IR Blob Tracking - choosing equipment, would like your input

  • Dear Isadorables,

    Am just embarking on an exciting project in a circus tent: four projectors , North, South, East and West pointing into the ring, allowing for many possibilities of projection both on to the circus ring, and on to performers in the air above it. Annoyingly the company making the work are set on using Avolite's Ai system, but I can send anything Isadora makes via Spout, NDI, OSC, Midi etc to Ai.

    I want to track performers around the ring, and was contemplating using an IR camera mounted in the top of the tent pointing straight downwards, and using an array of cheap IR LED lights around the ring to illuminate the performers. I've done this successfully with a maquette, now to scale up.
    One problem is that the camera will not be easily accessible, and the distance from camera to computer will be about 20 metres. What do people suggest for a camera? Something that can be turned on or off remotely, can be mains powered or powered via signal cable (eg USB) and that will cover a 42' diameter (that's 13m) at 10m height. The computer has HD/SD SDI input as well as analogue and HDMI capture.

    All suggestions, tips, tricks, etc gratefully received!


    Mark (the other one).

  • Beta Platinum


    I heard some good things about the Sony a7 that can be converted to IR.

    I use a a7s on stage (HDMI to sdi - sdi in (BM mini recorder)) and almost no latency
    The a7s also has a nice app that makes it possible to adjust focus, exposure,.... with a smartphone. and you can also see a preview.
    With a good lens I'm sure you can see the full stage.


  • @mark_m it depends on your budget, I use a lot of SDI security cameras and they are great, 12v powered and fine to leave on for days at a time. One thing to add to IR tracking is that even if you get an IR camera (generally meaning that the IR blocking filter is removed (or switchable in the case of the security cameras)) you get better results using an IR pass filter as well. This will block visible light and let only IR pass through making the tracking and lighting more  reliable and meaning it does not matter what your general lighting is. You can see a selection of filters here

    Another great camera option is the point grey zebra 2. It has gigeVision and HDsdi out, meaning you can control the camera settings via ethernet.

    I would avoid using a DSLR, especially if you have to irreversibly modify it to make it IR, they are also prone to overheating. Definitely avoid usb cameras for this job, the latency is too high.

    On the cheap scale here is an SDI security camera and there are many cheap lenses available

    And in the middle is this camera from Marshall

    Beware not all Marshal cameras have a moving IR filter.


  • Tech Staff

    I was going to mention Point Grey cameras as well (now owned by Flir).

    And I second Freds comments on the use of filters.

  • Beta Platinum

    If you can get yourself a cheap thermal spectrum camera you can save a lot of set-up time, because you can achieve IR tracking without the need for IR lighting. The thermal camera sees the heat of your performers bodies - so as long as the performers are emitting more heat than their surrounding environment it is a simple threshold calibration to separate them as tracking blobs. I continue to use a FLIR VSR6 for blob tracking - it was the least expensive 'surveillance' style thermal available at the time and I used an arts research grant to purchase it. The camera has serial controls and BNC analogue video output - I have never had to use the serial interface - just plug straight into the BNC video jack. It is analogue so not without latency when converting to a digital signal - however the time saving in reduced set-up worked for me as the original show toured for a few years and had many other interactive components including Kinect, along with eight blended projectors mapped around two 6 mtr scrim/gauze cylinders. The thermal camera was set at the top of one of the cylinders and tracked audiences that were in there - spatializing the soundtrack and visuals.

    The FLIR VSR 6 is no longer in production and might not have the field of view that you require, or the resolution (160x120 pixels). I was getting a tracking zone of around  4 x 6 mtr with the camera mounted at 6 mtr in the grid. I used simple cat 5 baluns to get the thermal video signal to the I/O unit and into Isadora for tracking. The tracking data was also converted to midi and sent out to a companion machine running max msp controlling a quadraphonic soundtrack.

    Thermal cameras appear on e-bay from time to time. A HD digital thermal camera carries a fairly hefty price tag.