2009

the error in favor of that tracker, reducing the distance between that tracker's
feature and object projection, while possibly increasing the error in other
trackers. If you bump weights on two or more features, the locking may
progressively lessen, since the algorithm distributes the improvements between
the high-weight trackers. Use weights of two to six to get a good lock.
Max Move/Frame Sets the maximum number of pixels that the tracked feature
moves from frame-to-frame over the entire tracking range and establishes an
initial motion search bounds box for newly created trackers. You can also set
this dynamically by adjusting the motion search bounds box directly in the
Movie window.
Resample on error You can make the tracker identify possible tracking errors
and you can use this during a manual tracking review and during actual
tracking to correct errors. Typical sources of error include frame-to-frame
jumps greater than the search bounds, image contrast changes, or a feature
changing shape over a sequence of frames, such as a corner might if the camera
moves by it. The error detector is controlled by measurement thresholds set
in the Error Thresholds rollout.
When you place a gizmo on some frame, a keyframe is created and a new
target feature image is sampled at that frame for searching in subsequent
frames. Turning on Resample On Error causes the tracker to detect errors
during tracking. If one is found, it backs up to the last good frame and places
a new keyframe there causing a new target feature image to be sampled at that
frame and continues tracking from that frame.
Subpixel Tracking Usually, an image feature won’t move an integral number
of pixels from frame-to-frame. With pixel-level tracking, however, the nearest
estimate for a feature center is always at a pixel boundary. This can lead to
camera match errors. With subpixel tracking you can zoom in on a feature
and position its gizmo within a pixel. This makes the tracker attempt to track
at that resolution by up-sampling the target image and search bounds, thereby
improving match accuracy.
You can turn on subpixel tracking selectively for each tracker by choosing a
level in the Subpixel Tracking drop-down menu on the Motion Trackers rollout.
This defines the resolution at which feature tracking is performed in the tracker
up to 1/32 of a pixel.
Two things happen when you select a subpixel level:
■ The grid over which you can position a tracker gizmo in the image window
is adjusted to the new subpixel level. You can position the gizmo can be
positioned inside pixels in zoomed views. You can zoom in on a tracker
gizmo by selecting it and pressing the I or O key to zoom in or out,
respectively.
Camera Tracker Utility | 3833