A number of methods have been recently proposed in the literature for the encryption of 2-D information using linear optical systems. In particular the double random phase encoding system has received widespread atten...
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A number of methods have been recently proposed in the literature for the encryption of 2-D information using linear optical systems. In particular the double random phase encoding system has received widespread attention. This system uses two Random Phase Keys (RPK) positioned in the input spatial domain and the spatial frequency domain and if these random phases are described by statistically independent white noises then the encrypted image can be shown to be a white noise. Decryption only requires knowledge of the RPK in the frequency domain. The RPK may be implemented using a Spatial Light Modulators (SLM). In this paper we propose and investigate the use of SLMs for secure optical multiplexing. We show that in this case it is possible to encrypt multiple images in parallel and multiplex them for transmission or storage. The signal energy is effectively spread in the spatial frequency domain. As expected the number of images that can be multiplexed together and recovered without loss is proportional to the ratio of the input image and the SLM resolution. Many more images may be multiplexed with some loss in recovery. Furthermore each individual encryption is more robust than traditional double random phase encoding since decryption requires knowledge of both RPK and a lowpass filter in order to despread the spectrum and decrypt the image. Numerical simulations are presented and discussed.
The aim of this research is to develop efficient algorithms for fractal imagecoding, which can be applied in digital image compression, image magnification and image denoising. Fractal imagecoding can provide a high...
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The aim of this research is to develop efficient algorithms for fractal imagecoding, which can be applied in digital image compression, image magnification and image denoising. Fractal imagecoding can provide a highly reconstructed image quality with a high compression ratio, is independent of resolution, and has a fast decoding process. The problem with fractal coding is its high computational complexity in the encoding process. Most of the encoding time is spent finding the best-matched domain block from a large domain pool to represent an input range block with respect to contrast and intensity offset, as well as the isometry transformations. The objectives of this research are to investigate and develop efficient techniques for fractal imagecoding, fractal-based image magnification and denoising. In this thesis, four efficient fractal image-coding algorithms have been proposed. The first algorithm is based on new feature vectors and the property of zero contrast. The proposed feature vectors can provide a better representation of image blocks, and thus result in a more efficient search of the domain block. The second algorithm is an efficient windowing scheme for fractal imagecoding based on the local variances method. In our method, windows covering those domain blocks whose variances are higher than that of the range block are considered according to a mathematical model. The exhaustive search algorithm can obtain the optimal result by searching all the blocks within the domain pool, but this process requires a high computational cost, which limits its practical application. A single kick-out condition is proposed which can avoid a large number of range-domain block matches when finding the best-matched domain block. An efficient method for zero contrast prediction is also proposed, which can determine whether the contrast factor for a domain block is zero or not, and compute the corresponding difference between the range block and the transformed domain b
In this paper, a new encryption mode, which we call the 2D-encryption Mode, is presented. 2D-encryption Mode extends ID-encryption modes, as ECB, CBC and CTR, to two dimensions. It has good security and practical prop...
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In this paper, a new encryption mode, which we call the 2D-encryption Mode, is presented. 2D-encryption Mode extends ID-encryption modes, as ECB, CBC and CTR, to two dimensions. It has good security and practical properties. We first look at the type of problems it tries to solve, then describe the technique and its properties, and present a detailed mathematical analysis of its security, and finally discuss some practical issues related to its implementation.
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