Adobe After Effects - Manual (Page 136)

Editable Layer Styles
Note:
Merge Layer Styles Into Footage
Note:
Masks and alpha channels
Adobe Photoshop supports a transparent area and one optional layer mask (alpha channel) for each layer in a file. You can use these layer masks
to specify how different areas within a layer are hidden or revealed. If you import one layer, After Effects combines the layer mask (if present) with
the transparent area and imports the layer mask as a straight alpha channel.
If you import a layered Photoshop file as a merged file, After Effects merges the transparent areas and layer masks of all the layers into one alpha
channel that is premultiplied with white.
When you import a Photoshop file as a composition, vector masks are converted to After Effects masks. You can then modify and animate these
masks within After Effects.
Photoshop clipping groups, layer groups, and Smart Objects
If the layered Photoshop file contains clipping groups, After Effects imports each clipping group as a precomposition nested within the main
composition. After Effects automatically applies the Preserve Underlying Transparency option to each layer in the clipping-group composition,
maintaining transparency settings. These nested precompositions have the same dimensions as the main composition.
Paul Tuersley provides a script on the AE Enhancers forum that crops the precompositions to the size of their contents, while retaining their
correct position in the main composition.
Photoshop layer groups are imported as individual compositions.
It is often valuable to group layers into Smart Objects in Photoshop so that you can import meaningful collections of Photoshop layers as individual
layers in After Effects. For example, if you used 20 layers to create your foreground object and 30 layers to create your background object in
Photoshop, you probably don’t need to import all of those individual layers into After Effects if all that you want to do is animate your foreground
object flying in front of your background object; consider grouping them into a single foreground Smart Object and a single background Smart
Object before importing the PSD file into After Effects.
Photoshop layer styles and blending modes
After Effects also supports blending modes and layer styles applied to the file. When you import a Photoshop file with layer styles, you can choose
the Editable Layer Styles option or the Merge Layer Styles Into Footage option:
Matches appearance in Photoshop and preserves supported layer style properties as editable.
A layer with a layer style interferes with intersection of 3D layers and the casting of shadows.
Layer styles are merged into the layer for faster rendering, but the appearance may not match the appearance
of the image in Photoshop. This option doesn’t interfere with intersection of 3D layers or casting of shadows.
Photoshop video layers
Photoshop files can contain video and animation layers. After Effects can import these files like any other Photoshop files, either as a footage item
with all layers merged together or as a composition with each Photoshop layer separate and editable in After Effects. (Working with Photoshop
video layers requires QuickTime 7.1 or later.)
After Effects can’t import a Photoshop video layer that uses an image sequence as its source.
In After Effects CS6 and later, video layer support in Photoshop .psd documents has been removed. The layers will still have a duration, but won't
play. Animating layers with available properties in the Photoshop animation timeline (like Position and Opacity) are supported.
3D object layers in PSD files
Adobe Photoshop Extended can import and manipulate 3D models (3D objects) in several popular formats. Photoshop can also create 3D objects
in basic, primitive shapes.
After Effects CS5.5, and earlier, can import these 3D object layers in PSD files and render them using the active camera in a composition. (See 3D
132