The Application Of Optical Image Processing Technology In Color Image Encryption

A method of color image encryption which is based on optical image processing is studied. Using tricolor grating, the color image is encoded to a gray level image, and then the gray level image is encrypted into steady white noise with Fractional Fourier transform random phase technology. The color image encryption is realized.The thesis is composed of several parts as follows:1. Tricolor grating is utilized to encode the original color image to a gray level image. Spatial filter at the Fourier spectrum plane is needed to bring out the first order spectrum of R, G, and B, and then the color image can be decoded by inverse Fourier transform. Both the encoding and decoding are carried out in white light systems. The encoding theory of tricolor grating and its applications are discussed.2. Fractional Fourier transform random phase encryption is applied to encrypt the encoded gray level image which contains the color information. The security is ensured in that it is difficult to decrypt the original image without knowing the phase keys because Fractional Fourier transform random phase encryption is robust to blind retrieval trials.3. The optical processes of several color images encryption are simulated by MATLAB programs, and the simulation results have proved that the color information is recovered successfully. The quality of decoded image is improved by merging the zero-order spectrum. The image quality is analyzed between decode color image and original color image. The effectiveness of the proposed methods is verified.The color image encryption method proposed here can be realized by all-optical system. Comparing with multichannel method, only one set of optical devices is needed in this method, thus the system is simplified and more practical. Comparing with double phase encryption, Fractional Fourier transform add the number of key from two to four, and the system increase the security.