Diffused Surface Illumination (DSI)
HOW IT WORKS:
DSI requires a special type of acrylic known as Endlighten, which has micorscopic mirror-like particles embedded throughout it. Using exactly the same LED configuration as FTIR, the infrared light fills the Endlighten acrylic. Because of the particles, the infrared light is reflected out of the acrylic, acting like a giant infrared emitter. Then, like a Rear Diffused setup, an object stops the infrared light, reflecting the light back to the camera and creating a blob.
How do I make an MT DSI setup?
The layers from top down are:
Touch Surface Acrylic or Glass
This is not needed but is one of the best things about doing a DSI setup since you can have a smooth, durable touch surface versus the damagable diffuser top layer in a FTIR setup.
Diffuser/Projection Layer
The diffuser stops the image produced by the projector.
Acrylic
The Endlighten acrylic doesnt need to be as thick as is used in a FTIR setup, but it is still recommended for strength and rigididy.
The source of infrared light for an DSI setup comes from infrared LEDs that are placed around at least 2 sides of the acrylic. Typically the more sides surrounded, the better the setup will be in IR prevalent lighting conditions.
The webcam is placed on the opposite site of the touch surface so that is can see the blobs.
(The following comparison is from the nuigroup.com/forum thread)
Advantages
No compliant surface (silicone)
Can easily switch back and forth between DI (DSI) and FTIR
Can detect objects, hovering, and fiducials
Is pressure sensitive
No hotspots
Even finger/object illumination throughout the surface
Disadvantages
Endlighten Acrylic costs more than regular acrylic (but the some of the cost can be made up since no IR illuminators are needed)
Blobs have lower contrast (harder to pick up by software) than FTIR and LLP
Examples of DSI setups:
NONE
Informative DSI Link
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