All posts by Bruce Bayne

Image of SCCA

How Substrate-Corrected Colorimetric Aims (SCCA) Work in SpotOn!


Recently, we have been trying to highlight various features within the SpotOn! Analyze and Verify software that both users and non-users may not know exist.

One of those features was Visual Match Scorecard. Another is SCCA or Substrate-Corrected Colorimetric Aims and that’s what we would like to discuss today.

What Is SCCA?

Substrate-corrected colorimetric aims refers to a mathematical formula that approximates the L*a*b* values on a different substrate.

According to the Idealliance site when describing SCCA:

“The value of SCCA in the G7 Master process is that it allows a print or proof made on a non-standard substrate to be judged for its “relative accuracy,” i.e. how it would appear to an observer in the absence of a comparison proof.”

That is why SCCA is referred to as substrate relative.

The SCCA Calculator

A while ago, we helped develop an SCCA calculator for Idealliance. It’s free and anyone can access it. You can view the calculator here.

If you take a look at the image below, you can see that in this example of the calculator we are referencing GRACoL 2013 (CRPC 6). The L*a*b* values of the substrate (first column and row under the Analysis chart) are 95, 1, -4.

On the left, we can choose a test chart, like the TC1617, and measurement condition, like M1. In the fourth option down on that left-hand column, we can alter L*a*b* values for our desired substrate. In this example, we changed the b* value to -6 instead of -4.

Back under the Analysis chart in the second column, you can see how the SCCA calculator adjusted the values for CMYK, RGB, and neutral colors based on the desired substrate’s b* value change.

In the third column labeled “Deltas,” you can see the effect of the substrate change on the CMYK, RGB, and neutral patches.

Image of SCCA

SCCA in SpotOn!

From the SpotOn! startup splash screen, you can choose Settings (the wrench and gear icon in the image below).

Image of SpotOn! startup screen

Choose to change the settings of Analyze/Verify in the top menu and choose Tolerance Sets (highlighted in blue below). The ability to turn on substrate relative or SCCA is one of the options in a tolerance set. We suggest picking an italicized tolerance set (system default tolerance sets) that doesn’t have SCCA turned on (G7 Targeted has it turned on) in the list at left and making a copy of it (duplicate). Then you can turn on the SCCA option by checking the Substrate Relative checkbox and Saving that tolerance set with a new name. I usually add SCCA to the end of the tolerance set name so I know that SCCA is turned on for that tolerance set vs. the original where it is off.

Image of Settings Screen

When Should You Turn On SCCA?

When you verify your print and your problem areas are in the whites or lighter colors, it’s often due to the difference between the substrate being printed on and the reference set substrate. Try using the new tolerance set you just made that has the SCCA or substrate relative option turned on.

Image of Substrate Patches

It’s important to note that substrate correction isn’t always the answer, but it can be a powerful tool in SpotOn! just like the SCCA Calculator.

Visual Match Scorecard: A Pictorial Explanation


SpotOn! users are probably pretty used to gauging their print consistency by just the basic pass/fail metric. Perhaps they don’t even venture from this Verify screen (as seen below) where the control strip is measured. Maybe this screen has enough information for them. But maybe not.

We’d like to explain how the Visual Match Scorecard in SpotOn! works at a higher level than just a pass/fail.

Image of SpotOn! Verify Control Strip

This was a verification of a press run, which is why it’s a single row control strip. The pass/fail metric is popular because it can show the press operator problems with CMYK or gray. But it doesn’t show you what the color is going to look like and that’s what makes Visual Match so much more effective. With Visual Match, you are getting an assessment based on the visual appearance between the print and the reference or proof.

For this particular press run, measurements were verified and compared to GRACoL® 2006 over time. Here’s a report of that press run over time using the pass/fail G7® Targeted metrics.

Image of Visual Match Scorecard Blog Pass-Fail Device Graphs GRACoL

 

Pretty confusing as to how that press run went, right?

Now let’s take a look at a report of that very same press run using the Visual Match Scorcard.

Image of visual match report new

 

The Visual Match Scorecard allows you to see the results of each measurement in a single metric, making it much easier to compare those measurements. In the report above, the measurement in yellow was the closest to GRACoL 2006.

Since that measurement was the closest to GRACoL 2006, we made that measurement the reference target. As you can see by the chart below, the last two measurements now stand out among the rest as having no visual difference from one another. (See the green bar color in the chart below.)

Image of Visual Match Scorecard Reference 2

So, by using the Visual Match Scorecard feature, we’ve gone beyond just the industry standard pass/fail metric. We’ve included the actual visual appearance into the verification process. The goal is to not rely on a bunch of pass/fail metric values that are great production control metrics (like solid ink density) but don’t inform us about the consistency or quality of the color. While press operators might like this approach for running an offset press, it isn’t helpful from the client perspective of needing their color to match what was printed last time.

Suppose you as a printer were tasked with printing another company’s business card with a brand color. Then three months later, they hire a new employee and need business cards for that person. You print the new cards and the brand color doesn’t match. Obviously, the client is not happy.

Sure, you can run the print with a control strip, measure it and compare it to a target to get a pass/fail. But the customer doesn’t care if the print passes when compared to GRACoL 2006. They care that the two business cards with the company brand color don’t match and are very visually different.

We recently published a blog post where we used a bull’s eye target to display the differences between two printers. A client had two printers of the same make and model. They used both printers to print the same job. Over time, the prints began to look visually different. When compared to GRACoL 2006, both printers passed. But when compared to each other by making one printer the reference point, they were far apart. That’s because the printers drifted in different directions.

Image of SpotOn! Bulls Eyes

On the left is the comparison of each printer to GRACoL. On the right is the comparison between the two printers. The colors represent the colors used in the Visual Match Scorecard.

The point here is that while the individual printers may result in a pass status, they may still be unable to print consistent color compared to one another. If you are only relying on the pass/fail metric to GRACoL, you wouldn’t be able to identify the true visual difference between the two printers. Visual Match Scorecard provides a true visual assessment that helps you better “see” your color consistency. When the Visual Match score indicates a change in color accuracy, you can actually see that difference.

If you would like a personal online demonstration of how Visual Match Scorecard works, please contact us and we will get it on the calendar!

Image of SpotOn! Dashboard

New Users And Frequent Users Alike Benefit From SpotOn! Demos


SpotOn! Analyze and Verify as a software package has a lot to offer. In fact, there are so many invaluable features and charts that it can seem overwhelming. And as we discovered in our previous post, some of our frequent users aren’t necessarily aware of some of the features within the software.

Look At All The Data!

When you look at the SpotOn! dashboard after measurement for verification, it may appear like there is too much data to absorb all at once. We believe that it is good to include as much data as possible in our software solutions (and we are always trying to improve upon it) because our current users and prospective users all have different color management strategies and workflows.

Image of SpotOn! Dashboard

Indeed, no one will probably use every single data chart and feature available in Analyze and Verify. Every client of ours has to decide what data is pertinent to their own facility’s workflow.

Personal Demos Available Upon Request

Often, we find ourselves chatting with current clients for other reasons and we ask them to describe their workflow to us. We can almost always recommend a certain data chart or feature that they can use to assist them in their color management strategy.

But until they reach out to us and talk to us about their workflow, we can’t make such recommendations. That’s why we want to put out the word that we are happy to schedule a personal online demo via Zoom where we can discuss your individual and your facility’s needs. We try to keep the demos to an hour or less, but we also want to make sure we answer all your questions.

What do the demos look like? Well, we are glad that you asked! Last month, we had a demo for a current user and a potential new user. We recorded it and below is a sample of some of the features we discussed.

If you would like to schedule a personal demo of SpotOn!, please contact us and we will be happy to pencil you in! Enjoy the video.

A SpotOn! User Learns New Features For Workflow


Last month, we published an interview with one of our clients who we referred to as “Jane.” She shared how she used SpotOn! in her color management workflow and what she considered essential features. You can read that blog post by clicking here.

We discovered during our interview that while Jane is a frequent SpotOn! user, we had the opportunity to help her with her workflow. There were some features in SpotOn! that she either wasn’t aware of or wasn’t using to her benefit.

For example, we realized Jane was exporting her results into an Excel spreadsheet so that she could share the data with multiple facilities in her company.

Image of Excel Chart Data

We were able to show her through a Zoom meeting (Zoom really is popular right now, isn’t it?) that SpotOn! has a reporting module where you can view a Verify Device Report. It’s easier to read visually and using this feature would save Jane some steps in her color management workflow.

Image of Verify Device Report Multiple Devices-1

 

In addition, we told Jane the store of Bonnie and Clyde, two identical inkjet printers that were originally calibrated to match the GRACoL® specification. Over time, both printers drifted away from the GRACoL target and then later the two printers were no longer printing the same as each other. The same file printed on both printers turned out very differently and it was quite noticeable.

However both printers were still technically passing the GRACoL specification so how could they be printing so differently?

We showed Jane our bullseye visual. The printers did drift, and they drifted in different directions. So while they both were within tolerance of the GRACol specification, they were far apart from each other visually.

Image of GRACoL Bull's Eye

 Above: Both printers compared to GRACoL.

Image of GRACoL Bull's Eye

Above: Printer 2 compared to Printer 1.

SpotOn! has many features in both Analyze and Verify. And as we have seen, even our most robust users aren’t necessarily aware of all of those features or how they can be of use in your color management strategy.

If you are a SpotOn! user who would like to learn more about the program’s features or if you are considering incorporating SpotOn! into your workflow, contact me to schedule a demonstration.

A SpotOn! User Shares the Benefits of Visual Match Scorecard


It’s easy for the developers and dealers of color management software to talk about the advantages and disadvantages of that software. We can use online demonstrations to explain how it works. We can talk to you about it at trade shows or during onsite training. We are always looking for better ways to explain our features; such as Visual Match Scorecard.

What we can’t do is tell you about the software as it is experienced by someone who decided to invest in it and use it as part of their daily color management strategy. So, we found someone who could.

Jane* is a regular user of our SpotOn! Analyze and Verify software. She also incorporates our Visual Match Scorecard feature into her everyday profiling.

We wanted to tell Jane’s story about her color management process and how SpotOn! is now a part of her strategy to maintain consistent color.

During a recent conversation with her, we realized that no one could tell her personal story but Jane herself. So, in a traditional question-and-answer style, we interviewed her. We invite you to read on and find out more about her path.

The Interview About SpotOn! Visual Match

Q: What kind of processes, substrates, printers, etc. do you use?

Jane: My company prints grand format dye sublimation prints on textiles. We use both the transfer and direct method of printing. We also use UV and latex printers. We have the capability to print on any rigid substrate as well as soft signage.

Q: What are your color management pain points or what issues do you run into most often?

Jane: One word: gray. To be more specific, neutral gray.

People have multiple opinions about gray and throw out the term without actually realizing what they are asking. Gray, by definition, is neutral. This means that there are no colors in it. Many people think that a color that does not have much chroma is gray, when in reality, it is a color.

One of the other problems I have run into is people are stuck in the dark ages of printing where relying on eyes and memory was the way to color manage. We have tools, like spectrophotometers, and software, like SpotOn!, that are driven by data as a means of measuring and analyzing colors, profiles and consistency.

Q: You’re a regular SpotOn! user. How do you use it most?

Jane: Regular might be an understatement. Not only do I use it every time I profile, but also when verifying profile validity. SpotOn! has been a game changer for me as a color manager. I use it to see how close our profiles are within different tolerance sets as well as how the profiles measure over time.

Editors Note: The image above is an actual report from one of Jane’s verifications. Step one is to get as close to an industry specification as possible, using Verify to compare to published specifications like G7 Targeted.

Q: How does the Visual Match Scorecard fit into your color management strategy?

Jane: The Visual Match Scorecard is critical for my position. I measure the profile once I complete it to see how we compare to the tolerances set by Idealliance. Then I make that my reference with the plant, machine, substrate, resolution and a date stamp.

I use this reference to compare the machine/profile/resolution combination to itself and to different machines across the company’s different locations. I have set up a profile verification program for each facility in our company to send me a control wedge along with other control prints and a nozzle check every two weeks. The visual match score is recorded in a simple spreadsheet to track the degradation of each printer/substrate/resolution combination. It helps us visualize possible issues.

Editors Note: The Visual Match Scorecard excels when it’s time to compare today with weeks or months ago when the baseline print was created. In the world of grand format dye sublimation there can be significant drift but maintaining a good visual match score has proven to be sufficient for the work Jane’s company produces.

Q: What’s the biggest color management challenge you have solved using SpotOn!?

Jane: Before I was hired, the most color “management” was having one profile that was created during RIP training many years ago. Our team members used their eyes and many workarounds to create an acceptable output. By managing the color and proving by numbers/science that we are now within industry standards, which they did not know about, was one of my initial challenges.

One of the biggest challenges has been using the data and visual match of our profiles over time to see if we have shifted and are within tolerances. We have been using the data I am able to pull from SpotOn! to prove when I need to re-profile, anticipate potential issues and confirm shifts we are seeing visually through data. I wouldn’t be successful in my position without SpotOn!

Q: What are the biggest advantages in using SpotOn! and Visual Match?

Jane: The biggest advantage of Visual Match is being able to see the consistency of a printer/substrate/profile combination. By tracking the performance of the printers, we are able to understand what variables are causing problems with data rather than relying on our eyes. Managing color across three facilities across the United States is not an easy task. This feature has allowed me to visually see how far the printers have drifted and when to get them back into tolerance.

Image of Jane's trending spreadsheet

Editor’s Note: During our interview, we discovered that Jane was exporting her data into an Excel spreadsheet to share with her different facilities. Since SpotOn! has powerful reporting tools that Jane either wasn’t aware of or just wasn’t using, we realized we had an opportunity to help a client with their workflow. The results of that opportunity will be published in our next blog post.

Q: In your opinion, what is the best feature of SpotOn!?

Jane: Visual Match Scorecard, without a question. It allows color management to go beyond tolerances and actually analyze profiles across multiple platforms. Two printers can hit the same tolerance but not visually match between the two. The human vision is limited and is different for each individual, but the data does not change and is not subjective.

Q: Tell us about your color management journey.

Jane: During my junior year, my school offered a class for printing and photography. I learned L*a*b* and printing techniques. Then in graduate school, I worked at two sister print facilities. Not long after graduation, I had the opportunity to work at a fast-paced fine art printing company to run their print department. Three years later, I took an SGIA Color Management Boot Camp with ColorCasters and decided to pursue color management. Now I am the color manager for three grand format printing facilities in the U.S.

*Editor’s note: Jane is a real person working with SpotOn! in a real-world printing environment. While she does prefer to remain anonymous for this post, we conducted the interview via email by asking questions which she replied with her answers. While her answers were lightly edited for grammar, spelling and punctuation, the answers given here are genuine.

A Year In Review With SpotOn!


2019 was a great year for SpotOn! Let us take you on a short year in review.

Earlier in the year, our own Bruce Bayne was featured on the IDEAlliance GAMUT Printing and Packaging podcast. The episode focuses on new BrandQ requirements and the Formula to Connect the Global Supply Chain. Listen to the podcast.

This year, we also completed some significant updates to both our Analyze/Verify and Flexo software. Both sets of software had two new releases this year.

Flexo Updates

Many of the 2019 updates to Flexo were general bug fixes. But there are two exciting features that are worthy to note.

Flexo is now able to measure SCTV, or Spot Color Tonal Value. The addition of SCTV allows users to calibrate tonal values of spot colors as defined in ISO 20654-2017. The methodology works with all inks and all printing conditions.

The other feature is the addition of a new measurement report. Now Flexo has two reports: a measurement report and a job report.

The difference between the two reports is that the measurement report shows a single measurement instance (although you could have multiple spot colors) while the job report shows the trend of all measurements for a job. 

Image of Flexo Measurment Report

Analyze and Verify Updates

Like Flexo, many of this year’s updates to SpotOn! Analyze and Verify were bug fixes.

Besides those fixes, here are some other improvements to the software:

  • Improved license check functionality to reduce error messages
  • Updated eXact driver
  • Improved Verify device report layout
  • Added instrument and mode to Verify when importing Barbieri data
  • Updated G7 Colorspace to 2019 specs

With the updates to Flexo, Analyze and Verify, Windows 32-bit operating systems are no longer supported. The minimum Windows configuration is now Windows 7, 64-bit. Operating systems below Windows 7 SP1 and Mac OS 10.10.5 will no longer be supported.

We are happy to continue to improve upon our products and services. We have already started working on Version 3 of SpotOn! and we are looking forward to its release in 2020.

If you have any questions about any of our software or other services, please email us at info@spotonpress.com.

Tricks to Matching Multiple Printers


Calibration of a single printing device is not always the easiest task, and matching multiple printers to one another is an even bigger challenge. One question that has come up frequently, especially with the rise of digital printing, is “what is the best way to profile multiple devices of the same model?”. 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.

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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 substate 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!

Real User Stories: Global Color Control


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Last year 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. Additionally, 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.

The details of our method are below.

Click Here to try SpotOn! Verify

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Using SpotOn! Verify to monitor and control presswork.

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.

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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 levelled 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.

my bar

Great color is within reach, and it can be maintained efficiently over time. What it takes is the desire to control the process.

 Joseph J. Pasky, Shenzhen

Test Form that Bob Signed

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

Click Here to try SpotOn! Verify

Which Wedge Is Best?


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 tradeoff 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.

I just dissected the TC3.5 patch set and found it to be lacking in the 3 color grays. There are not many patches and none are G7 compliant gray patches. In my opinion, this eliminates the TC3.5 for any G7 evaluation. In fact, most of the currently available charts are not very good in the gray areas, especially if you are trying to evaluate G7 compliance. Idealliance built the TC1617 to address this lack of G7 gray patches in the IT8.7-4, but even this chart has too many patches for day-to-day evaluations.

The 3-row 2013 12647-7 chart (the replacement for the 2009 2-row chart) was built as a very good compromise between patch count and patch value. It has a decent number of patches to effectively evaluate print consistency, which includes G7 compliant gray patches, the typical array of CMYKRGB tone ramps, pastel patches, saturated patches, and a good assortment of dirty patches. These dirty patches were purposely built with CMY values and then with 100% GCR values excluding the 3rd color and replacing it with K. This was done because many separations, especially those done with ink reduction products, are made with GCR these days. It’s hard to beat what’s in that 3-row, 84-patch control strip.

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The 3 Row Control Strip with key patches highlighted.

While considering charts and patch values, it’s almost more important to note the metrics and tolerances we place on these patches for conformance to specifications. If you look at the metrics we currently use for pass/fail, they are very CMYK printing press centric. Commercial print, specifically offset printing, has been the forefront of most industry standard and best practice development. Therefore much of the data gathering and evaluation is based on printing devices where C, M, Y, and K ink thicknesses are controllable by the operator. This means most metrics are tied to effective control of those ink thicknesses, which is largely irrelevant to the digital world.

We should be asking: “What are we passing and failing?”

For the G7 Colorspace metrics (currently the most stringent) we are evaluating:

  • Substrate – Paper color is good to evaluate
  • Solid CMYK – Very useful to press operators, but not much of a typical image or job is just solid C, M, Y, or K. This makes these patches poor for evaluating digital print consistency, especially visual consistency.
  • Solid RGB overprints – In my opinion, this is more important than Solid CMYK, as overprinted colors are what we see when we look at printed material. Still, these are only the solids, no tints.
  • CMY gray balance and tone – This is very important in controlling and evaluating print consistency, although it’s more important in print processes that lay down individual CMYK inks like offset.
  • All the other patches (pastels, saturated, dirty colors, skintones, CMYKRGB tints) are all lumped into a single metric called ‘All’ and then given a whopping average ∆E of 1.5 or 2.0 and a worst patch ∆E of 5.0 (95th percentile). That’s huge! A virtual barn door to let almost anything outside of grays and CMYKRGB solids pass.

These are not very visually oriented metrics and tolerances. So the big question to ask is what are you evaluating with your chart, or more importantly, what metrics and tolerances are you using to evaluate your chart? For G7 you could just use a P2P and eliminate the gray finder patches (columns 6-12), because the metrics are really only focused on CMYKRGB solids and the gray patches.

Bottom line, if we are looking for print consistency, we need to look at establishing new metrics that truly help us determine how visually consistent a print is. After a great deal of research, I believe this should be based on a cumulative relative frequency model (CRF) that evaluates all colors in a chart. In a CRF model, each and every one of the patches is relevant to visual consistency and is being counted within the evaluation. I have found the 3-row control strip does an excellent job of evaluating visual print consistency when using CRF. I’ve also performed the experiment in live production many times and have continued to get feedback from users who say using CRF and the 3-row control strip is the best method they’ve found to evaluate visual consistency.

If you would like to see the true power of CRF and real world metrics, try SpotOn! Verify. The trial is free, and our team will help you get started.