https://www.jianshu.com/p/b923cd47ac4a
http://fourier.eng.hmc.edu/e161/lectures/dct/dct.html
http://fourier.eng.hmc.edu/e161/lectures/dct/node1.html
http://fourier.eng.hmc.edu/e161/lectures/dct/node2.html
中文翻译过来的：http://blog.sina.com.cn/s/blog_626631420100xvxd.html
GitHub:
https://github.com/latex2html/latex2html/
维基百科：https://en.wikipedia.org/wiki/Discrete_cosine_transform
有图：https://www.cnblogs.com/byeyear/p/4513255.html
信号大全：https://www.cnblogs.com/byeyear/category/537879.html
