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Maximize Print Accuracy with G7

In the printing industry, the most prolific drain on profitability is process color print inaccuracy.

By Mike Ruff, Chief Technology Officer, Nazdar Consulting Services

In this article, I will share with you some important principles that have helped hundreds of printers maximize print accuracy and add thousands of dollars to their bottom lines.

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  • I spend most of my time developing productivity-enhancing plans for printing companies. One of the first things I do before starting the process is determine the client's "critical success factors" so that I can focus on specific objectives. The most common factor I've heard is: "We want to be more accurate to our color target in four color process." When asked why, they mention the many lost hours of production time in an attempt to match the intended color target. Clients say that even though they print nice looking prints, they rarely match the intended color. This is a major problem. In the printing industry, the most prolific drain on profitability is process color print inaccuracy. In this article, I will share with you some important principles that have helped hundreds of printers maximize print accuracy and add thousands of dollars to their bottom lines.

    What Defines Accuracy?
    Before the electronic confusion of digital files, embedded profiles, rendering intents and device link profile technology, color separations were done by cameras. After the camera era, very expensive scanners captured color images. Both of these methodologies required highly skilled technicians who understood the principles of accuracy to the original image that revolved around the concept of "neutral gray." When presented with a photograph to shoot or scan, professional separation camera technicians or scanner operators asked for a neutral gray reference in the photo. It was later cropped out of the final print, but used by the print professionals to balance the grays. If the grays were balanced properly, the print was naturally accurate because the reproduction process was not adding or taking away color from the original. Cyan, magenta and yellow had equal response and did not cause or add a "color cast" to reproductions of the original.

    In today's workflow, a client normally sends a digital file that is either proofed or printed. When they see the results, the client might not see the color they expected. The cause of this constant problem is that most printers do not know how to determine correctly the accurate output, nor can they define accuracy.

    How can you be sure you printed the file accurately? While you cannot be entirely sure, consider this definition of accuracy in printing: "Producing a print without adding or taking away from the values of the original file." In other words, do not add a color cast to the file. Just as professional color technicians did in the past, we currently can print colors accurately by understanding and monitoring the gray values.

    Today, we confuse this when we convert digital files that might be RGB and print CMYK or convert measurements taken on a computer file versus measurements taken by a reflective spectrophotometer or densitometer on a press sheet. Many color control technicians give up and resort to visual approvals and acceptance, a death spiral in print profitability. With our fragile profit margins, two or three color adjustments on a job reduce our profitability to zero. Industry survival demands that we define accuracy according to International ISO Standards - easy to understand, easy to verify and easy to monitor. G7 has provided this methodology.

    The idea behind G7 Neutral Print Density Color Control Methodology is: If our workflow is calibrated to neutral, any file we send through the process will come out neutral and accurate to the file. In Figure 2, I would remove the color cast in these images, but our job is to give the file's creator an accurate reproduction of their file. The constant questions challenging printers are: "Which one is accurate?" "Are my printing presses or prepress procedures adding the cast?" "Is the client's file yellow cast or blue cast?"

    Print A in Figure 3 is correct to the client's file, printed with no cast added by the printer. I know this because the G7 Gray Bars prove the press is producing neutral results. Print B shows an example of a color cast to blue. If the client submitted a file with a blue cast, I would print it with a blue cast if my printing workflow prints to neutral. As stated previously, the definition of accuracy is printing to "neutral print densities."

    Don Hutcheson, a top industry consultant, applied this definition to the most useful and accurate print methodologies in the world: G7. When a printer understands this simple concept, their print control world quickly becomes manageable. Also, you will not spend late nights at the press trying to understand why you can't match intended color targets. Remember this: The more confidence you have in your ability to accurately represent the original, the more profitable graphic reproduction becomes. Printing to G7 Neutral Print Densities provides this tool.

    How Do We Print to Neutral Print Densities?
    Neutral print densities are defined in L*a*b*. In Figure 4, the a* axis is green on the left and red on the right. The center is neutral. If I move to the right or the left on this axis with my printing, I am starting to cast my image in that direction. The b* axis is yellow on the top and blue on the bottom. If I print my image toward blue, red, yellow or green, I add a cast in my image in the same direction my gray moves. If I print "accurate neutral gray patches" to neutral (dead center of the gray balance on press), then I have produced the image accurately. That's the concept of G7.

    Understanding the G7 Measurements
    The ISO 12647 Print Standards Family governs internationally accepted print values that equal balanced printing. However, the problem is that they are dependent on all the elements of the standards in producing balanced printing and neutral grays. The elements that are required to be in compliance for gray to be neutral as specified by the ISO standards are:

    1. Ink color
    2. Paper color
    3. Dot gain or TVI (tonal value increase)
    This means that if you printed on a "non-standard substrate" and your dot gain is perfect, you would still be out of standard. If you printed with perfect dot gain on a perfect substrate with a "non-standard" ink, you would be out of standard. The ISO Print Standard was and is accurate and correct, but is dependent on all the metrics of the process. In our screen printing and digital industry, we rarely print on standard substrates, use standard inks or even have standard dot gains. G7 Methodology defines neutral in a different way from any previous color specification.

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    G7 identifies the neutral values of the international standards and converts them to L*a*b* aim point values, which are not dependent on substrates, ink or dot gain. The aim values specified in L*a*b* also are device independent; the printer calibrates all of its devices to G7 neutral print density regardless of substrate, ink color or dot gain. The G7 Neutral Print Density Methodology is the first color control calibration that meets the needs of the multiple ink types and substrate challenges inherent in our industry. However, please do not tell people that Mike Ruff said G7 makes all color matching perfect. It makes the best print with what you have to work with.

    Do G7 specifications guarantee that your saturated colors (reds, green and blues) match the intended target? In short, the answer is no. However, if the intended target has a smaller color gamut than the printing press, then it should. But if the intended target is outside the gamut of the printer, it is impossible to reproduce those colors. Printing to G7 neutral only guarantees that you are doing the best you can with the printer and substrate you are using and G7 quickly validates when you have achieved this. Gamut affects your accuracy to the file but only in the saturated colors.

    At the 2009 SGIA Expo, I heard someone say: "I don't print to G7 Specifications because I want a bigger color gamut." This person does not understand that G7 is not a color standard and does not have a color gamut. G7 is only a definition of neutral gray print density and a proven methodology to print to the definition. Color gamut only affects saturated colors because gamut printing is about the chroma capability of the printer and the ink set it is using. Define the solids and the overprints and you define the gamut.

    How Does G7 Work with Different Color Gamuts?
    G7 is simply a definition of neutral gray print densities produced from presses that are compliant to the ISO Standards and a methodology for doing it. By defining the grays in L*a*b* rather than CMYK, solids can be printed on a specific whiteness of paper with a specific ink. All print devices can be G7 compliant. They do not match in the solids and overprints, but by printing with both presses calibrated to neutral, most images produced will have a similar "neutral" appearance - they look close to the original file. The only deviation will be some out-of-gamut colors, or metamerism, caused by the substrate. This is the best you can do and a huge improvement for our industry.

    Huge Payoffs from an Accurate Workflow
    G7 Neutral Print Density has tremendous success in providing a common visual appearance as a print target for both screen and digital printers. Screen printers are printing shared appearances on different substrates at different line counts with different ink sets and on different presses. Digital printers are challenged more by time lost on set up because of shorter runs. A screen printer averages the time lost at set up when they have a two or three day print project. But as run lengths drop, setup time will eat up your profit. Digital printers are discovering what accuracy is, printing accurately and more easily identifying an accurate print and, as a result, are producing more with less cost.

    Accuracy to the file can be determined by a G7 Master Printer using the ISO Standards of neutral print density. This is simply printing without adding or subtracting color value from the file. Printing to G7 Neutral makes it simple for printers, managers and sales professionals to understand by removing the confusing conversions and fancy color theory. If our industry is going to stay competitive with other forms of printing, we must print accurately and know what accuracy means.

    Mike Ruff has been in the graphic printing industry for more than 39 years and is a member of the Academy of Screen Print Technology. He is a certified G7 Expert and is a regular instructor at SGIA's Graphics Four-Color Process Workshop in Fairfax, Virginia. He is a popular industry speaker and has authored numerous articles in domestic and international trade publications.

    This article appeared in the SGIA Journal, 1st Quarter 2010 Issue and is reprinted with permission. Copyright 2010 Specialty Graphic Imaging Association ( All Rights Reserved.

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