Game Development Reference
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practice removing the screen. The problem was that I usually
practiced this without a layer underneath the layer I was keying.
Using a black background is usually not the best way to see prob-
lems in your key. Instead, use a color that contrasts strongly with
the color of the green screen so that you can easily see any prob-
lems. You can also enable the transparency grid at the bottom of
the Composition panel to check your key. It's a good idea to pre-
view your key against a variety of backgrounds, just in case you
missed some stray pixels that don't belong.
Creating a Garbage Matte
Most of the time when keying a subject to remove a back-
ground, you don't need the entire layer. So, the typical process is
to create a loose mask, called a garbage matte, around the sub-
ject. It should be close enough to the subject to remove junk in
the frame, such as boom mics and any other equipment in the
shot, leaving only the blue or green screen. But it should not be so
close that the subject moves outside of the matte at any point in
time. Or, if they do move outside of the garbage matte, then you
must animate the mask to follow the subject so that it is always
completely encompasses the subject.
Let's say that I wanted to key out the background, and isolate
myself in the shot seen in Fig. 10.3.
Figure 10.3 The shot I want to
pull a key from.
M y fi rst step would be to create a mask that would get rid of
all the background stuff—the stuff I know that I don't want in the
fi nal result. This makes it so much easier for the keying effect to
remove the background. Even if the entire background was made
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