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Cropping structured light patterns

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

Cropping structured light patterns

Postby funtasma » Sat Jun 12, 2010 10:16 pm

The pocket LED-beamers are so cheap in the meanwhile, that I could not resist buying one to test structured light scanning. That thing has a real low resolution of 640 x 480 VGA. I red in the forum, that I should not simply resize the patterns but cropp them to the right size. I did so and first results are quite good. Anyway, I still wonder if it is correct how I did it, since Pattern10 has now no effect at all anymore. It's simply cutted too much:

Pattern10.jpg
The cropped Pattern10
Pattern10.jpg (4.03 KiB) Viewed 3355 times


Shall I use it like this or change it or even skip it?

-Benjamin-
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Re: Cropping structured light patterns

Postby Sven » Wed Jun 16, 2010 10:19 am

Hello Benjamin,

I think the reason why cropping may be better than scaling is that the edges between black and white should remain "hard" and not get smoothed. But the pattern should stay the same! E.g. pattern 12 must be black exactly in the upper half and white in the lower half. Pattern 10 must be (in exact 8th of the image height): black, white, white, black, black, white, white, black. You can't get that with cropping.
Maybe someone who has made a 640*480 pattern set can post it here?
Also you can use DAVID's pattern projection dialog and let it create the patterns, after settings the resolution of that screen to 640*480. Choose Structured Light Grabber, then click "Yes".

Sven

EDIT 2010-06-20: What I wrote about cropping is not quite correct. You CAN crop, but you have to crop the same image region from all images. Usually it is better to make new images or use the Pattern Projection Dialog with the right resolution.
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Re: Cropping structured light patterns

Postby funtasma » Fri Jun 18, 2010 7:33 pm

Thanks Sven!
I'll make some new patterns in Photoshop and put them online here.

-Benjamin-
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Postby hal » Sat Jun 19, 2010 11:39 am

Hello Sven,

do you think that could be possible to create a set of patterns for vertical camera view?
Obviously in this case the number of stripes change. If I work with 768x1024 resolution instead 1024x768 (rotating camera and projector), David read correctly the patterns?
Please, look at the images (Pattern08): is this "conversion" correct?

From this:

MatM_Orizzontal Pattern08.jpg

to this:

MatM_Vertical Pattern08.jpg

Or the dimension of black and white rectangle must be the same of the original proportions?


And other questions: Pattern from 02 to 05 have blurred stripes. Why?
If we resize these, the gray values and the right shape of these blurred lines, change (if we reduce the resolution the quality decrease). How we can create the different resolutions (and proportions) for these 4 patterns?


Thanks in advance,
Mattia
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Re: Cropping structured light patterns

Postby Sven » Sun Jun 20, 2010 4:50 pm

Hi Mattia,
Your "conversion" is correct. Should work fine.

About the "blurred stripes":
Four of the patterns are sine waves. Their wavelength must be the same as the width of the topmost stripe in the first b/w pattern.
For more info please look here: viewtopic.php?f=2&t=1145&hilit=sine

@Benjamin:
About cropping:
If you need patterns with reduced resolution, you CAN crop the original patterns. But you must crop the same image region from all of them. But usually you can make better use of the projector resolution when you create new patterns as described above.

Sven
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Re: Cropping structured light patterns

Postby funtasma » Thu Jun 24, 2010 9:40 am

As promised, I finally submit the 640*480 patterns. I produced new ones with Structured Light Grabber as Sven suggested. You can download them here:
SLPatterns.zip
640*480 Patterns
(85.65 KiB) Downloaded 168 times


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Re: Cropping structured light patterns

Postby Sven » Fri Jun 25, 2010 1:07 pm

Hi Benjamin,

Thank you! These patterns look perfect. :D

Sven
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Re: Cropping structured light patterns

Postby MagWeb » Fri Jun 25, 2010 3:27 pm

Hmm, maybe I got something wrong, but are you sure that a VGA res projector needs 12 patterns?
Shouldn´t one use less patterns and therefore a lower number of sin waves in image 3-6?

That way one could solve the problem to get equal sin waves (magnify the wave patterns and you'll see that the waves differ - which is due to the limited number of 480 lines)
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Re: Cropping structured light patterns

Postby Simon » Sat Jun 26, 2010 2:20 pm

Hi Gunter,
you are right, that's why I intially suggested to use a "cutout" (i.e. cropped version) of the 1024x768res pattern images when using a projector with lower resolution: viewtopic.php?f=2&t=1145
Of course, in the case of 640x480, less than 12 pattern projections would do the job, but currently DAVID SL does only support exactly 12 patterns. I know, there is much much room for improvements and I hope we have time to work on it soon...
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Re: Cropping structured light patterns

Postby Sven » Tue Aug 17, 2010 12:28 pm

For those who need pattern files in other resolutions, please see here:
viewtopic.php?f=15&t=2184
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