2D Tracking - Nuke 101: Professional Compositing and Visual Effects - page 204

Tracker Node Basics
Nuke's Tracker node is designed to do the two parts of tracking: accumulating position
dataand applying positiondata.TheTrackernodeisopenenough,though,sothatyoucan
use the accumulated data in many other nodes by using a linking expression.
In most applications, including Nuke, a tracker point is built out of a tracking anchor, a
pattern box, and a search area box. The tracking anchor is a single point that collects the
position data for the pattern box. The pattern box defines the group of pixels to follow
from frame to frame. The search area box defines where to look for those pixels in the
next frame. The tracker point's controls that define these three elements are shown in
FIGURE 5.1 .
Figure 5.1. Tracker point anatomy
To track, you need to choose a well-defined pattern—one that has different colored pixels
that don't look like other things close to it in the frame—and set the pattern box to engulf
that pattern. Then you gauge how far the pattern is moving from frame to frame and set
the search area box to cover that part of the image. The tracking anchor is normally auto-
matically set.