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G7: the basics

Sep 1, 2010 12:00 AM


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G7, a method defined by the “Print Properties and Colorimetrics (PPC) Working Group” of IDEAlliance, is designed to enable printers to reproduce a similar visual appearance across the spectrum of printing technologies and substrates. The G7 name represents its grayscale calibration technique and the seven ISO ink colors it requires.

Originally developed by the GRACoL Committee for offset printing, G7 currently is applied to a fullrange of printing technologies through use of digital imaging, spectrophotometry and computer-to-plate imaging. Based on existing ISO standards, it requires printing with inks defined by ISO 2846-1. so the dry solids measure as close as possible to ISO CIELab values for four primary colors and three 2-color overprints specified in ISO 12647.

IDEAlliance states, “Because our goal is to specify a simple calibration process that will help the printers reliably achieve a close visual match from proof to press, G7 breaks from tradition by focusing on colorimetric data for gray balance in the midtones rather than on densitometric aims, i.e. dot gain, for each color.”

G7 specifies the components of an image that define a similar visual appearance to the human eye. It defines a colorimetric definition for gray balance, then specifies gray balance in the midtones, image weight and image contrast from the highlights to the shadows.

G7 Summit

This year's G7 summit will be held during Graph Expo, October 3-6, 2010, in Chicago. The programs will range from the basics to guidance for new users and more in-depth sessions. Hands-on demonstrations will use live equipment on the show floor. See www.idealliance.org.