Working With Masks And Transparency - Adobe AFTER EFFECTS 5.5 Help Manual

Adobe After Effects Help
Using Help | Contents
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" on page 66 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:
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 ( ) 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.
Preserving underlying transparency during compositing
The Preserve Underlying Transparency option specifies that the opaque areas of a layer
display only when positioned over opaque areas in underlying layers. With this option,
you can make a layer display only when it is positioned over the layer below it. It's useful
for creating effects such as glints or light reflecting off a polished surface.
Using Help | Contents
| Index
| Index

Working with Masks and Transparency

Back
Back
165
165