Abstract: Concerning the single function of single watermark algorithm, a multi-purpose watermarking algorithm for color image combined with Discrete Wavelet Transform (DWT) and Quaternion Discrete Cosine Transform (QDCT) was proposed. Firstly, the DWT was applied to the three scrambled channels of a color image, and QDCT was applied to their low frequency subbands and medium frequency subbands, then some of the real coefficients were used to construct a coefficient matrix, and the robust watermark was embedded into the singular value of it by adding principle. Secondly, the image was divided into 2×2 sub-blocks and preprocessed with QDCT. The characteristic fragile watermark was generated by the low frequency modulus coefficients of QDCT and embedded into the Least Significant Bits (LSB) of the space domain. The experimental results show that the robust watermark has good robustness against JPEG compression, noise, contrast adjustment, cropping, rotating and hybrid attacks, and the fragile watermark is sensitive to tampering and has accurate tamper localization.

Key words: color image, dual watermark, Discrete Wavelet Transform (DWT), Quaternion Discrete Cosine Transform (QDCT)

摘要： 针对单水印存在功能单一的问题，提出一种基于离散小波变换（DWT）和四元数离散余弦变换（QDCT）的彩色图像多功能水印算法。首先，将彩色图像分通道置乱后进行DWT，选择低、中频子带作分块QDCT，利用部分实数系数构造系数矩阵，鲁棒性水印通过加法原则嵌入该系数矩阵的奇异值中；然后，将图像进行2×2分块的QDCT，特征脆弱水印利用QDCT的低频模值系数产生，并嵌入空域最低有效位（LSB）。实验结果表明，鲁棒性水印具有良好的抗JPEG压缩、噪声、对比度调节、剪切、旋转以及混合攻击的能力，脆弱水印对篡改敏感且具有精确的篡改定位功能。

关键词: 彩色图像, 双水印, 离散小波变换, 四元数离散余弦变换