Inspired by the brilliant use of an age old concept in the recent OKGo 'WTF' video (youtube.com/watch?v=TNeItlrTdvY) which in turn was inspired by this photo by Thomas Eakins (upload.wikimedia.org/wikipedia/commons/0/0d/Eakins,_Thomas_%281844-1916%29_-_Study_in_the_human_motion.jpg), I created this little open-source demo in processing. It works in real-time with a webcam. Check it out and download the source msavisuals.com/xmas2009

I tried to keep the source super minimal and as easy to read as possible. For better results, you can try running an erode on the subtracted image, do a contour analysis and smooth the edges slightly. It also helps to run it in front of an empty wall with stable lighting, and ideally a webcam which has manual exposure / shutterspeed / gain etc.

To run the source code you will need:
- processing, which can be downloaded from processing.org
- the ControlP5 library (to handle the UI) which can be downloaded from sojamo.de/libraries/controlP5/

P.S. Everytime I see this effect I keep thinking of the idclip cheat in doom!

P.P.S. Check out the King of Pop's version from over 3 decades ago here youtube.com/watch?v=vjW1iq4IO2k

P.P.P.S. Anton aka Vade has made a Quartz Composer version which can be downloaded from bit.ly/5v43tM

P.P.P.P.S. goto10 also has a sweet Quartz Composer version which can be downloaded from hybridvisuals.nl/downloads/m8-trace-quartz-composer-effect/

P.P.P.P.P.S. OKGo just released an 'official' processing app to do the same (not related to mine, but developed by Jonathan Bobrow). Check that out at okgo.net/wtf_holidays.asp

j vimeo.com/8218843

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