How to Convert from RGB to CMYK Color Mode in Photoshop CS6

By Barbara Obermeier

Sometimes in Adobe Photoshop CS6, your image starts out in one color mode and then you find you need to convert the image to another mode. Maybe you have to strip the color out of an image you’re submitting to the local newspaper. Or maybe you have to convert your RGB image to CMYK to get it ready for an offset print job.

When you convert modes, you’re permanently changing the color values in your image, so save a backup image, just in case.

The following pointers are for the most common conversions you’ll make. If you want to convert an image into an indexed color for the web, your best bet is to use the Save for web option.

CMYK is the image mode necessary for high-end composite printing and offset printing. You first want to perform all your necessary image-editing tasks in RGB mode for the following reasons:

  • The image size is smaller because RGB mode has only three channels.

  • The RGB color space provides more device independence because it isn’t reliant on inks.

  • You have full accessibility to filters and image adjustments.

  • RGB mode provides a large color gamut, so Photoshop preserves more colors after it makes image adjustments.

When you finish editing the image in RGB mode, you can convert the image from RGB to CMYK (you can perform fine-tuning in CMYK mode). If you’re new to this procedure, you may be surprised at the result. You may see a color shift (from slight to major) because the color gamut (range of colors) of the RGB model (16.7 million) is much larger than that of CMYK (approximately 55,000).

The extent of the shift depends on the colors in the RGB image and how many of them are out of gamut. Photoshop replaces RGB colors that are out of gamut with the closest match available within the CMYK gamut, often replacing the electric blues, fiery reds, and sunny yellows with duller, muddier CMYK equivalents.

Unfortunately, you can’t do anything to prevent this replacement. It’s just the way of the world of color. However, if you can select colors (instead of acquiring them from a scan), be sure that you don’t select any colors that are out of gamut to begin with. You can also soft proof colors (preview the effects of your CMYK conversion without actually converting) by choosing View→Proof Setup→Working CMYK.