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Using alpha channel or luminance values for a track matte


    Define transparency in a track matte using values from either its alpha channel or the luminance of its pixels. Using luminance is useful when you want to create a track matte using a layer without an alpha channel or a layer imported from a program that can't create an alpha channel. In both alpha channel mattes and luminance mattes, pixels with higher values are more transparent. In most cases, you use a high-contrast matte so that areas are either completely transparent or completely opaque. Intermediate shades should appear only where you want partial or gradual transparency, such as along a soft edge.

To create a track matte:

  1. Click the Switches/Modes button at the bottom of the Timeline window. The Transfer Modes panel appears in place of the Layer Features panel. You can also show the Transfer Modes panel and the Switches panel simultaneously. See Optional panels for information on showing panels.
  2. Arrange two layers in the Timeline window. Make sure that the designated matte layer is directly above the designated fill layer.
  3. From the TrkMat menu for the fill layer, define transparency in the next layer above by choosing one of the following:
  4. No Track Matte

    No transparency created; next layer above acts as a normal layer.

    Alpha Matte

    Opaque when alpha channel pixel value is 100%.

    Alpha Inverted Matte

    Opaque when alpha channel pixel value is 0%.

    Luma Matte

    Opaque when a pixel's luminance value is 100%.

    Luma Inverted Matte

    Opaque when a pixel's luminance value is 0%.

    After Effects converts the next layer above into a track matte, turns off the video of the track matte layer, and adds a track matte icon (the track matte icon) next to the track matte layer's name in the Timeline window. The Composition window displays the fill layer viewed through the alpha channel of the matte layer.

    Note: Although the video is turned off for the matte layer, you can still select the layer to reposition, scale, or rotate it. Select the layer in the Timeline window, and then drag the center (indicated by a circle with an X) of the layer in the Composition window.