What exactly is edge density?

Question

I'm kinda confuse of the meaning of edge density. From the equation,

edge density = sum(x=1,w) sum(y=1,h) e(x,y)/N

where e is the edge map image (magnitude of vertical edge at (x,y)), there are two version of N. 1st version - N = w x h (width x height) 2nd version - N = number of non zero vertical edge pixel

What I don't understand is how can I calculate the edge density? Is it just summation of the white edges pixels?

Edited

Hi all, from what I understand from reading the paper given by @Gilgamesh, the N is the area of the region, width times its height but from the answer given it seems there is a conflict whereby N refers to number of non white pixels(black pixel). So, which is the correct one? Here is another reference on the N value calculating edge density.

Answer 1

basically the edge density is really just a (local) average density, which you can either calculate over binarized images or, more common, over grey scale images.

And yes, it is basically just summing up over both x and y coordinates in a subimage in most cases, see equation (1) here

http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1517&context=infopapers

and averaging afterwards.

Regards, G.