Adobe After Effects - Manual (Page 175)

Alpha Add
Note:
Luminescent Premul
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Note:
Drop Shadow
Inner Shadow
Outer Glow
Inner Glow
Bevel And Emboss
cause more transparency than the darker pixels. Painting with pure white creates 0% opacity. Painting with pure black produces no change.
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.
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.
Prevents clipping of color values that exceed the alpha channel value after compositing by adding them to the composition.
Useful for compositing rendered lens or light effects (such as lens flare) from footage with premultiplied alpha channels. May also improve results
when compositing footage from matting software from other manufacturers. When applying this mode, you may get the best results by changing
interpretation of the premultiplied-alpha source footage to straight alpha.
Layer styles
Photoshop provides a variety of layer styles—such as shadows, glows, and bevels—that change the appearance of a layer. After Effects can
preserve these layer styles when importing Photoshop layers. You can also apply layer styles in After Effects and animate their properties.
You can copy and paste any layer style within After Effects, including layer styles imported into After Effects in PSD files. Richard Harrington
provides a video tutorial on the
Creative COW website that shows how to bring a library of layer styles from Photoshop into After Effects so that
you can use, modify, copy, and paste the custom layer styles in After Effects.
In addition to the layer styles that add visual elements—like a drop shadow or a color overlay—each layer’s Layer Styles property group contains
a Blending Options property group. You can use the Blending Options settings for powerful and flexible control over blending operations.
Though layer styles are referred to as effects in Photoshop, they behave more like blending modes in After Effects. Layer styles follow
transformations in the standard render order, whereas effects precede transformations. Another difference is that each layer style blends directly
with the underlying layers in the composition, whereas an effect is rendered on the layer to which it’s applied, the result of which then interacts with
the underlying layers as a whole.
When you import a Photoshop file that includes layers as a composition, you can retain editable layer styles or merge layer styles into footage.
When you import only one layer that includes layer styles, you can choose to ignore the layer styles or merge layer styles into footage. At any
time, you can convert merged layer styles into editable layer styles for each After Effects layer based on a Photoshop footage item.
After Effects can preserve all layer styles in imported Photoshop files, but you can only add and modify some layer styles and controls within After
Effects.
For details about each layer style and its properties, see Photoshop Help.
Layer styles that you can apply and edit in After Effects
Adds a shadow that falls behind the layer.
Adds a shadow that falls inside the contents of the layer, giving the layer a recessed appearance.
Adds a glow that emanates outward from the contents of the layer.
Adds a glow that emanates inward from the contents of the layer.
Adds various combinations of highlights and shadows.
Use the Bevel And Emboss layer style rather than the Bevel Alpha effect if, for example, you want to apply different blending modes to the
highlights and shadows of a bevel.
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