结合SURF特征的多功能彩色图像水印算法

针对目前大多数水印算法功能较单一，提出了一种可以同时进行版权保护和内容认证的多功能彩色图像双水印算法。首先，将原始图像由RGB空间转换到YUV空间，提取亮度分量的SURF（speeded up robust feature）特征点，根据特征点的主方向构造描述向量并将其拆分为两个子向量，分别计算它们与一个参考向量之间的余弦夹角，通过比较夹角的大小关系来构造鲁棒零水印序列；然后对原始图像进行2×2分块，对子图像块奇异值范数进行异或运算来产生脆弱水印信息，并将其嵌入至图像空域的最低有效位。版权归属鉴定时通过计算原始鲁棒零水印序列和从待检测图像中提取的水印序列之间的BCR（bit correct rates）相关系数作为鉴定的依据，内容认证时通过比较图像最低有效位和脆弱水印信息是否一致来实现篡改的检测和定位。实验结果表明，本文算法具有良好的透明性和较高的计算效率，同时具备版权保护和内容认证的双重功能。

Multi-purpose watermark algorithm of color images based on SURF

The single watermark algorithms always merely have a single function. In order to overcome this drawback, a multi-purpose dual watermark algorithm of color images based on the speeded up robust feature(SURF)is proposed in this paper. First, the original image was transformed from RGB to YUV space and the SURF points and vectors of original image are extracted. A 64-dimensional vector is constructed according to the main direction of the SURF point that meets the scale condition, then the vector is split into two 32-dimensional sub-vectors. The robust zero-watermarking sequence is produced by comparing the cosine angles between the sub-vectors and a secret reference vector. Then, the original image is divided into 2×2 sub-blocks and the fragile watermark is produced after XOR operations on the singular value norms of sub-blocks. Lastly, the fragile watermark is embedded into the least significant bit(LSB) in the space domain of the image original. copyright is identified by the bit correct rates(BCR)between the original robust zero-watermarking sequence and the watermark sequence extracted from the tested image. Content authentication is accomplished by judging whether the fragile watermark is consistent with the image least significant bit. The experimental results show that the algorithm not only has good invisibility and high computational efficiency, but also can achieve the dual function of copyright protection and content authentication.