On the basis of the existing digital image watermarking technology,in order to further improve the robustness of digital water-marking,propose a watermarking algorithm based on chaos and wavelet coefficient. The algorithm is carried out in three steps. First it uses the two-dimensional Logistic chaotic algorithm to scramble watermark,then uses the one-dimensional Logistic chaotic algorithm to gen-erate a sequence of coordinates and record the initial value and the control parameter value of chaotic sequence,and then make one level wavelet decomposition to the carrier image,extracted the horizon detail component and the vertical detail component,finally,according to the watermark information and chaos sequence,replace the specified step of horizon detail component by vertical detail component,inver-sing wavelet transform. The experimental results show that the use of this watermark embedding algorithm has good invisibility,the water-mark embedding accuracy and capacity can depend on steps. Meanwhile,it has better robustness under the attack of geometric,JPEG loss compression,shear attack,noise,etc. When choosing the right step length,shear attacks in 3/4 can still be extracted ninety-nine percent watermark.%在现有数字图像水印嵌入技术基础上，为了进一步提高数字水印的鲁棒性，文中提出一种基于混沌和小波变换系数的水印算法。该算法主要分为三个步骤：首先运用二维Logistic混沌序列将水印置乱，再用一维Logistic混沌方法随机生成坐标序列，并记录混沌序列初值和控制参数值；然后对载体图像做一级小波分解，提取水平细节分量和垂直细节分量；最后根据水印信息和混沌序列，将指定步长的水平细节系数替换为垂直细节系数，并做小波逆变换。实验结果表明，使用该算法嵌入水印具有很好的不可见性，可以根据步长确定水印嵌入精度和水印容量，并且在几何攻击、JPEG有损压缩、剪切攻击、噪声攻击等情况下均具有较好的鲁棒性，当选择合适的步长，在剪切攻击四分之三时仍然能够提取百分之九十九的水印。
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