User Manual

Masks are single-channel images that can be used to define which regions of an image you
want to affect. Masks can be created using primitive shapes (such as circles and rectangles),
complex polyline shapes that are useful for rotoscoping, or by extracting channels from
another image.
A Polygon node’s mask seen in the viewer.
Each mask node is capable of creating a single shape. However, Mask nodes are designed to
be added one after the other, so you can combine multiple masks of different kinds to create
complex shapes. For example, two masks can be subtracted from a third mask to cut holes into
the resulting mask channel.
Fusion offers several different ways you can use masks to accomplish different tasks. You can
attach Mask nodes after other nodes in which you want to create transparency, or you can
attach Mask nodes directly to the specialized inputs of other nodes to limit or create different
kinds of effects.
Attaching Masks to an Image for Rotoscoping
There are two ways you’ll typically attach a Mask node, such as a Polygon node, so that it adds
an alpha channel to an image for compositing later in the node tree.
Using a MatteControl Node
The MatteControl node is the main node used for combining masks in different ways and
inserting the result into an image stream. The MatteControl node is attached downstream of the
node outputting the image you want to rotoscope. You’ll typically attach a Polygon or B-Spline
node to the Garbage Matte input of the MatteControl node to use the spline as an
alpha channel.
Feeding a Polygon node to a MatteControl node to perform rotoscoping.
To use this setup, you’ll load the MatteControl node into the viewer and select the Polygon
node to expose its controls so you can draw and modify a spline while viewing the image you’re
rotoscoping. The MatteControl node’s Garbage Matte > Invert checkbox lets you choose which
part of the image becomes transparent.
Chapter – 71 Rotoscoping with Masks 1438