Graphics Reference
In-Depth Information
NOTE
If you remember from the Render Layer panel sidebar, objects that are not on the same layer as
a lamp will cast a shadow in a composite but will not receive illumination themselves. So, when
working with a setup like the one here, you must make sure that any key lamps are shared
across all layers that have objects that will receive light. In this case, it means the lamps in the
keylamps group should be on layers 1 and 2 for the characters, as well as 5 and 15 for the sets.
Now we must place the characters into the composite. In the previous example, an Alpha Over node worked
well. Trying that now, though, results in Figure 15.34. The problem is that the mother walks behind a portion of
the set where only her feet are seen, after which she disappears completely. We need to obscure the part of her
that should be hidden by the set. There are several ways to accomplish this, but the simplest, and the technique
used throughout The Beast , is to have the set act as an Alpha Mask for the character's Render Layer. This is done
by bringing up the character's Render Layer panel and
Ctrl-left mouse button clicking in each of the set's
layers. Figure 15.35 shows the result in the panel. Instead
of activating those scene layers for this particular Render
Layer, a black dot is added, indicating to the renderer that
objects in those layers should be used to generate Alpha.
When it is rendered, you get the full render but with an
Alpha channel properly knocking out anything in the
active layers that should be obscured. Now the Alpha
Over composite works properly. The raw Render
Layer is seen in Figure 15.36; the fi nal composite is in
Figure 15.37.
Figure 15.34 A bad composite, with the mother improperly
showing through the couch
Figure 15.36
The mother with Alpha knockout
Figure 15.35 The result of Ctrl-left mouse button clicking on
the set layers
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