Robert Klep

Ontmoeting

Ontmoeting («Meeting») is an interactieve video installation where old movies from Brabant (a Dutch province) engage in a relationship with current-day footage. The project was initiated by Ingrid van Zummeren and Marloes Hoogenstraaten, and was presented on October 20th 2008 (@ Stadskantoor, Eindhoven, Stadhuisplein 10).

Tech stuff

The interactivity of the installation consists of a walking path, initially in the Stadskantoor of the city of Eindhoven, The Netherlands. People moving along this path are being tracked by an overhead camera, and according to their position on the path, two movies (the «old» and the «new») are mixed together and shown on a large screen.

Together with Martijn Verhallen, I've implemented the technology behind this installation using Max/MSP+Jitter. Roughly speaking, we use this workflow:

  • take a frame from the webcam (jit.qt.grab), convert it to monochrome (jit.rgb2luma), determine difference with previous frame (combo of trigger and jit.op)
  • using the differential image, determine its boundaries (jit.findbounds) to determine the boundaries of movement within the image
  • correlate the up/down-boundaries to a location on the walking path, and using this, determine a fade-ratio which is used to fade the two movies
In reality, the workflow involves quite a bit more. Since the installation should function at different locations and has to be set up by people not familiar with Max/MSP, we had to create an easy to use UI where parameters like Region Of Interest and thresholding can be entered.

Also, to offload the main processor we are using an OpenGL-optimized videoplayer patch which we built according to tips we found here. Using it reduced CPU-usage considerably.

It did, however, introduce a problem when building a standalone application: the optimized player needs specific Jitter shader files (.jxs) which aren't included in the standalone application's bundle. We found the following solution to this problem:

  • build the application using this script in the builder: 
    open thispatcher
folder "MacOSX:/Applications/Max5/Cycling '74/jitter-externals"
folder "MacOSX:/Applications/Max5/Cycling '74/jitter-shaders"
folder "MacOSX:/Applications/Max5/Cycling '74/jsextensions"
    (names on your system might vary)
  • after building the standalone .app, go to Finder, right-click the application, choose «Show Package Contents», and navigate to «Contents/MacOS»
  • create a new folder named «support»
  • copy (not move!) the folder (the entire folder, not just its contents) «/Applications/Max5/Cycling '74/jitter-shaders» to the newly created «support» folder
After that, the application worked perfectly. Perhaps there's a better way of making this work properly, though.

Hard- and software

The installation runs on a single Mac Mini running Mac OS X 10.5 (Leopard). The camera we're using is an off-the-shelf Logitech QuickCam Vision Pro USB webcam, which works perfectly in Max. We started application development on Max 4.6, but moved to Max 5 (for no apparent reason apart from a *much* *better* workspace).

The Mac Mini has auto-login turned on, and automatically starts running an application which, in a continuous loop, runs our standalone Max-built application. If for some reason the app crashes, it will automatically be relaunched.

Because we experienced crashes of the Mac Mini due to overheating when running it continuously for several days, we're using the built-in Mac OS X features of shutting down and starting up at specific times: the Mac Mini shuts itself down each night around 21:00, and starts itself each day around 9:00. This seems to work just fine.

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