Robust and transparent watermarking scheme for colour images

In this study, a robust and transparent watermarking scheme for colour images is proposed. The colour features for the human visual system are utilised to design the colour watermarking scheme. Through the exploitation of the perceptual redundancy of colour images, the proposed watermarking scheme is perceptually tuned to embed and detect the watermark in the perceptually significant sub-bands of luminance and chrominance components of colour images in the wavelet domain. The employment of the uniformity in the uniform colour space and the masking effect mainly due to local variations in luminance magnitude leads to that the perceptual redundancy of colour images can be measured. By using the estimated perceptual redundancy in the form of error visibility thresholds of wavelet coefficients of the colour image, high strength watermarks are invisibly embedded into coefficients of the host colour image for resisting compression and malicious attacks. Simulation results show that the estimation of perceptual redundancy is helpful to the design of the watermarking scheme for colour images. The performance in terms of robustness and transparency of the proposed watermarking scheme is superior to that of the existing scheme.     

On the use of masking models for image and audio watermarking

In most watermarking systems, masking models, inherited from data compression algorithms, are used to preserve fidelity by controlling the perceived distortion resulting from adding the watermark to the original signal. So far, little attention has been paid to the consequences of using such models on a key design parameter: the robustness of the watermark to intentional attacks. The goal of this paper is to demonstrate that by considering fidelity alone, key information on the location and strength of the watermark may become available to an attacker; the latter can exploit such knowledge to build an effective mask attack. First, defining a theoretical framework in which analytical expressions for masking and watermarking are laid, a relation between the decrease of the detection statistic and the introduced perceptual distortion is found for the mask attack. The latter is compared to the Wiener filter attack. Then, considering masking models widely used in watermarking, experiments on both simulated and real data (audio and images) demonstrate how knowledge on the mask enables to greatly reduce the detection statistic, even for small perceptual distortion costs. The critical tradeoff between robustness and distortion is further discussed, and conclusions on the use of masking models in watermarking drawn.     

基于NSCT 的自适应乘性水印局部最优非线性盲检测算法

图像水印算法研究是多媒体技术领域中的重要议题。比较并结合当前两类主流的 图像水印算法,提出了一种基于非下采样Contourlet 变换的自适应乘性水印算法。借鉴Barni 的“pixel-wise masking”模型和冗余小波域掩盖效应建模的做法,建立非下采样Contourlet 变换域 掩盖效应计算模型。用广义高斯分布模型和Cauchy 分布模型描述非下采样Contourlet 变换系数 的统计特性,将水印的检测问题表述为一个复合假设检验。通过理论推导分别建立了乘性水印 的两种局部最优非线性盲检测器及检测门限的自适应确定方法。实验结果表明,非下采样 Contourlet 变换域掩盖效应计算模型使得水印嵌入算法具有良好的视觉不可见性,两种检测器在 无原始图像和自适应嵌入强度系数参与检测的情况下均能准确地检测到水印信息的存在。实验 结果同时显示,基于Cauchy 分布的盲检测器在检测效果和检测时间方面优于基于广义高斯分 布的盲检测器。     

DCT域图像水印方案的可靠性分析

基于一种全帧DCT域图像水印方案,推导了水印相关检测器的误检测概率公式．理论分析表明：检测器的误检测概率与图像本身无关,只取决于嵌入水印长度和嵌入强度因子．文中的分析显示了哪些因素会影响检测性能,有助于优化水印系统．最后,给出了相应的实验结果．     

Audio watermarking based on quantization index modulation using combined perceptual masking

In this paper, a robust audio watermarking scheme for MPEG-1/ Audio Layer II compressed domain is proposed. The scheme is implemented by modifying the subband coefficients using adaptive quantization index modulation. The watermarking procedure exploits perceptual frequency and temporal masking of the human auditory system (HAS) of MPEG coder to satisfy the requirements of robustness, security and transparency. This reduces the computational complexity of proposed scheme. The paper investigates the use of elevated masking threshold to improve detection and achieve higher robustness against re-encoding and awgn attacks. Experimental results show that high capacity of 6,840 bps with ODG ?0.5 without altering the MPEG/audio bitrate.     

DCT变换域乘嵌入图像水印的检测算法

目前大多数水印算法采用线性相关的方法检测水印,但是,当原始媒体信号不服从高斯分布,或者水印不是以加嵌入方式嵌入到待保护的媒体对象中时,该方法存在一定的问题.数字水印的不可感知性约束决定了水印检测是一个弱信号检测问题,利用这一特性,首先从图像DCT(discrete cosine transform)交流变换系数的统计特性出发,应用广义高斯分布来建立其统计分布模型,然后将水印检测问题转化为二元假设检验问题,以非高斯噪声中弱信号检测的基本理论作为乘嵌入水印的理论检测模型,推导出优化的乘嵌入水印检测算法,并对检测算法进行了实验.结果表明,对于未知嵌入强度的乘水印的盲检测,提出的水印检测器具有良好的检测性能.因此,该检测器能在数字媒体数据的版权保护方面得到了实际的应用.     

An adaptive watermarking scheme for e-government document images

This paper proposes an adaptive watermarking scheme for e-government document images. The adaptive scheme combines the discrete cosine transform (DCT) and the singular value decomposition (SVD) using luminance masking. As a core of masking model in the human visual system (HVS), luminance masking is implemented to improve noise sensitivity. Genetic algorithm (GA), subsequently, is employed for the optimization of the scaling factor of the masking. Involving a number of steps, the scheme proposed through this study begins by calculating the mask of the host image using luminance masking. It is then continued by transforming the mask on each area into all frequencies domain. The watermark image, following this, is embedded by modifying the singular values of DCT-transformed host image with singular values of mask coefficient of host image and the control parameter of DCT-transformed watermark image using Genetic Algorithm (GA). The use of both the singular values and the control parameter respectively, in this case, is not only to improve the sensitivity of the watermark performance but also to avoid the false positive problem. The watermark image, afterwards, is extracted from the distorted images. The experiment results show the improved adaptive performance of the proposed scheme is in resistant to several types of attacks in comparison with the previous schemes; the adaptive performance refers to the adaptive parameter of the luminance masking functioned to improve the performance or robustness of an image from any attacks.     

Detection of audio covert channels using statistical footprints of hidden messages

We address the problem of detecting the presence of hidden messages in audio. The detector is based on the characteristics of the denoised residuals of the audio file, which may consist of a mixture of speech and music data. A set of generalized moments of the audio signal is measured in terms of objective and perceptual quality measures. The detector discriminates between cover and stego files using a selected subset of features and an SVM classifier. The proposed scheme achieves on the average 88% discrimination performance on individual steganographic algorithms and 98.5% on individual watermarking algorithms. Between 75 and 90% discrimination performance is achieved in universal tests. Correct detection performance for individual embedding algorithms is roughly 90% when the detector can encounter any one in an ensemble of different embedding algorithms.     

基于视觉掩蔽特性的可见水印的设计与实现

根据可见水印性质和载体图像的噪声掩蔽性在小波域进行可见水印算法的研究。提出了一种根据载体图像视觉掩蔽性进行水印嵌入强度的方案。在此基础上又结合水印图像的纹理特性对于高频系数水印嵌入强度进行重新调制。另外还对水印可见性质量评估进行了探讨。实验表明,改进后的算法水印可见性质量更好。     

Perceptual audio hashing algorithm based on Zernike moment and maximum-likelihood watermark detection

A new perceptual audio hashing algorithm based on maximum-likelihood watermarking detection is proposed in this paper. The idea is justified by the fact that the maximum-likelihood watermark detector responds similarly to perceptually close audio using a non-embedded watermark (i.e. virtual watermark). The feature vector, which is composed of the total amplitude of low-order Zernike moments of each audio frame, is modeled by the Gaussian or Rayleigh distribution. Then, the maximum-likelihood watermark detection is performed on the feature vector with the virtual watermarks generated by pseudo-random number generator to construct the hash vector. Extensive experiments over three large audio databases of different type (speech, instrumental music, and sung voice) demonstrate the efficiency of the proposed scheme in terms of discrimination, perceptual robustness and identification rate. It is also verified that the proposed scheme outperforms state-of-the-art techniques in perceptual robustness and can be applied in content-based search, successfully.     

自然语言水印隐蔽性自动评测方法

对自然语言水印(NLW)隐蔽性评测的缺乏严重影响了该领域技术的发展,为此,结合NLW的特点和语言心理学,以人类对语言释义的速度及难易程度为依据,提出了NLW隐蔽性的感知模型和相应的评测方案：从语法错误、搭配错误和语义损失三个方面对隐蔽性进行评测。最后,针对四种不同水印技术(基于绝对同义词替换的T-Lex水印系统、相对同义词替换水印系统、基于句法树的水印系统和中文句法水印系统),一方面利用该方案进行自动评测,另一方面进行置信度为90%的人工评测。两种方法得到了相同的结论：基于词汇的NLW技术的隐蔽性优于基于句子的NLW技术,说明该自动评测方法是评测NLW隐蔽性的有效评测方法。     

基于小波视觉模型的乘性水印算法

虽然小波域加性水印算法具有较好的不可感知性,但其鲁棒性较弱。因此,结合小波域视觉模型,提出了一种基于小波视觉模型的乘性图像水印算法。在水印嵌入过程中,为平衡水印的不可感知性和鲁棒性,以中频子带作为水印嵌入空间,并根据图像的频域敏感度、亮度敏感度、纹理复杂度确定水印的嵌入强度。在水印检测过程中,采用广义高斯分布(GGD)对小波系数的统计特性进行刻画,并通过奈曼-皮尔逊(NP)准则确定水印系统的检测阈值,给出了水印系统的虚警概率和检测概率之间的接收者操作特征(ROC)曲线关系。最后通过实验测试了该算法在抗压缩、叠加噪声、缩放和剪切等攻击时的鲁棒性能。仿真结果表明：该算法具有较好的检测性能以及在抗攻击时具有较强的鲁棒性。     

基于特征子空间的数字水印技术

根据特五子空间的原理，提出了一种新颖的基于特征子空间的数字水印算法，水印可以嵌入到不同的子空间中从而可以发展为多水印算法，由于特征子空间之间的正交特性，不同子空间中的水印相互独立，其稳健性不随水印数目的增加而变化，水印强度参数根据视觉系统的照度掩蔽和纹理掩蔽特性适当地进行调整，从而同时保证二值水印图像的稳健性和不可见性，该文就单水印，双水印以及多水印情形进行了仿真并进行JPEG压缩，图像缩放，剪切等失真测试，实验结果表明该算法具有很好的感知质量和稳健性并验证了以上分析。     

一种图象质量的感知测量方法

基于人的视觉特性提出了一种图象质量的感知测量方法。此方法考虑了人的视觉所具有的亮度屏蔽和空间频率屏蔽特性。实验表明用此测量方法对图象进行质量测量获得的结果与图象的直观质量相一致。     

基于直接序列扩频码的图像空间域水印技术

提出了一种基于直接序列扩频码的图像空间域水印方案.在建立数字图像水印的通信模型的基础上,通过生成原图的视觉掩模以充分保证图像的逼真度,在数字图像相应的空间域嵌入扩频码调制水印,同时利用纠错编码技术来进一步增强水印的抗干扰性能.水印的检测通过计算像差图像和原扩频码的相关性来实现.实验表明,该方案提高了数字水印的稳健性和隐蔽性,具有较好的主观效果.     

一种基于掩蔽效应的数字音频隐藏方案

提出了一种新的基于掩蔽效应的音频信号隐藏方案,利用宿主音频信号的心理学模型得到的掩蔽阈值,对伪随机序列调制后的隐藏消息进行频域掩蔽,将掩蔽后的伪随机消息嵌入宿主音频。该方法充分利用了人耳听觉系统（HAS）的掩蔽效应,同时利用伪随机信号的相关性,能够对嵌入后的音频信号进行盲提取得到隐藏消息。实验结果证明,嵌入后音频具有良好的不可察觉性,盲提取得到的隐藏消息误比特率较低。     

基于支持向量机的鲁棒盲水印算法

提出了一种基于支持向量机的鲁棒盲水印算法.该算法首先用多尺度Harris-Laplace检测算子从载体图像中提取出稳定的特征点,然后根据特征自适应确定局部特征区域,在特征区域选择一些点作为嵌入水印的点,结合图像的邻域相关性,根据灰度图像特点,选取特征向量作为SVR训练模型,进而利用SVR进行预测,调节嵌入点的像素值进行水印的嵌入和提取.实验结果表明,用该技术嵌入水印后的图像具有很好的图像感知质量,时常规信号处理乖去同步攻击特别是JPEG压缩具有较强的鲁棒性.     

基于小波域HMM模型的稳健多比特图像水印算法

稳健性是多比特图像水印的关键问题之一,提出了一种基于小波域隐马尔可夫模型(hidden Markov model,简称HMM)的多比特图像水印算法,该算法的主要特点为:(1) 利用向量HMM模型精确描述图像小波系数间的统计特性,基于此统计模型的水印盲检测系统较之传统的相关检测器,在性能上有显著的提升;(2) 结合视觉掩盖特性,自适应地调整水印嵌入强度,使之在一定的嵌入强度下,视觉主观失真较小;(3) 提出了一种适合隐马尔可夫模型树型结构的多比特数据优化嵌入策略和最大似然检测.数值仿真结果表明,该算法可以较好地利用图像小波域的低频子带以实现较大容量图像水印的嵌入,并在抵抗Stirmark平台攻击,如JPEG压缩、加噪、中值滤波和线性滤波等方面具有很强的稳健性.     

基于渐近优化检测器的数字水印最佳检测阈值的确定

数字水印系统中检测阈值的大小会影响到检测器的检测效果。渐近优化检测器是一种采用Rao检验方式的盲水印检测算法,但其检测阈值是完全凭经验人为设定的,为了使渐近优化检测器阈值的确定客观与精确,利用最小差错概率准则对检测阈值进行了理论分析,并具体给出了一个水印检测系统错误率达到最小的最佳检测阈值的计算公式。实验结果表明,该方法能使水印检测系统的错误率在理论上达到最小,同时检测阈值的大小具有自适应性和客观性。     

基于视觉掩蔽的半脆弱水印技术研究

以人眼视觉系统的掩蔽特性为基础,提出了一种基于分组量化的自适应半脆弱水印嵌入方案,该方案能够在不参考原始载体的情况下对数字图像同时进行版权保护和内容认证。仿真实验结果表明,所提出的半脆弱水印方案不仅具有较好的透明性,对JPEG压缩、叠加噪声、平滑滤波等常规图像处理操作具有较好的鲁棒性,而且能够对剪切、替换等恶意图像篡改做出报警并确定被篡改位置。同时常规图像处理下其误检率与漏检率均比较低。