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Motion tracking for live action questions

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Eric Nicastro
Motion tracking for live action questions
on Mar 21, 2011 at 8:50:43 pm

I understand the concept of motion tracking and I've got AE CS5 and obviously Mocha to work with as well. What I need help with is the live action portion.

The concept we're doing is someone walking with the camera (similar to the HP spots except the camera is moving backwards, talent walking in front maintaining equal distance) with an iPad facing the camera and the talent swiping through the screen. Their finger will move across the screen. My assumption is to use a rectangular green object with tracking points on it then track and key in the iPad.

Here are my questions, should I use an actual iPad instead? Do I need to use tracking points? If I do use an iPad, can I just put up a green image with tracking points or do I need to tape off the screen with chroma key green tape?


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Dave LaRonde
Re: Motion tracking for live action questions
on Mar 21, 2011 at 8:59:25 pm

What kind of a camera will you use to shoot this?

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Eric Nicastro
Re: Motion tracking for live action questions
on Mar 21, 2011 at 9:02:42 pm

A JVC HM-700 with a standard ENG lens attached to a Varizoom Navigator.


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Dave LaRonde
Re: Motion tracking for live action questions
on Mar 21, 2011 at 9:23:09 pm

Sorry, I should have asked this, too: can it do at least 4-2-2 color sampling? If not, forget chroma keying: the result will be no better than chroma keying DV (ugh).

I see that camera can record at variable bit rates, so you'll want to use the highest you can. Quality counts when chroma keying.

And I'd also consider running a test using an old Etch-A-Sketch as a prop. I favor shooting this with a prop iPad, with a matte chroma key green surface and tracking points in a slightly different shade of chroma key green. Check out hollywoodeffects.com to see examples of the colors.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Joey Foreman
Re: Motion tracking for live action questions
on Mar 21, 2011 at 10:30:17 pm

The great thing about Mocha is that you don't need tracking points. It tracks planes, not points.

Check out this tutorial:

http://www.imagineersystems.com/videos/mochaimport-corner-pin-tutorial-for-...

Joey Foreman
Editor/Compositor/VFX Artist


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Eric Nicastro
Re: Motion tracking for live action questions
on Mar 22, 2011 at 2:54:04 pm

My camera shoots in a 4:2:0 color space. I've used it for key work before and the result was actually decent. Not incredibly perfect, but passable.

I tried using a prop. I took a piece of cardboard, painted it chroma key green, placed tracking points on it but when I tracked it in mocha, the tracking plane did not stay with the shape. The top X's and corner of the board stayed in place but the bottom corners kept growing outward and made some odd shape.

I've done the search for motion tracking tutorials and tips, but all I keep finding are videos or articles that pertain to software, not how to set up the live action portion.


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Eric Nicastro
Re: Motion tracking for live action questions
on Mar 22, 2011 at 4:35:56 pm

I came across this tutorial and it did help me so I wanted to share it: http://www.imagineersystems.com/videos/how-to-shoot-for-planar-tracking/vie...

While it doesn't cover everything, it does give a lot of information. Now it's just a matter of trial and error and testing out different ways of doing this. When I find one that works well, I'll be certain to share it.


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