Adobe Photoshop CS4 - Manual (Page 277)

270 USING PHOTOSHOP CS4
Selecting and masking
Last updated 1/10/2010
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 right-most 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, TIFF, PSB, or raw formats. DCS 2.0 format
preserves only spot channels. Saving in other formats may cause channel information to be discarded.
More Help topics
“ About spot colors ” on page 497
“ About masks and alpha channels ” on page 274
Channels panel overview
The Channels panel 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 panel
❖ Choose Windows > Channels.
Resize or hide channel thumbnails
❖ Choose Panel Options from the Channels panel menu. Click a thumbnail size or click None to turn off the display
of thumbnails.
Viewing thumbnails is a convenient way of tracking channel contents; however, turning off the display of thumbnails
can improve performance.
Show or hide a channel
You can use the Channels panel to view any combination of channels in the document window. For example, you can
view an alpha channel and the composite channel together to see how changes made in the alpha channel relate to the
entire image.
❖ Click in the eye column next to the channel to show or hide that channel. (Click the composite channel to view all
default color channels. The composite channel is displayed whenever all the color channels are visible.)
A
B
C