Yes, you can vectorize your bitmaps automatically, but the usual result is a set of very wiggly lines, not the clean edges you might imagine.
As John and Andrew concur, it can be much easier to hand trace an
image than to vectorize a raster image with an automated tool.
I’m also a big fan of Rhino’s modeling tools, but as others who have
tried it might attest, I personally find that MoI3d’s drawing tools
meet the needs of the typical 3D jewelry designer for this sort of
work with more fluidity and speed than Rhino’s.
Positioning and scaling bitmaps is more intuitive, there’s also the
option to make the bitmap as transparent as needed in order to see
where to draw. One of MoI’s innovative features is that a curve may
be shaped just by tugging any place on it, (rather than having to
grab onto a control point), but you also have the more traditional
option to move, add or delete control points and knots, as well.
With Michael Gibson’s help, I’ve created a “ring circle” plug-in with
ring-size standards for several countries. It can be found on the
Resource page http://moi3d.com/resources (under Petr’s MoI
page/custom commands), along with some jewelry videos in the tutorial
section.
For those who doubt that a $200 CAD program can easily create
beautiful models of all sorts, including jewelry, check out the new
gallery page, http://moi3d.com/gallery
You might be pleasantly surprised!
Jesse Kaufman