毕业论文 多媒体图象压缩 ――浅谈基于matlab平台的JPEG基本系统.doc

多媒体图象压缩 ――浅谈基于matlab平台的JPEG基本系统 摘要：本论文主要介绍了JPEG的编码和解码过程。该程序的编码部分能把一张TIF格式的24位真彩色图象进行JEPG编码，压缩成以二进制形式保存的文件；通过相应的解码程序又可以把图象解压缩出来。在图象传送过程中，我们经常采用JPEG格式对静态图象进行编码。JPEG基本系统是一种有损编码，无法完全恢复出原图象，信息有一定的丢失，称为有损压缩。尽管我们希望能够无损压缩，但是通常有损压缩的压缩比(即原图象占的字节数与压缩后图象占的字节数之比，压缩比越大，说明压缩效率越高)比无损压缩的高。JPEG编码先把图象色彩RBG变成亮度Y和色度Cr、Cb，它利用人的视觉对色度不敏感的特点，减少一部分色度数据，以达到压缩。 JPEG采取多种编码方式，包含有行程编码(Run Length Coding)哈夫曼(Huffman)编码行程编码 哈夫曼编码 Abstract: This paper introduces the encoding and decoding of JPEG and the specific realization of program on matlab platform。 The encoding part of this program can encode a picture whose format is 24-bits-turecolor TIF and save relevant data as binary system。 The decoding program can decode the compression data and reconstruct the origin image。 While conveying pictures we often encode still pictures into the style of JPEG。 JPEG is of lossy compression which can not recover all the image data， some data are losed。 Although we refer to non-lossy compression， however， the compression ratio of lossy compression( the times that data bytes before compression to that after compression )is bigger than that of non-lossy compression。 JPEG encoding translate image color from RBG to luminance Y and chroma r、Cb。 Because people’ eyes are less sensitive to chroma comparing with luminance ， some of chroma data are abandoned to reduce data size。 JPEG envolves some kinds of ways of encoding including Run Length Coding and Huffman Coding， so it has high compresson ratio。 Before Coding ，we divide data into blocks ， DCT and quantify each block 。 The low-frequency signals have more energy are maintained and others are rejected 。 While decoding ， data stream are readed ， decoded ， inverse-quantified and then IDCT 。 Keyword: JPEG lossy compression Run Length Coding Huffman Coding JPEG是联合图象专家组(Joint Picture Expert Group)的英文缩写，是国际标准化组织(ISO)和CCITT联合制定的静态图象的压缩编码标准。和相同图象质量的其它常用文件格式(如GIF，TIFF，PCX)相比，JPEG是目前静态图象中压缩比最高的。我们给出具体的数据来对比一下。例图采用Windows95目录下的Clouds。bmp640*480，256色。用工具SEA(version1。3)24位