Spatially Incoherent Optical Image Based Lighting Hidden

Information security is a serious problem in both economic development and social life. Information hiding methods based on optical theory and methods are attractive alternative in the data and information security. Optical information hiding technology has attracted great attention owing to its inherent ability of parallel operation, high space-bandwidth and multiple parameters. Application of optical methods to security has been widely investigated in recent years and various optical image encryption structures and algorithm have been proposed. However, most of the optical encryption structures and algorithm proposed so far are working under the coherent illumination, thus suffer from the high sensitivity to misalignment and coherent artifact noise. This shortage makes it difficult to apply those optical image encryption methods in practices.In this thesis, we propose a simple and efficient optical image encryption system with spatially incoherent illumination. The optical encryption procedure can be considered as the incoherent filtering of the input image with a random phase only mask. The original image to be encrypted is located on the input plane and is illuminated with the spatially incoherent light beam. The incoherent light modulated by the input image is filtered by a random phase only mask, then propagates through an imaging lens and captured by a CCD on the output plane. The decryption procedure can be performed digitally by means of inverse Fourier transform. The point spread function which is needed in decryption can be worked out if the random phase distribution is given. Due to the incoherent light used, the optical image encryption system is free of the artifact noise. Besides, only one random phase only mask and one Fourier lens are contained in this system and the encrypted image could be recorded by CCD directly without recording the phase information. All of this greatly reduces the complexity of optical image encryption system and make it feasible for applying optical image encryption methods in practices. The main works in this thesis are listed as follows:Firstly, we review the development of applying optical technology to information security at home and abroad. And some recent progresses in optical information processing with incoherent light are investigated.Besides, the modulation characteristics of Liquid Crystal Spatial Modulator (LC-SLM) and its simple applications are investigated in this thesis. The modulation curves of LC-SLM LC2002produced by the company HOLOEYE in German are measure experimentally. And we obtain a well reconstructed image by modulating the light with LC-SLM in the digital holography projection experiment.What’s more, the feasibility of proposed optical image encryption method with spatially incoherent illumination is discussed theoretically in the thesis. Computer simulations are carried out and the simulation result verifies the feasibility of the proposed method in both encryption and decryption processing. Finally, an optical experiment is designed and demonstrated as a verification of optical image encryption method with spatially incoherent illumination. The result shows that the original image cloud been hided totally and a high quality reconstructed image decrypted with correct key have been obtained in the experiment.