Create a rectangular or elliptical mask numerically

  1. Select a layer in the Composition panel, or display a layer in the Layer panel.
  2. Choose Layer > Mask > New Mask. A new mask appears in the Composition or Layer panel with its handles at the outer edges of the frame.
  3. Choose Layer > Mask > Mask Shape.
  4. Select Reset To, choose Rectangle or Ellipse from the Shape menu, and specify the size and location of the bounding box for the mask.