Supervised Tracking 手動トラッキング
カメラの3Dの位置とシーンの要素のために解析するためには、ショットの一部もしくは全部を通してトラッキングされるトラッカーの集まりが必要になります。
ショット内に、7または8個のトラッカーがあれば十分です(少なくとも6)、しかし、複雑なショットは、ブロックされていたり、フレームでおかしな移動しているトラッカーで、もっと多く必要になることがあります。
自動トラッキングが満足なトラッカーをもたらすことができないならば、直接トラッカーを加える必要があります。
または、自動的に生成されたトラッカーを改善するために、このテクニックを使うことができます。
特定の手動トラッカーは、特にオブジェクトを挿入するための、または、要望通り座標系を一列に並べるためのリファレンスとして役に立ちます。
Tip: You can create a tracker at any time by holding down the ‘C’ key and
left-clicking in the camera view. Or, right-click in the camera view and select
the Create Trackers item. In either case you will be switched to the Tracker
control panel.
Rewind to the beginning of the shot
.
Locate a feature to track: a corner or small spot in the image that you
could reach in and put your finger on.Do not select a reflective highlight
that moves depending on camera location. Left-click on the center of your
feature, and while the button is down, position the tracker accurately using
the view window on the command panel. The gain and brightness spinners located
next to the mini-tracker-view can make shadowed or blown-out features more
visible. Adjust the tracker size and aspect ratio to enclose the feature, and a
little of the region around it, using either the spinner or inner handle.
Adjust the Search size spinner or outer handle based on how uncertainly
the tracker moves each frame. This is a matter of experience. A smooth shot
permits a small search size even if the tracker accelerates to a higher
rate.
Create any number of trackers before tracking them through the shot. It is
easier to do either one or 3-6 at a time.
To track them through the shot, hit the Play
or
frame forward
button
or use the mouse scroll wheel inside the mini-tracker-view (scrubbing the time
bar does not cause tracking). Watch the trackers as you move through the shot.
If any get off track, back up a frame or two, and drag them in the image back
to the right location. The Play button will stop automatically if a tracker
misbehaves, already selected for easy correction.
Prediction Modes and Hand-Held
Shots
SynthEyes predicts where the feature will appear in each new frame. It has
different ways to do this, depending on your shot. By default, in
theSteady cameramode, it assumes that the shot is smooth, from
a steadi-cam, dolly, or crane, and uses the previous history over a number of
frames to predict its next position.
If you have a hand-held shot, selectHand-Held: Use
otherson the Track menu. In this mode, SynthEyes uses other,
already-tracked, trackers to predict the location of new ones. Start by
tracking a few easy-to-track features that are distributed around the image.
You will usually need a large search area, and to re-key fairly frequently if
the shot is very choppy. But as you add trackers, you can greatly reduce the
search size and will need to set new keys only occasionally as the pattern
changes.
Using the predict mode, you’ll sometimes find that a tracker is suddenly
way out of position, that it isn’t looking in the right place. If you check
your other trackers, you’ll find that one of your previously-tracked trackers
is off course on either this or the previous frame. You should unlock that
tracker, repair it, relock it, and you’ll see that the tracker you were
originally working on is now in the correct place (you may need to back up a
frame and then track onto this frame again).
If your shot and the individual trackers are very rough, especially as you
are tracking the first few trackers, you may find that the trackers aren’t too
predictable, and you can set the mode toHand-Held: Sticky, in
which case SynthEyes simply looks for the feature at its previous location
(requiring a comparatively large search region).
For some special situations, theRe-track at existingmode
uses the previously-tracked location, and looks again nearby (perhaps after a
change in some tracker settings). The search size can be kept small, and the
tracker will not make any large jumps to an incorrect location, if the track is
basically correct to begin with. SynthEyes uses this mode during fine-tuning.
Note: on any frames that were not previously tracked, Hand-Held: Sticky mode
will be used.
Adjusting While Tracking
If a tracker goes off course, you can fix it several ways: by dragging it
in the camera view, by holding down the Z key and clicking and dragging in the
camera view, by dragging in the small tracker interior view, or by using the
arrow keys on the number pad. (Memo to lefties: use the apostrophe/double-quote
key ‘/” instead of Z.)
You can keep an eye on a tracker or a few trackers by turning on
thePan to Followitem on the Track menu (keyboard: 5 key), and
zooming in a bit on the tracker, so you can see the surrounding context. When
Pan To Follow is turned on, dragging the tracker drags the image instead, so
that the tracker remains centered.
Or, the number-pad-5 key centers the selected tracker whenever you click
it.
Staying on Track and Smooth
Keying
Help keep the trackers on course with theKey
Everyspinner, which places a tracker key each time the specified
number of frames elapses, adapting to changes in the pattern being tracked. If
the feature is changing significantly, you may want to tweak the key location
each time the key is added automatically. Turn on theStop on
auto-keyitem on the Track menu to make this easier.
When you reposition a tracker, you create a slight “glitch” in its path
that can wind up causing a corresponding glitch in the camera path. To smooth
the glitches away, set theKey Smoothspinner to 3, say, to
smooth it over the preceding 3 frames. When you set a key, the preceding (3
etc) frames need to be re-tracked. If you turn onPre-Roll by Key
Smoothon the Track menu, SynthEyes will automatically back up and
retrack the appropriate frames when you resume tracking (hit Play) after
setting a key.
The combination ofStop on auto-keyandPre-roll by
Key Smoothmakes for an efficient workflow. You can leave the mouse
camped in the tracker view window for rapid position tweaks, and use the space
bar to restart tracking to the next automatic key frame. See the web-site for a
Flash movie example.
Warning: if SynthEyes is adding a key every 12 frames,
and you want to delete one of those keys because it is bad, it may appear very
difficult. Each time you delete it (by right-clicking in the tracker view, Now
button, or position spinners), a new key will immediately be created. You could
just fix it. Or, you should back up a few frames, create a key where the
tracker went off-course, then go forward to delete or fix the bad key.
Suspending or Finishing a
Track
If an actor or other object permanently obscures a tracker, turn off its
enable button, disabling it for the rest of the shot, or until you re-enable
it. Trackers will turn off automatically at the edge of the image; turn them
back on if the image feature re-appears. (If the shot has a non-image border,
use the region-of-interest on the Image Preprocessing panel so that trackers
will turn off at the right location.)
You can also track backwards: go to the end of the shot, reverse the
playback direction
,
and play or single-step backwards.
You can change the tracking direction of a tracker at any time. For
example, you might create a tracker at frame 40 and track it to 100. Later, you
determine that you need additional frames before 40. Change the direction arrow
on the tracker panel (not the main playback direction, which will change to
match). Note that you introduce some stored inconsistency when you do this.
After you have switched the example tracker to backwards, the stored track from
frames 40-100 uses lower-numbered reference frames, but backwards trackers use
higher-numbered reference frames. If you retrack the entire tracker, the
tracking data in frames 40-100 will change, and the tracker could even become
lost in spots. If you retrack in the new direction, you should continue to
monitor the track as it is updated. If you have regularly-spaced keyframes,
little trouble should be encountered.
When you are finished with one or more trackers, select them, then click
the
Lockbutton
.
This locks them in place so that they won’t be re-tracked while you track
additional trackers.
Combining Trackers
You might discover that you have two or more trackers tracking the same
feature in different parts of the shot, or that are extremely close together,
that you would like to consolidate into a single tracker.
Select both trackers, using a lasso-select or by shift-selecting them in
the camera view or graph editor. Then select theTrack/Combine
trackersmenu item, or the Shift-7 (ampersand &). All selected
trackers will be combined, preserving associated constraint information.
If several of the trackers being combined are valid on the same frame,
their 2-D positions are averaged. Any data flagged as suspect is ignored,
unless it is the only data available. Similarly, the solved 3-D positions are
averaged. There is a small amount of intelligence to maintain the name and
configuration of the most-developed tracker.
Note: the camera view's lasso-select will select only trackers enabled on
the current frame, not the 3-D point of a tracker that is disabled on the
present frame. This is by design for the usual case when editing trackers.
Control-lasso to lasso both the 2-D trackers and the 3-D points, or shift-click
to select 3-D points.
Filtering and Filling Gaps in a
Track
To produce even smoother final tracks, instead of Locking the trackers,
click the
Finalizebutton
.
This brings up theFinalizedialog,
which filters the tracker path, fills small missing gaps, and Locks the
tracker(s). Though filtering can create smoother tracks, it is best used when
the camera path is smooth, for example, from a dolly or crane. If the camera
was hand-held, smoothing the tracker pathscausessliding,
because the trackers will be smoother than the camera!
If you have already begun solving and have a solved 3-D position for a
tracker, you can also fill small gaps or correct obvious tracking glitches by
using the Exact button on the tracker panel, which sets a key at the location
of the tracker's 3-D position (keyboard: X key,notshifted).
You should do this with some caution, since, if the tracking was bad, then the
3-D tracker position and camera position are also somewhat wrong.
Pan To Follow
While tracking, it can be convenient to engage the automatic Pan To Follow
mode on the Track menu, which centers the selected tracker(s) in the camera
view, so you can zoom in to see some local context, without having to
constantly adjust the viewport positioning.
When pan to follow is turned on, when you start to drag a tracker, the
image will be moved instead, so that the tracker can remain centered. This may
be surprising to begin with.
Once you complete a tracker, you can scrub through the shot and see the
tracker crisply centered as the surroundings move around a bit. This is the
best way to review the stability of a track.
Skip-Frame Track
If a few frames are untrackable due to a rapid camera motion, explosion,
strobe, or actor blocking the camera, you can engage the Skip Frame checkbox on
the feature panel to cause the frame to be skipped. You should only skip a few
frames in a row, and not that many over all.
The Skip Frames track will not affect supervised tracking, but it affects
solving, causing all trackers to be ignored. After solving, the camera will
have a spline-interpolated motion on the resulting unsolved frames.
If you have a mixture of supervised and automatic tracking, see the
section on the
Skip-Frame
track in Automated Trackingas changing the track after automated tracking
can have adverse effects.