About masks – Working with Masks

Lesson overview

In this lesson, you’ll learn how to do the following:

  • Create a mask using the Pen tool.
  • Change a mask’s mode.
  • Edit a mask shape by controlling vertices and direction handles.
  • Feather a mask edge.
  • Replace the contents of a mask shape.
  • Adjust the position of a layer in 3D space to blend it with the rest of a shot.
  • Create a shadow effect.
  • Create a vignette.

This lesson will take about an hour to complete. If you haven’t already done so, download the project files for this lesson from peachpit.com/AfterEffectsCIB2024, following the instructions in the Getting Started section under “Accessing the lesson files and Web Edition.”

PROJECT: SEQUENCE FROM A COMMERCIAL

There will be times when you won’t need (or want) everything in a shot to be included in the final composite. Use masks to control what appears.

About masks

A mask in Adobe After Effects is a path, or outline, that is used to modify layer effects and properties. The most common use of masks is to modify a layer’s alpha channel. A mask consists of segments and vertices: Segments are the lines or curves that connect vertices. Vertices define where each segment of a path starts and ends.

A mask can be either an open or a closed path. An open path has a beginning point that is not the same as its end point; for example, a straight line is an open path. A closed path is continuous and has no beginning or end, such as a circle. Closed-path masks can create transparent areas for a layer. Open paths cannot create transparent areas for a layer, but are useful as parameters for an effect. For example, you can use an effect to generate a running light around a mask.

A mask belongs to a specific layer. Each layer can contain multiple masks.

You can draw masks in common geometric shapes—including polygons, ellipses, and stars—with the shape tools, or you can use the Pen tool to draw an arbitrary path. If you draw a shape when a layer is selected, the shape becomes a mask for that layer; the cursor displays a masked box (Cursor with masked box icon) as you start to draw. If you draw a shape when no layer is selected, After Effects creates a shape layer; the cursor displays a star (Cursor with star icon) as you start to draw.