JPEG标准中规定了4种压缩模式[15]：顺序编码（Sequential encoding），渐进编码（Progressive encoding），等级编码（Hierarchical encoding），无损编码（Lossless encoding）。应用最为广泛的为基于DCT变换的顺序编码，也称之为基准模式(Baseline mode)，其它几种模式都以此为基础。这里，采用了JPEG基准模式对图像进行压缩，在基准模式中，熵编码采用哈夫曼编码方法。

-JPEG standard specifies four kinds of compression [15]: the order of encoding (Sequential encoding), progressive encoding (Progressive encoding), class code (Hierarchical encoding), lossless encoding (Lossless encoding). The most widely used sequence-based DCT transform coding, also known as baseline model (Baseline mode), several other models are based. Here, using the JPEG image compression benchmark model, in the baseline model, the entropy coding using Huffman coding.