How to Convert Images from RGB to CMYK in Photoshop
Recently, I was working on the files for the Villages Collector’s Box and I ran into a problem–the color profile I had used to create the images was different from the one required by the printer, and Photoshop’s profile conversion process was making my colors dull. I needed a way to control the conversion a little more directly.
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Color Theory 101
A few quick notes, in case this is the first time you’ve heard any of these terms. Computer monitors display color using tiny RGB (red, green, and blue) lights. Using light to produce color is an example of additive color mixing–the more colors you add, the closer you get to white. Modern computer screens are able to produce a lot of vibrant colors this way– about 16 million of them.
But printing a card game onto paper requires ink, and many color printers use CMYK (cyan, magenta, yellow, and black) cartridges. Mixing different colors of ink or paint is an example of subtractive color mixing–the more you add, the closer you get to black, or at least some kind of dark brown.
These two methods of producing colors are wildly different, but image editing applications like Photoshop usually do a decent job of simulating limited CMYK color profiles on RGB screens. Sometimes, this conversion reveals only minor visual differences–but other times, your image comes out looking totally wrong. And that’s when you might need to help it along.
The Problem
Regardless of my final intention for an image, I almost always create my master copy in RGB. It’s the same philosophy that calls for keeping the master copy at a high resolution–it’s always possible to downgrade in terms of image size and color, but it doesn’t work the other way around. (Unless you’re in a TV show. Enhance!!)
So, following my usual methods, this is a card image I created in RGB. The checkerboard pattern is nice and bright.
When I sent this file to the manufacturer, they requested that I convert it to CMYK. Easy enough. I used Edit > Convert To Profile... and changed the Destination Space to my Working CMYK profile, U.S. Web Coated (SWOP) v2. Photoshop magic, go!
Suddenly, the nice contrast toward the top of the pattern vanished–I had been using colors that CMYK could not reproduce. I had already flattened the image and wanted to avoid going back to the beginning and choosing new colors. I needed a different solution.
The Solution
- Photoshop has a CMYK preview mode (
Ctrl+Y) you can use to see what your image would look like in a different color profile without actually making that change.
- With the preview mode turned on, I opened
Edit > Adjustments > Replace Color...and selected the color I was unhappy with–in this case, the lighter green color at the top of the checkerboard pattern. - I messed around with the fuzziness, hue, and lightness settings until I started to see more of a contrast between the light and dark green colors.
- Once I was happy with how it looked, I accepted those settings and made the actual CMYK conversion using
Edit > Convert to Profile....
And here’s the result!
Flip through the slideshow below to see the difference side-by-side. Even the corrected CMYK version appears muted next to the RGB version, but there’s no getting around that–at least some of the contrast from the original was restored.
