Here are some touch points if you are shooting a scene and will later track an actor's head or other body parts for a full 3-D rigid-body track.
- Use a reasonably tight shot of the head: the smaller the actor's head in frame, the harder to track it.
- Use a shorter focal length lens—by shooting from up close there will be more perspective to get 3-D.
- Keep shutter time short to avoid blurring tracking dots into oblivion.
- Maintain accurate focus.
- If you are tracking multiple heads, or a head plus the background camera, consider how you will set their relative scale, ie a distance measurement for each. This is impossible to determine from a single shot.
- Use as high-resolution source as you can; downsample after tracking.
- Try to maintain more than a dozen trackable points on the head at all times.
- Trackers must be on parts of the head that don't move relative one another—corners of the eyes, nose, ears, ...
- Don't use trackers on the jaw, mouth, eyebrows, or mobile portions of the cheeks.
- Consider tracking tiny facial details on the face and head.
- Consider drawing some dots on the actor, especially in areas that will later be replaced.
- Consider whether a 3-D mesh model of the actor's head is available; this will enable better results under more adverse conditions. If footage from enough angles is available, you may be able to customize a generic 3-D head model to match.
- Usually supervised tracking is required.
You can track the moving features of the actor's face independently using SynthEyes's motion-capture capabilities, if you use two cameras. See the manual.