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Inverted Mask Edge Problem

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Max JacksonInverted Mask Edge Problem
by on Sep 2, 2011 at 9:42:34 pm

Hi CC,

I'm having the classic add/subtract mask line issue where the aliasing is not including the edge.

I've seen a tutorial on how to fix this, been doing searches, but I can't seem to find the quick fix to solve this edge problem. I can move one of the masks a pixel over, but then I'm doing twice the roto work which would be really hairy.

Does anybody know of a tutorial that deals with this? I believe have to use masks as it's in reference to keying to separate sections of chroma key noise.

Thanks for any suggestions!


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ben g ungurenRe: Inverted Mask Edge Problem
by on Sep 2, 2011 at 10:42:41 pm

Not sure I understand the problem exactly, but if your masks are on more than one layer then you can set those layer's blend modes to "Alpha Add" and precomp your masked stuff. I do this all the time when keying, and I use expressions to link all the masks on each layer -- all I change is the mask blend mode (this one adds, this one subtracts, etc)

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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Max JacksonRe: Inverted Mask Edge Problem
by on Sep 2, 2011 at 11:00:49 pm

Yes! That's the answer. I remember it now.

However, I'm trying it now and it's not working. Could it be because I have a Matte Choker on it? That would affect it's ability to cover the edge I would think, right?

Does that sound familiar?


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ben g ungurenRe: Inverted Mask Edge Problem
by on Sep 2, 2011 at 11:10:44 pm

Yea, a matte choker will mess things up. Here's a common layer order that I use:


1. Keyed footage (Keylight) with display set to "Corrected Source" (without any alpha, in other words). I check the "Preserve Transparency" box (between the mode drop-downs and the trackmatte dropdowns)

2. ADJUSTMENT LAYER: Matte chokers, other matte tools, etc, as needed

3, 4, 5, 6 as needed: Keylight keys, masked exactly the same (except for mask blend modes). As long as the blend mode is Alpha Add, you can tweak the mask's shape, feather, and expansion -- as long as the masks are the same for all the layers. (I like to use expressions for this, having one of the layers be the "Master Mask" and the others referencing it.)

BOTTOM: Nothing. The background must be empty, so that the Preserve Transparency layer and the Chokers on the adjustment layer will work....

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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Max JacksonRe: Inverted Mask Edge Problem
by on Sep 2, 2011 at 11:26:53 pm

I see, okay cool. So matte chokers work best in an adjustment layer for this standard use of add/subtract keying/masking.

My situation's kind of odd as I'm using the Matte Choker to lighten up the key. I'm currently working on something that looks a lot like the Apple iPod silhouette ads. Except we did a real lousy job of keying (with blue material no less). We didn't use enough light so there's a lot of dirt.

Hence, the need for the double add/subtract method to portion out the good, the bad, and the 'my God what were you thinking?'.

Thanks Ben! :D


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