Mask Expansion question

[First Last]

I never noticed that before and I can’t figure out why it does that.

Is the expansion absolutely necessary? What’s the effect you’re looking for? There’s probably a work around.

Production Associate
Bend, Oregon, United States

[Riccardo Sinti]

Well, it’s just easier to use expansion instead of mask shape sometimes.
And sometimes you have lots of mask shape keyframes and you just want to expand the mask without tweaking all those shape keys.

Thank You

[Todd Kopriva]

Increasing mask expansion is not the same thing scaling a mask. Scaling preserves shape. Expansion says “Make it bigger by growing outward from each point a certain number of pixels.”

For each point on the original mask path, imagine a circle radiating outward by the number of pixels by which you’re expanding.

I’ve embedded an image below that should show what I’m talking about. The white rectangle is the original mask path. The red circles indicate the expansion radius. Note how these circles define a sharp inner rectangle, which is what you get with a negative expansion; and they define a rounded outer rectangle, which is what you get with a positive expansion.

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Todd Kopriva, Adobe Systems Incorporated
putting the ‘T’ back in ‘RTFM’ : After Effects Help on the Web
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[Curt Needs]

It would be a nice feature if we could have the option to expand a mask and keep the points. Since we don’t have a Mask Scale in the drop down, it would be nice to have the option to use Mask Expansion and click a box on whether we want it to expand as you describe it or scale as most people seem to want it to do.