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 - CSDN.NET

http://blog.csdn.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/