Comparing corrections in CMYK and RGB (Photoshop)

Even though you can perform all color and tonal corrections in RGB mode and nearly all adjustments in CMYK, 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.
• The range of colors in RGB spaces is much larger than that of CMYK spaces, so more colors are likely to be preserved after adjustments. For more information, see Understanding color space and gamut.

Using the Proof Setup and Proof Color 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.)

You can edit an image in RGB mode in one window and view the same image in CMYK colors in another window. Choose Window > Arrange > New Window for (file name) to open a second window with the image you're working on. Make sure Working CMYK is chosen for Proof Setup and then use the Proof Color command to turn on the CMYK preview in one of the windows.