DCT域加密自适应数字水印算法*

针对常规的DCT域数字水印算法自适应性差的缺陷，提出一种基于DCT(离散余弦变换)域加密和自适应相结合的数字水印算法。该算法在水印嵌入前先对水印进行Arnold变换，这样做一方面降低了水印数据间的相关性，另一方面也对水印数据进行了加密处理从而大大提高了水印的安全性。通过JPEG量化矩阵选取一定数量的DCT系数用于嵌入水印。嵌入过程中对水印的嵌入强度进行动态自适应调节，在确保了隐蔽性的前提下使得提取效果更好。实验表明，该算法对均值滤波、高斯噪声、椒盐噪声，以及JPEG压缩等攻击有一定的鲁棒性。

Encrpyted and adaptive digital watermarking algorithm in DCT domain

Aiming at the defect of self-adaptability in normal digital watermarking algorithm of DCT domain, proposed an encrypted and adaptive digital watermarking algorithm using Arnold and DCT transformation. Transformed the watermarking by Arnold transformation before being embedded. On the one hand, it reduced the relativity among watermarking data. On the other hand, it also hugely increased the security of watermarking through dealing with watermarking data. Embedded some DCT coefficients in watermarking by JPEG matrix. It dynamically and adaptively adjusted the embedded intensity, which made it have a good effect in embedding .At the same time, it ensured the concealed character of watermarking. The experiment shows that the proposed algorithm has very strong robustness for some common image processing operations such as median filtering, Gauss noise, salt-pepper noise and JPEG compression, etc attack.