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Motion tracking issue

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paolo mugnaini
Motion tracking issue
on Jun 3, 2010 at 1:20:47 pm

Hello Everyone,

I am trying to motion track a POV shot form inside a car in order to replace the sky. The problem I encounter is that once I track it and parent the sky shot to the null the sky goes all over the place, jerks, moves etc.
I've tried tracking motion as well as rotation and both but the result is still the same.
Can anyone please shed light on this so to help me understand what I am doing wrong?

Thanks!!

Paolo


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Tudor "Ted" Jelescu
Re: Motion tracking issue
on Jun 3, 2010 at 1:31:12 pm

Post clip- this will help us give feedback since motion track is based on ... well, motion!

Tudor "Ted" Jelescu
Senior VFX Artist
Bucharest, Romania
http://www.ennstudio.ro


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paolo mugnaini
Re: Motion tracking issue
on Jun 3, 2010 at 1:46:52 pm

Thanks Ted,

Do you want the clip without the sky, or the the "messed up" tracked one?

Thanks

P


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Tudor "Ted" Jelescu
Re: Motion tracking issue
on Jun 3, 2010 at 2:12:22 pm

the original clip should be fine- however if you can post the other as well it may help

Tudor "Ted" Jelescu
Senior VFX Artist
Bucharest, Romania
http://www.ennstudio.ro


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paolo mugnaini
Re: Motion tracking issue
on Jun 3, 2010 at 2:54:36 pm

Thanks!

Here is the original





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Dave LaRonde
Re: Motion tracking issue
on Jun 3, 2010 at 3:07:53 pm

I wouldn't even try to do a sky replacement. The footage is far too overexposed in the sky to get a good-looking shot. I would reshoot.

You have a phenomenon called light wrap on the edges of the palm leaves -- there is no clear-cut edge between sky and leaf, but rather a bright area at the edge, which gets darker farther from the edge.

Even if you could find sky footage that makes a right-hand turn at the same speed of your POV camera -- which is asking a LOT -- you're still faced with a dilemma over what to do with the edges. Do you create a key at the edges of the leaves, which will make them look unnaturally bright at the edges, or do you adjust the key to get rid of the bright edges, which will make the leaves look unnaturally thin?

Dave's Stock Answer #2:

When you're out on a shoot, and you say, "we'll fix this in post" without knowing PRECISELY HOW you're going to fix it in post, don't shoot it! You'll only end up shooting it over again.

Since post typically costs three times the cost of production, fixing something in post is not a way to save money, but rather a way to spend more of it.

And, before you say "well fix it in post," always consider who's doing the work, especially if you're the one doing the work.


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


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paolo mugnaini
Re: Motion tracking issue
on Jun 3, 2010 at 4:05:35 pm

Dave,

Thanks!

I didn't say "we'll fix it in post" and I agree with you but from what I understood it was a very bad day to shoot and there was no other choice but to shoot it and they wanted to be able to see the interior of the car which it would have disappeared if exposed to the clouds and it shot with a consumer camcorder.
But thanks for your help!

P


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Tudor "Ted" Jelescu
Re: Motion tracking issue
on Jun 3, 2010 at 4:22:18 pm

All Dave said is true, I second that. However since you're probably stuck with the shot, here's what I would do: definitely not a sky replace (it would be a lot of work for a not so great result). I presume you have the palm trees masked out. If so, duplicate the footage, apply mask on the top layer(so that you see the street and trees only) and color correct the layer below for the sky. There's a number of ways to go based on how much info is in your source footage, but from the looks of it I would try to tint it blue and see if I can bring in more mid tones. So basically a color correction job (I highly recommend Magic Bullet Colorista)

Tudor "Ted" Jelescu
Senior VFX Artist
Bucharest, Romania
http://www.ennstudio.ro


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Dave LaRonde
Re: Motion tracking issue
on Jun 3, 2010 at 4:38:28 pm

[paolo mugnaini] "...from what I understood it was a very bad day to shoot and there was no other choice but to shoot it and they wanted to be able to see the interior of the car which it would have disappeared if exposed to the clouds and it shot with a consumer camcorder. "

....um, not really.

If that's a LOCKED-DOWN shot -- and I mean the camera doesn't wiggle or jiggle one bit -- you could have composited two shots: one exposed for the sky, and one exposed for the car interior. The task then becomes a process of masking around a car interior that never moves, revealing a nicely-exposed sky. This is a far easier thing to accomplish than dealing with overexposed footage.

Sometimes you can't get everything you need in just one shot, a shot that accomplishes nothing. Whoever got the shot wasn't thinking like an effects guy.

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


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paolo mugnaini
Re: Motion tracking issue
on Jun 3, 2010 at 4:45:21 pm

Ted..>Thanks!

Dave...yes you are correct and thanks!



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