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Why 5? 
Posted: 07 January 2009 11:26 PM   [ Ignore ]
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Hey all,

I am wondering why is MS Surface using 5 cameras? What are the benefits? How can it be done? Thanks!

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Posted: 07 January 2009 11:38 PM   [ Ignore ]   [ # 1 ]
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Hi asadeddin,
Five cameras allows for a greater size of area to be covered without losing resolution or having a distorted image. Five cameras can give a very high-quality image - what I have heard is that the surface of the MS surface is divided up into four quadrants, and then there is one more left over (fiducials?). It also allows you to have a thinner table, without using mirrors, etc.

All you need to do it is an image stitching filter in your tracking software - a filter that takes many different camera inputs and ‘stitches’ it into one big, high res image for blob tracking. tBeta does not currently support image stitching, but I believe it is on the to-do list for devs.

Here’s one directshow filter that does it for two video streams: http://www.codeproject.com/KB/directx/DirectShowVMR9.aspx . Here’s another great thread that talks about a possible image stitching solution, using another directshow filter: http://nuigroup.com/forums/viewthread/3729/ .

hope this helps!
rbedi100

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Posted: 07 January 2009 11:43 PM   [ Ignore ]   [ # 2 ]
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Thanks! It did!

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Posted: 08 January 2009 02:47 AM   [ Ignore ]   [ # 3 ]
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Forget about 5th camera. They use 4 cameras as rbedi100 described (four quadrants + image stitching). They are used for contacts + fiducials. 5th camera is only a workaround.

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Posted: 08 January 2009 07:29 AM   [ Ignore ]   [ # 4 ]
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Daniel D - 08 January 2009 02:47 AM

Forget about 5th camera. They use 4 cameras as rbedi100 described (four quadrants + image stitching). They are used for contacts + fiducials. 5th camera is only a workaround.

Daniel,

i’m not so sure about that. I could imagine to use the 5’th camera to aquire some depth information about the object above the surface (like hands and other objects). This information could be “merged” with the stitched image to create a virtual “cut off” or “DOF” plane (like the techniques they are used by stereo vision ie:: http://vision.middlebury.edu/stereo/ ...) . I am just guessing, but after i saw some example videos of the raw input images of Surface i was wondering how they can focus so tightly over the surface....

my2c

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Posted: 08 January 2009 01:56 PM   [ Ignore ]   [ # 5 ]
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sandor - 08 January 2009 07:29 AM

Daniel D - 08 January 2009 02:47 AM
Forget about 5th camera. They use 4 cameras as rbedi100 described (four quadrants + image stitching). They are used for contacts + fiducials. 5th camera is only a workaround.

Daniel,

i’m not so sure about that. I could imagine to use the 5’th camera to aquire some depth information about the object above the surface (like hands and other objects). This information could be “merged” with the stitched image to create a virtual “cut off” or “DOF” plane (like the techniques they are used by stereo vision ie:: http://vision.middlebury.edu/stereo/ ...) . I am just guessing, but after i saw some example videos of the raw input images of Surface i was wondering how they can focus so tightly over the surface....

my2c

How close your “cut off” plane is to the surface depends largely on the diffuser gain. They use a diffuser with a very low gain factor, which enables the cameras to see only the closest objects.

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Posted: 08 January 2009 02:59 PM   [ Ignore ]   [ # 6 ]
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Sandor, my information (it’s not a guess) is from trusted sources wink

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Posted: 08 January 2009 04:29 PM   [ Ignore ]   [ # 7 ]
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Might be a trusted source, but still the 5th camera could and can eventually be used for many purposes. I’m not sure I would call it a workaround since it has a viable purpose.

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Posted: 08 January 2009 04:44 PM   [ Ignore ]   [ # 8 ]
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What viable purpose do you mean?

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Posted: 09 January 2009 03:23 AM   [ Ignore ]   [ # 9 ]
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Ancalagon - 08 January 2009 01:56 PM

How close your “cut off” plane is to the surface depends largely on the diffuser gain. They use a diffuser with a very low gain factor, which enables the cameras to see only the closest objects.

@Ancalagon: thank you for the explanation. Are there any estimations on the gain factor of the rearpro surface they are using? What i don’t understand though is why the published pictures of the camera source images you can see in the media are turning so nicely into black just after a few cm above the surface. I mean, they are using really powerfull LED illuminators (see how nicely and clear the objects on the surface appear) - so i would suppose that (just like in our setup) the illuminated area goes far beyond the surface - what would cause to illuminate more than just the hand (ie. large parts of the forearms etc.)… Also: there is allways a considerable amount of ambient IR what should show up in the source picture (at least this is our experience)… Any ideas on this?

@Daniel: sure, i trust you man wink Any ideas (maybe real infos) on the above?

Cheers,

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Posted: 09 January 2009 03:31 AM   [ Ignore ]   [ # 10 ]
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@ Sandor: The image they display on the surface is more than likely not the ‘raw’ image. It’s the image after being filtered a bit and contrast stretched which is why it looks so clear with a nice contrast and no noise. On the MS sphere video they show the various filters used, and the final image (after filtered) in the sphere video looks about the same as the one on the surface. Is there a different set of pictures I’m missing maybe?

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Posted: 09 January 2009 03:44 AM   [ Ignore ]   [ # 11 ]
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cerupcat - 09 January 2009 03:31 AM

@ Sandor: The image they display on the surface is more than likely not the ‘raw’ image. It’s the image after being filtered a bit and contrast stretched which is why it looks so clear with a nice contrast and no noise. On the MS sphere video they show the various filters used, and the final image (after filtered) in the sphere video looks about the same as the one on the surface. Is there a different set of pictures I’m missing maybe?

Thanks Seth. No i know only the picture sets posted here in the forum a while a go… (Sorry now for hijacking but do you have any contact with Michael Moore? We had shortly bovore christmas a private mail exchange regarding an article, but i did not heard from him since that...)

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Posted: 09 January 2009 03:52 AM   [ Ignore ]   [ # 12 ]
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@sandor: I would be glad to post my information, but I think rlevy and MS would not be very happy about it. I must admit, I don’t know if there were an NDA for PDC Surface session attendees.

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Posted: 09 January 2009 04:40 AM   [ Ignore ]   [ # 13 ]
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sandor - 09 January 2009 03:23 AM

@Ancalagon: thank you for the explanation. Are there any estimations on the gain factor of the rearpro surface they are using?

My guess is that they’re using a diffuser with a gain factor of about 1. Evonik Röhm sells several kinds of Plexiglas rear projection screens with comparable optical properties (Plexiglas RP; grade 99561, gain 1.6; grade 7D006, gain 1.0; grade 7D009, gain 0.4), though none of them are available in small sizes for private customers.

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Posted: 09 January 2009 06:45 AM   [ Ignore ]   [ # 14 ]
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99561 is very close to what Surface uses. It feels same if you touch it. And it produces very similar images.
Evonik produces “table plate” for Surface. Press release can be found in google.
I have got 30x20cm plate from online shop. Don’t know if they have online shop in US, but here is a german shop: http://www.plexiglas-shop.com/de/product_info.php/info/p423_PLEXIGLAS--XT-Grau-99561-RP.html

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Posted: 09 January 2009 06:56 AM   [ Ignore ]   [ # 15 ]
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Daniel D - 09 January 2009 06:45 AM

99561 is very close to what Surface uses. It feels same if you touch it. And it produces very similar images.
Evonik produces “table plate” for Surface. Press release can be found in google.
I have got 30x20cm plate from online shop. Don’t know if they have online shop in US, but here is a german shop: http://www.plexiglas-shop.com/de/product_info.php/info/p423_PLEXIGLAS--XT-Grau-99561-RP.html

Thank you Ancalagon and Daniel,

i will definitely check out the 99561 in one of the next builds. BTW: currently we are using the XRP3 from screen-tech (is a bit more expensive than the Evonic one, but has some additional features like passive stereo...)

Cheers,

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