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what are these waves?

Problems, solutions and discussion about scanning with a video projector and stripe patterns.

what are these waves?

Postby Lunat1c » Wed Sep 25, 2013 12:04 pm

Are these waves about the pixels of the DLP projector? Or are they produced by the constantly working fans?
Normal or anomaly?
They disappear when object gets out of the focus of the projector.
They pass into the scans creating noise and can be seen as imperfections on the fusion result if I choose the refinement option.
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Mitsubishi xd 206u, logitech pro9000, acer 3820tg
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Re: what are these waves?

Postby Lunat1c » Wed Sep 25, 2013 12:27 pm

the second thing can be seen in the last picture was talked about before in the forum.
viewtopic.php?f=2&t=1152&hilit=raised+lettering

It seems there is no solution for the problem for now. Best is to coat the object, or smooth it with a 3d modelling software.

From my experience I came to the conclusion that 90 percent of the objects should be coated. They are either shiny, or dark, or letters on it that fool David as if they have dimensions. Better is to coat. I've ordered this: http://www.swkenyon.com/frame10.html
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Re: what are these waves?

Postby Sven » Wed Sep 25, 2013 4:46 pm

Lunat1c wrote:They disappear when object gets out of the focus of the projector.

They are caused by the projector pixels (or the thin black lines between the pixels), which cause Moiré effect. Indeed it helps to change the projector focus (see user manual). Focus a little bit further away than the object.
Unlike one might expect, this will NOT decrease the sharpness/details of the scan result! The highest precision is obtained with the Phase Shift patterns (blurry sine wave lines, not the hard black+white patterns), and these patterns have no "resolution" anyway. Hard to explain...

Raised Letters:
In the Structured Light menu, increase the "Quality Check" filter value and watch how it changes the scan result at hand. DAVID cannot correct the "raised letters" effect, but in many cases it can detect where undesired effects may have occurred, and erase the respective data. That's the Quality Check filter.
The lost data will be interpolated in Fusion. That's the best DAVID can do about it at this time...

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Re: what are these waves?

Postby Lunat1c » Wed Sep 25, 2013 6:07 pm

David is just great! Talking about the controls, I've seen rhino, geomagic, meshlab, netfabb. Best of them isn't half close to the user friendly controls of david.
When the team upgrade david to be used with 2 cameras and 1 plane calibration, it will be the king of scanners.
2 webcams and a projector would still be affordable. :D
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Re: what are these waves?

Postby MayCrown » Sat Jul 26, 2014 12:34 pm

Sven

Is this moire effect what we see on some thin curtains?
http://www.shapeways.com/shops/MayCrown
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Re: what are these waves?

Postby Sven » Mon Jul 28, 2014 9:34 am

I think I see a little Moire in the scan above, near the bottom. But the main problem is usually something else, the main problem are regular waves/stripes. Moire is just a minor side effect, I think. It all depends a lot on the combination of camera and projector.

When the projector is set slightly out of focus, often the fine lines disappear, including Moire effects. In that case usually the projector resolution is too low compared to the camera resolution.

I'm not an expert on Moire. I think you get Moire effects when you have TWO DIFFERENT other undesired effects that combine.

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