The main Problem with most Diffused Illumination Setups is getting IR Light to spread evenly across
the screen surface. Normally, you use a couple of IR Illuminators as a IR source, and it takes lots of
effort to get the IR even, while also dealing with possible reflections from the Illuminators. But now
I found a material that make this a lot easier!

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Introducing DSI
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Instead of using Illuminators as a IR Source, DSI uses a special acylic to distribute the IR evenly across
the surface. So you basically use your standard FTIR setup with an LED Frame, and just switch to a
special acrylic, that does not frustrate the IR light from the edges. This acrylic uses small particles that
are inside the material, acting like thousands of small mirrors. So when you shine IR light into the
edges of this material, the light gets redirected and spread to the surface of the acrylic.

Illustrations showing the different approches:

FTIR:

DI:

DSI:

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Pros & Cons
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Pro

• no problems getting the light even, easy setup
• FTIR setup can be converted to DI easily
• no need to build a case for the setup (like other DI setups)
• fiducial tracking possible

Con

• less contrast compared to normal DI setups, because the
  plexiglass also redirects the IR towards the camera
• potentially more problems with ambient IR because of less contrast
• possible size restrictions because of the plexiglass softness

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How to make your own setup
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First of all, you need to get hold of the “Endlighten” plexiglas. I got my material from
a local acrylic dealer in Zurich. Since he didn´t have the material in stock, I had to order
a pretty big sheet (about 2×3m) which cost about 700 euros. I pretty muched used all
the material in the end, and my university paid for the costs (so I didn´t care..). If
you live in Germany or France, you can order directly from the “evonic” webshop,
otherwise ask you local dealer/distributer for ordering possiblities.

Evonic makes some different types of Endlighten. These vary in their thickness and also
in the amount of particles inside the material. Available thickness ranges between
6-10mm, follwing “L”, “XL” and “XXL” for particle amount. I have tested the 6mm
“L” and 10mm “XL” type. The 6 mm is to flexible for a table setup, the 10 mm works
nicely.

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Handling the material
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Because the plexiglas is softer than normal plexiglas, you really have to watch out when
working with the material. It scratches quite easily and these scratches show up on the
projecton and during camera tracking. So watch out…

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LED Frame
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You can use your “normal” FTIR LED frame for this setup. My tests showed that shining
light into all four edges of the sheet works better than only through two sides. It works with
two sides, but better with four! I also tried increasing the number of leds, which makes a
brighter image, but no contrast change. So potientally, brighter blobs means better recognition
with ambient IR. For example, on two setups I used about 100 Leds for all four sides on a active
screen size of 64×48cm. This may seem like to much, and thats probably right too! You could
use less, just make sure all four sides have leds.

Like most people, I use the Osram SFH-485 and Osram 485-P. I would recommen the “P” type
because the angle is wider than the normal 485s. The wider angle helps distribute the light on
the edges better so that the distance between leds and the active screen size is kept smaller.
Normal 485´s work as well, but if you can chosse, I would recommend the “485P”.

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Screen vs Sheet Dimensions
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You have to have some extra sheet material around the edges, so the ir from the leds can
spread evenly into the material. This also depends on the angle of the leds, so the 485 P need
less space (because of the wider angle), while the 485 nedd more (narrow angle). I would
recommend about 2-4 cm extra on all sides. So a active screen size of 64×48 cm would need a
sheet of 70×54 cm (with 3cm on all sides). That should be enough for both 485 and 485p leds.
These are just some numbers I found during testing, so other leds could behave differently.

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Other Components
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All other components (Projectors, Cameras, mirrors IR filters, etc…) are the same as other
multitouch setups. Either check Nuigroup.com or my blog for some info. The same projection
screen material that are used for DI can be used on DSI setups. I have tested tracing paper,
lee filter, geriets optitrans and lumin contrast screen. They all work good with DSI, but prices
and image quality vary…

Download the technical information about “EndLighten” from the Evonik website: link
German Evonik online shop to order EndLighten: link /// Same in French: link

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CamCaptures and Video
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Some Captures from my Setup with the FireflyMV from PtGrey:

Capture with all Settings set to default (auto):

Capture with Settings adjusted (manual):

Capture with Settings adjusted (manual):

Video camcapture: