Novel quaternion polar complex exponential transform and its application in color image zero-watermarking.

• A new type of QPCET, namely NoQPCET, is constructed. • A new color image robust zero-watermarking algorithm is designed based on NoQPCET. • This algorithm has very strong security by using chaotic system. • The low-order NoQPCET coefficients are used to extract the image feature. The robust watermarking method embeds the information in the image to protect the copyright. The embedding process will destroy the original image and cannot be effectively applied to the images used in the medicine and military with high integrity demand. A robust zero-watermarking algorithm for lossless copyright protection of color images without changing the original image was proposed in this paper. A novel quaternion polar complex exponential transform (NoQPCET) was firstly constructed with effectively improved performance; then the NoQPCET and chaotic system based robust color image zero-watermarking algorithm was suggested for lossless copyright protection of color images. In the proposed algorithm, the robustness against geometric attacks was enhanced due to the excellent geometric invariance of NoQPCET, and the security was also improved because of the initial value sensitivity of the chaotic system. Experimental results showed that this algorithm had very strong robustness against both geometric attacks and common image processing attacks, and was superior to other algorithms. [ABSTRACT FROM AUTHOR]