minimum distance between the edges of two closed shapes

I am wondering if anyone has any idea how I can approach finding the minimum distance between two fairly random shapes' edges that one encircles the other. I can separate the shapes' images out from one another into the same size image for comparison, but I can't get a good distance function since one encloses the other and by no means are these shapes regular enough to just compare the center points. If anyone can give me ideas, I would really appreciate it.

Answer 1

[Sean de Wolski]

The distance transform and some indexing will do that for you pretty easily.

doc bwdist

Post the image for more specific guidance.

[Image Analyst]

Sean's answer is what I suggest also. By the way, you may want to learn about alternative ways of measuring distance between polygons. Go to this URL

http://cgm.cs.mcgill.ca/~godfried/teaching/cg-projects/98/normand/main.html

to learn about the Hausdorf distance and several useful ways that it can be used.