Color Mode Basics
Photoshop CS6 Tutorial
How to Use Photoshop Color Modes
The most common color mode in Photoshop is RGB. Other image modes include CMYK, Grayscale, Index, Lab Color, Indexed Color, Duotone and Bitmap.
The RGB, CMYK and Lab Color modes can be used to create full color continuous tone images. Of the three options, Lab Color has the largest color range, followed by RGB. CMYK has the smallest color range or gamut.
To better understand each mode, we'll keep the Channels panel open as we examine the modes.
Open an RGB image in Photoshop (File > Open).
Notice that the image name and mode appear in the tab or title bar. This image is an 8 bit RGB image.
Another way to see the current mode is to choose Image > Mode. You can view the mode and bit count (8 bits/channel, 16 bits/channel or 32 bits/channel).
Open the Channels panel and notice that the image is defined with three channels; Red, Green and Blue.
To convert your image to CMYK (cyan, magenta, yellow and black), choose Image > Mode > CMYK Color.
The image now has four channels; cyan, magenta, yellow and black.
By choosing Image > Mode > Lab Color the image is now defined by a lightness channel and two color channels.
Choose Image > Mode > RGB, then Image > Mode > Indexed Color. . . to convert the image to Indexed Color. An Indexed Color image has a very limited color palette.
With Indexed Color you can set the number of colors that are used to define the image. You can also set the Dither to Diffusion or None.
To see your image in Grayscale mode, choose Image > Mode > Grayscale. The image now has one channel.
By converting the image to Grayscale, the Bitmap and Duotone options become available. Choose Duotone from the menu.
With Duotone, you can choose between one, two three or four inks. To set a color, click the Color box, then name the color.
You can select one of the Duotone presets to quickly tone your image.
By choosing Image > Mode > Bitmap the image is now defined by a series of black and white pixels.
Which Mode is Best?
Most people work in RGB mode because of it's color gamut. Color printers (i.e., HP, Canon or Epson) generally prefer RGB files. On the other hand, if you are creating an image to be printed in CMYK by a service bureau, then you may want to work on it in RGB and send the final output as CMYK.