导　　师： 陈武凡

学科专业： 0831

授予学位： 硕士

作　　者： ;

机构地区： 南方医科大学

摘　　要： 随着计算机和网络技术的飞速发展,信息安全问题愈来愈受到人们的关注。采用密码学方法加密多媒体对象的内容,在一定范围内起到了保护作用。然而,这仍然不能阻断盗版者和恶意内容篡改者的步伐。一旦多媒体数据被解密后,针对被保护对象的非法拷贝或篡改现象依然无法控制。而能够解决这一问题的良好途径是目前国内外正研究的数字水印技术。 数字水印技术通过嵌入算法将具有特殊作用的水印信息隐藏在多媒体信息中,可用于多媒体信息的版权保护和内容认证,目前已引起学术界和产业界的广泛关注,并得到广泛的研究与应用。 本文将主要研究基于数字水印技术的图像认证系统,主要工作如下:首先,介绍了数字水印的基本特征、原理、分类以及目前国内外的研究现状等基本问题,归纳了数字水印系统的基本框架,概括性介绍了目前常见的数字水印算法。接着介绍了小波理论、密码学基础、混沌理论及图像置乱等技术;并深入研究了小波理论在数字水印技术中的应用;就如何利用密码学知识提高水印系统的安全性进行了分析;介绍了利用混沌序列加密水印信号的方法;重点讨论了置乱技术在数字水印领域中的应用及其特点。最后,提出具有自恢复功能的脆弱数字水印算法。算法核心思想是:选取图像的小波重要系数进行SPIHT编码生成水印;使用Arnold变换确定其嵌入块位置并将其加密嵌入到图像数据低位;通过链式认证结构实现水印信号的检测和图像篡改数据的定位,由SPIHT解码完成篡改数据的恢复。实验表明,该算法在保证含水印医学图像具有良好视觉透明性的基础上,还可以定位并恢复被篡改区域内容。 最后,本文对全文内容和研究成果作了一个概要的回顾,指出了今后需要继续研究和完善的方面。文中所给出的数字水印算法都在VC++6.0平台上得以实现并进行了相关的实验,获得到了较为满意的结果。 With the rapid development of Computer and Network technology, the problem of information security has become increasingly important. The encryption methods can give the solution for this problem to some extent. However, this can not radically prevent the pirates and tampers. After the multimedia data is decrypted, it is in the clear and no longer protected. While digital watermarking which is one of the research focuses in the academic world presents a candidate key to the questions. The watermark with a special function is embedded into the multimedia information to protect the copyright of the original author and authenticate the integrity and authenticity of the multimedia information. The watermark technique has become one focus of researcher. The attention of dissertation is focused on constructing the image authentication system based on the watermarking, and the main work is listed as follows: First, an introduction of the characteristics, principles, classifications and current research situation of watermarking are given. The basic framework of the digital watermarking system is summarily proposed. And the present familiar digital watermarking algorithms are introduced briefly. Second, the theories of the DWT, cryptology, the chaotic encrypt and the image scrambling techniques are proposed. The application of the DWT theories is extensively studied. How to increase the security of the watermarking system by the knowledge of encryption is analyzed. The methods to encrypt the watermark by the chaotic sequences are introduced. The application and means of shuffling techniques within watermarking are extensively discussed. Third, an auto-restorable fragile watermarking algorithm for image content authentication is proposed. The main idea of this algorithm is described as follows: Important DWT coefficients are chosen to be coded with the SPIHT algorithm for generating watermarking. Then the improved security watermark scrambled by Arnold transformation is embedded into the lower bits of the image data. Finally, chain structure is used to detect watermarking and identify the changed positions .And the altered data in an image is restored by SPIHT decoding. The experimental results demonstrate that the watermarked image not only possesses good perceptual transparence but also can locate and restore the tampered content. At last, work of dissertation is summarized, and the further research direction is discussed. The digital watermarking algorithm given by the dissertation has been applied on the VC++6.0 platform. The experiment results are satisfactory.

关 键 词： 脆弱数字水印 医学图像认证 图像数据恢复 小波变换 编码 变换

分 类 号： [TP309.7]

领　　域： [自动化与计算机技术] [自动化与计算机技术]