参考：
方法一
Convert between cv::Mat and QImage 两种图片类转换 - Grandyang - 博客园
http://www.cnblogs.com/grandyang/p/5602360.html
方法二
QImage 与 cv::Mat 之间的相互转换 - Ivan 的专栏 - 博客频道 - ****.NET
http://blog.****.net/liyuanbhu/article/details/46662115
方法三
Converting Between cv::Mat and QImage or QPixmap
https://asmaloney.com/2013/11/code/converting-between-cvmat-and-qimage-or-qpixmap/