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Next, we’ll drag a connection from the MediaIn1 node to the Tracker1 node to automatically
connect the source clip to the Tracker1 background input. This branches the output from the
MediaIn1 node to the Tracker node so that the Tracker1 node processes the image separately
from the rest of the node tree. This is not required, but it’s a nice organizational way to see that
the Tracker node is doing an analysis that must be referred to in a way other than a “physical
connection.
Branching a Tracker node to use to analyze an image.
A Simple Tracking Workflow
The Tracker node is the simplest tracking operation the Fusion page has, and while there are
several ways of using it, an extremely common workflow is to use the Tracker node controls to
analyze the motion of a subject in the frame with motion you want to follow, and then use the
resulting motion path data by “connecting” it to the Center parameter of another node that’s
capable of transforming the image you want to match move.
Positioning the Tracker Onscreen Control
When the Tracker node is selected, a single green box appears in the viewer, which is the
default onscreen control for the first default tracker that node contains (seen in the Tracker List
of the Inspector controls). Keep in mind that you only see onscreen controls for nodes that are
selected, so if you don’t see the onscreen tracker controls, you know you need to select the
tracker you want to work with. Loading the tracker you want to work with into the viewer is also
the safest way to make sure you’re positioning the controls correctly relative to the actual image
that you’re tracking.
If you position your pointer over this box, the entire onscreen control for that tracker appears,
and if you click the onscreen control to select that tracker, it turns red. As with so many other
tracker interfaces you’ve likely used, this consists of two boxes with various handles for moving
and resizing them:
The inner box is the “pattern box,” which identifies the “pattern” in the image you’re
tracking and want to follow the motion of. The pattern box has a tiny handle at its
upper-left corner that you use to drag the box to overlap whatever you want to track.
You can also resize this box by dragging any corner, or you can squish or stretch the
box by dragging any edge to make the box better fit the size of the pattern you’re trying
to track. The center position of the tracker is indicated via X and Y coordinates.
The outer box is the “search box,” which identifies how much of the image the tracker
needs to analyze to follow the motion of the pattern. If you have a slow-moving image,
then the default search box size is probably fine. However, if you have a fast-moving
image, you may need to resize the search box (using the same kind of corner and side
handles) to search a larger area, at the expense of a longer analysis. The name of that
tracker is shown at the bottom right of the search box.
Chapter – 73 Using the Tracker Node 1513