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Masks and roto.

A mask decides which part of a piece of footage shows. Draw one by hand, let the roto models find a subject and follow it through the shot, or paint the frames where it needs help. Every mask is listed with its footage, and every correction is a step you can undo.

Four kinds of mask

Select a piece of footage. Its Masks section in the Inspector lists its masks and adds new ones; choose a kind and draw it.

Subject mask
A person or an object, found by the roto models from your clicks and followed through the shot.
Paint mask
Alpha you paint with the Brush, on one frame or across the clip.
Vector mask
A shape you draw with the Pen, the Rectangle or the Ellipse. It shows only the part of the layer inside it.
Holdout mask
An object to take out of the masks above it, such as a pole in front of a person.

The subject tools run models on your computer. If they aren't set up yet, the section says so and Roto models… opens Settings to set them up.

Cut out a subject

  1. Select the footage and choose Subject Select (W) on the Stage's rail.
  2. Click the subject. Alt-click an area to leave it out. Or use Subject Brush and paint over the subject.
  3. If Grapple picked only part of it, or too much, press C to step through the alternatives. The section says which one you're on, such as "Selection 1 of 3".
  4. Press Apply selection to apply it to this frame.
  5. Track it forward and backward through the clip, or a frame at a time. Stop keeps the frames already tracked.

Esc discards the marks you haven't tracked on this frame, and Clear marks starts again. A frame that isn't tracked says so: track from a marked frame, or mark the subject there.

Hair and soft edges

Choose Refine Edge on the rail and paint over hair, fur and other soft edges. It rebuilds them from the image, so the cut-out keeps the strands a hard edge would lose.

Paint a mask

  1. Choose the Brush (B).
  2. Choose whether new strokes hold for This frame or the Entire clip. Strokes you've already made keep their range.
  3. Set the Brush diameter; the circle on the Stage shows its size.
  4. Paint to hold areas solid, or switch to clear. Alt paints the other way for one stroke.

Use it to fix the frames where a subject mask slips, such as an arm lost against a busy background. Each correction is listed under Frame corrections.

Draw a vector mask

  1. Select the footage.
  2. Draw with the Pen (G): click for corners, drag for curves, and click the first point to close the mask. Or drag out a Rectangle (R) or an Ellipse (E).
  3. Select the mask in the Masks section to edit its points on the Stage.

Track a vector mask

A vector mask can follow the texture inside it, for a screen, a sign or a face. Choose its Motion: Position, Position, scale & rotation, or Affine. Set Tracking in and Tracking out for the frames to track, then track forward or backward. For a subject that changes shape, correct the points on later frames.

Holdout masks

Add a Holdout mask, then select and track the object to remove from the masks above it in the list. The order of the list matters: move a mask earlier or later in the stack with its arrows.

The Masks section

  • Each mask can be switched off to see through it, renamed with a double-click, or removed; Undo restores a removed mask.
  • Invert swaps the inside and outside, and Feather softens the edge.
  • Frame corrections lists the frames you painted, each a link to its frame.

Judge the edge

The Viewer's Mask display menu shows the footage as Source, Alpha, Overlay, Cutout or Composite. Look at the edge against black in Alpha, over a colour in Overlay, and against the real background in Composite.

Confine an effect

Every effect has Limit to: the Whole image, a mask, or a matte, with Invert. Grade a person and leave the background alone, or blur the background and keep the person sharp. See Effects.

Mattes between layers

A matte uses another layer's shape or brightness to choose which parts of this layer show: a video inside the letters of a title, or a reveal behind a moving shape.

  1. Select the layer to be shown, and press Add matte in its Inspector.
  2. Choose the Matte source: the layer that defines what shows.
  3. Choose Alpha to use its shape, or Luma to use its brightness.
  4. Turn on Hide source if the source layer shouldn't show by itself.

A layer can have several mattes, combined with Add, Subtract, Intersect or Difference, each with Invert, Expansion to grow or shrink it in pixels, Feather and Matte opacity. The layer's Blend mode is in the same section.