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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

    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. Locate and select the file and click Open.
  2. In the Interpret Footage dialog box, select an option for alpha channel type. If you select Treat As Premultiplied (Matted with Color), you can click the eyedropper and select a color.
  3. 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. Select Inverted to switch the opaque and transparent areas of the image, and click OK.

To set the default alpha channel interpretation:

  1. Choose Edit > Preferences > Import.
  2. For Interpret Unlabeled Alpha As, select the interpretation methods you want used by default, and click OK.