Cutting out a subject with the Roto brush

The Roto brush cuts a moving subject out of a shot from a few scribbles.

1. Stroke the base frame

1. Add a Roto brush effect to the footage layer.
2. Pick the Roto brush tool (Alt+W). Size on the options bar sets the scribble’s width.
3. Scrub to a frame where the subject separates well. It does not have to be the first frame.
4. Drag through the subject. The stroke draws green, and the matte appears when you release.
5. Where the matte grabs too much, hold Alt and drag through the background — a red stroke.

The frame you stroked first becomes the base frame; the effect’s card shows it, and Set to current frame moves it. If you draw no background stroke, the frame’s border counts as the background.

Set View on the card to Boundary to see the edge drawn over the picture, or Matte to see the matte itself.

2. Propagate

Press Propagate on the effect’s card. The matte is carried outward from the base frame in both directions as a background job, and you can keep working while it runs. The card shows how far the span reaches; Cancel keeps the frames already solved.

3. Correct a frame

Scrub the result. Where the matte leaks incorrectly rotoscopes:

1. Scribble across the region where it lost the subject, Alt where it added in the background.
2. Propagate again. Only the frames from the correction outward are re-solved.

Corrections carry forward, away from the base frame.

4. Refine the edge

Refine radius on the card sets how wide the softened band round the edge is. Where one spot needs more, pick the Refine edge tool (with the Roto brush on the strip) and paint over it; the band widens where you painted.

Related

• Roto brush
• Masks
• Mattes