How the G7 Calibration Method Helps with Printing Neutral Gray

With the widespread adoption of print standardization, integrating G7® into global standards for neutral gray printing/press methods allows for visual consistency regardless of CMYK print output. This applies to ISO standards such as ISO 19303-1 and 19303-2 for color workflow consistency, ISO 10128 for calibration, ISO 15339-2 for seven common reference printing conditions, and further integration into other ISO standards, as the G7 near-neutral gray output calibration method continues to be used by printers in over 40 countries/regions worldwide.

Many print service providers are familiar with the term G7, but what does it actually mean? Simply put, G7 is a calibration process aimed at improving color consistency and accuracy across different printing devices. It's an international standard developed by Idealliance, an independent non-profit organization focused on advancing industry standards for digital media and print production.

Why is G7 calibration important?

G7 calibration is crucial because it helps ensure quality assurance across multiple printing devices. Without calibration, significant differences may occur between runs from different presses due to variations in color management practices. This can result in inaccurate color reproduction on images and text elements or misaligned borders. By using G7 standards for calibration, you can ensure that prints maintain color consistency and stable quality regardless of which printer they come from.

How does G7 calibration work?

G7 calibration works by replacing the density-based linearization process with grayscale calibration. This process redefines gray from a*0, b*0, starting from the medium's white point and then gradually correcting inversely with ink coverage. This approach reflects a concept called "colorimetric adaptation." The human visual response automatically corrects changes in the white point. It also introduces Neutral Print Density Curves vs TVI to control contrast or "tone," known as "G7 gray." Depending on the application, slight adjustments can be made to set L*A*B target values for CMYK and spot color overprints (C/Y, C/M, M/Y). Target L*A*B values can be set for any color space and/or ink.

G7 Compliance Levels

There's no standard value for G7 compliance. However, in North America, the most common color space used for printing is GRACol. So, most printers aim for the colors defined by the GRACol standard when going for what's called 'G7 Targeted' compliance. 'Targeted' is the compliance level most offset printers aim for. The highest compliance level is called 'G7 Color Space.' This level is mainly for printing devices or inkjet printers. Besides simple 1D curves, it usually requires using ICC profiles. It uses a larger range of color samples within a specific color space and measures how accurately a given device can reproduce colors.

What's the difference between G7 and ICC analysis?

G7 is a calibration method that usually uses 1D curves for each color to achieve grayscale. Depending on the device, an ICC profile might be needed to meet target or color space compliance. ICC is a lookup table used to convert RGB or CMYK values to the corresponding L*A*B values. Since GRACol and other ISO12647-based color standards are based on offset printing data, you can achieve targeted color space compliance with a simple offset printing curve. For other processes like inkjet, flexo, and screen printing, which use different inks, ICC profiles can be combined with G7 calibration to meet the desired color standards.

How can print service providers get G7 certification?

Print service providers can work with G7 experts, complete the G7 certification process, and submit G7 calibration samples. Many leading technology providers, including kngColor, have Idealliance-certified G7 experts who can help you get G7 certification for any printing process. We also offer G7 color management and print standardization training, so press operators gain a clear understanding of the G7 method and its benefits, making process control easier and more intuitive.

G7® experts demonstrate expertise in color management, workflow, and quality control for proofing and printing using the G7 method. They can implement G7-based calibration and process control in the printing workflow, analyze color and printing-related issues, and take corrective action-applying a system and process control method to standards or specifications to achieve consistent, predictable results. All G7 experts have attended and successfully completed Idealliance G7 expert training, with at least 90% proficiency.