Wednesday, July 16, 2008

I.D Tags

The Fable computer program is designed to recognize the I.D tags when they are placed on the tables surface. 

Each tag is representative for each member of the family and also the photo frame.

The tags are made up of 2 different materials: a reflective film and mat black card.

As the webcam is adapted to see only infrared light, the program will only see the reflected part of the I.D tag; and as the above image shows, each reflective area for each tag is different in size.

The program basically counts the pixels of reflective area, and since each area is different, it is able to understand the difference between each tag.

Notice the asymmetrical layout of the tags. This enables the software to understand when a mug is rotated.

The frame works in the same way. As the following image shows, the reflective area for the frame is much larger than it is for the mugs. This means the software can easily differentiate between the frame and the mugs. The black spots on the side of the frames tag are for the software to understand the orientation of the frame so it can position a photo inside the frame and react accordingly if the frame is rotated.


As I mentioned in my last post about altering the webcam to see infrared light and block out natural light; I like to hack things.

I have an understanding of how electronic products work and how different materials can be used to replace existing parts to change a products behaviour. The story of how I made the i.d tags is an example of this.

I started of by looking at materials which absorbed or reflected infrared light.

Skin does this best. I built a simple touchscreen by embedding IR LED's into a sheet of acrylic. When skin comes into contact with the acrylic, it absorbs the IR light and creates a glow (or blob as it was referred to).

So I began to play with various materials which I thought could react in a similar way to infrared light; such as leather and silicon. But none of the materials worked.

Which lead me to the physics reflections: retroreflections

Some surfaces exhibit retroreflections. The structure of these surfaces is such that light is returned in the direction from which it came. A surface can be made partially retroreflective by depositing a layer of tiny refractive spheres on it. In this case, internal reflection causes the light to be reflected back to where it originated.

This is used to make traffic signs and registration plates on cars as the light would be reflected back to a cars headlights rather than into the drivers eyes.

This theory is also evident in reflective jackets, such as those worn by builders or cyclists. 

I bought some of these jackets and also bought a strip of reflective tape from 3M. The film that worked the best for my I.D tags were actually from a cyclists jacket I found in IKEA; of all places!

So I cut the film into circular sections and stuck them onto the bottom of the mugs. 

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