How can I extract and “flatten” footage that’s been tracked with Mocha to work with it directly in 2D?

[Alex Cameron]

Nah, I’ve used AE for quite a while but this is my first project that involves tracking.

The hand gets in the mix because it’s going to touch the wall, as the hand gets removed we see that there’s an imprint of the hand on the wall.

I’m definitely not thinking about hand keying as that would indeed be a nightmare, that’s why I wanted to use green screen. The blue thing is just to highlight the tracked area. I should have made it green as that’s what’s going to be the rough size of the green screen patch.

What I want, in the end, is to have a patch of green screen on the wall. Track it. Take that portion of the green screen, key it out so it’s just the hand and replace it with the hand imprint footage as the hand moves out of frame. It would be infinitely easier to key out and work with if I could actually look at that tracked section in 2D as opposed to having it move all over the place as it does right now.

[Alex Cameron]

Dave, I went back and edited my original post. I shot some quick footage to give a crude demonstration of what I’m looking for.

[Conrad Olson]

I think I know what you want to do. Are you basically trying to stablize your footage based on the planar track, so that the area of the wall stays rectangular in the same place all the time?

If that’s what you are trying to achieve then you need to create a reverse corner pin effect. The last time I tried to do this in After Effects I couldn’t find a simple solution, and I had to use expressions. But you should look in the export options of Mocha, to see if there is a stabilize or invert option.

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conradolson.com

[Conrad Olson]

I wasn’t quite clear, you would need to write the expressions inside a corner pin effect. The basic idea would be to pick the frame you want to use as your reference frame, then subtract the corner pin data, for every other frame, from that initial value, it should produce a reverse corner pin effect. You would need the same expression in each of the 4 points.

So something like this (this isn’t correct syntax)

cornerpin.point1.x.(reference frame)-cornerpin.point1.x.(currentframe)

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conradolson.com

[Alex Cameron]

Yes! This is what I’m looking for. Do you know if Nuke be able to pull this off? What would I even begin googling for, “reverse corner pin technique”?

[Conrad Olson]

I use Nuke a lot more than After Effect and it definitely works in Nuke. But I think Mocha has the inverse option for Nuke.

I know that if you do the planar track in Nuke X, with the native planar tracker, it gives you the option to stabilize when you create the corner pin node.

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conradolson.com

[Conrad Olson]

I’m in the middle of stuff right now, but if you can’t figure it out let me know and I will try and help you with the expression later.

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conradolson.com

[Alex Cameron]

Excellent, I’ll try this out with Nuke then. I’m assuming I can just attach a write node to the stabilized footage so I can toss it back to After Effects and achieve the effect?

Thank you Conrad!

[Ross Shain]

This is a very common mocha usage. You should not have an issue using the bundled mocha AE and After Effects to accomplish this effect.

BTW, mocha can export inverted corner pin or another option is the mochaImport+ script:
https://mamoworld.com/tools/mochaimport

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

[Alex Cameron]

I figured I was missing something obvious in Mocha. I looked around the program and still can’t find where to do it. Is it under the stabilize tab?

Thanks for your input!