A difficult tracking problem

There may not be a solution to my problem, but here's my question. I use Resolve 18.6 Studio. I have some experience with tracking in the Fusion tab. It often works; not always. This time I am trying to even out the drift back and forth in a flock of flying birds. Flying birds do not follow a script, go wherever they want, and following them accurately is really hard. Normally I track a single bird's head, and that works. This time there are many individuals. They constantly go in front of or behind each other and they all look alike. The tracker won't hold onto any one of them. I'd be happy if, on losing one target, the system would quickly grab another nearby one, but all it does is drift off. Are there settings that would allow rapid recapture of a similar target? I only need about 3 seconds of tracking.

If it is impossible, just say "Can't be done".

Thanks.

I think if you were to pseudo manually track 3 or 4 pf the less erratic birds with individual trackers it will average the movement out between them and give you a reasonable result. Just track each one till it loses its target then move the tracker back to the target and track forward again. You may have to do most of the tracking by hand but it should give you something useful. Setting the Adaptive mode to Best Match may also help you track deforming objects. Also version 19 has the very clever intellitrack and single frame tracking options which I'm not sure 18 does?

It would be helpful to see the video clip, but depending on how much of the screen the flock takes and for what purpose do you need the tracking data, there are different approaches you can try.

A small target, even eradic like small bird in flight can be tracked by increasing the pattern search area for the tracker to the point it covers the larger move distance of the bird between two frames. So if at some point bird makes a sudden shift in flight, there will be certain distance between two frames, one before the shift and one after. The search pattern needs to be large enough to cover that distance and if that is the largest distance bird covers in between two frames, and pattern search area is large enough to cover it, than all other movement should be tracked well enough.

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If the flock of birds is 20% of the frame surface area you can apply the same principle. Make the search pattern large enough to cover it, which will usually result in very slow frame by frame tracking but it might work.

Speaking of frame by frame tracking. Tracker plus, a variant of the regular tracker can be found on Reactor (fusion depository of all fusion goodies) and tracker plus has frame by frame tracking ability, so you can manually move frame by frame, and if it still loses the target you can use track center (append) function or do offset tracking.

Path Center

This menu determines how the Tracker behaves when repositioning a pattern. This menu is particularly useful when a pattern leaves the frame or changes so significantly that it can no longer be tracked.

— Pattern Center: When Pattern Center is selected in the menu, the tracked path continues from the center of the new path. This is appropriate when replacing an existing path entirely.

— Track Center (append): When Track Center (append) is selected in the menu, the path tracked by a new pattern will be appended to the existing path. The path created is automatically offset by the required amount. This setting is used to set a new tracking pattern when the original pattern moves out of the frame or gets obscured by other objects. This technique work bests if the new pattern is located close to the position of the original pattern to avoid any problems with parallax or lens distortion.

Adaptive Mode

Fusion is capable of reacquiring the tracked pattern, as needed, to help with complex tracks. This menu determines the Adaptive tracking method.

— None: When set to None, the tracker searches for the original pattern in each frame.

— Every Frame: When set to Every Frame, the tracker reacquires the pattern every frame. This helps the Tracker compensate for gradual changes in profile and lighting over time.

— Best Match: When set to Best Match, the tracker compares the original selected pattern to the pattern acquired at each frame. If the variation between the two patterns exceeds the threshold amount defined by the Match Tolerance control, the tracker does not reacquire the pattern on that frame. This helps to avoid Tracker drift caused by transient artifacts that cross the pattern’s path (such as a shadow).

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If you use Track Center (append) and best match with high enough tolerance but large enough search pattern area, you should be able to track most things.

You also have the option to use offset tracking. Meaning you track something that is trackable close by, like bird close by and than you offset manually the tracker to point to the bird that you wanted but could not track.

Because Fusion looks for the channel with the highest contrast automatically, you might end up tracking a noisy but high-contrast channel. Before tracking, it’s always a good idea to zoom in to your footage and check the RGB channels individually. Sometimes you can find best contrast in one of the channels that fusion is not targeting so that is worth a try.

Additionally you can add a node before tracker, like filter node set to sobel filter, and you have nice white outline around the birds, which makes it more contrasty, and easier to track.

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Also version 19 has the very clever intellitrack and single frame tracking options which I'm not sure 18 does?

That is another option. I had less success with small objects like single bird than larger objects with the new tracker, but its a great new addition to tracker tools.

Like I said I don't know what the footage is really like or use of the tracking data will be , but you can also try to deal with large flock of birds that go in all direction by tracking everything and generating motion vector data using optical flow and than using something like smart vectors to utilize the tracking data.

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You can play with settings to dial in the correct settings to capture all the birds, as it were.

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