Offset printing help: Conversion of PMS colors to process (CMYK)

Color conversion from PMS to CMYK can be tricky

Improvements in desktop publishing software and computer technology have made four-color process printing more affordable. Before this many pieces were printed in one and two colors. Four-color process uses varying strengths of standard blue (cyan), red (magenta), yellow and black (CMYK) inks to replicate many colors of the spectrum. For more information on how four-color process works, please read more on this site.

Another way to print colors is to print a specific color of ink. Let's say you are printing a simple newsletter and you want the headlines in red and everything else in black. The headlines would be printed in a specific red ink, identified by a PMS (Pantone Matching System) number. This system is similar to buying paint. You select a color from a swatch. The service person then makes your color by mixing a few base colors in varying quantities. You end up with the color that matches the swatch.

The PMS system works the same way. You select a color from a book of swatches. There are fourteen base colors that are mixed to yield other colors. The end product is denoted by a number, say PMS 285 for instance. You could have something printed in Chicago or Copenhagen and the color would look the same as long as they use the PMS system.

The limitation to the PMS system is that every color you want on your piece needs to be a separate color. That is impractical for reproducing a color image such as a photograph. Thus four-color process was born. The image is broken up into varying intensities of the four CMYK colors. When these are printed on top of one another they combine to form all of the colors in the image.

In truth, due to the amount of pigments in the base colors, four-color process can't produce all the colors you may want. As an example, look at the cyan color in the illustration above. As you can see, it isn't very dark. When an image calls for a dark blue, the basic building block color (cyan) isn't very dark. Therefore, dark blues have a tendency to lack vibrancy and power. Remember, standard PMS colors have 14 base colors whereas CMYK has only four. We'll get into this more fully later in the article. For now, just realize that CMYK can't produce all of the colors we see.

This isn't much of a problem in photographs. Most often the overall look of an image is fine. Issues arise when people expect colors that four-color process isn't capable of producing. Take a logo for instance. Let's say a large company such as The Home Depot wants to print its orange logo. They will specify a PMS match that can be reproduced anywhere. However the CMYK "equivalent" of the PMS color may not match exactly. If The Home Depot is picky about its logo, this may be a problem.

If you specify a PMS color in a piece to be printed in four-color process, the color will be converted to a CMYK mix. Changes in color can range from subtle to substantial. See the color chart below. The swatches on the left show PMS colors. The swatch on the right is a CMYK version, an approximation of the PMS color. As you can see, some colors convert quite well to process and some quite poorly.

Please note: These representations are being viewed on your monitor via the internet. Don't rely on them. They are for illustrative purposes only and are inherently not accurate. However I have made them relatively faithful. Those colors that transfer well from PMS to CMYK look so here. Those that don't, also look so here.

Color	Notes
Red	Darker reds convert quite well. Lighter reds lack the brilliance of the PMS counterpart.
Bue	Blues do not convert well. In CMYK, most blues end up looking dull or flat when compared to the PMS. They end up looking like "steel" blue instead of a nice, vibrant color.
Green	Lighter greens do not convert very well. They end up looking dull or dirty. Darker greens convert quite well with the exception of blue-greens. These colors don't convert well.
Purple	Most purples don't convert to CMYK very well. The exception is plum colors. These convert quite well. Vibrant purples convert especially poor.
Yellow	Lighter and brighter yellows convert well to CMYK. Darker and those yellows which tend towards orange do not convert well.
Brown	Most browns convert quite well.
Orange	The darkest of the oranges convert well but most others loose their vibrancy when converted to CMYK.

What can you do?
You’re looking for predictability. You want to have a good idea what the final printed piece will look like before it arrives on your doorstep. There are a few ways accurately predict in the design stage what the final printed piece will look like.

The best assurance you can get is to specify colors as mixes of CMYK and not PMS colors. Where do you find a chart of colors in CMYK? Well Pantone has produced a Color Imaging Guide swatch book. This tool shows side-by-side color swatches printed in spot PMS inks and the accompanying CMYK conversion printed in four-color process. If you do not yet have a Pantone book, this would be a good first one to purchase.

Think of the Process to Solid Guide as a large expansion of the color chart we have shown in this article. The book also details the CMYK mix so you can specify the color to be used. These books cost around $100.00 and are available from Pantone on the internet at www.pantone.com.

Talk to your printer about the accuracy of his or her proofs. You should be able to look at the proof he provides and be confident the final printed piece will look fairly close in color. If not, it's time to find another printer.

Finally, if you just can’t live with the process equivalent of a color, your piece can be printed with a PMS color along with the four base process colors. This technique is frequently used if a specific color is needed for a corporate logo or a substantial area such as a background. It's more expensive to add a "fifth color" but in the end may be the prudent path.

So don't be disappointed next time you receive your printed color piece. Arm yourself with proper information so you know what colors to expect.

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