2D and 3D

2D and 3D

The point of matching a 3D lens angle is typically to
composite in 3D over a 2D plate background. After Effects
helps this process in the following ways:
. A 2D background layer remains in place no matter
what happens with the camera and 3D layers.
. 2D adjustment layers set to comp size and default position
affect all layers below them, including 3D layers.
. 3D layers can use 2D Blending Modes (over 2D
elements, they obey layer order, and with other
3D elements, z-space depth).

You just need to be careful:
. Joining a 3D track matte to a 3D layer is almost never
the right idea, particularly with an animated camera. A
3D layer can use a 2D layer as a track matte; it is applied
just as it would be to a 2D layer. A 2D layer can use a 3D
layer as a track matte; the 3D perspective of the track
matte renders fi rst and is then applied. But combine
two 3D layers in this manner and the matte is fi rst translated
by the camera perspective once, then applied, and
then effectively translated again as the affected layer
also obeys camera perspective.
. Paradoxically, the only layers in After Effects that themselves
can contain true 3D effects are 2D layers (which
may nonetheless make use of the 3D camera perspective,

. A precomped set of 3D layers behaves like a single 2D
layer unless Collapse Transformations is enabled on
that layer. As described back in Chapter 4, this toggle
passes through all 3D data from the precomp as if those
layers lived right in the master composition.
Each point provides advantages provided you understand
how the image pipeline works.