Game Development Reference
You'll probably want to follow along with this one, especially
seeing how different it is from the other effects in this chapter.
I'll be using the Inner Outer Key.aep project from the Chapter 10
folder of the exercise fi les. This project contains a comp that has
in it some footage of Seattle. The difference here is that I have cre-
ated two masks. You see, what we want to do here is to isolate the
city by removing the sky and mountains in the background. The
Inner/Outer Key effect allows us to use these two masks to help
us in this otherwise challenging task (Fig. 10.17).
Figure 10.17 The Seattle footage
with two masks applied.
The Inner/Outer Key effect functions similarly to the Extract
plugin in Photoshop. You fi rst create two masks on your layer—
one to specify areas which should absolutely completely opaque,
and then another mask that tells the Inner/Outer Key effect
where the border is between the stuff we want and the stuff we
don't want. So, in this case, we have one mask around the city,
and there's nothing in that mask that we don't want to keep. With
the other mask, we encompass everything we want to keep, but
we also encompass some of the skyline. This mask covers all the
stuff we want (the city), which includes some of the stuff we don't
want (the sky and background).
Apply the Inner/Outer Key effect to the Seattle layer. Instantly,
it uses the mask of the city (Mask 1) as the Foreground (Inside)
mask, and the mask of the city with its edges and some of the
sky (Mask 2) as the Background (Outside) mask. Even the default
settings remove the background fairly well. If you were to use
another keying effect (such as Extract or Luma Key), the white
pyramid in the foreground (which, coincidentally, is actually
called the Key Arena) would also have been removed (Fig. 10.18).
More Than Two
Key effect actually
allows you to
use several masks if you
need to. The additional
masks can be chosen in the
Additional Foreground and
areas. These extra masks
can be used to cut holes in
the masks, if needed.