Research On Double Image Optical Encryption In The Fractional Fourier-domain

With the rapid development of multi-media technique, it is of importance that theinformation with certain relations is encrypted simultaneously with high-efficiency andhigh-security. Multiple-image optical encryption can offer the possibility of high-speedparallel, larger capacity and more key degrees of freedom. Multiple-image optical encryptionhas been applied widely in the field of military, government, commercial and medical care. Ina multiple-image encryption system, complex mode of multiple images and transformalgorithms directly affect the security of the system, the efficient of the encryption and thequality of decrypted images.The main content of this thesis is double image optical encryption based on fractionalFourier transform, one branch of the multiple-image encryption. Combining scramblingtechnique with chaos theory, some encryption algorithms improved are proposed in this thesis.The main contents are as follows:First of all, a novel technique for double image encryption based on fractional Fouriertransform is proposed. Both of the original images by the amplitude-phase modulation areencoded into a complex function, and the synthesized input signal is then encrypted intostationary white noise by utilizing random phase encoding in fractional Fourier domain. Thephysical structure of encryption system is uncomplicated with the utilization of only singlerandom phase mask, which will help the practical use of the encryption system. Second, anovel double image encryption method is proposed by utilizing double pixel scramblingtechnique and fractional Fourier random domain encoding. The security level ofamplitude-based image can be enhanced by the private key of pixel scrambling operation. Theproblem is solved that the key space of the amplitude-based image is lower than that of thephase-based image in the amplitude-phase modulation. Third, a new method of imageencryption is presented by utilizing fractional Fourier transform and chaotic pixel scramblingtechnique. Chaotic system is used to generate pseudo-random sequence instead of randomphase mask. The parameters of chaotic system serve as keys to make up for the obviousdrawback, that utilizing random phase mask as a key leads to the difficulty of storage,transmission and restructure. Finally, a new method of image encryption is presented by utilizing a multiple-parameter discrete fractional Fourier transform. The proposed encryptionalgorithm has considerable security by utilizing Multiple-parameter as multiple keys toenlarge the key space.The simulation results show that the proposed algorithms have better capability forrobustness, noise immunity and security. The schemes have simplified operation, lesscomputation and have great prospects of application.