Transparency effects with channel masks
Channel masks let you add transparency to images without altering
them permanently. A channel mask creates transparency without
changing any pixels in an image. You can remove a channel mask to
eliminate the transparency effect at any time.
To make an image transparent
To make parts of an image transparent to eliminate the back-
ground in a photograph, for example you can create a channel
mask from a selection. This procedure explains how to transfer a
selection into a channel mask to make selected areas transparent.
1
Choose Image > Show Channels to open the Channels palette.
Double-click the paint object to put it into edit mode. You can use
various techniques to select the areas you want to be transparent:
You can click the Wand tool to select similar colors through-
out the image. If a photograph has a colored background, for
example, click the background to select it. You can also use
the Color Range command to make a selection.
To soften the edges of the selection, you can use the Image >
Select > Feather command.
2
Click the Selection button in the Channels palette to save the
selection in a new alpha channel. In the alpha channel, white pixels
correspond to the selection. (A partial selection produces gray pixels
in the channel). Black pixels in the channel correspond to unselected
areas of the image. To create transparent areas from the selection,
you need to invert the channel.
3
Press Esc to deselect the selection in the image. Then, click the
alpha channel in the Channels palette to make it active. Choose
Image > Adjust > Invert. This reverses the white and black areas in
the channel.