Channel Basics; About Channels; Channels Panel Overview - Adobe Photoshop CS6 User Manual

Channel basics

About channels

Channels panel overview

Show or hide a channel
Show color channels in color
Select and edit channels
Rearrange and rename alpha and spot channels
Delete a channel
About channels
Channels are grayscale images that store different types of information:
Color information channels are created automatically when you open a new image. The image's color mode determines the number of color
channels created. For example, an RGB image has a channel for each color (red, green, and blue) plus a composite channel used for editing
the image.
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. (See About masks and alpha channels.)
Spot color channels specify additional plates for printing with spot color inks. (See About spot colors.)
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 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.
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.
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