The Study Of The Algorithm For Phase Restore To Designing The Phase-only Optical Anti-counterfeiting Mask

As the advanced technology is helping develop our society as well as the economy, crimes of swindling utilizing it to counterfeit certificates, credit cards and large bills are increasing even faster, which have caused a huge loss to the nation as well as individuals and brought very bad impact to our society. Thus make it very important to improve anti-counterfeiting ability for various certificates, meanwhile, continuously exploring better and more secure anti-counterfeiting technologies is always the most important research topic in the field of information security.As the traditional anti-counterfeiting methods are facing their challenges, the optical security system based on random phase coding technology has drawn the public attention for its unique anti-counterfeiting characteristic as well as the encoding methods, which has effectively developed the optical information security technology. The main task of this thesis is to do some in-depth study focused on the existing problems on the coding theory as well as the system security of random phase coding technology, trying to increase the PSNR of decode images by improving coding methods under the same quantization condition on the basis of the modern optical anti-counterfeiting mask manufacturing technology; meanwhile, introducing one-time pad chaos secret key during the coding process, which has made the anti-counterfeiting mask not only very hard to detect for normal intensity detector, but also guarantee the system security under algorithm level and improve its ability to resist known-plaintext attack and copy class attack. The main content of this paper is as follows:(1) Briefly introduced the production process and coding method for phase-only diffraction optical component. We introduce and analyze several representative iterative algorithms for phase retrieval, such as G-S、POCS、Simulated Annealing and Genetic algorithm. We simulated these algorithms in the environment of MATLAB on computer and verified the performance for every algorithm in image recovery.(2) On the basis of detailed analysis for traditional phase retrieval algorithm, focused on the advantages and disadvantages of GS, POCS, SA and GA, we put forward two improved joint algorithms, which named SA-GS and SA-POCS. We will talk about the principal of the joint algorithms. In addition, we verified their performance through computer simulation. The result of computer simulation shows that both the two algorithms are able to rapidly recover the phase distribution for various input optical field. Compared with original GS and POCS algorithm, the quality of recovered images for improved algorithm have been improved, so is the PSNR.(3) For further improvement for the anti-fake ability of the system, we introduced chaos secret key in both joint algorithms. Utilizing sensitivity for initial value of the chaos system, we realize "one-time pad" in a certain by introducing assistant key and personal key. At last, we verified the validity of the design through computer simulation.