小波变换域图像水印嵌入对策和算法

An Embedding Strategy and Algorithm for Image Watermarking in DWT Domain

稳健性是图像隐形水印最基本的要求之一.嵌入对策、嵌入公式、嵌入强度都影响水印的稳健性.提出了一个基于离散小波变换(DWT)的新的隐形水印嵌入对策.根据小波图像系数的分布特点和对小波系数振幅的定性、定量分析,水印应当首先嵌入小波图像低频系数,若有剩余,再按小波图像频带重要性的排序嵌入高频带.同时指出,水印嵌入到小波图像低频系数和高频系数需要用不同的嵌入公式.应用该嵌入对策,提出了一种把视觉系统掩蔽特性结合到水印编码过程中的自适应水印算法:将小波系数组织成小波块,采用一种新的方法将小波块分类,并根据分类的结果将不同强度的水印分量嵌入到不同的小波系数中.实验结果表明,应用本算法所实现的水印不可见,并对常见的图像处理和噪声干扰具有很好的稳健性.

Robustness is one of the most basic requirements for invisible image watermarks. Embedding strategy, embedding formula and the watermark strength all affect robustness of watermarks. In this paper, a new embedding strategy for watermarking is proposed based on DWT domain. Based on the wavelet coefficient distribution and a quantitative analysis on the magnitudes of wavelet coefficients, watermarks should be embedded in the low frequency subband firstly, and the remains of the watermarks should be embedded in high frequency subbands according to the significance of subbands. Different embedding formulae should be applied on the low frequency subband and high frequency subbands respectively. Applying this strategy, an adaptive algorithm incorporating the feature of visual masking of human vision system into watermarking is proposed. The algorithm organizes wavelet coefficients to form wavelet blocks and applies a novel method to classify these wavelet blocks. Watermark components with different strength are inserted into different wavelet coefficients based on the results of classification. The experimental results show that the watermarks generated with the proposed algorithm are invisible and robust against noise and commonly used image processing tech niques.