Motion Capture

Leon Rodriguez · February 4, 2004

I'm in a little frustrated in my planning maybe you guys who've done the bigger shoots can help me to achieve my goal. I have a green screen composite shot coming up. I'll shoot on 16mm transfer to HD and composites will happen from there. I'll shoot the background plate at a later date. I understand about backlighting for an even exposure on the green screen. and mark registrtion points for the compositors. I am torn between wanting to do a camera move on this shot and risking wrecking the composite. I really don't want to just do a static shot. What I'll have is a nice looking oil painting. If I have to do the static shot, I'll use a super slow zoom as imperceptibly as possible to give it some life but That's really not what I want. No money for special equipment, but I've got a great shop to build just about anything electro-mechanically. How can I get motion capture on the cheap? Anybody know any tricks? I'm really tempted to just wing it. I guess I could just get them both and see what works. Ideas?

Ozgur Baltaoglu · February 4, 2004

hi leon,

I havent done any big shoots but I know this... if what you mean by motion capture is motion control then I have to say it would be nearly impossible to build a m.c. rig at home since the device uses complex software to make multiple passes (infinetely repeating the same camera movement) however it is possible to make manual, human operated multiple passes, simpler the movement easier to repeat... I've tried this once; we tried a tracking shot (green box) we timed the move, marked the track and rehearsed quite alot and then shot the plates the next day trying to match the speed... the effects artist then composited them and it worked ok... lessons learned; we should have shot the plate first, it is easier to duplicate lighting and movement, you can also play back the plate on a separate lcd or video assist and time yourself little more accurately, also talking to the effects artist in advance might help because in this kind of poor man's hightech gear situations you may need unconventional precautions, in our case we had to place witness points for keying in the most unusual places. Also Zooming is pretty tricky. I know I couldnt be of much help but perhaps it may help... good luck

Mitch Gross · February 4, 2004

The are a few systems that can do motion tracking to match the background plate to your foreground element, and in fact that's the reason for the yellow balls for reference points on the greenscreen set (don't need them otherwise). But this does get very expensive to do properly. And what will your composited background come from? Will it be computer-generated material, which would need to be created in a 3-D not 2-D environment in order to follow the motion tracking? Or will it be a natural plate that you photograph conventionally--in which case you would need a servo-driven head and dolly system that exactly replicates the motion from the greenscreen stage.

You can do this without a lot of expensive hardware on set, but it simply means that you'll need a lot of expensive and time-consuming hardware and software in a digital suite somewhere, especially if you are doing it in HD as you mentioned. Sorry, no such thing as a free lunch.

Leon Rodriguez · February 5, 2004

I know. The background plate will be an intervalometer night shot that places a night-time cityscape across the horizon at the top horizontal third. The composited elements are: a HUGE 3D moon that feels like Orson Well's fish CU from Lady from Shanghai in that aquarium. And of course the timelapse auto and aviation traffic streaks. I'll shoot foreground movement at near realtime at, I'm thinking 30 f/s to smooth it a bit. So Rich blacks and tight grain will be the glue that hold it all together. I was trying to come up with a constant cable pull idea like some kind of common use wench or stepper motor and pull something like a western dolly across a marked path at a known angle. Maybe I shouldn't over think this thing. It's easy to get in trouble.

And yes, Ali I meant motion control. I'm working on a motion capture system for 3D animators so that was imbedded in my seven remaining brain cells. I wish we could afford tracks.