Game Development Reference
are the most common and helpful, from
my experience. Just remember that this
effect isn't supposed to do anything visually
interesting. But it does extract the key data
that you need to control other properties in
other effects to help you make the most out
of the 3D data in your fi les. The other effects
in this chapter would not be as useful with-
out the information extracted by the 3D
Channel Extract effect. Note that you do not
always need to keep the 3D Channel Extract
effect applied to your layer unless you need
its results to be used with other effects. In
some cases, you might apply this effect to
learn what you need about your 3D chan-
nels, and then delete it.
Figure 2.7 With the 3D Channel drop down set to Object ID,
the Info panel will now display the object ID of objects in the
Composition panel that you click on.
The Depth Matte Effect
The Depth Matte effect can mask out (remove) objects in your
3D scene, based on their Z-depth or distance from the camera.
This is helpful in an infi nite amount of circumstances. Let's say
that we want to remove the background added by the 3D artist,
and replace it with a matte painting from another artist. Because
it's the background, it will have the largest Z-depth, making it
easy to remove with the Depth Matte effect.
Another trick with the Depth Matte effect, and one that we're
actually going use here, is to composite a 2D layer into a 3D
scene. This is a great skill to master. You'll probably want to follow
along with this exercise, so open up the Depth Matte.aep project
from the Chapter 2 folder of the exercise fi les. This project con-
tains a comp with the 3D garage scene and a video of my buddy,
Paavo (creator of www.malachyte.net) riding a unicycle. I've
already keyed out (removed) the background for you. We want to
make Paavo look like he's jumping around behind the table and
in front of the garage door (Fig. 2.8).
It might seem like the next step is to apply the Depth Matte
effect. But we fi rst need to rearrange the stacking order of these
layers. Drag the paavo balancing.mov layer below the garage_
zoom0170.rpf layer. Now, we can apply the Depth Matte effect to
the garage_zoom0170.rpf layer.
When we fi rst apply the Depth Matte effect in this project,
the results are completely black, or in other words, completely
masked out. This is because the default depth value is such that
the entire image is removed. Remember from our previous look at
this fi le (when we covered the 3D Channel Extract effect) that the
object that is closest to the camera is −89 pixels away. So a value