Motion tracking with green screen

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Motion tracking with green screen
by Scott Swingle on Sep 11, 2012 at 8:48:01 pm

Ok, so we shot a scene with a window, and a green screen in the window. We also put markers on the screen so we could track the movement in post. I just can't figure out how to go about making it happen.

The shot I am having issues with is a moving shot, it pans up slightly, and then dollys across the room parallel with the green window. If I just track the motion and apply it to the background layer, the dolly motion doesn't look realistic. I figured the solution was to make the layers 3d and then move the background layer back on the Z axis but that still isn't working as expected.

How should I be going about this?

Thanks!

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Re: Motion tracking with green screen
by Angelo Lorenzo on Sep 11, 2012 at 11:10:56 pm

As a 3d layer try moving it even further in z-space. Since you didn't really describe why it feels/looks wrong to you, I'm assuming it's moving more than would be correct for the perspective. Also your 3d layer, for accuracy should be viewed with a 3d camera set to approximate the camera on-set.

Angelo Lorenzo
Fallen Empire Digital Production Services - Los Angeles
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Re: Motion tracking with green screen
by Vishesh Arora on Sep 12, 2012 at 5:03:52 am

Mr. Swingle
The problem is with the perspective. If you are using mocha for tracking then make sure you have checked " Perspective " option.

Vishesh Arora
VFX and Motion Graphics Artist

http://digieffects.wordpress.com

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Re: Motion tracking with green screen
by Scott Swingle on Sep 12, 2012 at 8:14:33 pm

I had not been using mocha to track the motion, used the one built into AE.
Does the mocha built into after effects have this option or do I need the purchased version of mocha?

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Re: Motion tracking with green screen
by Ross Shain on Sep 13, 2012 at 8:32:01 pm

mocha AE CS6 that is bundled has 2D planar tracking and roto tools.

mocha AE v3 (purchasable upgrade) adds 3D Camera Solver and support for FCP, BCC and Motion.

More info: http://www.imagineersystems.com/compare-products

Ross Shain
Imagineer Systems
http://www.imagineersystems.com

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Re: Motion tracking with green screen
by Scott Swingle on Sep 14, 2012 at 4:08:49 am

Thank you all for the suggestion to use mocha for tracking. Just used the 2D tracker in mocha but with the perspective option turned on. Took a little bit of tweaking but now the shot looks believable.

For what its worth I did try the AE 3d tracker and it wasn't doing the job either, but its quite possible I just wasn't doing it right.

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Re: Motion tracking with green screen
by Tom Daigon on Sep 12, 2012 at 9:21:47 pm

Without seeing the footage, I would say the 3D Camera Tracker is the way to go. Post a link to the clip and I will confirm that for you. :D

Tom Daigon
PrP / After Effects Editor
http://www.hdshotsandcuts.com

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