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Tracking and keying iPad screen replacement

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Jakob Berglund
Tracking and keying iPad screen replacement
on May 27, 2011 at 11:46:22 am

Hi everyone,

Tomorrow I'll start shooting and editing a presentation of a new iPad App. Practically all of the shots will be of an actor holding an iPad, which I'll screen replace in post.

I'm pretty new to this though, and have some issues and thoughts I hope you guys can help me out with.

My first instinct is to use a digital image as green screen (just open up a green full screen image in the iPad), shoot the entire thing, planar track the images using Mocha and corner pin the new screen. But can the use of a digital image as chroma be problematic? The iPad screen is very bright and leaves a lot of green spill on the actors fingers. Is it wiser to just stick a piece of green paper on the pad? Or skip the keying entirely and just rotoscope away the fingers and hands?

I'm using a 5D Mark II during the shoot. We are doing it in a natural environment without controlled lighting.

Any suggestions?

Thanks in advance!

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Brian Charles
Re: Tracking and keying iPad screen replacement
on May 27, 2011 at 2:09:55 pm

I wouldn't bother with green screen or any chroma key method.

Mocha may be all you need, it does a remarkable job with the sort of track you describe.

Here's an IPhone screen replacement tutorial:

If its a difficult track you may want to add tracking markers to the iPad. Then roto the fingers and Mocha Shape (comes with AE 5) can help there as well. Check the Imagineer website for some tips on roto in Mocha.

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Roland R. Kahlenberg
Re: Tracking and keying iPad screen replacement
on May 27, 2011 at 2:20:44 pm

Shoot once with a black screen from which you can easily grab a still for use as a reflection pass for the composite. Try to get a closeup of the screen so that you can move it about if needed when compositing the reflection.

If you're not going to have a lot of fingers moving across the screen, then simply shoot everything with a black screen. For lots of finger movements, I'll go with a green backing - pick a hue that minimizes the amount of spill.

If a green screen is going to be used, I'll put an image (photo) into the middle of the green screen (or an area where there is either zero or minimal encroachment from one of more fingers). The image is to provide a texture area to allow mocha to better track the screen.

Lots of ideas there for you to work on. Best to test out the preferred setup and workflow.

Good Luck!

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Alex Raccuglia
Re: Tracking and keying iPad screen replacement
on Jul 29, 2015 at 4:33:34 pm

Have you considered It can help with finger tracking on iPad surface, and it gives you keyframes in After Effects format.

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