Need Urgent Help! IR light reflecting everywhere! 
Posted: 27 August 2011 01:36 AM   [ Ignore ]
Joined  2011-01-06
Total Posts:  11
New Member

Hi guys. I am in urgent need of some expertise. My Senior major for Design and Technology is a multi touch table, made of aluminium and glass.


I only purchased 6 IR LED panels (36 LEDS) and wired those up to a switch. The problem is that they dont evenly spread across the screen, and because my table is built from highly reflective aluminum, there are lots of ‘hotpsots’ where CCV picks up these, but not the hand.

Im wondering if there is a quick and easy way of spreading out the IR light.

Also, the IR light doesnt seem to penetrate the ROSCO black projection film that i have?

A wierd thing i have noticed is when the IR is turned OFF, CL Eye Test picks up the hand and fingers extremely clearly. CCV just shows a black screen.


On another note, the projected image is extremely clear and quite large (31 inches). I am extremely happy with it.

Please help me out guys. Thanks in advance

Project is due Monday (Australian time), I know i left it REALLY late :s

Sorry about the image links ( i havnt worked out how to put them directly in a a post)

All images attached

EDIT: Its a Rear DI set up, PS3 camera from peau

Image Attachments
Posted: 27 August 2011 09:35 AM   [ Ignore ]   [ # 1 ]
Joined  2009-04-15
Total Posts:  187

i have read somewhere (i can not find it right now) that you can
make a DIY diffuser for your leds that works pretty well, when
you can not get anything else in a hurry.

It is thin paper soaked with oil. It shouldn´t block much of the IR
but will diffuse it. I have never tried that method, though.
Just in case you are completly out of ideas and ready to try anything. smile

Second thought, try to cover your aluminium with paper for example,
that should reduce the hotspot reflections.

When doing front DI like in your last picture (LEDs off, and IR Source outside) you should invert
tracking in CCV. Then you will get blobs from your fingers shadows.

also check the camera settings (gain and exposure).

good luck

Posted: 27 August 2011 09:50 AM   [ Ignore ]   [ # 2 ]
Joined  2011-01-06
Total Posts:  11
New Member

Ok. Thanks for your insight. Ill be sure to try the oil-paper method, sound pretty simple.

I dont know about covering the aluminium in paper. The markers on my project are pretty stricton aesthetics. But i guess function over looks right?

If all fails, ill try Front DI. I didnt see an invert tracking button in the time i spent poking around CCV

Thanks again

Posted: 28 August 2011 12:36 PM   [ Ignore ]   [ # 3 ]
Joined  2010-04-27
Total Posts:  150

Have you tried pointing your IR lights at the side panels? As you said aluminium acts like a mirror for your IR light, so why not take advantage of that to increase the effective distance of your light from the screen. Point your lights to the wall that is further away from it to essentially increase the size of hotspots to get a more even lighting. Try not to directly shine the light toward the surface. Let me know if that works.

Other that that, the way to do it would be using diffuser as you already know. Maybe some hardware stores are open and you can ask someone to go and pick you up a sheet of acrylic light diffuser. A large sheet of approximately 6 sq-feet is around $5 here in Canada. Good luck!


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Posted: 29 August 2011 03:14 PM   [ Ignore ]   [ # 4 ]
Joined  2008-09-12
Total Posts:  2225

As Aras suggested, point the lights away from the touch surface, preferably down at the bottom so that all the light bounces around and diffuses more evenly.


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