Hi Mik,

re:
> Canvas megapixel resolution = 15

Well that's really low actually so that's not the problem. You might want to bump that up to something like 50 or 60 or so to get some more accuracy if you find hidden/visible lines not quite meeting up properly. A higher value will also increase file size though because the shaded background image will be larger too.

It does do quite a bit of work so it's normal for it to take a while on complex files. It might be a good area to target for multi-core processing at some point.

- Michael