Write On Wall

The Write On Wall (WOW) Installation which lets you use light, specifically of your mobile phone screen to write graffiti on a glass wall

“Make your mark on your social network, not in the social network.”
Paraphrasing former New York City mayor Ed Koch.

For the Social Dev Camp 2010, together with Eelco Wagenaar and Mark Wubben, we made a simple and effective digital graffiti wall, on which you can write with a light: from your bike light to the screen of your mobile phone. Using an RFID card you post the result on your Facebook wall, like it on Facebook or clear the screen to begin fresh.

Multiple quick iterations during the camp brought us from a game using two lit cigarets and the smoke you exhale to control a boxing puppet and influence your opponents’ and other technically tricky games and toys to be applied in the smoking area of a venue (because the mandatory smoking areas in clubs and venues are often uninspiring non-places), to a simple digital graffiti wall. Having lots of tools and equipment available at Mediamatic BANK where we held the camp and having lots of bright minds at the same time, we were able to make a lot of small technical feasibility and play tests before deciding on the final project.

During these tests and demo setups, we found that the digital graffiti wall was actually really effective and convincing as real graffiti. When on the third day —or night it was already— we tried the setup outside the Mediamatic BANK, using its glass facade and a mobile phone as the light source to draw out a huge digital graffiti piece, a nearby police van immediately pulled over, stopped to see and inform what we were doing. On their first impression I must have looked like a genuine graffiti-”vandal” to be caught red-handed. Only after closer inspection the paint turned out to be projected light and my spray can an iPhone screen.

The Write On Wall (WOW) installation was simply made by using a camera on one side of the frosted window, picking up the light your mobile phone shines on the other side of the glass. A computer processes and analyses that feed, and sends the rendered image to the projector, which beams its light back onto the window. The illusion is created that you’re drawing on the glass wall.

As with a lot of computer vision projects the light conditions turned out to be crucial. The delicate interplay of minimal ambient light in front and behind the glass wall, a bright, but not too bright projector and a bright enough mobile light source made setting up arduous. Every iteration meant calibrating from scratch: new threshold levels for the changed light, and re-aligning and warping the camera image onto the projector setup. So we developed special calibration software that automated this 90% of the way. The season helped too: starting in wintertime, let us test and run the installation outside (which is where graffiti belongs) for much longer periods of the day than in summer.

And to ease the hook up of different software components of this installation: the computer vision and graffiti drawing part, the RFID reading part, the server communicating with the network and with Facebook, and the visual on-screen feedback of your RFID swiping actions, we used a node.js server and hacked a special purpose browser. This Transparent Web Browser rendered the feedback as a simple HTML and CSS styled text and animations on top of the CPU and GPU intense OpenFrameworks C++ application responsible for the graffiti.

Finally, we added the social network sharing functionality, so you can leave your digital graffiti on someone’s Facebook wall. This made the work engaging and attractive for a much bigger crowd. An interesting aspect of a social digital graffiti wall like this, is that it flips around the anonymous, yet public part of graffiti. Where traditional graffiti was to anonymously write your tag throughout the city to be visible in public, this work instead invites you to personally and publicly claim your piece using an RFID tag and share it privately, visible to only your own social network.

Write On Wall (WOW) was on display several months at Mediamatic BANK, during the Eurosonic Noorderslag festival in Groningen and during the 5DaysOff festival in Paradiso in 2011.