1
With an image in edit mode, choose Image > Show Channels.
2
Create a new channel to use as a selection mask by doing one
of the following:
If you have a selection in the image that you want to cus-
tomize by editing in a channel, use the Save command to
create a channel from the selection; see To save a selection
in a channel on page 33.667.
To start with a blank alpha channel, use the New Channel
command. Be sure to choose the Masked Area option under
Color Indicates in the New Channel dialog box.
3
In the Channels palette, click the new channel to activate it.
The channel appears shaded in the palette and the image changes to
show only the channel. Now click in the left column of the first
(composite) channel. The original image appears with a transparent
colored mask on the image. The color mask indicates the areas
that will be masked not selected by the channel.
4
Use painting tools or filters to edit the image in the channel.
The changes you make affect the active channel only.
5
To make a selection with the channel, load the channel by
choosing Image > Select > Load. Choose the channel name in the
pop-up menu and then click OK.
Channel masks
Channel masks apply transparency effects to objects, including paint
objects, vector objects, text objects, and group objects. A channel
mask creates transparency in proportion to the luminance of its
image.
A channel mask is a grayscale image channel. Black pixels in a chan-
nel mask produce 100% transparency in corresponding areas of the
masked object. White pixels in a channel mask produce 0% transpar-
ency in the masked object. Gray pixels in a channel mask produce
partial transparency in the masked object. Darker grays produce
greater transparency than lighter grays.
Channel masks are powerful because they let you use painting and
image-editing techniques to create transparency effects, and because
a channel mask can be applied to any type of object. An objects
channel mask is the same size as its bounding box. You can detach or
delete an objects channel mask to eliminate the transparency effect.
Canvas displays a shaded mask
representing an alpha channel
when the alpha channel and the
composite channel are visible
Shaded mask