A large-capacity zero-watermarking algorithm for color images based on combined transform domain

In view of the small watermark embedding capacity and poor robustness against geometric attacks in most of the existing zero-watermarking schemes for color images, a robust zero-watermarking algorithm with a large capacity based on combined transform domain and bit-plane decomposition was proposed. Firstly, the R, G, and B channels of a color carrier image were respectively subjected to fast finite shearlet transform (FFST), and each low-frequency sub-band after FFST was processed by non-overlapping blocking and scrambling. The block discrete cosine transform (DCT) coefficients of each sub-band after the scrambling were used to construct the quaternion discrete cosine transform (QDCT) coefficient matrices, and then two low-frequency coefficients were selected from each QDCT coefficient matrix. Eight binary robust feature matrices were constructed according to the sign polarities of the real parts and the imaginary parts from the above two coefficients. Finally, the gray-level watermark image scrambled and encrypted by the orthogonal Latin squares matrices was decomposed by bits. The eight binary bit-planes after decomposition were used for XOR operation with the above binary robust feature matrices and recombined to obtain the final gray-level authentication zero-watermark. In addition, before the watermark detection, the image to be authenticated was geometrically corrected by the oriented FAST and rotated BRIEF (ORB) algorithm. The experimental results show that the proposed algorithm has high watermark embedding capacity and security, and it is highly robust to both conventional geometric and non-geometric attacks.