Front Diffused Illumination (Front DI)
How It Works:
Light is shone from above the touch surface (the front). When an object stops the infrared light it creates shadows on the touch surface. The camera then converts the black blobs into touches. This setup works in inverse of the other setups, where all non-bright spots are considered blobs. This setup does not work as well as any of the other setups but is a great place to learn multitouch by building a simple MTminiHow do I make a MultiTouch Front DI setup?
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 diffuser is also needed so that the shadows have a plane to lie on and thus represent the objects placed near the touch surface. The source of light for a Front DI setup comes from the ambient room lighting, or an overhead light which covers the touch surface.
- No need for a compliant surface, just a 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) or just use ambient light
- Can track fingers and hovering
- An enclosed box is not required
- Simple setup Disadvantages
- Cannot track objects and fiducials
- Difficult to get even illumination
- False blobs from hovering objects can be a problem if unintentional
- Not as reliable (relies heavily on ambient lighting environment)
The camera is placed on the opposite site of the touch surface so that is can see the blobs.
Advantages