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![]() Color Verification: What It Is and Why You Should Be Doing It
By Dan Gillespie, Director of Technical Service, Color Management Distribution
Printers need to establish standard operating procedures for delivering accurate color as a manufacturing process that is not subjective.
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The process of color verification is generally quite easy and can be completely automated in some cases. Color patches are measured from your output and compared to target values, and the results determine a pass or fail. While the concept shouldn't be difficult to grasp, the reality is there are lots of technical details. Let's delve deeper and talk about things you should know and/or consider.
The Target Once the control strip is printed, it needs to be measured. In any color verification software, you must choose the data/profile you want to compare your measured values against. Therefore, you need to decide and define what you're trying to match. You could choose a North American printing specification as your target. (There are seven Characterization Reference Print Condition (CRPC) datasets and ICC profiles published for North America - "GRACoL2013_CRPC6" being one of them.) Some call these "standards," but they're officially regional "specifications" per the International Organization for Standardization. Or, you could choose to define your own target values/color space from one of your printers or presses. (You might want to compare several same make/ model printers to the original printer.) The values that you measure are compared to the "target" values, and a report is generated providing all the necessary feedback to determine whether that print has passed or failed. This eliminates the subjectivity of gauging color accuracy and provides scientific proof for everyone involved in the process. This means no more wondering or pointing fingers when there are problems.
Spectrophotometers
Software These RIPs can automatically add the control strip artwork to any incoming job, and they have many choices, including the North American IDEAlliance Control Strip/Wedge and the European UGRA/ FOGRA Media Wedge. Once the print is complete, you can return to the RIP, measure the control strip and print a label with a summary of results or a full report with the summary and details of every measured patch.
Automation HP's Z-series is an example of printers that currently all ship with integrated spectrophotometers. Epson offers an option called the SpectroProofer for their P-series printers, which is purchased separately and attached. If you have an integrated color measurement device, and the color verification software in your RIP supports it, you can completely automate the color verification process. In some cases, it can even be configured to print a summary label directly on each print after verification. If your printer does not have an option for an integrated spectrophotometer, you will have to measure the control strips manually. You may want to purchase a small label printer, so summary results can be printed and attached to prints/proofs.
Workflow Currently, all of the data that gets measured from the printed control strips lives on one particular computer within the company. If you're doing color verifications on multiple computers - or at multiple facilities - these data files are strewn all over the place. Using a software package that offers a database or using a cloud solution allows for all of your data to be neatly kept in one central repository. The cloud solutions have online dashboards where all of this data is accessible. This enables you to run reports and track devices, ink sets, substrates, an operator's performance, color accuracy, etc. In addition to setting up text and email notifications for any pass or fail verifications, you can import data you measured from another color verification package, so everything is in one place. My recommendation is to streamline the process and workflow to have all the data gathered in one place.
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Control Strip The aforementioned IDEAlliance ISO 12647-7 Control Wedge 2013 has 84 patches in three rows. This is a CMYK file and each of the patches are defined as specific CMYK percentages. All the patch values in this control strip are also patch values measured when creating an ICC profile. Therefore, the published measurement data and ICC profiles for printing specifications like GRACoL2013_ CRPC6 contain these same patch values. The software you use to do color verification will automatically extract the 84 patches it needs to compare to the 84 patches you measure. The colors in the control wedge are typical printing system colors: solids (CMYK), overprints (RGB), tints (CMYKRGB), gray balance (CMY/G7/NPDC) and a row of flesh/earth tones. These patches are great for monitoring the overall printing condition for all your printers/presses. (Companies who are doing color verification now are probably only doing this.) This control strip does not contain spot colors, RGB colors, or the colors that are prominent in your client's actual artwork.
Spot Color Verification A great example of how this can be done automatically is the functionality in EFI's Fiery XF RIP, Dynamic Wedge. Within the workflow properties, you can specify two control strips. One can be used to monitor printing CMYK device colors and the other to monitor client job colors. When you choose the Dynamic Wedge control strip, EFI Fiery XF will automatically scan the incoming job file and extract any spot colors, along with the most prominent colors in the images or artwork within that file, to build a 16/32/64 patch control strip on-the-fly. This is one of the only products with this capability. Having the ability to verify spot colors automatically is a critical function for many brands, printing and packaging companies whose clients require this information. If automatic is not an option, manually verifying spot colors usually requires measuring individual spot colors from within the artwork, and without a control strip, there is extra time and labor involved. The bottom line is, what do you want or need to measure and verify?
Tolerances Some patches may be important - like the three-color (CMY) gray balance patches (G7/NPDC patches) - and therefore have a very low tolerance they must be under to pass. The tolerances for printing specifications like GRACoL2013_CRPC6 are defined by IDEAlliance and are preset in most color verification software, since these are the most popular color spaces to verify to. However, you can specify your own tolerances (usually lower), if you'd like to maintain a tight tolerance between two printers in your shop and you aren't as concerned about the industry specification. Determining what your tolerances should be is up to you based on how critical color is for you and your clients. Also keep in mind that all the tolerances referred to here were for CMYK color spaces. Don't expect to hit that Home Depot orange or that John Deere green spot color within 3 Delta E, unless you have a printing device with additional ink colors beyond CMYK. The tolerance for this spot color may be 10-12 Delta E, because you simply can't match it any better than that. It is now common for brand companies to define their own color tolerances and specify them to their printing and converting partners. Instead of a specific Pantone(r) number, they may ask for a particular L*a*b* value. If they do, they not only need to specify the Delta-E tolerance, but they need to specify the comparison method (e.g., dE 2000) and the measurement mode (e.g., M1).
Comparison Methods
Comparison Results Some patches, however, have lower tolerances like the gray balance (G7/ NPDC) for their G7 Master Printer Program. Some patches have tolerances in addition to Delta-E. For instance, some patches also have tolerances for:
These values indicate exactly how the color is performing, whether it's the wrong hue, too light or dark, too saturated, not saturated enough, etc. Notice that density is not a metric included in any of the printing specifications or color verification results, because it is not a color measurement. Density can be derived from a color measurement, so a densitometer can still be utilized for process control in some cases. Knowing each of these metrics and values is essential to being able to fully understand what the numbers are telling you. In summary, you need to have the right tools and you need to use them religiously. This is what we teach in SGIA's Color Management Boot Camps, which offer hands-on training and are held across the country. Once you've got the proper hardware and software, start doing color verification on just one printer. Learn how the process works, get your targets and tolerances defined and establish an SOP for how all your devices will be monitored and maintained. As with any process, practice makes perfect. You'll be a color verifying pro in no time!
Dan Gillespie began his career with Lancaster Newspapers, where he introduced desktop publishing and honed his skills and proficiency in scanning and color separation/ reproduction for cold-set web printing.
He went on to work for GE Richards Graphic Supplies as an application specialist to train clients in graphics-related software. The only color specialist on staff, he installed scanners and proofing systems, teaching people color management around the country. In 1999, he started ColorGeek Inc., solving color workflow problems for photographers, printers, publishers and converters. He sold the business to Color Management Distribution, for which he is now Director of Technical Service, responsible for pre- sales and technical support for all its expert consultants, certified resellers and clients on design, printing, pre-press and pressroom solutions.
Besides his passion for digital imaging, printing and color, Dan is an avid professional photographer.
This article appeared in the SGIA Journal, September / October 2018 Issue and is reprinted with permission. Copyright 2019 Specialty Graphic Imaging Association (www.sgia.org). All Rights Reserved.
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