How to Match Multiple Printers

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Calibration of a single printing device is not always the easiest task, so it’s perhaps no surprise that matching multiple printers to each other is a significant challenge. With the rise of digital printing, our commercial printing customers frequently ask: “What is the best way to profile multiple devices of the same model?” The good news is there are tips you can follow to make color-matching across multiple printers a success.

If you are trying to achieve a close visual match between printing devices, there are three key things to consider before putting ink on the sheet:

1) Printer gamuts have to be pretty close between devices. This of course has a lot to do with substrate texture and ink texture (rough textured media and/or UV inks both exhibit more light scattering properties due to their roughness vs. solvent on glossy substrates).

2) It is necessary to evaluate more than just the worst ∆E value. You need to know how all the patches in a control strip compare in ∆E, not just the worst or the average. When choosing a control strip,the more patches, the better, as long as the chart doesn’t become too large for practical daily use. The more patches under 1 ∆E, the more likely the printing is visually close, as you are comparing all patches in the strip to themselves and ranking them on visual closeness.

3) You can’t compare to an industry reference, like GRACoL, when visually comparing devices. You have to compare one device as the reference to the other, because that’s what you’re looking at in the viewing area. You can’t see GRACoL, as there is no perfect GRACoL proof, but you certainly can see the difference between printer A and printer B, so make printer A the reference when comparing those two devices. Hopefully with grouping tests you can compare multiple devices to one device.

Tight calibration of the device and the ability to truly recalibrate back to the same known state the device was in when profiled is key. From my experience, the automated “recalibration” process does not always work well in the field. Some RIPs are better than others, but the bottom line is for true recalibration to work successfully it has to be a two-part process. First, you have to achieve the same solid ink value that was in the original calibration, and second, you have to then create the same curve along the values between 0% and 100%. Most RIPs do the latter, but few actually do the former during the automated recalibration process. This is important, because if you can’t fully recalibrate the printer, the original profile is eventually going to be too far off the mark to be useful.

Also consider: very rarely do two of the exact same devices that are exactly the same age print the same color right out of the box. I’ve proven this many times when evaluating color output data during calibration sessions. There is no way to successfully use a single profile for multiple devices that aren’t even close and achieve a tight visual match. My advice is to target the same source reference space (GRACoL as an example) for each device, then calibrate and profile each device as carefully as possible to achieve as tight a match as the RIP can provide to the source reference space. When finished you can compare how close each device is to one another by printing a test chart and comparing the measured results. Now that being said, RIPs that have iterative optimization have a much better chance of achieving a tight calibration between multiple devices than RIPs that can only rely on ink limits, linearization, and icc profiles alone.

You certainly can and should run comparison tests between all your devices (ideally on a single substrate all devices can print on) to identify which devices are the closest to one another and group them accordingly. The point here is to get to know each and every device (it’s gamut, how consistently it prints, etc.). Maybe you get lucky and find several devices that actually are close enough to calibrate using a single profile. Only after going through the process of calibration and evaluating the results can you truly know the color capability of each device.

I have installed many pairs of Epson aqueous printers and have never found two that calibrate the same or profile the same, however, following the process described above will get them to the closest possible visual match.

SpotOn! Verify is the ideal tool for comparing the calibration results of each printing device. SpotOn! Analyze is the ideal tool for setting ink limits and examining the color differences between each printing device. Try them for yourself!

Print Management Case Study: How One Customer Achieves Global Color Control

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A couple of years ago I was working with a well-established company in Pennsylvania that specializes in “museum quality” art and photography books. They were considering several titles for their first Asia production attempt, but the company was concerned the quality that their reputation was built upon would not be upheld by the new contract facility. At the same time, they wanted to implement a color control and monitoring process at their US factory.

The company’s ultimate objective was to bring the proofing of both facilities to within 90%+ of GRACoL 2013 target values using the SpotOn! Visual Match Scorcard. At press we matched the printing color to these accurate proofs. Achieving this goal would ensure their customers continued to receive the same high quality products regardless of where these items were printed, and the company would be able to efficiently control color in two facilities nearly 8,000 miles apart.

This was a job for color experts, so we asked Bruce Bayne from Alder Technologies to spend several days in the Pennsylvania facility and calibrate their new Epson SC9900 proofer. He also installed SpotOn! Verify to bring their quality monitoring and QC assurance procedures to the next level. Moving forward, Verify would be used to control the print process by monitoring and tracking the consistency and accuracy of proofs made in the US and abroad.

Next, the highly skilled Cathay America team used SpotOn! Verify to calibrate and monitor the Epson proofers at the printer’s new facility in Shenzhen, China. Verify’s Visual Match feature guided our calibration work and helped ensure proofers on two continents would match accurately.

Finally, the US based press was calibrated, and the Cathay America team calibrated the presses in China. Both were able to achieve GRACoL2013/CGATS/CRPC6 target values. This was the last step to bring all of the proofing and production devices into alignment.

The next step was to implement a global monitoring and QC assurance system (process control) that would allow our customer to achieve the same high quality presswork over time, regardless of where their books were printed.

Thanks to the support of Bruce Bayne, our China team, and SpotOn! Verify, our customer was deeply impressed by the quality of their first prints from Asia. Both the US client/printer and the photographer whose work we reproduced were thrilled with the quality of the images in this very impressive book. Most importantly, our US client was confident that he could print his high quality museum editions at our China facility.

Since this first successful printing last year, many more titles are now being produced with excellent color. This was possible because of our process control program enabled by SpotOn! Verify.

Details follow:

The printer had 10 fairly new, well-maintained Komori presses, each with an Intellitrax scanning spectro. But the intellitrax software was several generations old and didn’t report anything more that solid ink densities (SID).

This limited color data was simply not enough information to tightly monitor production printing and achieve the accurate and consistent color control that we required. The printed images were quite well known, and our client needed assurance the original images could be reproduced accurately.

We decided to print on a slightly larger press sheet so that we could add a second set of colors bars at the trailing edge of the sheet. One control strip was placed in each of the four alleys of the book pages, just below the Intellitrax scanner’s control strip. These 18-patch, custom color control strips were designed to be scanned by a i1Pro2. After scanning, the measurement data was sent to SpotOn! Verify.

Press proofing key images before the production run. Notice the SpotOn! Version 2 color control strips  that run vertically. This allowed for SpotOn! Analyse to measure and display comprehensive printing data.

If the press has shifted too far out of spec, the ink can be leveled accurately by scanning the press color bar with X-Rite’s Intellitrax system. The next step is to scan the custom color control strips in each of the four alleys with the i1Pro2 and SpotOn! Verify to monitor compliance with CGATS21/CRPC6 target values.

Verify clearly displays the data from each scan for the operator to evaluate compliance with the CGATS21/CRPC6 target values. If the press is out of compliance, the operator can take further corrective action to bring the press back into tolerance before running color-critical jobs.

Patches: C, C50, M, M50, Y, Y50, Red, Green, Blue, 3/c Black, 100k, 25k, 25cmy, 50k, 50cmy, 75k, 75cmy, paper white

Customer Q & A: Which Wedge Is Best?

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Recently, a color process control manager at a large print production facility wanted to know if there is a more comprehensive chart available for daily digital color evaluations than an 12647-7 proofing wedge. He pointed out the IT8.7-4 has too many patches, and the P2P51 has too many gray finder patches. Reiterating a thought we’ve all had many times, he asked: “Am I overthinking the value of additional patches?”

Great question!

There is a trade-off between patch count and how effective a chart is at gathering QC information. There is also something to be said for both extremes; too many patches and too few patches. Too many patches on a noisy (grainy, low screen ruling, etc.) printing device can cause unwanted noise in the measurement data (like using a 1 pixel eyedropper setting in photoshop to determine the dot percentage in a noisy image). Too few patches and you are not sampling enough colors to accurately model how the device is printing.

Read more at the SpotOn! blog