https://blog.csdn.net/wuqindeyunque/article/details/103694900
https://theailearner.com/2019/01/30/contrast-stretching/
https://docs.opencv.org/3.4/d5/daf/tutorial_py_histogram_equalization.html
cv.GaussianBlur参数选择
原文：https://www.cnblogs.com/ChevisZhang/p/13137937.html
