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Working with Masks in Adobe After Effects CS5

Article Description

This excerpt from Adobe After Effects CS5 Classroom in a Book shows you how to create a mask using the Pen tool, edit a mask, feather a mask edge, create a vignette, and more.

Note: This excerpt does not include the lesson files. The lesson files are available with purchase of the book.

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 the shot.
  • Create a reflection effect.
  • Create a vignette.
  • Use Auto Levels to correct the color of the shot.

This lesson will take approximately an hour to complete. Copy the Lesson07 folder into the Lessons folder that you created on your hard drive for these projects (or create it now), if you haven’t already done so. As you work on this lesson, you’ll preserve the start files. If you need to restore the start files, copy them from the Adobe After Effects CS5 Classroom in a Book DVD.


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.

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