Comparing corrections in CMYK and RGB (Photoshop)

Even though you can perform all color and tonal corrections in either CMYK or RGB mode, you should choose a mode carefully. Whenever possible, avoid multiple conversions between modes, because color values are rounded and lost with each conversion. If an RGB image is to be used on-screen, you needn't convert it to CMYK mode. Conversely, if a CMYK scan is to be separated and printed, you needn't perform corrections in RGB mode.

If you must convert your image from one mode to another, it makes sense to perform most of your tonal and color corrections in RGB mode and use CMYK mode for fine-tuning. Advantages of working in RGB mode include the following:

• You can save memory and improve performance because you are working with fewer channels.
• You have more device independence, because RGB color spaces are not dependent on inks. Corrections made to the image are preserved regardless of the monitor, computer, or output device used.
• The gamut of RGB spaces is much larger than that of CMYK spaces, so more colors are likely to be preserved after adjustments.

Using the Proof Setup commands, you can preview composite CMYK colors and separation plates using the CMYK working space defined in the Color Settings dialog box. Or, you can preview colors using a custom CMYK color profile. (See Soft-proofing colors.)

Monitor CMYK colors as you edit in RGB mode by choosing Window > Documents > New Window to open a second window. Turn on the CMYK preview in one window and leave it off in the other.