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Mask Constraint
If you want to solve footage that contains unwanted movement (e.g., a ball that rolls from left to right through the scene or undulating water, etc.), an animated mask can be used to define regions of the scene that should be excluded from tracking. Tracks that are excluded by the mask will be hidden or ignored. The Tracks will not be deleted. As soon as the mask is deleted, the Tracks will again be visible. The Object Tracker can be used in conjunction with the mask for the object to be tracked.
A mask can be created either prior to 2D tracking or afterward (but prior to solving).
If multiple masks are created whose surfaces intersect and lie in opposing positions (one masks on the inner and one on the outer region), the mask that lies the farthest to the right in the Object Manager will be given priority.
Masks with holes can also be created: For example, with the first tag that masks the outer surface and a second tag that lies within the first tag and masks Tracks that lie within it.
How can masks be created and edited interactively?
This activates the Create Mask tool, after which you can click in the Viewport to create the mask's corner points. Click the last point on the start point to close the mask and create the Mask Constraint tag.
Or:
Create a Mask Constraint tag. A rectangular mask will be created.
If the tag is selected, the following will apply: If a mask has been created, its end points can be selected (the Shift and Cmd/Ctrl keys (as well as the respective commands from the main Selection menu) can be used to add or remove selections) and moved.
Multiple selection of mask points is possible.
If nothing is selected, points can be simply grabbed and moved individually. If you Cmd/Ctrl+click on the edge of a mask or if you right-click on it and select Split Mask Edge Here), an additional point will be added at this location. Selected points can be deleted by pressing Del or right-clicking on it and selecting the Delete Selected Mask Vertices from the context menu that appears. If mask points are modified at a specific time in the animation, (linear) keyframes will be added automatically to animate the mask.
When creating animated masks you should initially create as few edge points as possible. Position the mask roughly in the Viewport with 3-4 corner points and animate it. If more points are required, these can be added as needed. This is much easier than, for example, creating 2 dozen points from the start and animating them!
Mask keyframes can be moved or deleted in the Timeline (contrary to all other Motion Tracker elements).