The Study On Digital Watermarking And Image Encryption Based On Fractional Fourier Transform

Fractional Fourier Transform (FRFT) is a new method of time-frequency analysis, which is very suitable for non-stationary signal processing. Combining FRFT and image processing together is more conducive to analysis the time and frequency feature. As an important transmission medium in digital communication, digital image’s security during transmission is extremely vulnerable to the outside attacks. If the image is copied, reproduced or tampered by the attackers during the transmission, it could cause great economic loss.This thesis is focused on the security issues during the image transfer process. According to the internal relationship between FRFT and digital image, the thesis is mainly focused on the image processing which includes two directions:digital watermarking and image encryption. The thesis mainly includes the following two aspects.The thesis is studying the chaotic digital watermarking algorithm based on FRFT and Non-subsampled Contourlet transform (NSCT), include gray image watermarking and color image watermarking. This algorithm uses pseudo-randomness of chaotic sequences, the variety of FRFT and NSCT to improve the robustness and security during the process of embedding and extracting the watermark.According to characteristics of FRFT, high dimensions and complexity of hyperchaotic chen system and variety of magic scrambling, a new method based on the hyperchaotic chen system, magic scrambling and FRFT encryption algorithm is proposed, which can enhance the key space and encryption effect, increase the difficulty of decryption and encryption, and improve the anti-aggressive ability of encrypted image.In addition to the above applications in digital watermarking and image encryption, FRFT can also be applied into other aspects, such as edge detection, image enhancement, etc. With the further researchers on FRFT, FRFT will have further development in the field of image processing.