I began this project knowing that I wanted to create an interactive installation for the BBC Big Screen in Leicester. Having that in mind, I started to gather ideas about what exactly I wanted to do. I thought about different techniques and visuals that I would like to see. I then decided fairly early on for example, that I wanted to use motion-tracking techniques, to allow some form of interaction between the users and the program.

I played with the idea of creating a game at some point but dismissed it quickly. I didn’t want the pedestrians in front of the screen to have to participate in order for something visually appealing to happen on the screen. I wanted it as simple as possible, with no big setup or helpers needed on site when screening the application. So I decided to create a “passive interactive” application instead.

After a long phase of research and looking for the right inspiration, I found the most suitable programming language and after that I could finally throw myself into coding. I started by trying to run all the examples of the openFrameworks library. Actually being able to compile my code and see examples run made the process a lot easier.

Then, for a long time my plan then was to create a sort of “trail” that shows the path of the people walking past the screen. I wanted this path to be able to interact with other paths, similar to the popular Tron car racing game I guess. I came across several problems with that though, so I had to dismiss that idea. I’ll discuss the problems for this at a later stage. And I have given some examples of what I mean with the Tron game in the next section.

In my first prototype I basically just played around with all sorts of stuff that I had learned during my research. The most important techniques I took from that were the background subtraction and the contours. I had started to play with ofxBox2d, a physics addon of openFrameworks, but it wasn’t running completely as I wanted it yet. At that point I wasn’t completely sure what to use that functionality for anyway.

So, then I changed my idea of having long trails in the form of lines, to having a history of previous frames and drawing several previous contours of a person, as seen in my prototype 02 in the top right corner. I was able to implement it that far and by adding the transparency attribute to colours, I could create a lot of really nice effects. Having each blob in its own colour was quite beautiful as well, including the option of filling out the contour as opposed to just drawing the outline. That alone opened so many paths for me, technically and artistically.

From there, I got the idea of just drawing a single historical contour next to the most current one, to create the effect of someone following after the real person. That’s how my “ghosts” came to life. I added a few more historical contours before the final one and made the transparency get less and less so that eventually the ghost would become visible slowly in a sense.