这是一个JPEG解码程序，很多从事图像处理工作的人都要用到它，现在他是C++下的一个类了，这样他的结构和组织更易于理解-This is a JPEG decoding process, a lot of people who work in image processing have used it, now he is under a C++ class, and so he' s easier to understand the structure and organization