My wife and I enjoy action/adventure movies. For us, there is nothing better than blowing some stuff up. I believe this article will be very helpful and informative, but to begin with, I need to blow up some misconceptions. So, here comes the first bomb drop: CMYK does not define a color. CMYK (Cyan, Magenta, Yellow, Black) is a device dependent color space. What the CMYK values look like depend on the device that is doing the printing. Colors the eye can see are defined in a device independent color space like L*a*b* and then translated into CMYK.
This leads me to my second bomb drop: There is more than one CMYK combination for any color. We see this all the time, especially in brand guides. A brand will call out a Pantone color like Cool Gray 7 and have one set of CMYK values listed, as if that is the only CMYK combination that will work on all devices and substrates. The truth is, except for a color at the very edge of a color space boundary (like 100% Magenta), I can make a color like Cool Gray 7 from dozens of different CMYK combinations. Remember, Cool Gray 7 is not defined by CMYK, it is defined by spectral data translated into L*a*b* values. Which CMYK combination gets you the closest to the color you are looking for depends (device dependent, remember) on the gamut of the device.
Spoiler alert: The bomb drops above will help you understand what comes next about Gray Component Replacement (GCR).
Why Should I Care?
You may be asking: “Why should I care? I send you my file and you print the CMYK values in it, right?” In a digital environment like inkjet, no; your printer is going to convert those CMYK values in your file to different CMYK values. If we think about it, all design work is actually created for litho/offset printing, usually US Web Coated SWOP v2 (the default in the Adobe Creative Suite). Most digital devices, especially inkjet, have a gamut either larger or smaller than SWOP. Also, the process color ink or toner in our digital devices usually looks nothing like SWOP CMYK inks. Therefore, in order to maintain the look of the design, the CMYK values in the file are converted into new CMYK values accurate for the digital device. This is where GCR comes in.
What is GCR?
GCR is a way of separating a color (defined by L*a*b*) into CMYK by removing amounts of CMY (the gray component) and replacing it with black. Another method for doing separations is UCR (Under Color Removal). The main difference between the two is UCR only affects the grays and shadow tones, while GCR affects all color ranges. While there are advantages to each method, most of the advantages of UCR are realized only in litho/offset printing, so we will be focusing on the advantages of GCR for digital/inkjet printing.
Most profile-making software allows you to control the amount of GCR in the separation. This can range from a very slight amount of added black to extreme amounts of added black. Which range you choose depends on the type of designs you are printing and the type of presses you are using. If you are unsure about what level you need, ask a color management professional (like me).
While the list of benefits from GCR is long, I would like to focus on a couple of ones that are most helpful.
Stability and Savings
Two of the biggest benefits to GCR are stability and ink savings. Regardless of printing technology, by removing amounts of three different inks and replacing them with black, you are simplifying the separation, making it, by its nature, more stable and less susceptible to variation. The more unstable a printing process, the more GCR can help improve stability. Very unstable printing processes like litho/offset can benefit greatly from GCR, which can stabilize things like gray drop shadows around an object. More stable inkjet devices can take advantage of GCR, as well. One concern with inkjet printing is laying down too much ink on a substrate, which can cause cockling. GCR can help combat this. The additional benefit of all of this is that if you are removing more expensive CMY inks and replacing them with less expensive black ink, you are saving money as well. And who doesn’t want to do that?
Increased Gamut
One benefit that is not often talked about is how GCR can increase your gamut in darker colors. Let’s take a very saturated red at 100% magenta and 100% yellow. If I want to darken that red, there are two ways: by adding cyan or by adding black. Which method will maintain a fuller gamut? Let’s look at some ramps below:
As you can see, adding black allows the color to get darker, while still staying saturated. Adding cyan makes the color darker, but grayer or duller, as well. Converting from RGB to a CMYK profile that uses higher GCR can allow you to capture more gamut in those dark colors.
Summary
Understanding and implementing GCR can greatly help you print better with inkjet. Whether it is better stability, better ink savings, or a wider color gamut, explore what GCR can do for you. As always, feel free to drop me a line with a question or comment.
Mike Todryk is a Color Technical Specialist for IWCO Direct. He has more than 20 years of printing industry experience and has specialized in Color Management for the last 18.