Rear Diffused Illumination (Rear DI)

How It Works:

Infrared light is shone from the opposite side of the touch surface (the rear). When an object stops the infrared light it reflects the light back to the camera and creating a blob.

How do I make a MultiTouch Rear DI setup?


Tutorial Video:



The layers from top down are:

  • Touch Surface Acrylic or Glass: All that is needed is a strong, durable surface that can take the pressure of user interaction.
  • Diffuser/Projection Layer: The diffuser stops the image produced by the projector.
The source of infrared light for an Rear DI setup comes from infrared LEDs that are placed below the touch surface.

The camera is placed on the opposite site of the touch surface so that is can see the blobs.

Advantages
  • No need for a compliant surface, just an diffuser/projection surface on top/bottom
  • Can use any transparent material like glass (not just acrylic)
  • No LED frame required
  • No soldering (you can buy the IR-Illuminators ready to go)
  • Simple setup
  • Can track objects, fingers, fiducials, hovering
    • Disadvantages
  • Difficult to get even illumination
  • Blobs have lower contrast (harder to pick up by software)
  • Greater chance of �false blobs�
  • Enclosed box is required

Examples of Rear DI setups:

EfeNDy's Table
Multi-Touch Research Platform (Lancaster University, UK)
Fairlane's ORIONmt