I just used the default settings for that image Molly.It started out as an indexed black and white image.
I believe if the image has more contrast (such as his hat and the bg) colors.The lines of circles follow the edges more.
Actually because they are two different colors and the circles are each one solid color it seems that way to the eye.

All i did to the image was change the image mode from indexed to RGB, flattened the image.
I ran the Circlism filter after that and got those results.

So the more contrast in an image the more your going to get those type of edge results i think.

Great, thanx Rod. that last one you did turned out great.

PS MareQ
In case you already refreshed the filter overwriting that file...well i suppose you will need to ask David for a copy of the older filter code ...i bet he has a back up

@ Lylejk

your last is really cool !!

And i bet your guess right a halo cause a aument of contrast between edges and the surrounding
If that is correct also use Unsharp Mask as usually should not , to create halo should help

Thanks Molly.

Hey PC; simple unsharp mask sharpening really didn't make much of a halo. Using the Pen preset is the best I believe. Might try other experiments (no need to show my unsharp mask result) to see whats a good edge contrast change would be benificial to create more detailed results. Thanks for the comments too by the way.

OK; posting one more (my Dad this time). It took well over an hour (more like 1.5 hours) to render. Running G'MIC Pen Drawing is definitely an asset to getting edge detail quality imo.

Very Nice Lyle, did you run circlism at the default?

That's all good work but I don't have patience for the dotting here and there

The dotting is all done by the script Lorri.