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
Choose
Windows > Channels.
Choose
Palette Options from the Channels palette 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