Alpha channels are very important in the scheme of things. They are used to hold selections and masks. You can also use alpha channels to create intricate selections by using painting tools, editing tools, or filters and, by the same token, to modify existing selections and resave them. By painting with black-and-white and shades thereof, you can also create some very interesting bevels and contours if you then use the Lighting Effects filter and select the alpha channel as the source for the texture channel (see Chapter 18). Before the advent of Layer Styles, this was the way they were created. Some people still swear by them—although others swear at them from the sanctuary of the Layer Style dialog box!
Alpha channels resemble the default color channels in more ways than they differ from them. They differ only in that they cannot be interchanged with the default color channels and are always addendums to the default channels; otherwise, they hold the information in the same way as the default color channels: as grayscale images (Figure 3-5).
To create an alpha channel, choose New Channel from the Channels palette menu or click the Create New Channel button.
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