VC++基于JPG标准的图像压缩算法+代码+论文 第3页

论文摘要
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BMP格式的图象进行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)和哈夫曼(Huffman)编码，有很高的压缩比。在编码前，先对数据进行分块，离散余弦变换（DCT）及量化，保留能量大的低频信号，丢弃高频信号以达到压缩。解码时，进行熵解码，反量化，反离散余弦变换（IDCT）。

关键字：JPEG;有损压缩;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 vc++ platform. The encoding part of this program can encode a picture whose format is BMP 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 Cr、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 compression ratio. Before Coding ，we divide data into blocks ， DCT and quantify each block. The low-frequency signals that have more energy are maintained and others are rejected . While decoding ， data stream are readed ， decoded ， inverse-quantified and then IDCT .

Keywords:  JPEG;lossy compression;Run Length Coding;Huffman Code

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