Create a rectangular or elliptical mask numerically
- Select a layer in the Composition panel, or display a layer in the Layer panel.
- 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.
- Choose Layer > Mask > Mask Shape.
- Select Rectangle or Ellipse, and specify the size and location of the mask’s bounding box.