Building a DSI multi touch table

MT (Multi Touch) technology is exploding right now with Microsoft Surface in the lead. We see multi touch cell phones, tablet PCs, the Macbook touchpad, DYI MT tables, and so forth. And the list is growing – fast!

My first physical contact with multi touch interfaces was during the technical fair in Stockholm 2007. Natural User Interface Technologies AB was demonstrating their multi touch table next to our fair booth so we had the chance to try it out. Before that I had only seen Jeff Han and his demos on Youtube. Since then I’ve been fascinated by the possibilities with multi touch interfaces and how you aren’t restricted to a single mouse cursor.

I’m currently designing and building a multi touch table at work. The table will be located in our new office and we have some ideas using it as a creativity tool when having brainstorming meetings. We’re also thinking about using it as a conference tool where we have several tables on different locations where the tables share all objects placed on the surface.

Diffused Surface Illumination

The technology I’m using in the table is called DSI (Diffused Surface Illumination) and works upon the principle that IR (Infrared Light) is emitted from a surface and reflected by the fingertips. The reflections are registered by a camera that has a band pass filter that only lets a certain wavelength through to the sensor (which happens to be the same wavelength as the emitted IR light). A computer processes the images from the camera and converts the reflections – “blobs” – to touch points that can be used in a MT software such as the famous photo application where you can rotate, scale and move photos on an infinitely large surface.

The IR-emitting surface is a special kind of transparent acrylic called Endlighten that contains microscopic particles that acts like mirrors. The acrylic is mounted in a frame with IR leds that shine through the edges of the sheet. When the light hits the particles inside the acrylic it leaves the sheet and make the acrylic light up like a big lamp (but invisible for the human eye.)

Diffused Surface Illumination - Image from Tim Roth - http://iad.projects.zhdk.ch/multitouch/

Normally when you let light into the edge of standard acrylic you get an FTIR (Frustrated Total Internal Reflection) effect which is the one Jeff Han uses in his demonstrations. The difference to DSI is that no light leaves the acrylic until you affect the surface with, e.g. your finger. FTIR MT surfaces are often layered with a thin film of silicone or other adhesive layer to get better blobs when fingers are dragged.

There is several more techniques used to create MT tables but I will not go through them here. Instead I recommend a visit to the NUIGroup website which is a community with people designing and building MT tables. You can also download the software for tracking blobs at that webpage.

I will continue posting images, movies and screenshots of the table and will hopefully be able to show some of our own MT applications.

출처 : http://www.iterate.se/2009/07/25/building-a-dsi-multi-touch-table/