Digital Holographic Image Encryption And Watermarking Technology

In recent years, with the rapid development of modern communication and computer network techniques, we have entered the information era. Information techniques provide us with many conveniences; meanwhile, they put forward high demands of information security. Traditional encryption techniques based on cryptography have difficulty in dealing with increasing information capacity, not to mention their limited processing speed. Optical information processing, which operates at light speed, has parallel processing capability. Furthermore, optical wave's high frequency and short wavelength make it possible to handle enormous information capacity. Therefore, optical information processing shines a new path for future information techniques. Incorporating the advantages of optical processing with high security level of traditional encryption method needs hard work of researchers of information optics, cryptography and computer science, and its practical application lies on study of convenient and practical algorithms and the development of portable, energy-saving, high integration level Micro-Opto-Electro-Components.Based on optical principle, digital holography can successfully handle the optical process such as propagation, diffraction, Fresnel transform of lens, interference, recording and reconstruction of holograms in digital approaches. Its advantages of high flexibility and easiness in use enable researchers to utilize it in many areas, especially in image encryption and watermarking. For example, the introduction of random phase mask into image encryption has greatly strengthened the security of encrypted images and then found wide use in practice.The aim of this thesis is to give a comprehensive review on the recent development of the techniques of image encryption and watermarking, and then propose some novel methods and techniques of digital image encryption and watermarking, which are more convenient and easier to realize from the viewpoint of image transmissionvia Internet.The main research work in this thesis includes the following:(1) We proposed a digital image encryption technique with double random phase masks and phase-shifting interferometry, and introduced a watermarking method to further hide the encrypted data.(2) Considering the sensitive selectivity of random phase masks, we proposed a multiple image encryption and watermarking technique, which can realize image encryption and watermarking for 2 ~ 4 images at the same time in one set of interferograms. This method can considerably increase the efficiency of data transmission.(3) A comparative study of image reconstruction from only one gray-level transmitted image, namely, only the real part, the imaginary part or the phase information of the encrypted complex image, has been made. It shows that the phase information can give much better performance. Based on this idea, we proposed a new technique of phase-only encryption and watermarking and have verified its effectiveness by computer simulations. This method can greatly decrease the amount of transmission data.(4) We proposed a purely digital watermarking technique, which may be called "picture-in-picture", by hiding a secret image in a host image without any apparent change of the latter. This technique may make it impossible for an unauthorized receiver to be aware of the existence of the encrypted image and then significantly lower the chance of its unauthorized decryption. This method may find wide use in secrete communications.