【作者】 陈伟；

【导师】 吴谨；

【作者基本信息】 武汉科技大学 ， 控制理论与控制工程， 2006， 硕士

【摘要】 近年来,随着计算机和因特网的普及,作为先进计算机技术和视频、音频以及通信等技术集成的产物,多媒体已经渗透到人们的生活当中,也成为当前计算机行业最热门的技术之一。多媒体技术和通讯技术的日益发展,使得多媒体娱乐、多媒体通信、数字音频广播和高清晰度电视等各类实际应用对信息数据存储和传输的要求不断提高,因此,多媒体技术和Internet的应用发展所面临的主要问题之一就是解决对庞大图像数据信息的表示、传输和存储。为了达到令人满意的视觉和传输效果,对图像数据进行有效的压缩编码,是需要解决的关键技术之一。数字图像压缩编码的目的就是要以尽可能少的比特数来表征图像,同时又必须保持恢复图像的质量。本文首先对图像压缩编码的发展、图像编码的主要方法、图像编码性能的评价标准以及目前图像编码的国际标准进行了介绍,并对小波变换理论进行了比较全面的阐述,在此基础上探讨了小波变换实现图像数据压缩时的一般步骤。其次,图像经小波变换后,对小波系数的压缩是小波变换编码的关键步骤。在小波系数的压缩方法中,小波系数的零树方法充分利用了相应子带间的相关性,是基于小波图像压缩编码的一个有意义的突破。对基于零树结构的EZW和SPIHT算法,本文进行了详细的分析和讨论。最后,为了更为充分的利用小波变换的特点,本文从多个角度对EZW、SPIHT算法进行了改进。1、通过改变扫描路径,避免了大量的重复扫描,减少了EZW的编码耗时;2、在运用EZW算法对图像进行编码时,‘P’‘N’符号不包含表示后续节点重要性的信息,当后续节点都不重要时,编码结果中就出现连‘T’现象,并且,由于‘T’符号包含有表示后续节点重要性的信息,而最高频区节点没有后续节点,所以‘T’符号自身也存在冗余,本文针对EZW编码后存在的‘T’冗余,对EZW算法进行了改进,提出一套‘T’冗余的解决方案;3、在SPIHT算法的基础上,利用多阈值编码和节点位置反馈的方法,减少了大量用于表示后续节点重要性的码元和位置信息冗余;4、引入二叉零树的数据结构,结合节点位置反馈法,减少了兄弟节点间的冗余信息和位置信息冗余,极大的提高了EZW算法的压缩率。实验结果证明,改进后的各个算法在性能上均优于原始算法。更多还原

【Abstract】 In recent years,because of the popularization of computer and internet, as the outcome of computer, video, audio and communication technology, multimedia has became an indispensable part of human ordinary life, and has also became one of the pop technology in computer field. As the rapid development of multimedia technology and communication technology, multimedia entertainment, multimedia communication, digital audio frequency broadcast and high definition television etc, these practical applications enhance the requirement of information data storage and transmission. One of the main problems, which confronted with multimedia technology, the applications and developments of Internet, is to solve the denotation, transmission and storage of the image data information. In order to obtain satisfying vision and transmission effect, effective image data compress coding, is the key technology to solve. The purpose of digital image compress coding is to token the image within the limit of bit, and to maintain the quality of renew image.Firstly, we introduce the development of image compression, the method of image compression, the metewand of image compression performance and the international standard of image compression. Otherwise, we fully discuss and analyze the theory of wavelet transform, and study the approach of image coding through wavelet transform.Secondly, because wavelet transform can realize time-frequency localization and multi-resolution, it has been the main aspect of current image compress coding research. Zerotree makes use of the relativity of child band, which is a meaningful breakthrough based on wavelet image compress coding. EZW and SPIHT algorithms based on zerotree structure, which enhance the image compress ratio largely, are discussed and analyzed in detail.Finally, in order to make the most of the characteristic of wavelet transform, we improve EZW and SPIHT algorithm in different aspect. Firstly, by changing the scan route, some repeated scans are avoided and the encoding time decreases. Secondly, as coding with EZW,‘P’and‘N’don’t contain the information of the subsequence’s significant. If the subsequence isn’t significant, much sequential‘T’appears. Furthermore,‘T’contains the information of the subsequence’s significant, and the leaf-nodes haven’t subsequence, so‘T’includes redundancy. In this paper, we propose a scheme based on EZW to reduce‘T’redundancy. Thirdly, SPIHT with multi-threshold and feedback of node, reduces the bits which to denote the significance of subsequence and the position redundancy. In the end, the Bin-zerotree-structure, together with feedback of node, can reduce the redundancy of brother and position, so it improves the compression ratio of EZW. Experimental result proves the effect of the improved algorithms.更多还原