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2D/3D-Effect - how to apply tracking data?

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Jan Wulf
2D/3D-Effect - how to apply tracking data?
on Jul 25, 2016 at 10:54:33 pm

Hello kind people! :)

I have a problem with creating my desired visual effect in After Effects and hope to get some ideas how to do it.
The actor of my scene is supposed to "take a piece out of the world". To illustrate, I exported some stills / mocked the desired result with Photoshop.

== The Shots ==
I have a plate-shot with a box of cornflakes standing on the table:

And then a shot in which the actor reaches for a piece of green and lifting it:

(Please ignore the second piece of green lying on the table in this shot, it is irrelevant to this effect/question.)

== What the result should be ==

He is supposed to reach for the box ... (please ignore the badly masked layer ;) )

... and (accidentaly) take a "2-dimensional" piece out of the world: (I mocked it (also badly) with PS so you get the idea)

(Some Cornflakes fall to the ground behind it, but that is irrelevant to the effect itself.)

== What I have ==

So far I created a tracker with 4 tracking points (I have the German version installed, so not sure what the name is in english, sorry) to track the piece of green.
That works fine so far: When I simply apply the tracking data to a color matte, it moves nicely, the movement seems okay and of course I know how I would apply keying / a mask to put the actor's hand properly above the moving matte - that will be no problem.

But I don't know how to get the actual part of the plate shot (the box of cornflakes and some of its background) to move as I wanted to - or if it's possible at all. When I simply apply the tracking data to the plate shot (which creates the animated Corner Pin effect), of course the whole thing gets distorted:

And when I mask the area around the box before, it's of course wrong as well because there's only something small left:

Does anybody have an idea, how I could achieve the desired result at this point? Would I need to use the tracking data differently (just for movement of the plate-layer and create a mask on that for the part around the green piece) or something?

I appreciate any ideas/hints/suggestions and hope, I was able to explain my problem/plan comprehensibly.

Thank you,

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Kalle Kannisto
Re: 2D/3D-Effect - how to apply tracking data?
on Jul 26, 2016 at 6:26:10 pm

I believe all you need to do is to cut that specific piece from the footage (in Photoshop) taking everything else out, meaning crop it so that there are no transparent pixels around the piece, straighten it out so it fills a rectangle, import that piece in AE and apply the corner pin.

The transparent areas in the layer is what is messing this up, which is why you can't simply mask it.

If you need the piece to be animated, you would need to do this in AE: precomp a copy of the layer, resize the comp to that size, then first use corner pin to straighten the piece to rectangular, and finally apply your tracked corner pin.

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Jan Wulf
Re: 2D/3D-Effect - how to apply tracking data?
on Jul 28, 2016 at 10:10:07 am

Awesome, thank you! The idea of first corner-pinning the part to a rectangle was what I wasn't able to come up with. :) I think I can go on from here...

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