Calibrating, Printing and Proofing by the G7™ Method

Calibrating, Printing and
Proofing by the G7 Method
1 Introduction
1.1 About this document
Version 6, August 2006
This document describes how to calibrate a printing press, proofing system, or any CMYK imaging
device to the new GRACoL 7 specifications, and how to maintain those specifications during production.
The calibration process is broken into two stages. The first stage uses ISO-standard colorants and
substrate, and the new G7 method to match the NPDC (Neutral print Density Curve) and gray
balance of neutral gray tones. The second stage uses ICC (International Color Consortium) or similar
color management to optimize the match to a reference characterization data based on ISO-standard
print conditions, such as produced by FOGRA, GRACoL, SWOP, etc.
Simply using the G7 calibration method will often be enough to match multiple devices to each other, at
least in neutral gray tones. But in other cases, for example with non-standard colorants, to set up a
digital proofer, or when repurposing from one print method to another, additional color management will
be needed, with G7 acting as an optimized and repeatable calibration basis.
1.2 Changes to this version
Version 6 of this document corrects a number of small errors and omissions in earlier versions and adds
several new items. The main changes between version 6 and versions 4 or earlier are;
• Adds new variables 'SC' (Shadow Contrast) and 'HC' (Highlight Contrast)
• Broader tolerances for ink color and press gray balance
• Minor changes to gray balance formula and NPDC curve shape
• New 'fan-type' graph paper simplifies re-drawing graphs
• Adds references to the new IDEAlink Curve software
• Expanded or revised illustrations, charts and glossary
• Clarifies the use of CIE-based (instead of density-based) TVI curves
• Corrected errors in some charts and formulae
1.3 What is GRACoL 7?
GRACoL 7 is the seventh edition of the GRACoL specification. GRACoL 7 differs from previous editions
of the GRACoL specification by;
• Defining substrate and colorants in colorimetry rather than status T density
• Defining tonality in 'Neutral Print Density Curves' (NPDC) instead of TVI
• Defining gray balance as a primary colorimetric variable, rather than a secondary function of CMY
TVI
• Defining a GRACoL 7 characterization data set that represents an ideal printed sheet
5 Copyright © International Digital Enterprise Alliance, Inc. [IDEAlliance] (2006). All Rights Reserved.