What Are Channels

Photoshop uses Channels to store color information about an image or to store selections. Photoshop creates color information channels automatically and all Photoshop images contain at least one channel.

Bitmap-mode, Grayscale, Duotone, and Indexed Color images are each single-channel modes. An Indexed Color image has one channel containing up to 256 levels of density.

Indexed Color The Web Palette with its 256 colors is an index color. It ensures predictable color on the Web or the Intranet.

Color Modes Modes are found under the Image menu item. The default is 8 bits per channel. Only in RGB mode is 16 bits per channel available. RGB is my default working mode.

Filters and Plug-ins functional in... They do not function in...

RGB Modes CMYK Modes Grayscale Modes Duotone Modes Bitmap Modes Indexed Modes

RGB Color Mode An RGB image contains three channels made up of Red, Green, and Blue color data as shown in the sample below.

RGB output mates well with the monitor RBG electron guns. The direct color match can produce excellent color on the monitor screen. Professional monitors are pricey but they can be tuned or matched to very precise output settings.

CMYK Color Mode CMYK is designed to convert well into the printer's environment with its four-color plates of Cyan, Magenta, Yellow, and Black.

Counter Intuitive CMYK contains 1 more channel than RGB but it has a smaller color gamut. Its color gamut is designed to meet the narrower color range needs of the four-color printing process.

24 Channels Except for the Bitmap-mode image, all images in Photoshop can have up to 24 channels. These are frequently called alpha channels. Sometimes, the alpha channel can be used to decrease file size.

Palettes

Study the palette titles to the left. Photoshop Layers Palette usually includes the Channels and Paths as tab selections. I added the Actions to my Palette set by a simple drag and drop process. Grab the Actions tab and drag it off to remove it from the Palette.

A working knowledge of Selections and Masks are prerequisites to using the Channels concept effectively. Selections were already covered at the start of this section. The next Topic will be Masks.

Additional Resources:

• W3C Color names and sRGB values
• Color / Colour
• Color Resources
• Victor Engel's No Dither Netscape Color Palette
• Thalia's Guide: The Color Page

The Crop Tool
Introduction to Web Design with Adobe Photoshop | Table of Contents
What Are Masks