介绍傅里叶变换比较透彻的文章。
https://zhuanlan.zhihu.com/p/19763358
https://en.wikipedia.org/wiki/JPEG
https://en.wikipedia.org/wiki/Discrete_cosine_transform
https://www.ibm.com/developerworks/cn/linux/l-cn-jpeg/
https://blog.csdn.net/u014518566/article/details/46432621
https://segmentfault.com/q/1010000000510683
https://blog.csdn.net/newchenxf/article/details/51719597
https://blog.csdn.net/shenziheng1/article/details/52965104
https://blog.csdn.net/gxiaoyaya/article/details/54571128
https://blog.csdn.net/qq_20613513/article/details/78744101
http://dsqiu.iteye.com/blog/1636888
https://zhuanlan.zhihu.com/p/33845296
http://blog.sina.com.cn/s/blog_626631420100xvxd.html
实现源码：
https://github.com/tobygameac/DCT-IDCT/blob/master/source.c
http://www-igm.univ-mlv.fr/~mac/ENS/DOC/COMP/DCT.C
http://www.voidcn.com/article/p-vslmeedh-bqs.html
pdf 文件
JPEG File Interchange Format jpeg文件格式协议。