Optical color image encryption based on computer generated hologram and chaotic theory

A novel technique of optical color image encryption and decryption based on computer generated hologram (CGH) and chaotic theory is proposed. The tri-color separated images of an image to be encrypted are encoded with three random phase arrays constructed by a chaotic sequence of the deterministic non-linear system, respectively. Then Burch's encoding method using the modified off-axis reference beam is adopted to fabricate the CGH as the encryption image. A clear original color image can be reconstructed as long as the correct initial value of chaotic sequence and the correct system parameters are given. The initial value of chaotic function with a very small change will lead to the generation of an entirely different chaotic sequences. As a result, the random phase array changes dramatically and the original image cannot be recovered rightly. Serving as the secret keys, the initial values of chaotic sequence and system parameters reduce the amount of the key data. And the digital encryption image is also more favorable to be stored and transmitted. The feasibility and its robustness against occlusion and noise attacks are verified by numerical simulations.