纠正同步错误的反转级联水印码的迭代译码

为提高插入删节信道下反转级联水印码(Reverse Concatenated Watermark Code)的译码性能,本文设计了一种反转级联水印码的硬判决迭代译码方案。该方案在反转级联水印码内译码器中引入外译码器输出的硬判决估计序列,交织后的硬判决序列和水印序列的异或作为内译码器的更新后的参考序列,从而减小了码字序列对水印码的影响,改善了水印译码器的参考信息。前后向估计方法利用该参考序列和更新后的有效替代错误概率计算输出概率,进一步用于计算前向度量值和后向度量值,提高了内译码器输出的每个比特的似然信息的可靠度,改善了整体性能。仿真结果表明,当反转级联水印码方案采用硬判决迭代译码算法时,整体性能得到有效提高。

基于QR码的DWT-DCT数字水印算法

为了提升版权信息的完整性和有效性,水印需要具备高强度的隐蔽性和抗攻击性。因此,提出了一种结合快速响应码(QR)、混沌系统和DWT-DCT的鲁棒性水印方案。首先通过混沌系统产生的混沌序列对QR进行加密;然后将宿主图片进行DWT操作,并且对低高频子带进行4×4分割和DCT操作;最后利用水印信息产生2×2矩阵,叠加到DCT变换后矩阵的右上角。在水印信息提取时,通过对比叠加矩阵中的元素并统计元素变化率,以此确认提取的水印信息。模拟实验分析表明,该方案不仅能够增强水印信息的透明性,而且在涂画、切割、噪声、过滤和JPEG压缩等攻击中具备较强的抗攻击能力。

基于三重特征码水印的电子印章检测方案

针对公文中电子印章很容易受到复制与篡改攻击,提出一种新的解决方案.利用特征码来区分每一个公文;由公文信息与数字签名等信息,可以生成特征码并转换成对应的特征码水印;利用数字水印技术,向电子印章中嵌入特征码水印.在验证检测过程中,通过三重特征码水印(所提取的特征码水印、原始的特征码水印与当前公文的特征码水印),设计的方案不仅可以检测公文的内容是否被篡改,还可以检测电子印章是否被复制,电子印章是否伪造.

基于Goppa码的数字水印技术

在图像数字水印算法中引入Goppa码技术,在水印嵌入前经过Goppa码编码来提高系统的抗误码能力。根据HVS的亮度掩蔽特性,选取并比较DCT的中频系数来嵌入水印。实验结果表明,利用该算法实现的水印具有很好的视觉掩蔽效应和鲁棒性。

针对非二进制同步错误的高效水印调制方案

低密度奇偶校验码级联水印码的编译码方案可纠正非二进制同步错误。为了提高上述系统中水印码识别同步错误的能力,提出了扩展多个符号子集的改进水印调制方案。具体而言,该改进方案将每个传输符号携带的水印信息扩展至两位,对应地将传输信号的子集扩展为四个。扩展后的系统星座图的划分更为精细,提高了借助更多水印比特码识别同步错误的能力。仿真结果表明,与传统方案相比,在加性噪声较小情况下如信噪比为10 d B,当误帧率为10^(-3)时,改进方案可以纠正的同步错误概率达13%,且适用于非线性信道。

一种强鲁棒性的彩色图像数字水印技术

目的提出了一种彩色图像数字水印技术,解决数字水印在大数据量水印、不可见性和鲁棒性之间的关系。方法该算法对彩色QR码水印和彩色载体图像分别进行RGB三通道分解,彩色水印单通图像进行混沌加密;对彩色载体单通道图像进行Contourlet变换;按对应通道将水印嵌入到载体图像低频经奇异值分解后的对角矩阵。结果该算法在水印嵌入和提取仿真实验结果为PSNR>50 d B;鲁棒性仿真实验结果表明,该算法在抵抗任意旋转攻击和基本图像处理操作的攻击下,提取出来的彩色QR码颜色未失真,并且均能够成功解码和自动识别。结论该算法具有较强的鲁棒性和较好的不可见性,能够很好地将彩色水印嵌入彩色图像,可应用到实际的数字版权保护中。

一种安全的数字音频水印方案

提出一种安全的数字音频水印算法,利用密钥生成的序列作为水印同步码,并在时间域嵌入同步码。水印信息采用分块结构化编码方式,水印分块中采用校验码机制,水印内容采用量化方式嵌入在小波变换域,水印分块在音频段中循环冗余嵌入方式,以抵抗同步攻击的能力。提出的算法不仅具有较好的不可感知性,对低通滤波、噪声、重量化、重采样、MP3压缩等信号处理具有较好的鲁棒性;同时对抵抗随机裁剪攻击、抖动攻击、时间延展等同步攻击具有很好的鲁棒性。

基于小波变换的静态二维图像数字水印算法研究

对基于小波变换的静态二维图像数字水印技术提出了一种新的算法,利用小波图像系数各层间的关系,进行水印的嵌入,并根据所设计的算法,对原灰度水印图像及彩色水印图像进行预选择或构造特殊的伪码水印对算法进行改进,获得了很好的鲁棒性及隐蔽性.通过仿真试验也充分证明了这种算法的可行性和正确性.在版权保护、数据鉴别、数据检测、用户跟踪以及保密通讯等领域有着广泛的应用前景.

二值图像数字水印生成、管理及检测

利用水印控制码对生成的数字水印图像加以控制 ,产生8*8的小图块 ,每一块只可选两种颜色之一。在检测时充分利用该特性 ,可以使检测结果准确 ,实现简单 ,具有较强的抗JPEG压缩鲁棒性。

数字水印与组合加密QR客票防伪方法

QR码客票编解码格式高度公开,安全防伪性较差。针对此问题,提出一种基于数字水印技术与数学加密技术的安全防伪QR码客票方法。利用DES算法对客票明文加密,编码生成载体QR码;运用RSA算法对DES密钥加密;将密文DES密钥生成水印QR码嵌入载体中,耦合源信息解密与水印验证过程。水印嵌入算法充分利用QR码的高纠错能力,以离散续弦变换(DCT)和奇异值分解(SVD)为基础进行水印嵌入与提取。实验结果表明,该算法不影响QR码快速识别特性,在保证良好视觉效果的前提下具备较高的鲁棒性。

MULTI-WATERMARKING SCHEME FOR GROUP USERS BASED ON VISUAL CRYPTOGRAPHY

All watermarks are shared into shadow images using VCS(Visual Cryptography Scheme). Only one specific shadow (as a new watermark) is embedded into the host signal and the other ones are distributed to every user in each group as a key. In the watermarking extraction procedure, users in different group can obtain different watermark by combining their shadows with the extracted one from the watermarked signal. Analysis and experimental results show that the new watermarking method is novel, secure and robust.

Using the Wavelet as the Private Key for Encrypting the Watermark

Watermarking is an effective approach to the copyright protection of digital media such as audio, image, and video. By inspiration from cryptography and considering the immensity of the set of all possible wavelets, it is presented that in wavelet domain watermarking, the associated wavelet can be considered as the private key for encrypting the watermark so as to enhance the security of the embedded mark. This idea is partly supported by the fact that from computational complexity viewpoint, it is very time-consuming to search over the immense set of all candidate wavelets for the right one if no a priori knowledge is known about it. To verify our proposal, the standard image 'Lena' is first watermarked in a specific wavelet domain, the watermark recovery experiments are then conducted in the wavelet domain for a set of wavelets with the one used for mark embedded in it,separately. It follows from the experimental results that the mark can be recovered only in the right wavelet domain, which justifies the suggestion.

A multiple copyright identification watermarking algorithm based on code division multiple access

A multiple watermarking algorithm is presented according to the multiple accessing technique of the code division multiple access （CDMA） system. Multiple watermarks are embedded into digital images in the wavelet transform domain. Each of the watermarks is embedded and extracted independently without impacts to each other. Multiple watermarks are convolution encoded and block interleaved, and the orthogonal Gold sequences are used to spread spectrum of the copyright messages. CDMA encoded water-mark messages are embedded into the wavelet sub-bands excluding the wavelet HH1 sub-bands. The embedment amplitude is decided by Watson＇ s perceptual model of wavelet transform domain, and the embedmeut position in the selected wavelet sub-bands is decided randomly by a pseudo-random noise （PN） sequence. As a blind watermm＇king algorithm, watermarks are extracted without original image. The watermarking capacity of proposed algorithm is also discussed. When two watermarks are embedded in an image at the same time, the capacity is larger than the capacity when a single watermark is embedded, and is smaller than the sum of the capacity of two separately embedded watermarks. Experimental results show that the proposed algorithm improves the detection bits error rate （BER） observably, and the multiple watermarks have a preferable robustness and invisibility.

Blind and readable image watermarking using wavelet tree quantization

A blind and readable image watermarking scheme using wavelet tree quantization is proposed. In order to increase the algorithm robustness and ensure the watermark integrity,error correction coding techniques are used to encode the embedded watermark. In the watermark embedding process, the wavelet coefficients of the host image are grouped into wavelet trees and each watermark bit is embedded by using two trees. The trees are so quantized that they exhibit a large enough statistical difference, which will later be used for watermark extraction. The experimental results show that the proposed algorithm is effective and robust to common image processing operations and some geometric operations such as JPEG compression, JPEG2000 compression, filtering, Gaussian noise attack, and row-column removal. It is demonstrated that the proposed technique is practical.

Digital Watermarking Applied To MEPG-2 Coded Video Sequences Exploiting Motion Vector

This paper proposes a video watermarking technology to hide copyright information by a slight modification of the motion vector in MPEG-2 video bitstream. In this method, the watermark is embedded in the motion residual of the large value motion vector, then the motion residual is regularized into a modified bitstream, from which the watermark information can be retrieved easily and exactly. From the experimental results, this technology has the advantage of little influence on the MPEG decoding speed, degrading the perceptive effect little, and the capability to embed watermark in a short video sequence, and can be used to watermark directly on the compressed and uncompressed video sequence.