Color Zero-Watermarking Algorithm Based on SURF and Halftone Mapping Encryption

A color zero-watermarking algorithm based on speeded-up robust features (SURF) to correct geometric distortions and halftone mapping encryption is proposed to address problems associated with poor robustness against geometric attacks in existing digital watermarking algorithms and low efficiency due to excessive embedded color copyright image information. First, the feature points of the carrier image based on SURF algorithm were extracted and feature point information was saved as a key for blind detection. In the copyright verification process, after the feature points of the attacked image were extracted and keys were matched, the geometric correction of the attacked image was implemented based on affine matrix estimated by filtered feature points. Simultaneously, the copyright identification was preprocessed according to the halftone principle. The color image was represented by a three-channel binary matrix with pixel expansion, and the watermark image was encrypted by halftone sub-block mapping according to the encryption rules. In proposed algorithm, the color and structure information of the copyright images were retained while the amount of embedded information was reduced, and the security of the watermark information was increased. The experimental results demonstrate that the proposed zero-watermark algorithm is robust against geometric and nongeometric attacks and the generated zero-watermark information is more secure.