Alpha Mask Edges

#1

Hey guys,
I was hoping someone could help me figure out what’s going on with the edges of my masked compositions–

I’ve set up a comp with layers like:

Black Vector of Leaf (layer1) [visibility off]
White to Black Gradient Solid (layer2) [multiply] [alpha]
Black Vector of Leaf (layer3) [visibility off]
Leaf Texture JPG (layer4) [alpha]

I get just what I’m hoping for–the texture cut into the shape of the leaf vector with a gradient overlay. The only problem is, when I drop this comp into my main comp, it has a white outline around it.

I’m not sure what would cause that :curious: . Is there a way to play with anti-aliasing within AE?
Thanks!!!

#2

See this page for more information. Here’s an excerpt:
"Alpha Add
Composites layers normally, but adds complementary alpha channels to create a seamless area of transparency. Useful for removing visible edges from two alpha channels that are inverted relative to each other or from the alpha channel edges of two touching layers that are being animated.

Note: Sometimes, when layers are aligned edge-to-edge, seams can appear between the layers. This is especially an issue with 3D layers that are joined to one another at the edges to build a 3D object. When the edges of a layer are anti-aliased, there’s some partial transparency at the edges. When two areas of 50% transparency overlap, the result is not 100% opacity but 75% opacity, because the default operation is multiplication. (50% of the light gets through one layer, and then 50% of the remainder gets through the next layer, so 25% gets through the system.) This is like partial transparency in the real world. But, in some cases, you don’t want this default blending. You want the two 50% opacity areas to combine to make a seamless, opaque join. You want the alpha values to be added. In these cases, use the Alpha Add blending mode."

#3

I see, thanks!

Alpha Add completely removes the effect of overlaying a gradient, tho (obviously, since it was set to multiply first! ha). Am I setting the wrong layer to Alpha Add? Again, I’ve only got 4 layers for each one of these little comps-- Two of the mask vector, one for the solid w/ gradient(/ramp) and one with the texture.

:frowning:

#4

Yes, you are degenerating your Alpha. Mathematically perfectly logical and expected. Either unmultiply your Alpha before doing the blending in the sub-comp or force-cleanup the whole thing by using your leaf again as a 5th layer and assigning it as Stencil Alpha.

Mylenium

#5

I see! Thanks so much.

#6

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