Roto brush
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Roto brush is a Utility effect.
What it does
Section titled “What it does”Turns strokes into a matte and carries it through the shot.
For a tutorial, see Cutting out a subject.
Parameters
Section titled “Parameters”| Parameter | Control | Range | Default | Unit |
|---|---|---|---|---|
| Propagate | Button | - | - | - |
| Cancel | Button | - | - | - |
| Seed from | Dropdown | Strokes · Segment | Strokes | - |
| Matte mode | Dropdown | Matte · Matte inverted | Matte | - |
| View | Dropdown | Result · Matte · Boundary | Result | - |
| Refine radius | Slider | 0 to 64; up to 256 | 8 | - |
| Flow resolution | Dropdown | Native · Half · Quarter | Half | - |
| Flow smoothness | Slider | 0 to 100 | 50 | - |
What each control does
Section titled “What each control does”- Propagate: carries the matte outward from the base frame. Only one propagation runs at a time.
- Cancel: stops the job and keeps the frames already solved; a later Propagate resumes from them.
- Seed from: what the base frame’s matte starts from. On Strokes, the scribbles alone. On Segment, a tap with the Roto brush tool on the base frame is a prompt a segmentation model reads; Alt makes the tap a negative one, and a drag still lays a stroke.
- Matte mode: keep the subject, or drop it.
- View: the cut-out picture, the matte itself, or the picture with the matte’s edge drawn over it.
- Refine radius: how wide the softened band round the matte’s edge is — room for hair, motion blur and smoke. The Refine edge tool paints the band wider where one spot needs more.
- Flow resolution: the resolution the propagation’s motion is measured at. Native is slower and rarely better.
- Flow smoothness: how strongly that motion is regularised.
Frames the propagation has not reached render untouched — the effect never holds a neighbouring frame’s matte over them.
Seed from set to Segment asks for a segmentation model, which is an addon installed from Settings ▸ Addons. Without it the propagation is refused and the status line says so.