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Need help with tracking and IR



  • Hello all…

    I have a question that's bugging me for a long time now…
    The thing is, I have a dancer on stage and I want to project some graphics around her… But I want this image to follow her, kinda like an aura.
    In order to do this, I was thinking of using Eyes and the background subtraction technique, but, won't it be getting back feed from the projection?
    So I though on two alternatives… the easier one doing a color tracking… and the best one, with an IR setup.
    But here's the catch… I have zero budget for this experimenting… so no way I could buy an IR camera.
    Which got me thinking… those DIY hacks with a cheap webcam and burn film really works? I have a Canon T4i and was thinking of buying an IR filter (those that screw in front of the lens), should it work the same as an IR camera? What about the lighting? The projection really doesn't output IR? Should I be able to find an IR lighting source or it's best that I buy some LEDs and make it myself?
    Thanks in advance


  • Put a battery powered IR LED on a dancer so the camera will see it. If you got IR light then you illuminate the background(floor, screen) that the dancer appears as a shadow.

    BW security cameras will see IR very well(actually most webcams and digital cameras somewhat as well). On some cameras the IR cut filter is rather easy to remove. Piece of film on front of the lens for experimenting will do.


  • an IR filter that fits onto a camera lens is likely to be an IR cut filter - that will stop infrared frequencies from entering the lens. this is the last thing you want. you need an IR pass filter or 'hot mirror'. the cheapest way i have found is to use an old black and white cctv camera and make a filter out of a bunch of dark lighting gels. a dark blue, a dark green and a couple of dark reds usually cut out all visible light. this will enable your camera to see stuff that is illuminated, but not see the projected light. most standard theatre lanterns will output IR naturally alongside their regular spectrum light (they get hot) so if you need to illuminate the dancer and project onto the back wall, you need to focus the lanterns onto the dancer but make sure there's no spill on the back wall. LED theatre lanterns don't output IR.

    if you're working in blackout, with just the dancer lit by the projector, you'll need to illuminate the dancer OR the back wall with just IR. this can be done with security LED floods, or with theatre lanterns gelled up with the same gels as your IR filter.
    the most straightforward method though, would be to borrow a kinect from someone and syphon the ghost into Izzy. this will provide its own IR and certain software will isolate human forms. i use NIMate, but its a bit expensive if you're on a tight budget. i'm sure there's a bunch of other ways of getting the data you need into Izzy.


  • Thanks @dbini

    I think this filter is exactly an IR "enabler", because there's a trend amongst photographers of taking IR photos… So I think this kind of filter is exactly to cut-out the other frequencies and enable only the IR. But I'll have to test it.
    Thanks for the great tip on using a bunch of gels together… I didn't thought of that… It'll be an easy thing to try.
    And also @vanakaru, thanks for the tip on the security camera… I think it'll be easier to get than an actual IR camera.


  • Paulo_Rosa

    Old security camera will not be only easier but many times cheaper. You are right about the IR filter. I have used the R85 ones
    http://en.wikipedia.org/wiki/File:IR_filters_01_Pengo.jpg
    Also I have experimented with IR cut filter on the projector. It was very hard to find at the size of projector lens and very expensive. The improvement was there, but not that important.
    So get old CCTV camera. If you see a filter inside the camera over the sensor - remove it. Put the IR filter (anything from 700-900 nm) on the lens and you should be fine. I have had good and very easy/cheap solution with keychain LED lights with replaced IR LED mounted on subjects head for tracking.


  • Did some IR tracking years ago, used  wii remotes, as IR cams and Osculator to send the tracking values, midi or OSC to QuartzComposer, should also work with Isadora, not sure if still the same procedure. best …



  • Your t4i will be a pain to get into the computer. Many cameras have an IR cut filter on the sensor. These can be removed and you get all the IR coming in. For the feedback you can put a small amount of polarising filter on the camera and on the projector in the opposite orientation. There is a post about it recently here. A security camera will be great and some don't have IR cut filters. Then you can use an ir pass filter to get only ir. This will give a good clear signal.



  • The t4i is already a pain… I have to use canon2syphon and is not at all reliable… I'll try to find an old CCTV camera and get started with the testing… thanks a lot

    And I didn't knew it was possible to use the wiimote… I have one laying around here… will give it a try

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