Identifying gradient direction of edge (inwards\outwards)

[poster]

I am trying to find whether the gradient of an edge is pointing inwards or outwards (out of image) in order to identify tumors. Any ideas on how to do this elegantly?

boundaries image example (http://i.stack.imgur.com/s8SI5.png)

Thanks!



更多... (https://stackoverflow.com/questions/37905063/identifying-gradient-direction-of-edge-inwards-outwards)