Blind color image watermarking algorithm in quaternion domain based on QR decomposition

To provide a solution to the copyright protection problem of color images, a blind color image watermarking algorithm in the quaternion domain based on QR decomposition is proposed. Firstly, the Contourlet transform are applied to the R, G and B channels of the carrier image respectively, the low-frequency subbands are taken to construct a quaternion matrix, and the quaternion discrete cosine transform is applied to the quaternion matrix, then the inverse discrete cosine transform is performed on the real part matrix after the quaternion discrete cosine transform to get the intermediate process matrix. Finally, the above intermediate process matrix is split into non-overlapping blocks, the encrypted binary watermark is embedded into the upper triangular matrix obtained from the QR decomposition of non-overlapping blocks. The experimental date demonstrate that the watermark images extracted by the algorithm are still discernible after some common image processing attacks, so it has certain robustness.