User Guide

13
Using Alpha Channels
The primary function of an alpha
channel is to store a selection you
might want later. You can save
multiple selections in a channel.
Understanding Alpha
Channels
An alpha channel is a mask through
which you can paint on, and apply
effects to, an image. The alpha
channel stores 8 bits of information
per pixel, which means that each pixel
can be assigned one of 256 (2
8
) levels
of gray—from 0 (black) to 255
(white). White areas of the channel
are selected, and black areas of the
channel are protected. Intermediate
levels of gray are partially protected.
For example, areas that are 50% gray
will allow 50% of the brush stroke or
effect to get through the channel to
the image.
Alpha channels work like selections.
Selections, however, are available only
when working with the active image
during the current session. You can
save your selection, which creates an
alpha channel. Channels remain
inactive (for canvas control) until you
load them to a selection. You can think
of a channel as a “dormant selection.”
For more information about
selections, refer to “Working with
Selections” on page 203.
Corel Painter lets you create up to 32
alpha channels. The channels are
listed on the Channels palette, where
you can select and control them.
You can edit a channel in a number of
ways and then load it as a selection.
Stored channels remain part of the file
when you save in Corel Painter or
Photoshop format. No matter how
many times you work on a file, the
channels are available whenever you
need them.