The Write On Wall digital graffiti installation is projected on the front store windows of the Mediamatic BANK. People standing outside can write messages or make drawings on the wall by using their mobile phone color screen (or any other light) as a brush. When you scan your rfid tag underneath the wall, it freezes the images, and allows you to post the result on your facebook page or on the facebook wall of one of your friends.
The advanced version of the same installation where you would use a lit cigarette instead of a bright shining light, was slaughtered in the brainstorming session after the first test results of using an infrared camera to track the burning cigarette were disappointing and proved that this IR-method would only work in a much (±50 cm) setting.
The first iteration of the project used image composition. i.e. copying pixel data on top of previous pixel data, creating noisy bitmap results. We're now considering using blob tracking algorithms and drawing vector images instead of pixels. That way we expect to have more control over the resulting image.