Does anyone have the same problem? My camera sees a bright spot which is casted by the projector lense reflecting in the acrylic. Although I have IR pass and cut filters applied, the bright spot doesn’t go away. My camera can’t see the projected picture but the bundled light of the lense seems to strong for the filter (like looking directly into the projector)
Only if the position of the projector is far outside of the acrylic, the spot is gone (otherwise the acrylic works like a mirror).
Did someone else had this problem?
Do you guys have to use an IR cut filter for the projector? The projectors I tried (small and big ones) seems to cast a lot of IR light.
I also tried different filters.
but even with BG substraction the FTIR effect would be quit hard to track at this exact spot. The bright spot is bright white, any IR light caused at this point is not going to be brighter than the spot itself which means you have no blobs. Perhaps the fingers would make a blob at this spot because they are dark, but this would be a quit dirty way to solve this.
Have you tried out touching at the position where the bright spot is? Does it really work as good as elsewhere?
marek: i’ll test touching the brightspot next time my at the research lab.... im thinking that if the bright spot poses a problem, what if i adjust my mirror from 45 degrees to around 47.5 degrees....that way the reflection wont be orthogonal to the arcylic and reflect back into the camera??
hype!: i dont want to put my diffuser underneath the arcylic because my diffuser is also my compliant surface and i dont want parallax from the arcylic itself)
@nima: I already fooled around with mirror position and such, this won’t help as long as you position the projector far outside the acrylic plate (which leads to stronger image distortion).
I wonder if there is a filter based solution and why exactly the lense-light (...well ok, it’s really bright...) is not filtered out as the projected picture.
How big is the bright spot? assuming you have a good visible block filter it shouldnt be too big. I find touchlib background subtraction is still able to track blobs over the brightspot quite well. The only problem is if the table is knocked and then the brightspot is mistaken for a blob.
I did think about getting an IR block filter to put infront of the projector.
yeah, in my experience the brighspot re-emerges if the table is knocked.....but the system learns to block it out again after 12 seconds or something
what i’ll try is to place a polarizing filter with an IR filter on my camera (i have a polarzing filter for a nikon camera that i can use as a test)..... light bouncing off a surface is polarized so the filter ought to block out any reflected light from the projector bouncing off the arclyic..... in theory it should work but because of the intensity of the light from the projector is so intense it might not....
Light becomes somewhat polarized when glancing off non-metalic surfaces, that is how polarized sunglasses cut glare. I suspect that a polarized filter wouldn’t help cut light that is bouncing back perpendicularly. Another approach/theory is to use a polarized filter over the projector lens, and another over the camera, if they are at right angles to each other, reflected light from the acrylic should be blocked from reaching the camera by the second polarizer.
how hot does the projector lens get over time? If you’re putting anything over it make sure it wont melt.
I put in front an cheap IR block foil with a distance of some centimeters. It doesn’t get to hot and blocks IR light good enough. though not the strong lense itself :(
putting some spray wax on the acrylic can help a lot.. Anyway, the only other option is to get a heat mirror for the projector which will probably run you about 100$. Edmund optics (http://www.edmundoptics.com/) sells them and also other types of useful things (like filters).
@ white, placing projection screen behind acrylic isnt really that cool tho, since u dont actually directly touch the image that you’re working on, but i’m not telling u something new, just clarifying ur post
