Cross-talk-free double-image encryption and watermarking with amplitude-phase separate modulations

A novel digital method of double-image encryption and watermarking by constructing a complex field with one non-negative image as its amplitude and another as its phase and then encrypting this complex field by means of digital optics, such as phase-shiffing interferometry with double-random phase encoding, is proposed. Since no direct addition of the information of two hidden images is employed in the encryption process, each image can be perfectly retrieved without cross-talk caused by the existence of the other. The feasibility of this method and its robustness against occlusion and additional noise from watermarked images with different weighting factors are verified by computer simulations. The signal-to-noise ratio and mean square error of the retrieved images are calculated for different distortions. This technique can considerably improve the efficiency of data transmission, and it is particularly suitable for the image transmission via the Internet.