5

To convert a mask to a shape
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In the Layers list, select a mask and do one of the following:
• Choose Object > Convert To Shape.
The shape moves to the bottom of the group.
• Drag the mask between two objects in the Layers list.
• Drag the mask onto the group layer and pause, holding down the mouse button. When
the drop menu appears, choose Move Shape To Group.
Manipulating Alpha Channels Using Filters
In addition to using shape and image masks to create transparency in layers, there are
also filters you can use to manipulate or even replace a layer’s alpha channel.
For example, the Keying filters create transparency by generating an alpha channel based
on colors or luminance values in that layer. Keying filters are usually used on layers that
have no alpha channel information; these filters add a new alpha channel to the layers
to which they’re applied. For more information on the use of the keying filters, see Keying.
The process of improving a keying effect or of customizing an alpha channel created
using shape or image masks may require the use of special filters. Although you can apply
any filter to a shape or image mask to modify that mask’s effect, the filters described in
this section modify a layer’s entire alpha channel, including the sum of all masks and
other filters applied to that layer.
1226 Chapter 20 Using Shapes, Masks, and Paint Strokes