基于MPEG4视频数字水印的DCT算法研究

西北师范大学硕士学位论文基于MPEG-4视频数字水印的DCT算法研究姓名：徐书魁申请学位级别：硕士专业：计算机应用技术指导教师：张贵仓2008-11-16摘要随着信息技术和计算机网络的飞速发展，人们不但可以通过互联网和CD-ROM方便快捷地获得多媒体信息，还可以得到与原始数据完全相同的复制品，因此，作为数字媒体版权保护的重要手段，数字水印技术近年来已成为国内外研究的热点。

数字水印是信息隐藏技术的一个重要分支，是一种全新的数字产品保护技术，它是将标识作者的版权保护信息和认证信息嵌入到图像、音频、视频或软件等各种数字产品中，以达到区分非法拷贝传播和保护知识产权的作用。

随着MPEG-4视频标准应用越来越广泛，如网络视频通讯，视频编辑等等，必须要有如数字水印这样的技术来保护MPEG-4视频数据的版权。

本文研究了面向MPEG-4系列标准的视频水印技术及其应用问题。

MPEG视频主要基于空间及时间冗余进行压缩，在基于多媒体的压缩方面，MPEG主要采用了和H.261相一致的8×8区域DCT变换方法。

正是由于DCT变换是目前多媒体视频压缩几大标准中共同采用的技术基础，基于DCT的水印方案在压缩视频中具有显著的优势该方案不但无需引入额外的变换以换取视频(帧)的频谱颁布，且能有效抵抗其中DCT参数重新量化的影响，因此，基于DCT的压缩视频水印算法具有非常重要的研究意义和应用前景。

针对MPEG-4未压缩域和压缩域视频分别提出了离散余弦变换DCT的视频数字水印的两种新的改进算法。

本文主要研究工作及创新如下：1、本文首先结合研究问题的背景，指出MPEG-4视频水印技术对于科研及工业生产的重要意义，对水印技术的研究现状及发展趋势进行了分析和总结；2、综述了数字水印和MPEG-4技术相关的一些基础理论知识，针对视频水印技术进行了深入地研究。

3、本文在研究了前人算法的基础上[5]，分析了将现有的静态水印技术加之于MPEG-4视频上的可能性以及可能出现的问题，提出了一种实用的用于MPEG-4非压缩域的视频水印算法：利用块分类的DCT域自适应扩频图像水印算法，并给出了分析和实际验证的结果。

嵌入的水印是一个可视二值图像。

用两个不相关的伪随机序列分别代表水印信息中的0和1，从而达到扩频的目的，将扩频后的水印信号，嵌入到分块DCT域的中低频段系数中。

仿真实验表明：图像经过JPEG有损压缩、低通与中值滤波、剪切等图像处理操作后仍是稳健的。

4、本文在分析研究了文献中Patrick Bas, Nikolaos, V.Boulgouris, Adnan M.Alattar[8]等人的几种经典算法的基础上，设计并实现了一个在MPEG-4位流中嵌入水印的版权保护方案，通过对选定的DCT系数进行微小变换，以满足特定的关系，来表示一个比特的信息。

为了不受量化过程的影响，本方案将水印嵌入在量化后的DCT系数中，从而提高了水印生存的稳定性。

在MPEG-4压缩算法中，DCT系数的量化是关键，它直接影响视频的质量和码流控制算法。

为此，MPEG提供了一个供参考的标准量化表。

该表根据人类视觉模型(HVS)建立。

考虑到人眼对高频信息损失的敏感度较低频损失小很多，因此通常把水印嵌入到中低频信息中，从而提高了水印信息的鲁棒性。

另外，根据人眼对亮度信息的变化比色度信息较敏感这一特性，为最大限度地保持视频质量，本方案将水印嵌入到色度子块的DCT系数中。

由于DCT是目前多媒体视频压缩中被广泛采用的技术基础，因此，基于DCT的视频水印方案具有显著的优势。

将水印信息嵌入到IVOP 色度量化后的DCT直流系数中，不但无需引入额外的变换以获取视频的频谱分布，且水印信息不受DCT系数量化带来的影响。

实验表明，算法在MPEG-4水印视频经过滤波、旋转、尺度变化、代码转换编码等处理后，在可见性和鲁棒性等方面取得了良好的效果，能够很好的抗MPEG-4压缩。

5、最后分析了MPEG-4数字水印的研究方向以及可能的应用前景。

关键词：数字水印；MPEG-4；DCT；视频水印AbstractWith great development of the IT and network technology, we easily have multimedia by Internet and CD-ROM, and these media are duplicates of original data. So as an effective method to provide copyright protection for digital media, digital watermarking has received considerable attention all over the world in recent years.Digital watermarking is an important branch of information hiding and a new digital products protection technology. It is a process of embedding a watermarking, such as author’s copyright information or authentication information, into various digital products, such as images, audio, video or software etc. By this way, watermarking can distinguish the illegal copy and embezzlement of the digital products and protect intellectual property right. As MPEG-4 video standard is more and more used for applications such as video editing, network video communications, the MPEG-4 video data must have a copyright protection such as watermarking to protect the copyright.In this paper, applications of watermarking video content and main technical thoughts in video watermarking are studied. Two new and improved DCT(discrete cosine transformation) algorithms are put forward in this thesis for MPEG-4 video: Aimed at Uncompressed MPEG-4 domain, a new DCT watermarking algorithm is proposed based on Watson model. The embedded position is fixed on by Watson model. In order to encrypt the watermarking, the spread-spectrum is introduced. This scheme has strong robustness; An improved DCT-based digital watermarking technique is proposed in this article. Through analysis of MPEG standard, different watermarking schemes are given for intra-frames and non-intra-frames respectively. The whole method and its implementation are presented in detail. Several experimental results have demonstrated that the proposed watermarking algorithm is robust against some typical attacks in terms of geometric clipping and linear interpolation. It is hoped the proposed method can be effectively applied to Web2 based video applications.The major research works and innovatory points in this thesis are as follows:1. This paper firstly points out the important meaning of digital watermarking to the science research and industry production based on the background of problem studied, and analyzes the current status and developing trend of the digital watermarking.2. The basic principles, features and problems of watermarking and MPEG-4 are summarized. The video watermarking is researched thoroughly.3. 1. A new discrete cosine transformation (DCT) watermarking algorithm is proposed based on Watson model. The embedded position is fixed on by Watson model. In order to encrypt the watermarking, the spread-spectrum is introduced. This scheme has strong robustness.4. Several algorithms for MPEG-4 watermarking are studied, such as Patrick Bas, Nikolaos, V.Boulgouris, Adnan M.Alattar[8]. A method for watermarking of MPEG-4 compressed video is presented. Spread spectrum technology is used to improve the security of watermark sequences. A synchronization template is used to combat geometrical distortion such as cropping, scaling, and rotation. Both signals, synchronization and watermark are embedded in the bit stream. A drift compensator is used to eliminate the distortion due to AC/DC prediction in I-VOPs and motion compensation in P-VOPs, to maintain robustness of the watermarking and the quality of the video, and resist format conversion attack. A bit stream control mechanism is introduced to main the data rate after the embedding manipulation. From the experiment results, it indicates that, after the watermarked MPEG-4 videos suffer filtering, rotation, scaling and transuding, the watermarking possesses good imperceptibility and robustness.5. The research direction and possible prospect of the digital watermarking for MPEG-4 video text document s are analyzed.Key words: digital watermarking, MPEG-4，DCT，Video watermarking独创性声明本人声明所呈交的论文是我个人在导师指导下进行的研究工作及取得的研究成果。