Quote Originally Posted by torstan View Post
Okay, I pulled out the rock area, selected it and stroked it with Gimp's default pencil sketch#2 brush with a .4 jitter. I used the selection to cut out the strokes that fell within the tunnels and set the whole layer to overlay.
As a quick suggestion - instead of stroking the selection, turn the selection into a path and stroke the path.

I have discovered that this seems to give significantly better results. (The conversion to a path does some bezier interpolations around the selection that seem to prevent some "jaggie" artifacts that stroking a selection seems to have.) Now this might not matter when the jitter is high, but try it and see if there is a difference.

-Rob A>