Types of Trackers

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‌Types of Trackers

SynthEyes supports the following types of trackers, as controlled by a dropdown button on the tracker control panel:

- pattern-match trackers ,

- white and black spot trackers,

- symmetry trackers,

- planar trackers, and

- and neural net trackers.

Pattern matching trackers are the most commonly used type for supervised tracking: they allow any feature that you can see to be tracked, since you position the tracker directly. SynthEyes searches subsequent images for the same image found within the tracker's interior (specified by its size and aspect). Pattern match trackers can be thrown off by scenes with rapid overall illumination changes, especially explosions and strobe lighting. For such scenes, set up the image preprocessor to perform high- pass filtering.

Spot trackers are produced by auto-tracking, though you may use them as well. As the name suggests, they look for the center of a white or black spot, positioning the center of the spot exactly at the center of the tracker. If you have a suitable feature, they can be tracked easily through the shot without drift. You'll need to adjust the size of the tracker properly through the shot: if the tracker is too big, surrounding imagery will influence the tracker position; if it is too small, the spot will jump around between small local maxima within the tracker. Note that typically there are many small local spots (local maxima) that might be selected—SynthEyes uses a preliminary low-resolution

pattern match to identify the right spot from frame to frame. As with straight pattern match trackers, this preliminary match can be thrown off by adverse conditions in the shot, hence your supervision.

Symmetry trackers look for locations where the interior of the tracker is symmetric—it looks the same when it is reversed top to bottom and left to right simultaneously. This encompasses spots as well as other more complex patterns with shapes similar to X's, H's, and often (weaker) nearly-symmetric features such as C's and U's.

Neural net trackers use advanced “brain-based” processing to try to figure out the right location, using the same technology used to identify facebook pictures and drive autonomous cars. While they are generally similar to other tracker types, see the separate section on Neural net tracking for more details.

Planar trackers are substantially different, because they track a whole rectangular (in 3-D) region, not a single point feature. They are pattern-match trackers on steroids, if you like. For clarity, planar trackers are described in the separate 3-D Planar Tracking Manual (available from the SynthEyes Help menu).

When dragging a spot or symmetry tracker in the camera view, tracker control panel mini-view, or SimulTrack view, the tracker position will automatically snap exactly to nearby peak locations, so that key locations can be set precisely to match subsequent tracked frames. In the tracker mini-view and SimulTrack view, an X marker will appear to show the nearest potential tracker location. If required, you can suppress snapping by holding down the ALT/Command key while dragging.

The spot trackers created by autotracking are tracked only to the nominal shot resolution, while spot trackers that are supervised are tracked at a higher resolution controlled by the high-resolution setting at bottom of the Track menu (typically 4x resolution). So you'll see some small off-centering in the X tracker location when viewing autotrackers with the tracker mini-view or SimulTrack. A simple re-track of auto- trackers will not eliminate those differences, because the positions are all keyed directly. To re-run the autotrackers at the higher resolution, use a Fine-Tune with a Key Spacing of one (ie without converting to pattern matches).

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