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rough surface texture

Questions, problems, comments and tips regarding the 3d scanning process.

rough surface texture

Postby jbeale » Mon Aug 13, 2007 6:56 pm

I tried out the scanner software for the first time last night. I used a cheap laser-leveller from Radio Shack with a beam about 2 mm wide, and it was much brighter at one end than the other. I mounted the laser on a video tripod head so I could scan it smoothly. This worked well, I was easily able to paint every pixel with a single pass. My camera was a Sony FX1 camcorder, which is HDV but I used the DV mode via firewire to my laptop. The camera was set to black and white mode and pseudo-progressive scan "cineframe mode". I had a completely dark room with the camera at +12 dB gain for consistent beam detection since my laser is not very bright.

My results show a bumpy "orange peel" type texture, which gets worse as the laser-camera angle is smaller. The target (ceramic face about 16 cm high) is much smoother than the scan appears.
Image
Image
Is my problem laser speckle and/or noise in the camera? Would I get better results with a brighter laser or more sensitive camera?

I wasn't able to get DAVID to read in the OBJ file without a camera connected, so the 3D screen grab is from another program "MeshLab".
Attachments
Scan2-Aug13-07.png
two scans at deep and shallow laser angle, showing rough texture
jbeale
 
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noise averaging possible?

Postby jbeale » Mon Aug 13, 2007 7:19 pm

It appears to me that the DAVID software calculates a single depth value per image pixel and once a pixel is "painted" that value stays, until you erase or reset the entire image.

Is there some way to turn on an "averaging" mode, so that a single pixel can be calculated as many times as it is illuminated, and then an average taken? Maybe even a weighted average since the software can form an error bound estimate based on frame-to-frame noise and camera-laser plane intersection angle. I believe this would give you a real improvement in the case of random noise. Low-noise cameras and powerful lasers are expensive, so I bet I'm not the only one with a noise problem.
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Re: rough surface texture

Postby Simon » Mon Aug 13, 2007 8:36 pm

Hello jbeale

jbeale wrote:Is my problem laser speckle and/or noise in the camera? Would I get better results with a brighter laser or more sensitive camera?

Difficult to say. The camera is the weak point in most cases. It would help if you post a camera image of you laser line.
Apart from that, I commend to wait a few days. We have just improved the sub-pixel laser line detection of DAVID. With the next update, the accuracy will be much better.

jbeale wrote:I wasn't able to get DAVID to read in the OBJ file without a camera connected, so the 3D screen grab is from another program "MeshLab".

You can read your scans with DAVID-Shapefusion.

jbeale wrote:Is there some way to turn on an "averaging" mode, so that a single pixel can be calculated as many times as it is illuminated, and then an average taken?

This is exactly how DAVID works. It calculates a weighted average of all measurements in one pixel. Later pixels get more weight than earlier. You can even continue to scan after inspecting the 3D result. That allows you to refine regions with outliers.

jbeale wrote:Maybe even a weighted average since the software can form an error bound estimate based on frame-to-frame noise and camera-laser plane intersection angle. I believe this would give you a real improvement in the case of random noise.


Good idea. We will bear it in our minds.
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averaging strategy

Postby jbeale » Mon Aug 13, 2007 9:24 pm

Thank you for the quick reply! I didn't realize you already do weighted averages.

You might also consider an option to use a plain, unweighted average. This might be best where you have a good scan setup that maintains good geometry and the main problem is just camera noise. In that case the old and new scans are all equally good (perhaps I should say "equally bad"), and you just want to average a lot of them together to remove random noise.
Last edited by jbeale on Fri Aug 17, 2007 9:08 pm, edited 1 time in total.
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next update?

Postby jbeale » Thu Aug 16, 2007 7:08 pm

Apart from that, I commend to wait a few days. We have just improved the sub-pixel laser line detection of DAVID. With the next update, the accuracy will be much better.

I am very much looking forward to trying out the next update, do you know yet when it will be? Thank you!
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Postby Simon » Fri Aug 17, 2007 8:11 pm

We intend to upload the update next week (no guarantee).
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