一种利用正交码扩频技术的数字图像水印算法

本文提出一种利用正交码扩频技术的数字图像水印算法。该方法在发送端先分别用两个相互正交的Walsh序列对同一水印进行扩频，再将扩频信号嵌入到载体图像的DCT变换域的中频和低频系数中；在接收端先将调制信号从频域中提取出来，然后采用相关检测技术解扩。实验结果表明，该方法能有效地抵抗噪声、剪切口EG压缩等攻击，对中值滤波也具有一定的鲁棒性。

A Digital Image Watermark Algorithm Taking Use of the Orthogonal Code Spread Spectrum Technology

A digital image watermark algorithm, which takes use of the orthogonal code spread spectrum technology is proposed. First of all, the watermark is modulated by two orthogonal Walsh codes respectively. Then add these two sequences to obtain one to be embedded. Finally, this spread sequence is embedded into the medium frequency and low frequency coefficients of DCT of the original image. At the receiver, the spread signal is extracted first, then demodulated in the correlation detector respectively by the two orthogonal codes, thus two sequences can be obtained. At last, combimng them to obtain the final withdrawn watermark. Experimental results show that, the proposed method is of very good performance under noise, cropping and JPEG attacks. Furthermore, it is robust to median filtering.