Graphics Reference
In-Depth Information
Fast vector-based motion blur is easy to
add in the compositor, and a few changes
to the default values will produce excel-
lent results. The Add
Vector
Blur node, shown in Figure 15.57, requires
three inputs: an image, a Z channel, and a
Speed channel. These correspond to the
regular RGB (
>
Filter
>
Alpha), Z and Vec passes
in the Render Layers panel. For simple
composites, all that is required is to con-
nect the familiar sockets on the Input and
Vector Blur nodes, then send the image
output either to a Composite node (if it
is the last item in the node tree) or to the
next input. The example in Figure 15.57
shows this simple confi guration.
Figure 15.57
A basic motion blur setup
For most cases, you will be able to achieve good results by raising the Samples value to 64 and enabling the
Curve option. S amples increases the quality of the blur and can go as high as 256 for objects that are mov-
ing very quickly. C urve allows the node to generate a curved blur for objects that move in an arc during
the course of the frame. Without this option, a ball that is fl ying in a circle will generate a straight-line blur
between its beginning and end points on each frame instead of a proper curve.
The diffi culty in using motion blur arises
when objects from different Render Layers
have motion blur. In those cases, you will
need to blur each Render Layer individu-
ally. There are two ways to do this. The
fi rst method, and the one that produces
the best results, is to apply the blur after
the element has been combined with the
rest of the scene. Figure 15.58 shows this
technique. Note how the “mom” Render
Layer is added to the background, then
blurred, before proceeding to the next.
The danger of this method is that a mov-
ing object from one Render Layer can
blur the already-blurred streak of an object
added from an earlier Render Layer.
Figure 15.58 Building up layers of motion blur
The slightly less desirable way to do this, and one that will prevent the kind of artifacts just mentioned, is to
add each Render Layer into the growing composite, then blur them in order of addition. Figure 15.59 shows
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