How to put the legend out of the plot
https://stackoverflow.com/questions/4700614/how-to-put-the-legend-out-of-the-plot
Setting a fixed size for points in legend
https://stackoverflow.com/questions/24706125/setting-a-fixed-size-for-points-in-legend
difference for image channels(RGB, BGR) for cv2 and matplotlib
add_axes-and-add_subplot
https://github.com/supersheepbear/Notes_for_myself/wiki/add_axes-and-add_subplot
