8

Camera Track e r: Movie Stepper Rollout 653
You can also reduce feature tracking times by
makingtheinnerfeatureboundsboxinthegizmo
as tight as you can w hi le st ill retaining a couple of
pixels worth of surrounding contrast. Search t imes
are proport ional to the feature b ounds box size.
Track Range
Use these when a feature moves off-screen or is not
visible in the Movie window.
Set Start—Setsthestartoftheactiveframerange
for a tracker .
Set Stop—Sets the end of the active frame range
for a tracker .
You use the Set Start and Set Stop buttons in the
Setup box together with the Movie Stepper rollout
to set the active range. Pressing the buttons will
set the start or stop point at the frame currently
shownintheMovieStepper.
Tracke r Keyframes a nd Position Data
Any time you manually position a tracker gizmo,
suchasatthefirstframeoratsometrackingerror,
youcreateaspecialkeyframeposition.Thetracker
never attempts to reposition these keyframes, but
uses them as start points for the frames that follow
them up to the next key frame. At keyfr a mes, you
can adjust the position and the feature or search
bounds.
During tracking, the selected feature at a keyframe
is sampled and that feature becomes the search
target for subsequent frames. Using any adjusted
search bounds up unt il the next key frame,
provides the start point, target feature, and search
bounds box for the f rames that follow.
Thepositiondataforeachframeineachgizmo
canbeoneofthreepossibilities:
•Akeyframedefininganewstartposition,target
feature image, and search bounds box.
• A tracked position.
•Unknown.
All f r ame positions except the first are initially
unknownandwillbenamedastrackingproceeds
or gizmos are positioned. When you manually
set a keyframe, any previously tracked positions
followingthatkeyframeupuntilthenextkeyframe
are deleted and so become unknown. The
Complete Tracking button in the Batch Track
rollout searches for unknown positions in the
currently enabled trackers and tracks those f r ames.
The Check Status button in the same rollout
checks for any currently unknown positions as
well as tracking errors. See
Batch Track Rollout
(page 2–655)
.
Camera Tra cker: Mov ie Stepper
Rollout
Utilities panel > Utilities rollout > More button > Util ities
dialog > Camera Tracker > Movie Stepper rollout
The Camera Tracker ut i lit y’s Movie Stepper rollout
browses through the movie during the tracking
phase either to set start and stop frames, to review
tracking results or to manually perform a track
over a sequence of frames. The Movie Stepper
rollout consists of a frame counter, a set of stepper
buttons, and some option check boxes.