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1.
在资源受限的无线多媒体传感器网络中进行图像编码和传输,需要综合考虑能量消耗、压缩率和图像质量三者之间平衡的图像编码方案.研究无线多媒体传感器网络中视频监控图像序列的压缩,提出一种基于变化检测和改进JPEG算法的低复杂度图像编码方案.通过变化检测算法定位监控图像中的运动目标即感兴趣区域,仅传输兴趣区域以显著减少数据传输量...  相似文献   

2.
有效判定经拷贝攻击之后图像的版权归属是当今图像拷贝检测研究的热点和难点之一.现有的检测算法对于噪声、拉伸、旋转、等比缩放等常见攻击具有较好的鲁棒性,而对于裁剪、平移攻击则比较脆弱.针对上述问题,提出一种基于SIFT局部特征和整体DCT系数顺序测度的图像拷贝检测算法.该算法首先通过匹配的SIFT特征划定内容保持不变的区域,然后对内容不变区域的亮度分量作整体DCT变换,并将DCT系数低频交流成分的顺序测度作为图像特征,最后通过该特征判定拷贝是否存在.由于匹配的SIFT特征可以精确定位拷贝发生区域,因而对裁剪、平移攻击具有较好的抵抗能力,又由于引入整体DCT系数顺序测度作为特征,因而可以很好地抵抗其他常见攻击.同时提出翻转补偿策略,使本算法能抵抗水平翻转和垂直翻转攻击.实验结果证明,在抵抗裁剪和平移攻击方面,给出的算法相对于已有算法具有较高的查准率和查全率.  相似文献   

3.
离散余弦变换(DCT)具有图像信号处理后对图像显示效果影响不明显的优点。本文针对离散余弦变换(DCT)系数在人脸识别中的应用,研究不同的DCT块进行编码后其系数对图像质量和识别结果的影响,提出利用快速2D-DCT(二维离散余弦变换)代替普通DCT的人脸特征提取方法。该方法可以使得在对人脸进行平均分割后的图像块处理时间大大减少,从而能够在同样的时间内提取更多的DCT系数用于人脸识别。实验结果表明,该方法快速而且是有效的。  相似文献   

4.
定义了图像块的 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 .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 .实验结果表明 ,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  相似文献   

5.
基于DCT变换的数字水印算法研究   总被引:1,自引:0,他引:1  
提出了一种基于DCT变换嵌入到图像的中频带水印改进算法。该算法在DCT变换水印算法的基础上,调整DCT对应系数,然后将其嵌入到原始图像的中频系数中。从实验结果来看,该算法真正做到水印的盲监测,实现水印能够抵抗常见的噪声、裁剪、JPEG压缩等攻击,使水印具有较好的不可见性和鲁棒性。  相似文献   

6.
DCT域中的快速分形编码   总被引:3,自引:1,他引:3  
冯永超  谢立宏  贺贵明 《计算机工程》2002,28(4):173-174,275
分形图像压缩应用了图像的自相似性,目前许多对分形编码特性的研究都是在图像域中进行的。该文却试图探索在频率域中分形编码的特性。首先,综述了图像域中分形编码的特性,然后导出在离散余弦变换(简称DCT)域中仿射变换的伸缩因子和偏移量的对应公式。应用DCT的能量压缩特性,在度量图像子块和母块之间相似性中通过使用少量的低频DCT系数提出一种快速分形编码算法。接着进一步提出一种可能的快速混合分形编码的算法,该算法将快速搜索方法、统计规范化、频域比较结合起来。  相似文献   

7.
提出了一种在分块DCT低频区域上,以相邻DCT系数的平均值为基准,根据水印图像信息的二值性选择不同的偏移量来嵌入水印的算法。在水印提取时不需要原图像,是一种盲水印算法。并通过Arnold置乱来保证水印的安全性。实验结果表明,水印不可见性好,而且对于常见的噪声、裁剪、JPEG压缩具有较好的鲁棒性。  相似文献   

8.
自适应图像分块压缩算法的实现和性能分析   总被引:1,自引:1,他引:1  
自适应图像分块压缩算法是一种根据区域特征自动调整DCT变换尺寸提高编码效率的图像编码方法,该文提出了这种算法的快速实现方法,分析了这种编码方法的算法复杂度和编码效率,并用标准图像进行了测试。  相似文献   

9.
罗钧  焦荣梅 《微机发展》2007,17(10):37-39
DCT变换以其优良特性被图像和视频的数据压缩编码所广泛采用。通常先把图像分成8×8的块,然后再对图像块做DCT变换,之后再对DCT系数进行量化,以压缩掉视觉不敏感的高频信号。而粗糙的量化常常会导致解码图像产生块效应、振铃现象等问题,从而影响图像的视觉质量。在分析块效应产生原因的基础上,着重介绍了一种有效改善块效应图像质量的处理方法。由于块效应图像在不同的区域有不同的表现形式,因此可以根据区域各自的纹理特点采取相应的处理方法。实验证明,这种处理方法能够有效消除块效应,同时对图像的亮度和细节损失不大。  相似文献   

10.
DCT变换以其优良特性被图像和视频的数据压缩编码所广泛采用.通常先把图像分成8×8的块,然后再对图像块做DCT变换,之后再对DCT系数进行量化,以压缩掉视觉不敏感的高频信号.而粗糙的量化常常会导致解码图像产生块效应、振铃现象等问题,从而影响图像的视觉质量.在分析块效应产生原因的基础上,着重介绍了一种有效改善块效应图像质量的处理方法.由于块效应图像在不同的区域有不同的表现形式,因此可以根据区域各自的纹理特点采取相应的处理方法.实验证明,这种处理方法能够有效消除块效应,同时对图像的亮度和细节损失不大.  相似文献   

11.

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.

  相似文献   

12.
段新涛  彭涛  李飞飞  王婧娟 《计算机应用》2015,35(11):3198-3202
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.  相似文献   

13.
基于改进层式DCT的压缩感知图像处理   总被引:1,自引:0,他引:1       下载免费PDF全文
尹晓慧  张宝菊  王为  雷晴 《计算机工程》2012,38(9):226-227,247
为改善图像压缩质量,提出一种基于改进层式离散余弦变换(DCT)的压缩感知图像处理方法。该方法保留层式DCT变换的最高层系数,只对其余层高频子带系数进行压缩感知随机测量。利用正交匹配追踪算法对高频系数进行恢复,通过DCT反变换重构图像。实验结果表明,与基于层式DCT的方法相比,在相同压缩比的情况下,该方法重构图像的峰值信噪比较高。  相似文献   

14.
一个新的基于DCT的自适应数字水印算法   总被引:1,自引:0,他引:1  
本文提出了一个利用DCT系数的关系来进行水印嵌入和提取的算法。该算法利用人类视觉系统HVS的特点,通过巧妙调整DCT系数之间的相互关系来嵌入水印.从而使得图像在嵌入一个比较稳健的水印后的视觉失真尽可能最小。水印提取不需要原始图像。实验结果表明本算法的图像保真度较好,并对JPEG压缩、剪切等常见的图像处理方法具有较好的稳健性,并优于文献上的相关算法。  相似文献   

15.
In the framework of maximum-likelihood detection for image watermarking schemes, the conventional Generalized Gaussian Distribution (GGD), Cauchy and Student’s t distributions often fail to model the pulse-like distributions, such as Discrete Cosine Transform (DCT) coefficient distribution. Meanwhile DCT DC coefficients are often neglected in the image watermarking schemes. In this paper an improved full band image watermarking algorithm with utilization of Weibull distribution modeling the DCT AC and DC coefficients is proposed. Experiments indicate that compared with other popluar distributions such as the GGD, the Weibull model gives a closer fit on the distribution of AC coefficients in absolute domain with a smaller Kullback-Leibler (KL) divergence and lower Mean Square Error (MSE). The watermarking scheme with Weibull modeling the DCT AC coefficients (Weibull-AC) exhibits strong robustness under the attack of scaling and median filtering. The watermarking scheme with Weibull modeling the DCT DC coefficients (Weibull-DC) yields a better detection accuracy for bright and more detailed images. Combining the above two advantages, the proposed Weibull based full band watermarking in DCT domain (Weibull-FB) further improves its robustness under the attack of JPEG compression and achieves 10.47 % overall increment in the detection accuracy compared with the baseline system while maintaining good invisibility in the view of structural similarity (SSIM).  相似文献   

16.
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。  相似文献   

17.

With the development of digital forensic techniques, the image disguise (also called image tampering or image manipulation) is challenged greatly. When the tampered JPEG image is saved, it was re-compressed. This progress causes radical change in the histogram of the discrete cosine transformation (DCT) coefficients. The amounts of some coefficient values decrease greatly or even disappear. It is easily to detect this pattern by statistics methods. To remove the fragility of image disguise, we need to revise the abnormal distribution of DCT coefficients. But random change in the coefficient values degrades the image quality. So we established an image disguising evaluation model aims at the JPEG recompression detection which can be solved by Tabu Search algorithm. Under the restraint of the evaluation model, the traces of double compression are removed, and the image quality is well preserved.

  相似文献   

18.
提出了一种基于HVS和量化的自适应盲水印算法,基于HVS的视觉模型使用亮度掩蔽系数,纹理掩蔽系数,频率掩蔽系数来自适应地调整水印的嵌入强度。算法选择在DCT域,通过用JPEG量化表量化DCT系数,比较量化后的DC系数|DC|与选定的量化后的AC系数|AC|之间的关系来嵌入和提取水印,并实现了水印的盲检测。由于DCT系数基于JPEG量化表来量化,对JPEG压缩具有很好的抵抗能力,对叠加噪声、模糊等常规的图像操作也具有很好的鲁棒性。实验结果证明,该算法是一种行之有效的方法。  相似文献   

19.
The comblike histogram of DCT coefficients on each subband and the blocking artifacts among adjacent blocks are the two main fingerprints of the image that was once compressed by JPEG. Stamm and Liu proposed an anti-forensics method for removing these fingerprints by dithering the DCT coefficients and adding noise into the pixels. However, some defects emerge inside the anti-forensically processed images. First, the noise distributions are abnormal in the resulting images; and second, the quality of the processed image is poor compared with the original image. To fill these gaps, this paper proposes an improved anti-forensics method for JPEG compression. After analyzing the noise distribution, we propose a denoising algorithm to remove the grainy noise caused by image dithering, and a deblocking algorithm to combat Fan and Queiroz's forensics method against blocking artifacts. With the proposed anti-forensics method, fingerprints of the comblike histograms and the blocking artifacts are removed, noise distribution abnormality is avoided, and the quality of the processed image is improved.  相似文献   

20.
We present an algorithm for the application of support vector machine (SVM) learning to image compression. The algorithm combines SVMs with the discrete cosine transform (DCT). Unlike a classic radial basis function networks or multilayer perceptrons that require the topology of the network to be defined before training, an SVM selects the minimum number of training points, called support vectors, that ensure modeling of the data within the given level of accuracy (a.k.a. insensitivity zone /spl epsi/). It is this property that is exploited as the basis for an image compression algorithm. Here, the SVMs learning algorithm performs the compression in a spectral domain of DCT coefficients, i.e., the SVM approximates the DCT coefficients. The parameters of the SVM are stored in order to recover the image. Results demonstrate that even though there is an extra lossy step compared with the baseline JPEG algorithm, the new algorithm dramatically increases compression for a given image quality; conversely it increases image quality for a given compression ratio. The approach presented can be readily applied for other modeling schemes that are in a form of a sum of weighted basis functions.  相似文献   

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