Why you should provide CMYK files for print

We’ve seen it dozens of times. Clients who supply RGB artwork often find that the color on their finished piece has shifted. The fact is that all full-color print files should be created and supplied to your printer in CMYK. There are cut-and-dry reasons for this. Lets take a minute and try to unravel why CMYK is king of print. First, lets define the key players when it comes to color:

RGB Color Space
RGB is a color space intended for the screen. Its acronym stands for Red, Green and Blue. All of the colors within the RGB color space are created by some combination of red, green and blue light. RGB is what is known as an ‘additive’ color space. When the colors are added together you get the color white. Likewise, when you remove all of the color, you create black. The RGB color space has a large range of colors that it can create—16 million to be exact. This range is known as ‘gamut.’

CMYK Color Space
Conversely, CMYK color space is intended for print. Its acronym stands for Cyan, Magenta, Yellow and Black (denoted as ‘K’ so it is not confused with blue). CMYK is often referred to as four-color-process. It is called a “subtractive” color space, because the removal of all colors results in white, where as the addition of all colors results in black. Although you can produce thousands of colors with CMYK, it has a much smaller range—or gamut—of colors than RGB does.
Now that we have called out the players, we can start to understand why RGB artwork doesn’t translate well to print:

Differences in Gamut
After studying the definitions of RGB and CMYK color spaces, the concept that RGB has a much larger gamut than CMYK is pretty evident. When an RGB file is supplied to a printer, the printer must convert the file to CMYK. There is just no other option. Because of the difference in color ranges (gamut), when the RGB file is converted, it is forced into a smaller range of colors. Through the conversion process, the software analyzes the image and reconfigures the colors into the closest CMYK equivalent. This can leave the new CMYK image looking dull in comparison to the original RGB image.

Differences in Medium
RGB is for screen. CMYK is for print. The two color spaces are created for their own specific purpose and in order to get the best results, they need to be used as they were intended. When colors get duller in RGB to CMYK conversion, its not because CMYK is a inferior color space, but that RGB simply has properties that it cannot replicate. Techno-bright colors can be achieved in RGB because the colors are created from light, whereas the paper CMYK inks are printed on cannot emit light and thus, cannot produce as bright of colors. The fact is that sometimes screen colors are just not reproducible with ink and vice-versa.
Now that you have all this RGB/CMYK knowledge, you probably want to know what to do to make sure you don’t have to deal with RGB to CMYK print conversion surprises. There are a couple tips that should make your print projects turn out as you have envisioned them:

Edit your photos in RGB, but place them in CMYK
If you have to make edits to photos used in your piece, you will want to make the major edits in their native, RGB format and then convert the final image to CMYK. The reason for starting in RGB is because the gamut is greater, you have the ability for much more precise editing. Once your edits are made, convert the file to CMYK and save a copy of the image for placement into your artwork.

Design in CMYK
Always make sure to design in CMYK. If you are working on a design element in Photoshop, make sure to be working in CMYK, or you could get an unpleasant surprise when you go to convert the file to send for printing. This also goes for files created in InDesign and Illustrator. Both of these programs give the option to work with RGB colors or in RGB mode, so make absolutely sure you are working in CMYK by making sure all swatches are created in CMYK (in InDesign) and that your Document Color Mode (in Illustrator) is set to CMYK.

When you have a solid understanding of RGB and CMYK color spaces, it makes it easy to produce the right kind of art for the right medium. Hopefully this little primer on RGB and CMYK usage will serve you well and help you avoid unexpected color conversions in the future.