[OpenCV] moment

每次都有不同的認知
https://chtseng.wordpress.com/2017/03/24/%E4%BD%BF%E7%94%A8moments%E6%8F%8F%E8%BF%B0%E8%91%89%E7%89%87%E9%A1%9E%E5%9E%8B/
https://en.wikipedia.org/wiki/Centroid
https://en.wikipedia.org/wiki/Image_moment
https://dsp.stackexchange.com/questions/4868/contour-and-area-raw-spatial-and-central-image-moments
http://www.aishack.in/tutorials/image-moments/