Abstract: In view of watermark is added into wavelet coefficients in some watermark method，which causes the pixel value over the maximize of the gray image and not extracting the watermark correctly.A watermarking classified DWT coefficients algorithm based on blending is presented in this papers.The algorithm using different embedding methods on the base of classifying wavelet coefficients which can limit the pixel value within gray image.The other coefficient is added into watermark directly.The experimental results show that the algorithm can reduce boundary error while extracting watermark，the watermarking image is of the higher PSNR，and can enhance watermark similarity.

Key words: digital watermark, wavelet coefficients, blending, classified embedding

摘要： 部分数字水印算法中水印直接添加到图像小波系数，造成在最大灰度值附近的像素值产生越界，引起水印提取不准确。提出基于混合的小波系数分类数字水印算法，算法在边界值处采用混合嵌入方法，保证了嵌入水印后的像素值不会超出图像灰度范围；其余非边界系数采用叠加水印方法。实验结果表明，该算法避免了水印提取时边界附近产生的误差，水印的相似度也明显提高，嵌入水印后的图像具有较高峰值信噪比。

关键词: 数字水印, 小波系数, 混合, 分类嵌入