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(May 2007) posted on Thu May 24, 2007

Tired of tying up presses and personnel as you try to emulate the output of your printing equipment? Discover some powerful methods you can use to improve color matching with any CMYK inkset, substrate, or line count on any printing device.

By Mike Ruff

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G7, which should not be confused with GRACoL 7, is an innovative calibra­tion methodology developed to modern­ize and improve the latest versions of GRACoL and SWOP (Specifications for Web Offset Publications). IDEAlliance promotes the G7 method as a constant component of all future print specifica­tions, and the group offers it openly for adoption by all standards associations for all types of imaging or media, worldwide. The main purpose of G7 is to simplify the calibration of any printing device, such as a prepress proofing system or a commercial press, to the IS0 12647-2 printing standard. The -2 at the end of the specification designates litho, but G7 can be applied to any type of printing tech­nology that uses a CMYK color space, regardless of which inks are used or how the ink is put on paper. It even applies to digital output. Digital output desperately needs help with standards.

 

A common misunderstanding is that G7 is an official standard. G7 is not a standard. It’s a specification of a calibra­tion methodology designed to attain the grayscale appearance implied in the ISO 12647-2 standard while bypassing the ambiguous and visually inconsistent TVI (dot gain) definitions in the current stan­dard document that relates to different line counts and paper grades. G7 adjusts the device via typical CMYK RIP curves, or other device-calibration utilities, to match a pre-defined NPDC and gray bal­ance. G7 assumes the use of ISO-standard inks, for which precise L*a*b* values are defined in ISO 12647-2, but even if a device were to use non-ISO inks (differ­ent hues), G7 calibration would give it the same natural grayscale appearance as all other G7 devices (Figure 2).