如何从QGraphicsScene中获取像素点击或在Qt 5中通过鼠标悬停的RGB值？

I'm writing a application. I need to get the position of a image showed in QGraphicsScene, and then get the RGB value of the pixel. How could I do that? It seems that I need to rewrite mouse move event, but I don't know how to do it. It will be great if there is a minimal example.I'm writing a application. I need to get the po