Sky replacement question

[Thilo-]

Fairly new to after effects.
I create a ramp gray mask to replace a washed out sky with a blue solid. It keys the sky fine, but there is part of a guy's shirt that is white which it won't differentiate as non-sky. How do I tell it to not key out that small area without going frame-by-frame and coloring the mask with black?
I'm sure there's many ways to do this, any suggestions are appreciated.

[ProfessorU]

You can use the mask tool. Exactly how you'll use it depends on how you've set up your key, but you can basically duplicate your source layer, trace a shape around the shirt but not the sky with the mask, and move the mask around with keyframes if necessary. Put your sky layer on the bottom. If you have a semi-stationary well-isolated subject, it's a five-second fix.

[robertwerden]

try this
http://www.videocopilot.net/tutorials/advanced_sky_replacement/

[Thilo-]

Okay thanks. I did that tutorial and the sky correction works fine.
I've tried for hours and I can't seem to get the mask to keyframe.. I use the tracker but all it does is track the footage within the mask and not the mask data itself. Is there a secret to easily tracking a mask area?

[Arson]

You cant apply a track to a mask.
But you can apply the mask to a layer (duped footage or a solid) and then apply the track to that whole masked layer.
It's a work around. That way you only have to keyframe the mattes shape over time and let the track deal with its position.

AE handles masks as a series of points connected by splines. To AE a mask has no movement it only has point deformations, because it is a part of a layer and not an actual layer.