Instruction Manual

Chapter 19 Filters 757
Manipulate alpha channels using lters
There are lters you can use to manipulate or even replace a layer’s alpha channel. For example,
the Keying lters create transparency by generating an alpha channel based on colors or
luminance values in that layer. Keying lters are usually used on layers that have no alpha
channel information; these lters add a new alpha channel to the layers to which they’re applied.
For more information on the use of the keying lters, see Keying overview on page 487.
The process of improving a keying eect or of customizing an alpha channel created using shape
or image masks may require the use of special lters. Although you can apply any lter to a
shape or image mask to modify that mask’s eect, the lters described in this section modify a
layer’s entire alpha channel, including the sum of all masks and other lters applied to that layer.
For example, if you’ve applied a keying lter, you can use the following lters to modify the
resulting alpha channel even though no mask appears for that layer in the Layers list or Timeline.
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Channel Blur: This lter, found in the Blur category of the Filters library, lets you selectively blur
the alpha channel. You can set the amount of horizontal and vertical blur independently.
Original (color channel)
Original (alpha channel)
Channel Blur (color channel)
Channel Blur (alpha channel)
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Matte Magic: This lter, found in the Keying subcategory of the Filters library, lets you
manipulate various qualities of an alpha channel, shrinking, feathering, and eroding the alpha
channel to ne-tune it. For more information, see Matte Magic on page 508.
Blur lters
Blur lters overview
Blur lters can be used to simulate the real-world blurring that occurs due to the depth of eld in
photographed material. They can also be used to create designed eects.
For a description of each Blur lter, see the lters list in the Help table of contents (the sidebar to
the left of this window).
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