抗仿射变换的扩频图像水印算法

稳健性是数字水印算法的重要性能指标之一.本文提出了一个抗仿射变换攻击的图像水印盲检测算法.该算法从影响水印稳健性的因素-嵌入策略、水印结构和水印检测的同步三个方面(特别是水印检测同步)来提高水印的稳健性.有意义的水印经过直接序列扩频调制后与一个训练序列一起嵌入于图像DWT域的低频子带.在图像DFT域的中频我们嵌入一个匹配模板.检测时,先检测匹配模板,得到图像所受几何攻击的参数并作几何校正,然后在DWT域根据训练序列作平移同步后检测水印信息.应用所提出的算法,我们把一个由44个字符构成的水印(264 bits)嵌入到一幅512×512×8的图像中,实验结果表明所提出算法在隐藏数据量、对抗常规信号处理和线性几何变换的稳健性方面大大优于已报道的算法.

Spread-Spectrum Watermarking Resists to Affine Transformation

Robustness is one of the most important issues in watermarking.In this paper,a blind image watermarking algorithm robust against affine transformation is proposed.This algorithm improves the robustness in three aspects:the embedding strategy,the watermark structure and the synchronization of the watermark.In the algorithm,the spread-spectrum-based watermark with a training sequence are embedded in the coeffcients of LL3 subband in DWT domain while a template is embedded in the middle frequency components in the DFT domain.In watermark extraction,we detect the template in the possibly corrupted watermarked image to obtain the parameters of geometric attacks and recover the image back to its original shape.Then we perform translation synchronization in the DWT domain by using the training sequence and extract the watermark.With the proposed algorithm,we hide a character string with 44 characters (264 bits) in a 512×512×8 image.Compared with other watermarking algorithms reported in the literature,the watermark thus generated is more robust,especially against geometric distortion,while having much higher bit rate.