G7 printing standard/process provides an efficient method to calibrate a printing press

By Catherine Haynes

The G7 Process

The process looks something like this:

1|Define the goal—What is your definition of gray/neutral? At this point the most common target aims are GRACoL2006 Coated1 or SWOP2006 Coated 3 or Coated 5. Your customers may already be “helping” you out by defining this for you.

2|Run your gray balance target—The most commonly used target is the P2P25. It is small and should fit most print dimensions. Figure 3 shows the P2P25 target.

3|Measure and analyze the target—This was the complicated and time-consuming part of gray balancing a press, where many of us would get stuck and give up. There is now a clearly defined procedure that includes fan graphs to help ease you through the steps to manually calculate your curves; however, if that still sounds too draining, there are also a few different software solutions available, such as Curve3, that make it extremely quick and easy to do. Using the fan graph method or software, you can generate the compensation curves that will assist you in achieving your targeted neutral appearance. Figure 4 shows the recommended curve corrections to gray balance this process to the targeted reference.

4|Apply the curves to the file—This step is really no different then current curve management processes and is typically managed in the RIP.

5|Run the gray balanced plates—This step verifies the accuracy and success of the compensation curves. For processes that have more variability, further curve modifications to fine tune the results may be needed. In all cases, I can not stress enough the importance of sampling. The more samples collected the better you can confirm the consistency of your process, or accommodate for the natural variability of your process. The verification run validates the curves were successful and will pass for G7 Master Qualification.

6|Profile—Depending on your process and the ingredients you have to work with (inks and substrate primarily) you may still need to profile your process and apply color management. In this case different processes will still share a common neutral appearance, but due to ink and substrate impurities and printing characteristics like ink laydown and ink trap, color management must still be employed.

Gray Balance and G7® are two terms that are hardly new to the printing industry. Gray balancing your process is a concept we have accepted for decades as a logical step towards process control and color management, and yet still today it is not widely practiced. In essence, gray balance on press is simply calibrating the printing process similar to what we did for scanners and analog film photography in days past.

So the question we might ask ourselves is, "Why wouldn't you want to calibrate your printing press?" We calibrate all types of devices in all facets of the production process. In fact, if we step back from the daily grind of our jobs, we can cite instances where we calibrate instruments we use in our non-professional lives, too. Two obvious examples are our automobiles and musical instruments. Why do we do this? What is the benefit of calibrating a proofer or a guitar or a car? What is the relevance?

Calibration has a two-fold benefit. First, it brings a device into a known state, often one defined by standards that direct us to a commonly agreed state of order. We tune a guitar to ensure the sound is pleasing. But lets take it a step further; the real benefit is that by knowing how the guitar should sound and will react to our finger placement and strumming of the strings, we can then combine sound combinations to compose something even more pleasing than the singular sounds we have calibrated. Secondly, calibration can help extend the life of our process (or instrument). In the case of your car, it is commonly understood we should go in for regular tune-ups and oil changes. Again, the initial purpose is to bring the car back to a known state of order, to get it back into spec as it were. But I think we can all agree that there is an added benefit of improving the longevity or extending the life of the car as well.

So lets go back to the pressroom. Why is there still some resistance to adopting this concept to our printing processes? We calibrate our proofer; we calibrate our monitors; we calibrate our spectrophotometers; why not our presses? Ten years ago you could have attributed this resistance to the basic fact that it was too painful a process to complete. There were only a few resources or tools available to assist in calibrating your press and in reality it was still a fairly subjective process. This is no longer the case.

Now, we could play devils advocate here and point out that whether we know it or not, we really have been calibrating our printing process all along. Perhaps, you have been using colorimetric targets such as the IT8.7-4 to generate ICC profiles, or basic press compensation curves to help correct for printing challenges. This could be considered calibration; however, you could challenge this statement by asking, "In these processes do we target a standard, a known state that is commonly agreed upon within the industry?"

So this is exactly where gray balancing, or G7, steps in. In reality, the basic steps outlined in the G7 process are very similar to using compensation curves. The difference is in how we refine what the aim point is. Perhaps you are already applying curves in the prepress process targeting a desired gain curve or ISO curve. If so, then you have already grasped a very basic concept that is essential to successful press calibration—knowing what you want. If you get this concept then G7 is probably going to make a lot of sense. The big shift with G7 is understanding that we are now targeting a desired description of gray. We are still using compensation curves, but no longer to target a specific gain curve, rather a specific color gray or near neutral appearance. Figure 1A (p. 24) illustrates the target color primaries for GRACoL2006_coated1v2. Figure 1B shows how well the sample matched the target ink and paper standards.

If you are already using curves, which most everyone is, then this process probably sounds pretty familiar, only because it is. G7 did not reinvent the wheel, it just allows the wheel to handle the road a little better. To that point, there are some things you must have in place to make the process successful (again, this should not be shockingly new insight).

Prep work

Before I start G7 implementation with a customer there are some housekeeping items I insist we complete. First, it is essential to get buy-in from all participants of the process. It is best to start by educating management, production, and prepress on what it is we are trying to accomplish. This really sets the tone for the success of all future efforts. What everyone has to understand is that this process should be treated like your most valued customer. If everyone doesn't get this, they aren't going to take the process seriously and the project is most likely to fail.

Secondly, you must ensure your process is optimized. That includes tooling and materials used in the press room (such as mounting tapes, plates, anilox rolls, blankets, inks, substrates, etc.). However, this extends to prepress functions as well. Platemaking materials, times, temperatures, solutions, bulbs, reliefs, etc. must all be managed. Graphic screening solutions, output resolutions, output equipment, and proofing must also be dialed in.

Finally, once you have the process optimized you need to validate that the process is repeatable—every day, every shift, with every operator. Just having spectrodensitometers press side and taking measurements is not proof either. Track a few jobs between presses, shifts, and operators to identify where there may be inconsistencies requiring more attention. Now obviously, process control is not unique to G7 or gray balance. It is one of those 101-level concepts that we all know we should do, but often we don't treat it with the importance it deserves. Just like a musical instrument, the longer you put off checking and tuning your process, the further it drifts from its desired calibrated state.

Time for G7

Once you confirm you are optimized and have good process control, you're now ready. If you choose to become a G7 Master, you must then hire a G7 Expert or qualify an internal G7 Professional. The role of the G7 Expert is to facilitate the process of implementing the G7 process and submit documentation and samples to IDEAlliance on your behalf. Because G7 Experts work with other printers and are familiar with the challenges of the printing process, they can help you to navigate each step. In many cases, depending on how well the printer has prepared for the test event, it takes up to two or three days to complete the process. Depending on your efficiencies (makeready times, press speeds, turnaround times for plates, access to graphics, etc.) you may be able to complete the process for multiple substrates and/or presses in this time. With practice and good process control, this improves.

Staying qualified is then simple—provided you have good process control. A year later, you call your G7 Expert once again to analyze a new production run of the same G7 compensated test form and submit documentation and samples to IDEAlliance for re-qualification.

Perhaps this sounds a bit complicated, or maybe not, but there are several significant advantages to going through the effort to calibrate your printing process.

1. Calibrating all your processes (printing presses and substrates) to a common, known state means you can now generate one proof because all of your processes share a similar neutral appearance. This, in contrast to having to generate a proof that only reflects the capabilities or expectations of a single process. Figures 2A and 2B illustrate the pre- and post-G7 Neutral Print Density Curves. The verification run validates the curves were successful in aligning the press to the target NPDC.

2. If color management is still necessary, having calibrated to a neutral gray among all your processes will still ensure a similar neutral appearance, allowing color management then to reflect the changes in the more saturated areas of the gamut. Also, by gray balancing first, you improve the accuracy and longevity of the profiles used for color management (just like regular tune-ups for your car may add miles to its life).

3. The G7 process requires process control to be successful, and using process control is going to provide unexpected returns in making you a better printer and improving your efficiencies. By giving your operators specific targets and the tools to help them manage the process there is no need to constantly tweak the press conditions. If they hit the aims established through the process, they will match the proof.

4. To appeal to the sales folks out there, this is an opportunity to prove you can provide your customers with products that will help them achieve a common appearance across all their product lines. Remember they may have products printed by a variety of processes and if you can help them to simplify the process and target a common standard then you come out looking like one of the good guys.

About the author—Catherine Haynes is a qualified G7 Expert and a member of the Technical Solutions Group at All Printing Resources. pP