When you Bake an image with Margins, it fills some area outside the edge of the UV island. For example, here is a section of a Normal map with a margin of 10 on the left, and 0 on the right. If you don't have Margins, you end up with visible seams when using the texture.
What process exactly is used to get this data outside the UV island? Is it like a post process smudge? I thought it was something like the Inpaint node in the compositor, but it does not give the same result. Is it possible to rebuild in the Compositor, or do in an external program?