Studies On The Image Hiding Based On The Double Random Phase Encoding

Information is powerful, mankind has had this knowledge for millennia. Nowdays, in this information age, especially in the mid-80s, with the advent of the computer and the internet, information security is becoming more and more important. Optical security technique based on the Fourier optics has become one of the most important issues in information security domain. With the advance of high performance CCD cameras and spatial light modulators (SLM), optical information security technique has developed rapidly and becomes more and more attractive for optical realization of security certificate, information encoding and information hiding. Various kinds of optical security techniques and systems have been proposed to solve the problem of security in the transmission of information, these excellent results will push us to take more further and detailed study to find more powerful system on this topic.In this thesis, optical processing procedure and digital technique are used, the optical image hiding techniques for binary, gray and color image hiding based on the double random phase encoding (DRPE) are proposed. The major contributions of this thesis are summarized as follows:This thesis begins by summarizing an overall rationale and development of the information security, and by focusing on the characteristics of information hiding in Chapter1. The classification and development of the optical security techniques are also presented in this part. The purpose and significance of this thesis are pointed out. The rationale of optical security such as:the Fourier transform characteristics of lens, optical hologram technique, the joint transform corrlator and the phase retrieval algorithm are also introduced in this part.Chapter2will follow with a discussion of the proposed system for the binary image hiding. In this Chapter, based on the joint transform correlator architecture and holographic technique a new method for image hiding is presented. A hidden image encrypted by joint transform correlator architecture is embedded in the Fourier hologram of the host image. Inverse Fourier transform can be used to get the watermarked image, and joint transform correlator architecture is used to decode the hidden image from the watermarked hologram. Unlike other watermarking technique, by information prochoosing, noise added to the recovered hidden image by the host can be reduced. And unlike other watermarking systems based on double random phase encryption, no conjugate key is used to recover the hidden image. The robustness of the proposed system for resisting of attacks such as occlusion, noise and filtering are also introduced.In Chapter3, based on the joint Fresnel transform correlator, a new system for double images hiding is presented. By this security system, dual secret images are encrypted and recorded as intensity patterns employing phase-shifting interference technology. To improve the system security, a dual images hiding method is used. By digital means, the deduced encryption complex distribution is divided into two subparts. For each image, only one subpart is reserved and modulated by a phase factor. Then these modified results are combined together and embedded into the host image. By the phase modulation, the cross talk caused by images superposition can be reduced for their spatial parallel separation.Chapter4details the thesis of hiding a color image into another color image. In this part, a new method is proposed for color image hiding and extracting by use of phase retrieval algorithm in fractional Fourier transform domain and Arnold transform. Based on a cascaded phase iterative FRFT algorithm, the3-channel (R, G and B) of the secret color image permuted by ART are encrypted. Then the encoded information is embedded in Blue-channel (B-channel) of the enlarged color host image. The random phase mask, the wavelength, transform parameters are provided as keys for decryption.In Chapter5, we propose a new method for multiple color images hiding by using of triplets recombination. In this proposed technique, triplet (R, G and B) components of the secret color image is recorded simultaneously as a real and positive gray image exploiting parallel multi-wavelength recording technology. Arnold transform and phase retrieval algorithm adapted to Fresnel transform domain are used to encode the parallel hybrid result. By using of the proposed technique, each color image is encrypted into a pure phase distribution and combined by superposition. Phase modulation is introduced to eliminate the cross-talk caused by multiple images superposition. The wavelength, transform parameters are provided as keys to enhance the system security.Finally, we summarize the main conclusions in this thesis and anticipate a more efficient, reliable and significant work would be done in the future for the optical security applications.