I started digging into Inkscape features after Kongorilla's excellent post, and discovered the 'Inset path' feature. I used it to create these strange fills. Whaddya think? If anyone's interested I'll post the technique, it's dead simple though.

Blimey! I spend too much time watching the Polargraph now 🙂
Regarding the colour separation, I split the drawing into multiple colours, and draw them in sequence lightest-darkest.
The basic sequence is like this:
I start by using 'trace bitmap' using the colours option, usually 6-8 works ok.
1. clean up paths, deleting/merging similar colours until I have between 3-5
2. seprate each colour into a separate layer, simplyfy/edit each as required (the one above required a lot of editing because Inkscape created overlapping paths)
3. select a path, do a copy/paste in place
4. Inset, repeat as many times as needed to get the effect desired - in the above piccy, 5 times for each path
5. go back to three, selecting the newly inset path and repeat until the fill is done. This sounds tedious, but in fact (on Windows) its 'Ctrl-C, Ctrl-Alt-V, Ctrl-( ( ( ( (' - it got very quick after a while!
6. save out a version of the pic with a single layer for each colour
7. Load each colour file file into the PG Controller, tweak 'shortest vector' etc and then draw each layer in sequence with pens of your choice (in my case I exported each queue to a file on an SD card and then printed them on the PG standalone)
8. bask in artistic warm feel good glow 🙂
I'm experimenting with a new drawing at the moment, very different in style though even though the technique is similar.
Steve

The lines outside the lettering make me think of Roger Dean logos. Wild stuff!

Glad you like it 🙂 I have lots of ideas for this technique.
Thanks for the comment Kong - Roger Dean is one of my favourite artists and when I was a teenager I used to use A-level art classes as an excuse to re-create his album covers (badly), so I guess that's coming out in that image!
Sandy, I agree strongly that the manual aspect of it is a good thing, it makes it feel more like 'art' and less like 'process', if you know what I mean. I have been trying to do some more complex images and have run into a limitation/bug in Inkscape, when the path gets quite complex, after the first inset it just has a bit of a fit and doesn't create the path - and then more often than not crashes. I've moved over to Illustrator for this next image and have found that while it isn't very intuitive, it can handle the much more complex paths I'm now creating - I'll write up the Illustrator technique and post a new image tomorrow, hopefully.
The more complex image I have been working on this week has been very intensive on the manual side, but I'm really encouraged by the results so far. My Polargraph is drawing even as I type this... only 4 more pen changes to go, total of 60,000 plus commands 😉