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Rear Diffused Illumination Multitouch Technique

In Rear DI, infrared light is shined at the screen from below the touch surface. A diffuser is placed on top (preferred) or on bottom of the touch surface.  When a finger or object touches the surface, the infrared light hits the object and is reflected downward and seen by an infrared camera below the surface. Depending on the diffuser, this method can also detect hovering objects, hands, and fingers above the surface. An image is displayed by using a projector connected to a computer pointed towards the projection material.


Parts List

  • Clear, Sturdy Surface (Glass, Acrylic, Polycarbonate, Plexiglass, etc.)
  • Infrared Lighting (Infrared LEDs, Infrared Cluster Illuminator, Infrared Lamp, etc.)
  • Diffuser/Projection Surface (Vellum, Mylar, Lee Filter, other, etc.) – For displaying an image and scattering light. *Note: The Diffuser/Projection Surface must let some light through.
  • Infrared Camera/Modified Webcam

Camera Image Examples




Video Examples



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  • diehard

    angle of the IR led?

  • Yeeshu

    Hi Seth, I am also trying to make a DI touch surface. Just wondering i have an image i am getting, but reflective infrared light shining on it, How can i solve that. Is it maybe the LED light placement ?

    • Yeah, you might need to angle the LEDs so that they don’t shine into the camera (or angle the camera). You can find how other people have done it on http://nuigroup.com/forums.

    • Yeeshu

      THanks a lot man really appreciate it

  • Yeeshu

    What diffused surface did u use…i tried perspex…but i dont tihnk its diffusing. i see you have placed another diffuser surface on top of the perspex..

  • Yeeshu

    Hey Seth i know i keep bothering, but desperately need help too.
    These are the images i am getting now..clear and all..just dono how to set the threshold in matlab before i do blob detection. Dono if u want to see my code

    • I haven’t ever used matlab, so I’m not really sure. Have you tried posting on NUIGroup? I’m sure some people there use matlab.

  • Yeeshu

    Hey Seth, How are you. I sorta have things working on MATLAB now. But now next stage is openCV, which im killing my skull about, have 4 days to present, and wanted to surprise the department that i can do in real time. Cos i have blobs from images and all. Please any guidance as to approaching for results like your last video. It would be really helpful. Thanks

  • guspelin

    I have a big problem, follow the instructions to remove the anti disk IR, then I put a piece of magnetic film disk 3/5, I have tried everything but the camera does not see sufficient infrared light , have tried with another web cam and all, I have proven with increasing power strip IR leds , with IR security cameras only see the light when the leds pointing to the center of the chamber. change slightly as the angle disappears

    CAM1 WEBCAM GENIUS WIDECAM HD720P 5MP 120 DEGREES : http://www.seusweb.com.ar/uploads/producto/big-producto-641_5.jpg

    CAM2 Logitech WebCam C -920 High Definition Video Full Hd :


    LED Strip IR: 850nm

    LEDS : 36 LEDs IR Φ5 Illuminator Board of CCTV Security Camera


    Obviously covering the light sensor to it strong shine .

  • guspelin

    would someone kind to help me?, all the examples I see the hand looks very clear in my project is not anything, I use a crystal, recommend any specific camera?, you maybe the old Ps3 Cam Camera Eye? THANKS