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Managing Color in RGB-CMYK Conversions

(May 2008) posted on Fri May 02, 2008

Find out how image-file preparation and color-space conversion can affect color control in prepress and digital print production.


By Rick Mandel

The benefits of an RGB workflow are many. It’s far easier to maintain an accurate gray balance in RGB images, because equal amounts of RGB indicate a balanced gray. Edits to RGB images won’t result in out-of-range shifts, either, as maximum blacks and minimum whites are set to the right level automatically when CMYK conversion is accomplish-ed using a good profile.

 

Profiles

Ah, the profile—a most misunderstood part of managing color. Profiles and color management are the roadmaps for color predictability. The profile fingerprints your printing device and directs the color-management system to treat colors that won’t be reproducible on a specific device (out-of-gamut color) in a specific fashion (color intent).

We have options, for example, when reflex blue can’t be represented on a digital print device. Do we set the profile to cut it off and throw it out (absolute color intent), or compress the out-of-gamut colors to fit under the umbrella? These are two choices with two radically different results. The right one depends on the project and color needed. Therefore, it sure helps when the printer, not the producer of the file, has control of color conversion. In a nutshell, you have the understanding of your equipment’s capability, which is why color conversion is best left to you—most of the time, assuming that you work in a perfect world. I will offer counter arguments later.

Color-management systems generally perform conversions. They use color profiles that describe the space to which they’ll convert the colors. As you may have guessed, each different location in which conversion takes place has a different color-management system (software/look-up tables), which results in different color-space results. CMYK generally has a smaller color space or gamut compared to RGB.

Profile is a term that is tossed around with many meanings. Literally, a profile is a description or personality snapshot of the results a particular device will deliver. The device may be a scanner, digital camera, a monitor, or a printer. The activity results are re-orded within a profile file.


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