Cascaded Fresnel digital hologram and its application to watermarking

A cascaded Fresnel digital hologram (CFDH) is proposed, together with its mathematical derivation. Its application to watermarking has been demonstrated by a simulation procedure, in which the watermark image to be hidden is encoded into the phase of the host image. The watermark image can be deciphered by the CFDH setup, the reconstructed image shows good quality and the error is almost close to zero. Compared with previous technique, this is a lensless architecture which minimizes the hardware requirement, and it is used for the encryption of digital image.

Watermarks encrypted in the cascaded Fresnel digital hologram

A cascaded Fresnel digital hologram (CFDH) is proposed, together with its mathematical derivation. Its application to watermarking has been demonstrated by a simulation procedure, in which the watermark image to be hidden is encoded into the phase of the host image. The watermark image can be deciphered by the CFDH setup, the reconstructed image shows good quality and the error is almost closed to zeros. Compared with previous technique, this is a lensless architecture, which minimizes the hardware requirement. (c) 2006 Elsevier GmbH. All rights reserved.

基于弱信号检测理论的离散小波变换域数字水印盲检测算法

水印检测是数字水印技术的一个关键步骤,但是目前所提出的绝大多数水印检测算法既不具备赖以支撑的理论基础,其检测性能也不是优化的.利用数字水印的不可感知特性,应用弱信号检测理论进行水印检测的研究.首先从图像小波变换系数的统计特性出发,利用广义高斯分布(GGD)来建立小波细节子带系数的统计分布模型;然后针对水印嵌入强度未知的情况,将水印检测问题转化为非高斯噪声中具有未知参数的确定性信号的检测,在弱信号条件下提出一种离散小波变换(DWT)域图像水印的优化盲检测算法.检测性能分析表明,该检测算法能够实现恒虚警率水印检测.实验结果验证了检测性能理论分析的有效性和实际性能的优越性.

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 transfom）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．

公开可验证的零知识水印检测

对称水印方案的水印检测密钥可以被用来伪造和移去水印，因此要求它在检测过程中也是保密的．零知识的水印检测方案利用密码学中零知识和知识证明的思想和算法，实现在水印检测时使得验证者确信水印存在性的同时又不泄漏水印检测密钥．提出了公开可验证的零知识水印检测的安全需求，给出一个公开可验证的承诺方案和一个证明知道被承诺值的离散对数的零知识知识证明协议．在此基础上提出了一个公开可验证的零知识水印方案，并讨论了它的安全性．

DCT域图像水印的局部优化检测性能研究

水印检测是数字水印技术最关键的步骤之一.水印检测的传统方法是采用线性相关的方法,但是该方法存在问题.本文根据数字图像离散余弦变换(DCT)域交流系数的广义高斯分布模型,对图像水印的局部优化检测方法进行了推导,并给出了水印检测器检测性能的理论分析结果.实验结果验证了图像水印局部优化检测方法检测性能理论分析的有效性,以及实际检测性能的优越性.

Local histogram based geometric invariant image watermarking

Compared with other existing methods, the feature point-based image watermarking schemes can resist to global geometric attacks and local geometric attacks, especially cropping and random bending attacks (RBAs), by binding watermark synchronization with salient image characteristics. However, the watermark detection rate remains low in the current feature point-based watermarking schemes. The main reason is that both of feature point extraction and watermark embedding are more or less related to the pixel position, which is seriously distorted by the interpolation error and the shift problem during geometric attacks. In view of these facts, this paper proposes a geometrically robust image watermarking scheme based on local histogram. Our scheme mainly consists of three components: (1) feature points extraction and local circular regions (LCRs) construction are conducted by using Harris-Laplace detector; (2) a mechanism of grapy theoretical clustering-based feature selection is used to choose a set of non-overlapped LCRs, then geometrically invariant LCRs are completely formed through dominant orientation normalization; and (3) the histogram and mean statistically independent of the pixel position are calculated over the selected LCRs and utilized to embed watermarks. Experimental results demonstrate that the proposed scheme can provide sufficient robustness against geometric attacks as well as common image processing operations. (C) 2010 Elsevier B.V. All rights reserved.

Local Feature Based Geometric-Resistant Image Information Hiding

Watermarking aims to hide particular information into some carrier but does not change the visual cognition of the carrier itself. Local features are good candidates to address the watermark synchronization error caused by geometric distortions and have attracted great attention for content-based image watermarking. This paper presents a novel feature point-based image watermarking scheme against geometric distortions. Scale invariant feature transform (SIFT) is first adopted to extract feature points and to generate a disk for each feature point that is invariant to translation and scaling. For each disk, orientation alignment is then performed to achieve rotation invariance. Finally, watermark is embedded in middle-frequency discrete Fourier transform (DFT) coefficients of each disk to improve the robustness against common image processing operations. Extensive experimental results and comparisons with some representative image watermarking methods confirm the excellent performance of the proposed method in robustness against various geometric distortions as well as common image processing operations.