Hello,

Before I jump into this project, I was curious if anyone has attempted this concept yet?

It is similar to the City Wall project, during its ‘day-mode’.

-Array of LEDs surrounding surface on edges, slightly raised above the surface and all angled downward to the surface.

-The cameras would be set to highcontrast for a higher threshold of detection, and if I can figure it out, stitch each image together to obtain higher resolution. I suppose a second concept would be to point each camera to the center and overlay each camera image ontop of eachother, to increase accuracy of touch location on the surface by comparing each image, similar to our eyes and depth perception-- I don’t know if this would increase ‘touch resolution’(is there a term for this?)

-The projector would probably be placed further away and use a mirror to reflect onto surface.

-Underneath surface would be projectors material to collect light and show image.

-Surface would probably be acrylic, or possibly just glass.

concept: Cameras underneath recording activity, however they would be set to see only darkness on the surface-- the camera would normally be flooded with the iR light, and when an object was close to the surface, the dimming of light would be considered a blob. This is a bit of a reverse of normal DI, but I think might be more accurate in determining where the actual fingers are placed and not hovering, as it would presumably result in zero iR transmittance underneath the finger when contacting surface.

Please see the picture for my diagram

Questions, comments, criticism welcome!

This is still DI. This is front diffused illumination (compared to rear). There’s a couple people who have tried it. Nima is using this technique on his LCD display and there’s a couple others I know trying this out. It’s the same concept as using ambient IR as your IR source, but in this case controlling it so the light don’t have to be on. If you can get it calibrated right it should be fine. Good luck! =)

It is truth that this is front DI cerupcat, but the handling of the blobs is a little different as how scape describes it I think. He intends to use the lack of IR caused by gestures/fingers as ‘blobs’.
It might be interesting because if this works you might have a solution wich can be used with a lot of daylight.

I only think it is essential to have some box around your cam/projector setup to completely keep IR surrounding light outside because your black blobs wont be detectable as they get washed away by IR light between your cam and screen, right? and if so, your projector might cause some problems…

good point. perhaps I could calibrate it’s threshold to offset this small leakage of ir light?

Jarno, this exactly how front DI works. Instead of white blobs you get black ones. You set the touchlib filter to invert the blobs so they become white. No IR will not washout the blobs because IR can’t get in between your finger and the screen.

Allright!

I guess you just have the same setup problems with rear DI (like aiming/diffusing the Led’s right) but then the other way around.

But why isn’t this commonly used? because it does look like a better way to handle daylight? Or am I wrong here?

I could guess it has to something to do with fiducial tracking wich still is not possible this way, so front DI is almost the same as FTIR?

it could be overcome by having very specific object shapes, or perhaps intricately designed objects that let a small portion of light under it to illuminate the sticker markings… i thought about this too! i’m not too sure how to overcome that.

This is done by Tangent way back when, and they have a say they have a patent pending on it (not public yet afaik)
linky: http://zima.ch/tangent/?page_id=6