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Tracking from the Compositor

Tracking

Four-Point Tracking

 

Effects > Tracking and Stabilizing > Tracking > 

One-Point and Two-Point Tracking

In both one-point and two-point tracking, you select the object that follows the pattern on the back clip by assigning the tracking data to its axis in Action.

For one-point tracking, you use only one tracker (usually Tracker1) to generate position information. For two-point tracking, you use a second tracker (usually Tracker2) to generate rotation and/or scaling information. The Stabilizer obtains this information by comparing the position of Tracker2 to that of Tracker1.

Before you select the two reference points on the back clip, note the task of each tracker:

• Tracker1 follows the horizontal and vertical translation of the reference point. You should position Tracker1 over a point on the pattern that you want to track.
• Tracker2 tracks the rotation and/or the change in size of the pattern. In the first frame, the rotation is always 0 and the scaling factor is always 100%. In subsequent frames, a rotation and/or scaling factor is added if the relative position of the two trackers changes. You should position Tracker2 over a point that represents the rotation or change in size of the pattern.

When you open the Stabilizer from Action for two-point tracking, you can select whether you want rotation information, scaling information, or both. The choice depends on the movement of the object to track and on the camera movement in the clip.

To perform one-point or two-point tracking in Action:

1. Load a front and back clip in Action.

   The front clip contains the object and the back clip supplies the pattern that you want to track.

2. In the Axis menu for the selected media, make sure that the motion path is disabled (Path button).

   
   

   (a)  Stabilizer button  (b) Stabilizer Option box  (c) Tracking Rotation Option box  (d) Tracking Scale Option box  (e) Motion Path button  

   NoteDo not move the axis from its default position at the centre of the image window before entering the Stabilizer, or else the tracking data will be overwritten. Use the offset axis to add an offset to the tracker movement instead.
3. In the Stabilizer Option box, select Track.
4. From the Tracking Rotation option box and Tracking Scale option box, set the tracking options.

   Select:	To:
   Rotation Off and Scaling Off	Do one-point tracking.
   Rotation On and/or Scaling On	Do two-point tracking.
   Rotation Inv	Invert the rotation data.
   Scale Inv	Invert the scaling data.

5. Click the Stabilizer button.

   The Stabilizer opens and the back clip appears.

   NoteIf the wrong clip appears in the image window, return to Action and change the back clip to the clip that contains the pattern you want to track. For more information, see Changing Media Clips.
6. Position the tracker(s) over the pattern(s) that you want to track, and click Analyse to generate the tracking data.
   NoteYou can fine-tune the tracking data if necessary. See Tracking Difficult Shots and Correcting Errors.
7. Once you are satisfied with the tracking, make sure the trackers you used are still active, and then click Return.

   The Axis menu in Action reappears. The tracking data is applied to the front clip.