基于JPEG的固定背景视频压缩算法研究

为了对固定背景视频进行压缩并获得较高的压缩比,在JPEG静止图像压缩标准的基础上提出了一种新的应用于固定背景视频压缩的算法.对第一帧图像进行JPEG格式的压缩并保存量化后的离散余弦变换系数,对第一帧后的每一帧图像,在进行离散余弦变换和量化后,先同存储器内的第一帧图像的离散余弦变换系数进行异或运算再进行熵编码.通过使用该算法和H.264视频压缩标准对同一段固定背景视频进行压缩并比较压缩后的数据量,表明了该算法具有较高的压缩比.     

Feig快速DCT算法及其处理器的体系结构设计

离散余弦变换是ＪＰＥＧ和ＭＰＥＧ中的关键技术之一。当前ＭＰＥＧ的普遍应用是在解码中使用，一个解码的例子是ＶＣＤ，ＩＤＣＴ是静止／运动补偿帧解码的关键部分。为了要得到较好的性能，ＩＤＣＴ通常被硬件逻辑实现而嵌入产品中，但该方法有一个缺陷。那就是ＩＤＣＴ的硬件逻辑实现不能完成ＭＰＥＧ所需要的其它功能，如音频解码，视频／音频的比特流可变长度解码等等。文中提出的Ｆｅｉｇ快速ＤＣＴ算法的并行顺序指令流实现Ｉ     

No-reference image quality assessment based on localized discrete cosine transform for JPEG compressed images

In this paper, we propose a new no-reference image quality assessment for JPEG compressed images. In contrast to the most existing approaches, the proposed method considers the compression processes for assessing the blocking effects in the JPEG compressed images. These images have blocking artifacts in high compression ratio. The quantization of the discrete cosine transform (DCT) coefficients is the main issue in JPEG algorithm to trade-off between image quality and compression ratio. When the compression ratio increases, DCT coefficients will be further decreased via quantization. The coarse quantization causes blocking effect in the compressed image. We propose to use the DCT coefficient values to score image quality in terms of blocking artifacts. An image may have uniform and non-uniform blocks, which are respectively associated with the low and high frequency information. Once an image is compressed using JPEG, inherent non-uniform blocks may become uniform due to quantization, whilst inherent uniform blocks stay uniform. In the proposed method for assessing the quality of an image, firstly, inherent non-uniform blocks are distinguished from inherent uniform blocks by using the sharpness map. If the DCT coefficients of the inherent non-uniform blocks are not significant, it indicates that the original block was quantized. Hence, the DCT coefficients of the inherent non-uniform blocks are used to assess the image quality. Experimental results on various image databases represent that the proposed blockiness metric is well correlated with the subjective metric and outperforms the existing metrics.

     

Automatic caption localization in compressed video

We present a method to automatically localize captions in JPEG compressed images and the I-frames of MPEG compressed videos. Caption text regions are segmented from background images using their distinguishing texture characteristics. Unlike previously published methods which fully decompress the video sequence before extracting the text regions, this method locates candidate caption text regions directly in the DCT compressed domain using the intensity variation information encoded in the DCT domain. Therefore, only a very small amount of decoding is required. The proposed algorithm takes about 0.006 second to process a 240×350 image and achieves a recall rate of 99.17 percent while falsely accepting about 1.87 percent nontext DCT blocks on a variety of MPEG compressed videos containing more than 2,300 I-frames     

奇偶量化DCT系数实现文本信息隐藏

提出了一种基于图像载体的文本信息隐藏算法。引入一种新的基于地址错位的随机发生器算法,对所嵌入信息进行置乱。根据置乱后信息按照特定规则对图像量化系数进行奇偶处理,从而实现文本信息嵌入。针对图像压缩时所导致的误码,利用JND模型,提出了一种新的基于提取对比的误码修正算法。实验表明,该算法具有较强的鲁棒性和不可见性,在抵抗JPEG压缩、噪声、剪切等干扰具有较优良的性能。     

Render2MPEG: A Perception-based Framework Towards Integrating Rendering and Video Compression

Currently 3D animation rendering and video compression are completely independent processes even if rendered frames are streamed on‐the‐fly within a client‐server platform. In such scenario, which may involve time‐varying transmission bandwidths and different display characteristics at the client side, dynamic adjustment of the rendering quality to such requirements can lead to a better use of server resources. In this work, we present a framework where the renderer and MPEG codec are coupled through a straightforward interface that provides precise motion vectors from the rendering side to the codec and perceptual error thresholds for each pixel in the opposite direction. The perceptual error thresholds take into account bandwidth‐dependent quantization errors resulting from the lossy com‐pression as well as image content‐dependent luminance and spatial contrast masking. The availability of the discrete cosine transform (DCT) coefficients at the codec side enables to use advanced models of the human visual system (HVS) in the perceptual error threshold derivation without incurring any significant cost. Those error thresholds are then used to control the rendering quality and make it well aligned with the compressed stream quality. In our prototype system we use the lightcuts technique developed by Walter et al., which we enhance to handle dynamic image sequences, and an MPEG‐2 implementation. Our results clearly demonstrate many advantages of coupling the rendering with video compression in terms of faster rendering. Furthermore, temporally coherent rendering leads to a reduction of temporal artifacts.     

基于DCT快速变换的图像压缩编码算法

在JPEG标准中,基于图像压缩的有损压缩算法中的离散余弦变换（DCT）,应用于很多图像压缩场合,并且在实际操作中,能获得较高的压缩比,同时压缩后的图像与原始图像的视觉效果基本相同,因此得到了广泛应用。为了达到提高图像质量的目的,文中提出了一个基于二维离散余弦变换（DCT）的图像压缩改进算法,该算法通过设置量化系数来控制图像压缩数组的大小。同时,在图像压缩部分利用DCT快速算法。仿真实验结果表明：该算法进一步提高了图像的峰值信噪比（PSNR）和主观视觉质量。     

Forensics for partially double compressed doctored JPEG images

Digital image forensics is required to investigate unethical use of doctored images by recovering the historic information of an image. Most of the cameras compress the image using JPEG standard. When this image is decompressed and recompressed with different quantization matrix, it becomes double compressed. Although in certain cases, e.g. after a cropping attack, the image can be recompressed with the same quantization matrix too. This JPEG double compression becomes an integral part of forgery creation. The detection and analysis of double compression in an image help the investigator to find the authenticity of an image. In this paper, a two-stage technique is proposed to estimate the first quantization matrix or steps from the partial double compressed JPEG images. In the first stage of the proposed approach, the detection of the double compressed region through JPEG ghost technique is extended to the automatic isolation of the doubly compressed part from an image. The second stage analyzes the doubly compressed part to estimate the first quantization matrix or steps. In the latter stage, an optimized filtering scheme is also proposed to cope with the effects of the error. The results of proposed scheme are evaluated by considering partial double compressed images based on the two different datasets. The partial double compressed datasets have not been considered in the previous state-of-the-art approaches. The first stage of the proposed scheme provides an average percentage accuracy of 95.45%. The second stage provides an error less than 1.5% for the first 10 DCT coefficients, hence, outperforming the existing techniques. The experimental results consider the partial double compressed images in which the recompression is done with different quantization matrix.     

抵抗JPEG的自嵌入内容认证水印方法研究

针对JPEG压缩,提出一种自嵌入的半脆弱内容认证水印方法.采用离散小波分解提取原始图像的稳态特征并映射成水印信息,在密钥控制下生成混沌序列对水印信息进行加密;将水印嵌入到离散余弦变换的量化系数中,最后进行逆量化和逆离散余弦变换变换得到含水印图像.当图像的内容需要认证时,可以区分正常的压缩和恶意篡改,而且还可以进行篡改定位.实验结果表明,该方法对JPEG有损压缩具有较好的鲁棒性、安全性和良好的不可见性.     

Malicious inter-frame video tampering detection in MPEG videos using time and spatial domain analysis of quantization effects

In this paper, a new algorithm is proposed for forgery detection in MPEG videos using spatial and time domain analysis of quantization effect on DCT coefficients of I and residual errors of P frames. The proposed algorithm consists of three modules, including double compression detection, malicious tampering detection and decision fusion. Double compression detection module employs spatial domain analysis using first significant digit distribution of DCT coefficients in I frames to detect single and double compressed videos using an SVM classifier. Double compression does not necessarily imply the existence of malignant tampering in the video. Therefore, malicious tampering detection module utilizes time domain analysis of quantization effect on residual errors of P frames to identify malicious inter-frame forgery comprising frame insertion or deletion. Finally, decision fusion module is used to classify input videos into three categories, including single compressed videos, double compressed videos without malicious tampering and double compressed videos with malicious tampering. The experimental results and the comparison of the results of the proposed method with those of other methods show the efficiency of the proposed algorithm.     

一种改进的JPEG算法研究

图像压缩技术是视频信息存储和传输的关键技术之一,本文首先分析了标准JPEG算法的过程和不足,理论上讨论了切匹雪夫(HEBYCHEV)算法较DCT变换的优越性,并且引入自适应量化算法对标准JPEG的量化表加以重构,通过微机仿真表明在相同压缩比的条件下较标准JPEG的恢复图像信噪比有所提高,同时恢复图像的质量也有改进,这种方法有一定的价值和实用性。     

视频压缩流简化帧处理中若干问题研究

数据压缩技术主要用于减小视频数据的大小,以满足存储和传输的需要,但现有的图象处理技术必须先将视频压缩流完全解压后才能进行处理,本文讨论了不需要完全解压缩或仅需很小的解压就能直接对视流进行处理的方法,如ＭＰＥＧ压缩视频流中Ｐ帧和Ｂ帧以及常用的压缩域处理方法以及存在的问题,最后证明了在半象素运动矢量情况下ＭＰＥＧ简化帧抽取的准确性问题,视频压缩流在压缩域处理的特点是不仅减少了解压缩所需要的计算时间,而     

基于DCT压缩域的图象字符定位

为了能够利用图象中所含的文字信息来进行图象的快速高效浏览检查，其中，快速字符定位是很重要的工作，为此设计了一种直接在图象压缩域中进行字符定位的方法，该方法主要是利用图象中字符纹理所具有的方向性特点，首先直接在DCT域中提取字符的横向、竖向、斜向纹理的方向信息，然后根据各自的阈值把字符区域从图象背景中分割出来，在处理过程中，用形态滤波的方法可有效地消除噪音点，该算法可直接处理JPEG、MPEG等以DCT为编码基础的压缩数据，仅需少量的解码过程（Huffman解码）即可完成字符定位，因此要处理的数据量较少，用该算法既提高了处理速度，又减少了对计算机资源的需求，试验结果表明，此方法具有较高的准确率。     

基于输入图像内容的比特率控制

在静止图像的压缩中 ,为得到固定大小的码流文件 ,有必要根据输入图像的特点 ,自适应地控制量化器的参数 ,从而控制输出压缩图像的比特率 .JPEG标准未给出比特率控制方法 ,而一些传统的比特率控制方法为专用的压缩解压缩系统设计 ,并不适用在于开放的基于交换格式的 JPEG压缩系统 .本文提出一种和 JPEG标准完全兼容的比特率控制算法 ,按照输入图像的活动性 ,计算相应的压缩质量因子 ,自适应地为每个 8× 8的块分配比特数 ,并且在熵编码时调整各块的比特数 ,适时启动块截除 ,保证压缩文件的大小不超过预先给定值 .本算法适用于存储容量有限的静止图像压缩的场合 ,可以保证存储规定帧数的压缩文件图像     

基于量化噪声的JPEG图像篡改检测

JPEG图像篡改引入的双重压缩会导致篡改区域的原始压缩特性发生改变,因此可以利用篡改区域压缩特性的不一致性来检测图像的篡改。利用该原理,提出了一种基于量化噪声的JPEG图像篡改检测算法。算法对待检测图像进行分块,计算每块的量化噪声,求取图像块的量化噪声服从均匀分布和高斯分布的概率,从而检测出篡改过的双重压缩区域。实验结果表明：该算法能有效检测双重压缩的JPEG图像篡改,并能定位出篡改区域。     

基于三维离散余弦变换的彩色图象压缩编码

离散余弦变换对图象信号有近似最优的去相关能力，但多维的变换公式一直没有给出，为此深入研究了三维离散余弦变换，提出了任意尺寸的三维函数f(x,y,z)的正交离散余弦变换公式，克服了以前系数的取值必须相等的缺点，并将之应用于彩色静止图象的压缩编码中，使得彩色图象的R，G，B3帧可以作为一个整体同时进行变换，极大地去除了图象R，G，B3帧间的相关性，理论分析和实验结果表明，在大幅度地增加压缩比的同时，峰峰信噪比也有明显提高，并且与国际标准JPEG，MPEG有很好的兼容性。     

基于JPEG双量化效应的图像盲取证

JPEG图像的双量化效应为JPEG图像的篡改检测提供了重要线索.根据JPEG图像被局部篡改后,又被保存为JPEG格式时,未被篡改的区域(背景区域)的离散余弦变换(DCT)系数会经历双重JPEG压缩,篡改区域的DCT系数则只经历了1次JPEG压缩.而JPEG图像在经过离散余弦变换后其DCT域的交流(AC)系数的分布符合一个用合适的参数来描述的拉普拉斯分布,在此基础上提出了一种JPEG图像重压缩概率模型来描述重压缩前后DCT系数统计特性的变化,并依据贝叶斯准则,利用后验概率表示出图像篡改中存在的双重压缩效应块和只经历单次压缩块的特征值.然后设定阈值,通过阈值进行分类判断就可以实现对篡改区域的自动检测和提取.实验结果表明,该方法能快速并准确地实现篡改区域的自动检测和提取,并且在第2次压缩因子小于第1次压缩因子时,检测结果相对于利用JPEG块效应不一致的图像篡改盲检测算法和利用JPEG图像量化表的图像篡改盲检测算法有了明显的提高.     

基于压缩感知的低功耗高效率CMOS图像传感器设计

提出一种基于压缩感知的低功耗高效率CMOS图像传感器(CIS)设计.在这种压缩感知CIS中,帧存储、帧差求解和帧压缩等过程分别集成于像素级、列级和芯片级电路中,实现了图像传感过程和图像压缩过程的融合.这种融合提高了CIS在功耗、传输带宽和输出数据等方面的效率.所提出的CIS设计已采用Global Foundries 0...