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Author Topic: Type of pattern projection  (Read 9368 times)

Mfranquelo

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Type of pattern projection
« on: December 09, 2013, 06:57:26 PM »
Hello all,

I?ve finally made some improvements on my 3d scanning rig, the next step for me (at the same time as improving light conditions) is to develop a pattern projection.

So my doubts are the following:

1. What kind of noise projection should i use ? I know that SIFT algorithm tries to find "corners" so as little as possible squares would be very appropriate. But maybe noise(dots) pattern works best ? anyone had any experience with this ?

2. Im going to use a flash with a 35mm transparent slide and a lens to project the details onto the surface, however using this method i?ll loose my diffuse light conditions...
The problems are that:

- The projection has to be much more powerful than the default light conditions so i can achieve contrast... otherwise noise projection would be useless i suposse.
- I?ll have to lower the exposure of my flashes so the noise pattern projection flash fires with more intensity in comparison to the other flashes (this however, will kill my diffuse light)

How could i overcome this ?

- I?ve read that i could use laser with different patterns however this is dangerous for the eyes
- IR not an option ?
- UV maybe ?

Thank you for your always kind responses!
Manuel.
« Last Edit: December 09, 2013, 07:00:19 PM by Mfranquelo »

meshmixup

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Re: Type of pattern projection
« Reply #1 on: December 10, 2013, 07:31:45 AM »
HI, have you think of using projector and change the aperture?

Mfranquelo

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Re: Type of pattern projection
« Reply #2 on: December 10, 2013, 01:35:50 PM »
The problem with the DLP projector is that its light doesnt give me enough intensity (to have a good contrast ratio) in comparison to the exposure of the flashes.

Mr_Curious

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Re: Type of pattern projection
« Reply #3 on: December 10, 2013, 03:36:08 PM »
The problem with the DLP projector is that its light doesnt give me enough intensity (to have a good contrast ratio) in comparison to the exposure of the flashes.

The solution is to move your projector closer to the subject -- or get hold of a projector with a higher lumen output.


Mfranquelo

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Re: Type of pattern projection
« Reply #4 on: December 10, 2013, 03:50:15 PM »
However, this will kill my diffuse illumination set up, is it worth it ?
A really high lumen projector usually costs more. Isnt it better to use a strobe light projection ? with a flash attached to a 50mm lens for example ? (or even wider) (and a slide ofc)

- From what i?ve read on the forum, strobe light projection have more advantages to DLP projection method.

Thank you for your kind responses!
Regards,
Manuel.

Mr_Curious

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Re: Type of pattern projection
« Reply #5 on: December 10, 2013, 03:55:32 PM »
However, this will kill my diffuse illumination set up, is it worth it ?
A really high lumen projector usually costs more. Isnt it better to use a strobe light projection ? with a flash attached to a 50mm lens for example ? (or even wider) (and a slide ofc)

- From what i?ve read on the forum, strobe light projection have more advantages to DLP projection method.

Thank you for your kind responses!
Regards,
Manuel.

I use both methods and agree that a powerful projector does cost quite a lot.  I would therefore recommend that you try to use the strobe projection method first.  The downside of this method is that it takes quite a bit of experimentation to get everything setup properly, whereas with the projector the setup time is quick and easy.  The strobe method however can easily be synchronized and even delayed if needed so each method has pros & cons.

Try the strobe method first, in comparison it's inexpensive and effective!

Let us know how you get on!


Mfranquelo

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Re: Type of pattern projection
« Reply #6 on: December 10, 2013, 04:00:34 PM »
I?ll try it this week and post results :)
Do you think the results (Improvements in the n? of points detected) is worth the money investment ?
Do you use more than one strobe light projector for the sides of the head ? or just one ?

- I?ve been thinking on using it because some girls have a really smooth skin, this would cause problems.

Thank you!

Mr_Curious

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Re: Type of pattern projection
« Reply #7 on: December 10, 2013, 04:19:39 PM »
I?ll try it this week and post results :)
Do you think the results (Improvements in the n? of points detected) is worth the money investment ?
Do you use more than one strobe light projector for the sides of the head ? or just one ?

- I?ve been thinking on using it because some girls have a really smooth skin, this would cause problems.

Thank you!

Yes, I do think it can be helpful, especially on objects that are smooth and lack features and would otherwise fail, such as smooth skins and fabrics.

I would suggest that you try using strobes first... see what results you get as it will produce the same if not better results than the projector at a fraction of the cost.

Like I said, the only downside of the strobe is that setup is a serious pain, but if you have a studio where you can leave things set up, then once you have everything working, you can leave it be.

One tip, getting the focus just right can be made easier if you shine a bright light (such as a flashlight /torch through the camera back/slide transparency in very dark room onto your test subject.  This will make it easier for you to get the lens in focus initially..which is really the most difficult part of using a strobe based projector.

Regarding multiple projectors, I've collected many of them over the years.  The answer is yes, I generally use multiple projectors, so that at least 180 degrees can be covered at once.

If you have 4 projectors you can place them at each corner of the room and assuming that your subject is placed in the center all beams can converge for 360 degree coverage.

Regarding the washing out of your diffuse textures, the solution to this is to have your system fire twice.  What I mean by this is that you can first take a shot with the speckle pattern being projected and then a split second later, take another this time with the projection muted. The second shot will NOT have patterns projected and this can be used for your texture.  Provided that the subject doesn't move much it will work. The key to this is to have the 2nd shot fire as fast after the first as possible. To do this you will need to use some sort of flash delay control device (such as the camera axe or pocketwizard max). This can also be done with dlp projectors, but a custom shutter system will have to be constructed, either electronic or mechanical.

I hope this will give you some ideas :-)

Good luck with everything and please post your results so that others can learn from your experience.

« Last Edit: December 10, 2013, 04:21:36 PM by Mr_Curious »

Mfranquelo

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Re: Type of pattern projection
« Reply #8 on: December 10, 2013, 04:28:39 PM »
Thank you a lot Mr_Curious, this lot of information is more than good enough for me to start moving things.
I?ll probably start buying two strobe light projectors and see the results. (My budget is not very high) (And im just scanning 180? of the face at the moment, not 360? head)
- What i meant with the loose of the diffuse illumination was not for the texture, but for the feature point calculation (to have some parts of the head in shadow because of the projector flash)

I?ll keep you informed.

xManuel.



Mr_Curious

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Re: Type of pattern projection
« Reply #9 on: December 10, 2013, 04:47:22 PM »
Thank you a lot Mr_Curious, this lot of information is more than good enough for me to start moving things.
I?ll probably start buying two strobe light projectors and see the results. (My budget is not very high) (And im just scanning 180? of the face at the moment, not 360? head)
- What i meant with the loose of the diffuse illumination was not for the texture, but for the feature point calculation (to have some parts of the head in shadow because of the projector flash)

I?ll keep you informed.

xManuel.

Awesome!

Keep at it, experimentation is the key to success.


t234594

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Re: Type of pattern projection
« Reply #10 on: October 28, 2016, 06:41:14 AM »
What strobe projectors do you recommend? What noise pattern to proejct?

rajyadav77

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Re: Type of pattern projection
« Reply #11 on: January 27, 2017, 11:20:18 AM »
Hi Mfranquelo,

Have you tried strobe projection and if you have tried, can you please share your experience.

Thanks in advance.