A new structure-preserving quaternion QR decomposition method for color image blind watermarking

•The three strong correlations in the quaternion matrix Q are analyzed for the first time to design a high-capacity scheme.•Generalized Arnold transform and random coordinate sequences are used to enhance the security of the proposed scheme.•QQRD realized by the structure-preserving method makes the computational load of the proposed watermarking scheme very small.•The proposed color blind watermarking scheme based on QQRD can effectively resist geometric attacks and common attacks. Most of the existing color image watermarking schemes are designed to mark each color channel individually, which ignores the correlation of different color channels and the synchronous embedding of watermarks. In this paper, we propose a robust blind watermarking scheme based on quaternion QR decomposition (QQRD) for color image copyright protection, while using algebraic structure-preserving method to release its computational complexity. In watermark embedding process, QQRD is applied to non-overlapping 4×4 image blocks in a whole manner, whereupon three strong correlation coefficient pairs determined by the Normalized Cross-Correlation (NC) method are modified to embed color watermark within factorized matrices. This avoids layered processing that causes abnormal sensitivity to attacks and less correlation that causes excessive modification of coefficient values. Numerical results show that the newly proposed watermarking scheme has strong ability to resist most image processing attacks and is error-free under no attack, brightness adjustment attack and Poisson noise attack. Its superiority over other state-of-the-art methods is also experimentally demonstrated. [Display omitted]