| A method of single-channel encryption for color image which is based on white light information processing is studied. Using tricolor grating, the color image is encoded to a gray level image, thus the three channels of R, G, and B are transformed into a single channel. Then the gray level image is encrypted into steady white noise with double phase technology. The single channel encryption of color image 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, thus the three channels of R, G, and B are transformed into one channel. 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. Double 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 double-phase encryption is robust to blind retrieval trials.3. The optical processes of single channel encryption of several color images 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 chromatic aberration is analyzed by color similarity coefficient in the RGB space. The effectiveness of the proposed methods is verified.The single-channel method of color image encryption proposed here can be realized by all-optical system. Comparing with multichannel method, only one set of optical devices is needed in this single-channel method, thus the system is simplified and more practical. The security is ensured by double phase encryption. |
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