best settings for bitmap tracing simple line art .png?

[dixdance]

I'm a banjo maker, new to cnc, wanting to cut pearl inlays and pockets.  My .png drawings are simple, just fine black lines, sometimes on a black background.  Wondering what settings I should use for the bitmap trace function to get the best quality .svg files to import in to Fusion 360.

Thanks,
Richard

[brynn]

Welcome Richard!

Black lines on a black background?  That won't be tracable, because if we humans can't see the lines, Inkscape can't either.

But that is really irrelevant, because Trace Bitmap does not produce the kind of paths that you'll need for your cutting machine.  It will give you sort of a double path -- a path along the outer edge of the line and a path along the inner edge.

If they are simple lines, then it might not be very hard to hand trace them in Inkscape.  I've written a series of tutorials for this kind of thing, and this one probably would be the best one for you.  http://forum.inkscapecommunity.com/index.php?action=articles;sa=view;article=45

Although having seen an example of the drawings, I might suggest another.

[dixdance]

Thanks brynn

I have looked at your tutorials, and found them very useful.  I tied manually tracing, and that certainly works, but I'm not yet comfortable manipulating bezier curves.  And I was hoping there was a way to use the software, especially when things get a lot more detailed and complex.  Here are a couple of relatively simple .png drawings typical of what I would use.  I want to get pats for the outline to cut the pearl and the pocket, I blacked out the engraving lines to create an edge for that.  For laying out the engraving lines I get twin paths, but thats ok. I think I can use the v engraving feature in Fusion, but just scratch it in with a diamond drag tool.  And then do the engraving by hand, so I can vary the line thickness.

My question was what the best settings are for tracing either of these drawings to get the cleanest and smoothest tool paths.

[brynn]

Ok, well I would say hand drawn paths are almost always better.  But if the double lines are ok, and especially if they are needed, then Trace Bitmap is a good solution. 

To be honest, this is a point I'm a little confused about with some of the CNC type projects.  And the person who designed most of those extensions doesn't participate otherwise in the community, so you have to go to his (Russian) forum to get help.  I've even posted there, offering to write tutorials, if someone would explain it all to me.  No replies.  So I don't know, does the machine need 2 paths to cut out wood between them?  Or can the machine make a specifically wider or narrower cut along a single path?  And then when we try to help people with their projects, they rarely come back and tell us the result.  So we can't make use of their experience.  It's an unfortunate "no-man's land" sometimes, using those extensions.

Anyway, I find that almost every time I use Trace Bitmap, I do a lot of trial and error, to find the best result.  From my experience, I would say all the defaults should give an acceptable result.

Mode tab > Single Scan
 -- Brightness Cutoff 0.450

If you want to try for more precision, there are also some options on the Options tab, which can help.  But for some reason, those options aren't updated in the Preview.  I've actually submitted a feature request to have them included in the preview.  Anyway, that's why I say trial and error will probably be needed.  Plus that preview is tiny....although I haven't used it for a while, maybe the preview is larger now?

Options tab
 -- Supress speckles (if it's a very clean image, not photocopied or otherwise scanned in - this can be ignored - otherwise, it can help to clean up images which may have been scanned in)
 -- Smooth corners (in my experience, I would say this needs to be a low value.  Otherwise those points on the flower-like design might get rounded)
 -- Optimize Paths (I would say give this a high value, but again, you can experiment to see what works best)

In case you've never used Trace Bitmap yet -- the trace result comes out right on top of the oringinal, and often it looks like nothing has happened.  This is one of the many times when the status bar is so helpful.  It tells you what kind of object is selected.  So if, after the trace, it says "Path....." that's the result.  If it still says "Image...." it's not finished yet.  After it's finished, you can drag the new paths away from the PNG.

[dixdance]

Thanks again brynn

I have yet to cut anything on the router, but I'm sure we only want a single path.  The CAM software offsets the cutter appropriately so that both the inlay and the pocket are just about the same size.  A little clearance is needed for the inlay to actually fit in.  I can get single lines by filling in the shape black.

For the engraving layout, a single line would be ideal, but I can work with a double line if need be.  By setting up the CAM for a v-carve bit, the tool will go right down the middle of the twin lines, varying the depth of cut to suit the distance between the lines.  But by actually using a spring loaded diamond point tool, I'll get a single scratch line up the middle.

I'll try your suggested settings with my drawings, and report back when I have some definite results. May be a week or so before I can get to it tho.

But you may be right about just tracing them manually...

[Moini]

Try the centerline trace extension from here: https://github.com/fablabnbg/inkscape-centerline-trace

(only use png files, that do not have any transparency in them, for this)

[brynn]

I haven't tried that particular centerline tracer.  But the ones I have tried, have not produced very satisfying results.  Sure can't hurt to try though