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Sky Key

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Jennifer AdamsSky Key
by on Jun 24, 2014 at 12:17:58 am

Hey everyone,

I have a shot where I'm trying to do a sky replacement and it's turning out to be a little more difficult than I expected.
It's shot with a static camera, and the guy in the photo runs over to the little cabinet in the center, about 2.5 seconds.


There are pretty good edges here, but due to the low contrast, I'm having trouble creating a black-white luma matte for use with Colorama. Keylight and color range keys also haven't helped too much because of the transition to grey in the bottom part of the sky.

On the surface, it seems like a pretty easy shot to do this with... Can anyone share what he/she might do?

Thanks a lot!

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Jeff KayRe: Sky Key
by on Jun 24, 2014 at 1:16:28 am

First thought is to have a feathered mask parallel with the horizon such that only the top 3/5 or so of the frame actually has the sky replaced. At which point I believe you could create the matte via chroma.

While extremely lacking in fine tuning, I've had luck with using a chroma key rather than creating a matte for similar effects. Same process as green screen footage. Its one of those things that you should know very quickly whether or not it can be cleaned up sufficiently to be worth pursuing.

Its a pretty short shot, so you could always rotoscope.

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Todd KoprivaRe: Sky Key
by on Jun 24, 2014 at 4:27:00 am

I'd give the Roto Brush and Refine Edge tools a go. The Refine Edge tool is surprisingly good with things like those bushes.

Todd Kopriva, Adobe Systems Incorporated
After Effects quality engineering
After Effects team blog

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Erik LindahlRe: Sky Key
by on Jun 26, 2014 at 6:02:38 am

Or using mocha for a rough mask and refine edge in AE for edge perfections where needed.

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