A study on optical image encryption and data embedding by using fast algorithms based on the lensless Fresnel domain

• Main Authors: Hone-Ene Hwang, 黃宏彥
• Other Authors: Wen-Nung Lie
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/17162628487653345421

博士 === 國立中正大學 === 電機工程所 === 98 === Abstract There is widespread interest in the development of optical image encryption and data embedding systems. The advantages inherent in an optical approach to encryption and data embedding include such as a high-speed parallel data processing and the difficulty in data accessing, copying or falsification. Conventionally, optical image encryption is achieved by double random-phase encoding in the Fourier domain (also in the Fresnel or fractional Fourier domain), where two statistically independent random-phase masks placed at, the input and the Fourier (Fresnel or fractional Fourier) planes, are to be designed. While these two random-phase codes are generated traditionally by using an iterative algorithm, such as Projection Onto Constraint Sets Algorithm (POCSA), which is inefficient due to a long iterative process. How to develop a more efficient method than the previous works on creating two statistically independent random-phase masks, without losing the security of the system, is an important issue in this research. This is done by exploiting the modified Gerchberg-Saxton algorithm (MGSA) instead of traditional POCSA (Chapter 3). Similarly based on the proposed MGSA, we present a concealogram-based method for optical data embedding by using halftone encoding based on CGH technique (Chapter 4). A concealogram is generally created by encoding both the magnitude (intensity) and phase of a hidden image into a halftone host image, as a fashion of modifying the area and position of binary dots therein. The magnitude (intensity) and phase information for an image to be embedded, are generally obtained by using an iterative POCSA algorithm, which is inefficient due to a long iterative process. In the second important issue in this research is to develop a more efficient method than the prior works on creating concealograms for optical data embedding results. Actually, our research results show that the proposed MGSA-based method can not only achieve the data embedding purpose without losing the system security, but also provide a faster method than previous works. The final topic in this study is about optical multiple-image encryption (Chapter 5). Methods based on a single random-phase mask and double random-phase masks, are both proposed. They can also to be done by exploiting the MGSA instead of POCSA. Furthermore, the extension of the proposed algorithm to color-image encryption is also discussed. A crucial issue to this goal is to reduce the crosstalks between encrypted images, which accordingly increases the number of images that can be encrypted simultaneously (or, the multiplexing capacity). Our research results show that the crosstalks can be significantly reduced. In summary, the proposed MGSA is identified to be a powerful encoding tool in the development of both optical image encryption and data embedding.