基于匹配滤波的有意义图像水印算法

图像隐形水印是解决数字媒体版权保护的有效手段.目前的大多数水印算法采用伪随机序列构成水印,因而只能给出"Yes"(有水印)或"No"(无水印)的回答.嵌入有意义的水印在一些应用场合更加重要,但同时也带来了更多的困难.嵌入有意义的水印必须解决二个问题:(1)嵌入的水印具有一定的数据量;(2)从有失真的水印图像中正确地提取嵌入的水印.本文应用数字通信的理论和方法,提出了一个嵌入有意义字符串的DCT域隐形水印算法.该算法采用BCH编码和匹配滤波来降低误码率.应用所提出的算法,把一个32个字符组成的水印嵌入到256×256的图像中并达到了较好的稳健性.在水印图像信噪比受Gaussian加性噪声干扰下降到26dB时,仍实现了对嵌入水印零错误概率的检测.

An Algorithm for Meaningful Watermarks Based on Matched Filtering

Invisible image watermarking is an effective method to provide protection for copyright ownership of digital media.Most image watermarking algorithms use pseudo random sequences as watermarks and so they can only give the answer of "Yes" or "No".Embedding meaningful watermark is important in some applications but results in more difficulties.There are two problems in embedding meaningful watermark as follows:(1) the embedded watermark must have a certain bit rate.And (2) the embedded watermark must be detected correctly from possibly distorted watermarked image.In this paper,we apply the theory and methods in digital communication to watermark embedding and propose an invisible image watermarking algorithm in DCT domain for embedding meaningful watermarks.The algorithm reduces error probabilities of detection by exploiting BCH code and matched filtering.With the proposed algorithm,we embed a meaningful watermark composed of 32 characters into an image of 256×256 and the watermark thus generated is robust.The watermark can be detected with zero error probability even if the quality of watermarked image is as poor as 26 dB in PSNR after corrupted by additive Gaussian noise.