Bidirectional Auto-Tracking

Track objects forward, backward, or through the full video, DICOM, or NIfTI sequence from one reliable seed.

Bidirectional Auto-Tracking propagates a verified object from one reliable seed through a temporal sequence. It supports full, forward, and backward runs so an annotator can start from the clearest frame or slice rather than the beginning.

Multi-object Auto-Tracking in a video sequence

Current Unitlab product visual: a selected group of objects is propagated while separate identities are preserved.

Bidirectional lesion tracking across a medical sequence

Current Unitlab medical visual: the same region is tracked across the sequence and remains available for expert correction.

Supported data and actions

Surface	Sequence unit	Current tracking actions
Video	Frames	Full annotation, forward, backward
DICOM	Frames or slices in the medical sequence	Full annotation, forward, backward
NIfTI	Volume slices / sequence positions	Full annotation, forward, backward

Supported temporal object geometries include bounding boxes, polygons, masks/brush annotations, and cuboids where the active editor and class allow them.

Choose a direction

Action	Range	Use it when
Track full annotation	Both directions from the selected frame	The best seed is in the middle and the complete sequence is required
Track forward	Selected frame to later frames	The object first appears clearly at or after the seed
Track backward	Selected frame to earlier frames	A later frame contains the clearest appearance

Backward is unavailable on the first frame. Forward is unavailable when no later frame remains.

Track one object

1

Choose a reliable seed

Navigate to the frame or slice where the object is clear, sufficiently large, and minimally occluded.

2

Create precise geometry

Draw the object using the project’s required class and geometry. A loose or incorrect seed propagates error.

3

Open the object action

Right-click the object or its selected timeline segment, choose Auto track, and select full, forward, or backward.

4

Monitor progress

The timeline displays the growing object track and keyframes. The object menu changes to Stop Tracking while a run is active.

5

Review discontinuities

Inspect occlusion, re-entry, camera cuts, fast motion, blur, scale changes, and crossings with similar objects.

6

Correct and continue

Edit the first unreliable frame, preserve identity, and rerun a shorter segment when necessary.

Track multiple objects

Hold Command on macOS or Ctrl on Windows/Linux and select several supported objects. Open Auto track, then choose the direction. Unitlab submits the selected objects together but writes each result to its own track.

Multi-object tracking preserves separate identities. It does not merge selected objects into one annotation.

Tracking versus interpolation

Question	Auto-Tracking	Interpolation
How intermediate labels are created	Model prediction	Geometry between manual keyframes
Best fit	Complex but visually trackable motion	Smooth change between known states
Main risk	Identity drift or confident false geometry	Missed non-linear motion or topology change
Review focus	Occlusion, re-entry, crossings, drift	Keyframe placement and transition shape

Video demo

Medical guidance

For DICOM and NIfTI work:

• start from the slice where the finding or anatomy is most distinct;

• verify every anatomical plane or synchronized view used by the project;

• inspect entry and exit slices carefully;

• correct partial-volume boundary drift;

• route clinically significant output through expert review;

• avoid treating propagation as volumetric ground truth without slice-level inspection.

Review a completed track

• Confirm the track begins and ends at the correct positions.

• Scrub through every transition around occlusion, re-entry, and motion change.

• Check identity when similar objects cross.

• Inspect geometry at representative zoom.

• Verify required dynamic properties at their change points.

• Confirm the object’s class and relations remain correct.

• Submit the item through the configured review route.

Full tracking is bidirectional propagation from one seed, not automatic approval. A reviewer must still verify the complete temporal range.

Troubleshooting

Symptom	Recovery
Tracking action is disabled	Move away from the first/last boundary or select a supported object
Track drifts after occlusion	Stop, correct the first unreliable frame, and restart from a new seed
Two identities swap	Split the run around the crossing and verify each object separately
Mask degrades over time	Add a corrected mask keyframe and rerun a shorter segment
Medical boundary disappears	Seed a clearer slice and review the entry/exit range under expert policy

Related guides

• Video Annotation

• Medical Annotation

• Validation and conditional logic