通过利用一个新视觉模型计算图像分块的临界噪声阈值矩JND阵，提出了一个基于分块DWT的图像自适应公开水印技术的文本信息加密算法。该算法以一个文本文件为水印，先对文本文件进行Reed Solomon纠错编码，再转换为二值序列作为水印，并进行随机置乱。然后在原图像8×8分块的Hilbert扫描序列中选取两相邻块分别进行一层DWT，再根据各分块JND阈值，不同强度地调整两相邻块各对应细节子带均值之间的大小关系以自适应地嵌入水印。实验结果表明，即使在较低的峰值信噪比下嵌入水印也具有很好的透明性，同时，该算法对16种常见图像攻击有较高的鲁棒性，特别是信号增强操作处理几乎不影响加密信息的正确提取。

The JND (just noticed difference) threshold matrix based on block was calculated by a new human visual model, and then a text encryption algorithm based on image adaptive public watermarking technique operating in DWT domain was presented. Firstly, the text in a file was encoded with Reed Solomon codes for robust and transferred into a binary sequence, which could be permuted randomly to a final watermark. Then, two neighboring blocks were selected from the Hilbert scanning sequence of the host image blocks in turn, and transformed by 1 level DWT. By JND, the final watermark was embedded into the host image by modifying the average values of the two corresponding subbands. The experimental results show that the embedded watermark is invisible to human eyes at a low PSNR, and the algorithm is robust to common image processing operations, especially to signal enhancement. The conclusion is that the algorithm is effective and practical.