Adobe Photoshop CS3 - Manual (Page 272)

PHOTOSHOP CS3
User Guide
265
• Alpha channels store selections as grayscale images. You can add alpha channels to create and store masks, which
let you manipulate or protect parts of an image.
• Spot color channels specify additional plates for printing with spot color inks.
An image can have up to 56 channels. All new channels have the same dimensions and number of pixels as the
original image.
The file size required for a channel depends on the pixel information in the channel. Certain file formats, including
TIFF and Photoshop formats, compress channel information and can save space. The size of an uncompressed file,
including alpha channels and layers, appears as the rightmost value in the status bar at the bottom of the window
when you choose Document Sizes from the pop-up menu.
Note: As long as you save a file in a format supporting the image’s color mode, the color channels are preserved. Alpha
channels are preserved only when you save a file in Photoshop, PDF, PICT, Pixar, TIFF, PSB, or raw formats. DCS 2.0
format preserves only spot channels. Saving in other formats may cause channel information to be discarded.
See also
“About spot colors” on page 501
“About masks and alpha channels” on page 269
Channels palette overview
The Channels palette lists all channels in the image—composite channel first (for RGB, CMYK, and Lab images). A
thumbnail of the channel’s contents appears to the left of the channel name; the thumbnail is automatically updated
as you edit the channel.
Channel types
A. Color channels B. Spot channels C. Alpha channels
Display the Channels palette
❖ Choose Windows > Channels.
Resize or hide channel thumbnails
❖ Choose Palette Options from the Channels palette menu. Click a thumbnail size or click None to turn off the
display of thumbnails.
A
B
C