Correction, I have a super hacky and currently manual process. It is entirely possible that it is scriptable, but I will hold off on looking into that until I am sure I have the result down.
More or less my starting region, with a whitespace border.
To begin with, I create an inverse annotation to my region of interest, and then delete the original region of interest. If you are using 0.2.0 you do not need to delete the region of interest as you can CTRL+SHIFT draw inside of locked annotations.
With the only the inverse annotation left, I can CTRL+SHIFT brush tool an edge to the annotation where I want it to be considered for the expansion. Be as careful as you like with this part, I clearly was not!
Once done with the drawing, Select the outer, inverse region, and make inverse again. This restores the original region that was outlined. Select the hand-drawn thin strip of region, and expand it. Select the expansion and expand it again. Repeat as needed.
Use this script
to split your annotations into contiguous parts, which will result in a lot of duplicate annotations. Delete the duplicates.
And that is what I ended up with. You would definitely want to be a bit more careful than I was with the first annotation.
Another way I thought of doing this afterwards might be more programmatic in the future. I made a 10um expansion on the original annotation, eliminated the whitespace part of the expansion, and then did another 1um expansion to get an inner rim. I duplicated the original annotation then intersected the duplicate with the 1um expansion, which resulted in:
Which sounds very much like what Tkilvaer just posted! Only it wasn’t within the parent annotation, so I’ll need to look into that.
Actually, correction, Tkilvaer’s idea should work better, just using the intersect for the whole process!