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Hand animation can be a useful technique to create approximate tracking data when an object is occluded and the camera or object motion is very smooth, ie the camera is on a crane or dolly. It is not useful when there is a lot of vibration from a hand-held camera; in that case use Offset Tracking. Hand-animation is typically used
when there are few available trackable features, ie for object tracking. If there are many trackers, there's little incentive to go to the trouble.
Hand-animation uses the By Hand button on the tracker control panel. Suppose you're tracking a corner of a building and a pole passes in front of the corner. On the first occluded frame, turn on By Hand ( instead of turning off Enable).
Hint : Follow what By Hand does by using the Camera & Graphs view. Open it to your selected tracker with the U Pos, V Pos, Enable, and Hand Animated curves displayed.
The tracker graphic's search rectangle disappears, because it is no longer searching. If you run forward a few frames, the tracker remains stationary, no longer following anything: you're hand-animating!
When the tracked feature has reappeared, drag the tracker graphic back to the correct location, and turn off By Hand. The tracker is now tracking again, and if you continue to move forward into the shot it continues to track the feature.
What's interesting is what has happened in the middle, while By Hand was on.
The tracker is now linearly interpolated between the two endpoints. You can adjust the keyframe where you turned off By Hand, and the intervening path updates accordingly.
Furthermore, you can now add additional tracker position keys in the middle of the interpolated region to generate a desired trajectory. You can add keys by repositioning the tracker in the camera view on the appropriate frame, or in the graph editor using the Add Key mode. Either way, those keys are artistic decisions based on your tracking skill.
Warning : When you disable and later re-enable a tracker, you are saying you don't know what happens in between. That's safe. When you use By Hand, you are claiming you know what happened. If you aren't close to right, you will make the solution worse. Therefore, if you have many trackers, it makes sense to Enable and Disable. Hand-animation makes sense when there are few trackable features and every one counts.
The By Hand button is an animated track, so you can have multiple separate hand-animated regions during the shot, for example, each time a telephone pole goes by. And you can adjust the keys at any time. (It also works fine for forwards or backwards trackers.)
To better understand what it is doing, here's a brief explanation. When you change By Hand or set a tracker position key, a spline interpolation routine runs. It looks to see if the frame where a change was made is in, or immediately adjacent to, a sequence of frames where By Hand is on. If so, it acquires all the tracker keys in that region, plus the tracker position immediately before and after the sequence of frames.
Those keys are then interpolated and those positions stored on every frame that is not a key.
If you originally used Enable and re-enabled for a temporary occlusion, you can later go back and change it to use By Hand. Just go to the first occluded frame (which will be disabled), and turn on By Hand. SynthEyes will re-enable the tracker for the disabled section, and animate By Hand to be on for exactly the that previously-disabled section. Magic!
NOTE: You can animate enable on and off within a hand-animated section. Any tracker position keys during the disabled portion will not be included in the spline process.
There is a more advanced case worth pointing out where By Hand may appear not to be working, but is being safe. That's when you have a nicely-tracked tracker with a dodgy section in the middle, and you want to replace the dodgy part with a hand- animated part.
In that case, when you turn on By Hand, note that initially it will be on for the entire rest of the shot. If SynthEyes were to blindly do the spline interpolation described above, it would overwrite the entire rest of the track (except for any keys). That wouldn' t be a permanent disaster, since you could just have it Play through the rest of the shot (or Undo), but it would be inconvenient.
To avoid that, when the By Hand region extends to the end of the shot, SynthEyes stops the splining process at the next following tracker key. That protects the rest of the already-tracked frames, limiting the potential damage (often to just the right spot).
IMPORTANT: Limiting the spline process in this way causes the tracker results to be inconsistent, in that tracking through them will change the results, even though the right results could have been deduced earlier. Playing through (tracking) a tracker’s entire lifetime is recommended to eliminate any possible inconsistency. We’ve chosen to allow this inconsistency because not doing so is more frequently problematic, it’s just a trade-off.
If you need to control what frames get replaced precisely before turning on By Hand, either set a tracker position key at the frame you will turn off By Hand, or animate the Enable on and off for the right section, so that the usual simple case applies. In any case, once you've adjusted the By Hand region, you can just play through some frames after the end of the region to restore them if they had been replaced.
Note that if you try to animate a tracker completely from scratch using By Hand, it won't go interpolate past the second tracker key and you may think something is broken, but that is just the protective mechanism in action. Turn By Hand off on the very last frame of the shot and put a final position key there and splining will be active for the entire duration.
©2024 Boris FX, Inc. — UNOFFICIAL — Converted from original PDF.