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How to replace this green screen?

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Josh Pigford
How to replace this green screen?
on May 24, 2012 at 3:32:56 am

Doing some test shots for an upcoming shoot and trying to figure out how I'll pull this off in AE.



What I ultimately need to do is replace the green screen with a video. But I'm having trouble narrowing down how to replace the footage effectively.

My current process:
1) Track the green screen in Mocha
2) Export the shape data from Mocha to a mask of the source footage in AE
3) Export the corner pin data from Mocha and apply it to the replacement footage

Is that the best way to handle this? Or is there some more efficient way to handle it?

Possibly worth noting, those white cards that are covering up parts of the green screen footage will actually be place on top of the green screen during the shot.

The real footage will be really well lit and shot at 4K, so I'll have solid footage for keying and tracking.


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Tudor "Ted" Jelescu
Re: How to replace this green screen?
on May 24, 2012 at 8:07:16 am

Will the camera move or will it be a locked shot?
Base on that and on how complex the move is you may want to use a 3d tracker.
One other thing to consider is animating the cards that come on top in post.

Tudor "Ted" Jelescu
Senior VFX Artist


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Josh Pigford
Re: How to replace this green screen?
on May 24, 2012 at 12:45:00 pm

Camera will be moving all over the place (up, down, left, right, tilt, pan, etc). It'll be a huge scene with dozens of these little green cards I'll need to track and key.


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Tudor "Ted" Jelescu
Re: How to replace this green screen?
on May 24, 2012 at 1:03:31 pm

I would choose a 3d tracker then for this.
I am still wondering why not build everything in AE... what would be the advantage of shooting? You can have a lot more control in post over the camera moves, timing of elements and so on.

Tudor "Ted" Jelescu
Senior VFX Artist


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Josh Pigford
Re: How to replace this green screen?
on May 24, 2012 at 1:16:43 pm

The entire shot (over 3 minutes long) will make use of literally hundreds of photos. Some will be plain photographs, others in frames...all set down by various hands. It's not possible to setup the entire shot in AE (or even a 3D program like Cinema 4D).

So, I definitely need to figure out how to properly track/mask/key this stuff.


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Tudor "Ted" Jelescu
Re: How to replace this green screen?
on May 24, 2012 at 4:06:45 pm

Could it be possible to shoot the hands laying down photos on chroma and build the whole ensemble in post? It may take a bit of planning but I still think you have more options and control.

Tudor "Ted" Jelescu
Senior VFX Artist


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Josh Pigford
Re: How to replace this green screen?
on May 24, 2012 at 4:08:03 pm

Not possible. Shoot is tomorrow morning. Don't have time to change all that.


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Tudor "Ted" Jelescu
Re: How to replace this green screen?
on May 24, 2012 at 7:23:21 pm

Just as a safety, shoot a locked down shot of all hands coming in and out of the frame and laying down the cards. This way you'll have at least a safety if the rest does not work as planned.
Mocha is a great tracker and it may work if you can split the piece in pieces, but for one long moving shot I maintain my initial opinion- a 3d tracker will be best.

Tudor "Ted" Jelescu
Senior VFX Artist


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John Kaley
Re: How to replace this green screen?
on May 24, 2012 at 2:01:53 pm

Since everything is on a 2D plane, I'd definitely use Mocha for the tracking. You won't need the shape data; only the corner pin data, as your green screen will cut the shape for you.

Be careful not to put your tracking markers in the shadows of the overlying pictures or you'll have to paint the shadows back in. Mocha will not need that may tracking markers either; the five markers in the center are more than enough.


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Josh Pigford
Re: How to replace this green screen?
on May 24, 2012 at 2:58:33 pm

I don't see how I can get around NOT needing the shape data. Adjusting the key color will almost certainly affect the rest of the shot, so I'll have to mask all non-chroma footage for each green screen layer so that it doesn't screw up the color for everything.


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John Kaley
Re: How to replace this green screen?
on May 24, 2012 at 8:09:08 pm

I assume you're planning on pulling a key from the green card; this will create your mask. So I'm not sure what you mean by "adjusting the key color". You can simply garbage mask anything else in the scene that happens to be close to your green key color. You can also mask out the tracking markers after you've pulled the data from them.


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Josh Pigford
Re: How to replace this green screen?
on May 24, 2012 at 8:19:00 pm

This is what I'm referring to:



You can see where, to get a decent key, I had to bump up levels a good bit. I've got a garbage mask already (as you can tell), but I don't know how I'd get around this without pulling shape data out of mocha to mask every green area.

Maybe I'm missing something obvious though...


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Roland R. Kahlenberg
Re: How to replace this green screen?
on May 25, 2012 at 1:21:10 am

You will need to export mocha shape as well as the corner pin data. In AE, the mocha shape goes into a solid which will then be used as a track matte layer. mocha shape only contains shape & transform data - ie no perspective information.

mocha's Corner-pin data will be used on the fill layer (ie layer beneath the track matte layer).

BTW, mochaAE/mochaPro V3 includes 3D camera solve. Go here to view a related tutorials.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Roland R. Kahlenberg
Re: How to replace this green screen?
on May 25, 2012 at 1:29:26 am

BTW, you do not need markers on the edge of the cards - they just make it more difficult to remove. Just place markers in the middle of the cards. This is ideal since the card is a single plane. Your mocha spline just needs to encompass the markers while the surface area can be a larger area than the spline.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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