Choosing an interpretation method for alpha channels

You can change the interpretation method for a file after you import the file. You can also change the default alpha channel interpretation in the Import Preferences dialog box, in the Interpret Unlabeled Alpha As pop-up menu. This is especially useful for importing footage from an application that consistently uses one type of unlabeled alpha channel.

The interpretation methods include:

Ask User

Displays a dialog box containing interpretation options each time you import an unlabeled alpha channel.

Guess

Attempts to determine the type of alpha channel used in the image. If After Effects cannot guess confidently, it beeps.

Ignore Alpha

Disregards all transparency data in the file.

Straight (Unmatted)

Interprets the alpha channel as straight alpha. If the application you used to create the footage does not premultiply the alpha channel, select this option.

Premultiplied (Matted with Black)

Interprets the alpha channel as premultiplied with black.

Premultiplied (Matted with White)

Interprets the alpha channel as premultiplied with white.

To import a footage file containing an alpha channel:

1. Choose File > Import > File.
2. Select the name of the file you want to open. If the file does not appear, select the option for showing all files from the Files of Type (Windows) or Show (Mac OS) pop-up menu.
3. Click Open (Windows) or Import (Mac OS).
4. Select an option for the alpha channel in the Interpret Footage dialog box, and click OK.

To set the alpha channel interpretation method for a file:

1. In the Project window, select a footage item that includes an alpha channel.
2. Choose File > Interpret Footage > Main.
3. In the Alpha section, select an interpretation method.
4. If you want to switch the opaque and transparent areas of the image, select Invert Alpha.
5. Click OK.

To set the default alpha channel interpretation:

1. Choose Edit > Preferences > Import (Windows) or After Effects > Preferences > Import (Mac OS).
2. Choose a default interpretation method from the Interpret Unlabeled Alpha As pop-up menu, and click OK.