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Old January 18th, 2006, 12:43 PM   #1
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dumb question about basic mattes and tracking

How do you make a matte move the same as the camera is moving in the green screen shot? Do people use AE for this? What are the good programs out there?

Just so I'm being clear, I want to shoot interviews on green screen where the camera is slowing zooming in and otherwise moving or panning a little, and then I want to use a video background, like let's say a shot of a golf course, and I want the background shot to be tracking the same as the interview shot when I put them together (meaning the background, since it's further away, will move slightly differently than the foreground).

I've done keying where the shot on the person is locked down, and the background is locked down, but I want to be able to put movement into the greenscreen layer, without opening a huge can of worms.

What are the ways and programs people use to do this? Do I need a greenscreen which has some sort of dots on it? What program(s) make this easy?
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Old January 18th, 2006, 01:14 PM   #2
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My guess:
You can put dots on the background (the green screen) to aid in motion tracking. The motion tracker has to be able to track 4 points at once to get the position correct.

The dots should be visible when you're zoomed in as far as you want. It should be easy to garbage matte them out.

Programs like Combustion will do this. I also believe that AE, Commotion, Boris Red will also do this.

I haven't played around with this at all so take this with a grain of salt.
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Old January 18th, 2006, 01:40 PM   #3
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AE Pro (not standard) includes a sub-pixel accuracy motion tracking tool that has allowed me to do composites I absolutely would not have been able to get done without such a tool. Can't speak to the other vendors, but I'm sure their solutions are good, too.

The manual green-screen with dots would be PAINFUL! If you're into this enough to be doing green screens...life's too short to do that kind of work manually, frame-by-frame!
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Old January 18th, 2006, 01:44 PM   #4
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Glenn's description is correct for a simple 2 dimentional track, which is generally fine if the background is "distant" from the live action you don't have direct contact between the person and comped background. You'll need the Pro version AE to get the tracking functionality.

For digital elements that are closer to the subject, or even in CONTACT with the subject (like a CG floor) you need to go to 3D tracking. No program makes it "easy" but a set of programs can make this routine. The process is called matchmoving or camera tracking... and it happens to be my specialty :)

There's a great book on the topic by Tim Dobbert (matchmove supervisor from The Orphange) called Matchmoving: The Invisible Art of Camera Tracking.

Two of the most common software packages used for this includes RealViz Matchmover Pro and 2d3 Boujou. There's also a rather inexpensive program out there called "SynthEyes", but I worked with it extensively enough to gauge it's capabilities against the more widely used apps.

You CAN buy Boujou as a plugin for AE, but you are a little limited in what you can do, since a shot like the one you describe typically also involves some basic 3D modelling not supported in AE. You don't have to be an all out CG artist. Just setup some basic shapes, like a flat surface, box or ball to "project" backgrounds onto in 3D so you get proper paralax as the camera moves.

Since you're in California, I'll mention that Tim and I are presenting a 3 day Matchmoving Intensive course in San Fran in mid Feb. PM or email me if you're interested in details.

For some example matchmove shots, here's a little demo reel I threw together for my MFA application that shows some shot breakdowns of matchmoved shots. The first three shots are matched in 3D, but the last one with the ipod is just a 2D track like Glenn describes:
(~20 Meg)

Hope this helps.
Nick Jushchyshyn Matchmoving, Compositing, TD
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Old January 19th, 2006, 08:31 PM   #5
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Very cool

Thanks for the responses. Nick -- wish I could make your demo in San Francisco, sounds like it would be very valuable. Going to play around and see if I can get something working along the lines described here.
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