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Diffused Surface Illumination

DSI is similar to FTIR in that infrared light is placed at the edges of an acrylic panel directed towards the inside. A special acrylic with small particles inside, acting like thousands of small mirrors, is used to evenly distribute the infrared light. When a finger or object touches the diffuser, it lights up from the infrared light escaping from within and is seen by a camera below the surface. The effect is similar to diffused illumination. An image is displayed by using a projector connected to a computer pointed towards the projection material.


Parts List

  • EndLighten Acrylic
  • Infrared Light Source (LEDs or similar)
  • Projection Material (Rosco Grey, Vellum, Mylar, Paper, other, etc.) – For displaying an image and scattering light.
  • Infrared Camera/Modified Webcam

Camera Image Examples



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  • Wuu

    Thanks very much for writing this article. I’ve always wanted to make a Multi-touch coffee table. The articles on your websites is so helpful 🙂

    Got a few questions.

    Q1: Is the “Projection Material” the “Diffuser” in the diagram above?
    Q2: Which of the “Projection Material” (Rosco Grey, Vellum, Mylar, Paper, other, etc.) is the best?
    Q3: Can I put a layer of glass above the “Diffuser”? If yes, what’s the maximum thickness of the glass? Reason for asking is that I plan to put something hot on the MTT.

    • Q1. Yes, diffuser is the projection material.
      Q2. There’s no ‘best’ necessarily. It depends on the brightness of projector and other factors.
      Q3. Yes, you can put a thin layer of glass above.

      I recommend going to http://nuigroup.com/forums where there’s hundreds of other people that can help you along the way.

  • cyrusso

    Hello Seth, I’ve looked everywhere in nui group and so forth and I’m just wondering which technique is compatible with LCD? Or are they all compatible with LCDs? I am especially interested if DSI is compatible. Thanks a lot.

  • Moosa Mahsoom

    Seth, which method do you think is best and easiest to try out? the quality of IR available to me are not very good and resources available are questionable.

    • FTIR is probably the hardest since there’s more components involved. DI is easier, but it requires a lot of trial and error to get the lighting good. I’d read more on http://nuigroup.com/forums.

  • fred

    Hei Seth, itry to make a DSI-Setup. I placed the LEDs around the Plexyglas and in CCV the Image looks pretty much the same as above on your page. But there are NO Blobbs recognized. When i put a Finger on the Surface nothing happend. Do you have any idea why?

    • Are you using regular plexiglas or endlighten? For DSI you need endlighten. It’s hard to say what the problem could be. Have you tried posting on http://nuigroup.com/forums? It’s the best place to get help.

    • fred

      I use the endlighten version. I will try it tommorow with another Projection Material. I ordered some of rosco grey. Does the LED have to had direct contact to the plexiglas or must be some distance? Thx for ur help and your blog! It realy helped me for my work. All credits will go to you.

    • The LEDs can be contact the plexiglas. A different projection material can help.

    • fred

      The result is even worser than before. I dont get any Blobs. Nothing happend

    • It’s likely the projection surface. It might be blocking too much light. You may need a thinner material. Have you look on NUIGroup? I’d check the forum to see what others are using for a projection material with DSI.

    • fred

      I removed the Projection Material. It doesn´t work either. With only the Endlighten, i don´t get blobs eather. What else can it be except the Projection Material. I posted my Problem on NUI group, but nobody answered.