Applications Of Phase Retrieval Algorithm And Fractional Wavelet Transform In Image Encryption And Digital Watermarking

With the rapid development of digital communication and computer network techniques, information security has been receiving more and more attention. The research on the image encryption for digital image protection and the digital watermarking techniques for copyright protection has wide potential applications in the fields of intellectual property rights protection, bill anti-counterfeit and so on. Compared with the conventional computer and electronic techniques, optical information processing techniques have many advantages, such as large parallel data processing capability, more degrees of freedom, and high-level data security. Consequently, the approaches for information security based on the principles and methods of optical image processing have been extensively studied and played an important role in this area.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 based on phase retrieval algorithm, fractional wavelet transform and phase-shifting interferometry. The main research work in this thesis includes the following:(1) We have reviewed the history and progress of the techniques of optical image encryption and digital watermarking, and given a general introduction about various methods of the optical image encryption and the correlated theory of the digital watermarking.(2) The theoretical basis of light-wave diffraction is introduced in general, while the iterative phase retrieval algorithm is introduced in detail, and an image encryption method with the use of this algorithm is given. On the basis of these methods, a novel digital image watermarking system employing iterative phase retrieval algorithm is proposed. This watermarking method has good imperceptibility and strong robustness, and can eliminate cross-talk noise resulted from direct information superposition. Computer simulations have verified the feasibility and validity of this method.(3) The theories of the fractional Fourier transform, the wavelet transform, and the fractional wavelet transform have been introduced, and an image encryption method based on fractional wavelet transform and three-step phase shifting interferometry is proposed. This encryption method combines the virtues of both the fractional wavelet transform and the phase-shifting interferometry in image encryption. The fractional orders and scaling factors of fractional wavelet transform and the arbitrary phase shifts can serve as different kinds of keys for decryption to greatly improve the security of the system. Computer simulations have verified the feasibility and validity of this method.