基于方差的奇异值分解域鲁棒零水印算法

 针对已提出的奇异值分解域鲁棒水印算法往往将水印嵌入在奇异值矩阵的奇异值上,利用奇异值分解产生的两个正交矩阵提出一种基于方差的鲁棒零水印算法.将图像分割成互不重叠的子块,对每个子块进行奇异值分解,通过判断每个子块U矩阵第一列元素平方的方差与V矩阵第一列元素平方的方差之间的大小关系产生零水印序列.算法实质上没有对原始图像做任何修改,具有非常好的不可见性.算法进行抵抗重采样、平滑处理、加噪音和JPEG压缩攻击实验测试鲁棒性.实验结果表明该算法在以上攻击中表现出很强的鲁棒性.

Design of Optical Comb Filters Based on Cascaded Phase-Shifted Linearly Chirped Fiber Gratings

A novel optical comb filter is designed with two cascaded phase-shifted linearly chirped fiber gratings.According to the transmission matrix method and Fabry-Perot resonant cavity theory,the characteristics of reflection spectrum of the optical comb filter are numerically analyzed for the different combinations of two chirp gratings,the value of chirp,the index modulation and the phase-shift.The results show that the distribute density of reflection peaks is different for the different combinations of two chirp gratings,that is,the spacing between reflection peaks is equal if the signs of two chirps same,it can be used to design a uniform filter|on the other hand,the distribute of reflection peaks shows the characteristic density gradient if the signs of two chirps opposite,which can be used to design a non-uniform filter.And the greater the chirp of gratings,the wider the bandwidth of reflection spectrum of the filter,and the lower the reflectivity|however, the reflectivity will be improved with the increase of index modulation|furthermore each of the reflection peaks moves with the change of phase-shift,which is useful to select a filter window by changing the phase-shift.