;然后分别将图像块对应的模系数送入PCNN模型聚类分析后,对比模系数的点火次数,选取合适图像块系数,得到8个新的图像块系数;最后使用PCA算法将8个图像块合成一幅完整图像块。对输入图像的图像块重复融合过程可得完整的融合图像。     

H．264整数DCT的FPGA实现

H.264整数DCT变换算法有助于减少计算复杂度,提高编码速度,进一步提高视频或图像的压缩效率。分析H.264整数DCT变换的快速算法及其实现原理,并提出一种用来具体实现一个4×4块的DCT变换的结构;同时给出用VHDL语言实现4×4块DCT变换的内部模块的源代码和仿真波形。仿真结果表明用该算法可快速实现一个4×4块的整数DCT变换。提出一种切实可行的用于H.264整数DCT变换的结构,该结构可完全用硬件电路快速实现;对于用FPGA实现H.264整数DCT变换做了一次实践性的尝试,对深入理解H.264整数DCT变换及其算法的具体实现具有一定的实践意义。     

利用数字压缩技术频域内积和方差的分形编码算法

文中定义了图像块的数字压缩技术(DCT)频域内积,并证明了该内积等于时域内积, 从而可根据频域内积大小来作为分形编码中最佳匹配块的判断,并推导出DCT域上恒等变换与其余7种对称变换的关系。本文将值域块分为平稳、中间和活跃三类,研究对于不同类型的值域块,求频域内积时,保留低频系数个数和解码图像质量之间的关系,并提出了基于DCT域内积和方差的分形图像编码算法。在实验中,将本文算法分别同文献[ 2 ]、[ 3 ]中方法进行了比较,结果表明,本文算法能在基本保证解码图像质量的同时,大大提高编码速度。     

离散余弦变换编码的现状与发展研究

1974年由Ahmed和Rao提出的离散余弦变换,至今已有30年历史。此间,DCT编码已发展成为JPEG、MPEG、H.26x等图像/视频编码标准中的核心。尽管Shapiro的EZW以及Said等人的SPIHT小波编码的成功应用,对传统的DCT编码提出了挑战,但Xiong等人利用嵌入式DCT块变换之间的直流相关性,以及对DCT后的系数进行策略性重组或层式DCT同样具有小波多分辨率图像的分解特性。此外,基于层次嵌入式DCT、形状自适应DCT、截短DCT、感兴趣区域支撑DCT以及形态DCT等改进形式的编码,都是将基于DCT变换编码推向更高层次。就DCT改进的变换,以及DCT系数的应用,如利用DCT系数实现信息隐藏等,也使得基于常规的DCT变换编码有了更广阔的应用与发展空间,文章就此作了广泛的比较和深入的研究,并指出了发展方向。     

基于整数DCT变换的数字水印算法的研究

提出了一种基于整数DCT变换的数字水印算法,该算法利用其变换的整数特点,首先对频域嵌入系数进行定量分析,找出适合嵌入的系数与嵌入阈值的大小关系,接着提取每个图像块的DC系数组成一幅新图,选择新图中具有复杂纹理的图像块再次进行整数DCT变换,最后将水印信号嵌入到这些图像块中。仿真实验结果表明,该算法既保证了水印的掩蔽性,同时具有很好的鲁棒性,对JPEG压缩、噪声、滤波等攻击都具有很好的免疫能力。     

双重功能图像水印算法

提出一种能同时实现内容认证和版权保护双重功能的图像水印算法.首先,对原始图像进行分块奇异值分解(SVD),计算所有子块最大奇异值的均值,通过比较各子块的最大奇异值与所有子块最大奇异值的均值间的数值关系产生鲁棒零水印序列.然后,对原始图像进行分块离散余弦变换(DCT).调整图像子块DCT高频系数的数值大小,建立同一子块两...     

H．264／AVC中的整数变换与DCT变换的比较

数字视频技术在通信和广播领域获得了日益广泛的应用,视频信息和多媒体信息在网络中的处理和传输成为当前我国信息化中的热点技术。运动图像专家组和视频编码专家组给出一种更好的标准,确定为MPEG-4标准的第十部分,即H.264/AVC。简述H.264的研究意义及DCT的原理。为了减少运算量,分析H.264中如何对宏块的整数变换,详述H.264的编码变换的方法,给出整数变换方法与传统的DCT的区别和联系,并给出H.264的整数变换方法的快速算法即蝶形算法,这与传统的DCT变换是不同的。     

Edge-based motion compensated classified DCT with quadtree for image sequence coding

The motion compensated discrete cosine transform coding (MCDCT) is an efficient image sequence coding technique. In order to further reduce the bit-rate for the quantizied DCT coefficients and keep the visual quality, we propose an adaptive edge-based quadtree motion compensated discrete cosine transform coding (EQDCT). In our proposed algorithm, the overhead moving information is encoded by a quadtree structure and the nonedge blocks will be encoded at lower bit-rate but the edge blocks will be encoded at higher bit-rate. The edge blocks will be further classified into four different classes according to the orientations and locations of the edges. Each class of edge blocks selects the different set of the DCT coefficients to be encoded. By this method, we can just preserve and encode a few DCT coefficients, but still maintain the visual quality of the images. In the proposed EQDCT image sequence coding scheme, the average bit-rate of each frame is reduced to 0.072 bit/pixel and the average PSNR value is 32.11 dB.     

Entropy Coding for a Hybrid Scheme with Motion Compensation in Subprimary Rate Video Transmission

Entropy coding has been investigated for motion-compensated interframe (MC) prediction followed by two-dimensional discrete cosine transform (DCT) for prediction error. In particular, variable word length coding methods for motion vector and transform coefficients have been discussed assuming low bit rate such as 384 kbits/s for transmission of videoconference sequences. For motion vector information, it is advantageous to employ a one-dimensional code set common to both horizontal and vertical components of motion vectors. The code set can be obtained using a combined distribution of the two components. In order to encode transform coefficients, different methods are applied to significant and insignificant blocks. Run-length coding is adequate for representing clusters of insignificant blocks. In encoding transform coefficients in significant blocks, a zone coding method which encodes transform coefficients within a minimum area enclosing all nonzero coefficients is suitable. Simulation of video sequences shows that a combination of the coding methods described here can achieve high coding efficiency for videoconference sequences.     

使用区域搜索的DCT域分形图像编码方法

为降低ＤＣＴ域分形图像压缩的编码复杂度,文中引入了平坦块的概念,对那些经过ＤＣＴ变换后,能量非常集中的块不做块匹配,而是直接编码输出。同时经统计发现,对于给定的区块,与它匹配最好的域块通常位于这个区块的上方或附近,文中利用这个事实构造了一种优化的自适应搜索方案,大大减少了编码所需要的时间。实验表明,与一般的ＤＣＴ域分形图像压缩方法相比,文中方案在提高了编码速度的同时降低了比特率。     

A direct computation of DCT coefficients for a signal block takenfrom two adjacent blocks

A direct computational algorithm for obtaining the DCT (discrete cosine transform) coefficients of a signal block taken from two adjacent blocks is proposed. This algorithm reduces the number of both multiplications and additions/subtractions compared to the traditional method, which requires inverse transforms of two received coefficient blocks followed by a forward transform. The proposed algorithm is efficient and useful for speech coding and image processing, especially for real-time applications     

Prioritized DCT for compression and progressive transmission ofimages

An approach is based on the block discrete cosine transform (DCT). The novelty of this approach is that the transform coefficients of all image blocks are coded and transmitted in absolute magnitude order. The resulting ordered-by-magnitude transmission is accomplished without sacrificing coding efficiency by using partition priority coding. Coding and transmission are adaptive to the characteristics of each individual image. and therefore, very efficient. Another advantage of this approach is its high progression effectiveness. Since the largest transform coefficients that capture the most important characteristics of images are coded and transmitted first, this method is well suited for progressive image transmission. Further compression of the image-data is achieved by multiple distribution entropy coding, a technique based on arithmetic coding. Experiments show that the approach compares favorably with previously reported DCT and subband image codecs.     

基于多线性子空间KL变换的可伸缩视频压缩方法

该文提出一种基于多线性子空间KL(Karhunen-Loeve)变换的可伸缩视频压缩算法。该算法将纹理不同的图像子块投影到多个线性子空间中去,然后分别进行KL变换编码,使得每个子空间内变换系数更接近高斯分布,从而最大限度地在变换编码阶段提高压缩效率。同时,该算法结合多尺度小波分解,实现了质量可伸缩的视频编码,提高了视频压缩率。通过与DCT、小波变换以及多向DCT算法进行比较,证明该算法可获得更好的率失真性能。     

Improvements of Transform Coding Algorithm for Motion-Compensated Interframe Prediction Errors-DCT/SQ Coding

A new hybrid coding method for transmitting videoconferencing images at a bit rate 384 kbits/s is proposed. Considering the characteristics of motion-compensated interframe prediction errors for typical videoconferencing scenes, a filter is introduced to separate pulsive components on which conventional discrete cosine transform (DCT) coding method does not work well. These separated pulsive components are coded by using scalar quantization (SQ). The remainder are DCT coded. For DCT coefficients, an adaptive coding method based on the classification of DCT coefficients is applied in order to improve the coding performance. Since the proposed method employs both DCT coding and SQ of prediction errors, it is named "DCT/SQ coding method." Experimental results show that the DCT/SQ coding method is effective to reduce so-called mosquito effects, and thus it can improve the quality of decoded images.     

Image filtering in the block DCT domain using symmetric convolution

Processing of images in the transform domain saves computation by avoiding inverse and re-transform operations. In this paper, we present a technique for filtering of images in the transform domain using symmetric convolution in the block DCT space. Due to the application of convolution-multiplication property in the DCT domain, the filtering operation requires significantly less computation than its equivalent in the original signal/image space. To take care of discontinuities along boundaries of blocks, filtering is performed on a larger DCT block composed from adjacent blocks. Subsequently, the filtered DCT block is obtained by decomposing it. The proposed filtering technique achieves the same results of linear convolution in the spatial domain with reduced cost. With the proposed filtering, it is possible to significantly speedup the operation by ignoring some elements in the filtering matrices whose magnitudes are smaller than a threshold value. Typical sparseness of DCT domain input blocks is also considered for further reduction of computational cost. The proposed method uses simple linear operations such as matrix multiplication, which is appropriate for efficient hardware implementations. We also demonstrate its applications in image sharpening and removal of blocking artifacts directly in the compressed domain.     

Variable length coding of interleaved DCT coefficients for digital HDTV

This paper proposes an algorithm to redcue the bit-rate for transmission of the quantized DCT coefficient data in digital HDTV coders. The variable length coding compresses the quantized DCT coefficient data by removing their statistical redundancy. Zigzag scan is an effective way to improve the performance of the variable length coding. In order to reduce bit-rate further, we propose a new scanning method. Each DCT block is classified into the interleaving group and the non-interleaving group according to the number of non-zero DCT coefficients, and the DCT blocks in the non-interleaving group are encoded using the segmentation and interleaving of DCT coefficients, and the DCT blocks in the non-interleaving group are encoded using only zigzag scan. Simulation results show that the proposed method improves the bit-rate reduction performance by 6.8% when compared with the conventional method.     

Image vector quantizer based on a classification in the DCT domain

A classification algorithm in the discrete cosine transform (DCT) domain for the classified vector quantization (CVQ) technique is proposed. The classifier employs four DCT coefficients of 4×4 subblock as edge-oriented features. The classifier is designed using a cluster-seeking algorithm to ensure that the centroid of a set of vectors in a class always belong to that class. Since the classification is performed in the DCT domain, this approach can be easily extended to the DCT transform coding technique. Simulation results show that a good visual quality of the coded image at fixed rates in the 0.625-0.813 b/pixel (bpp) range is obtained with comparable complexity. The weighted MSE (WMSE) analysis in conjunction with the proposed classifier is discussed