Calibrating, Printing and Proofing by the G7™ Method
Calibrating, Printing and Proofing by the G7™ Method
Calibrating, Printing and Proofing by the G7™ Method
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<strong>Calibrating</strong>, <strong>Printing</strong> <strong>and</strong> <strong>Proofing</strong> <strong>by</strong> <strong>the</strong> G7 <strong>Method</strong> Version 6, August 2006<br />
6 Calibration Test<br />
NOTE: This section refers mainly to a press calibration run, but is also applicable to o<strong>the</strong>r devices,<br />
6.1 Ink sequence, drying, <strong>and</strong> coating<br />
The suggested ink sequence for offset printing is K – C – M – Y. O<strong>the</strong>r sequences may cause a<br />
significant difference between your characterization data <strong>and</strong> <strong>the</strong> published GRACoL 7 Characterization<br />
Data, due to different ink trapping <strong>and</strong> opacity effects.<br />
Presses with inter-station drying usually have better two-color saturation, but may not match<br />
characterization data created on wet-trap presses (see Appendix G.6).<br />
Aqueous coating was found to minimize drying time during <strong>the</strong> 2005 GRACoL 7 press tests. If aqueous<br />
coating is usually applied, apply <strong>the</strong> same process to <strong>the</strong> calibration run. Even if coating is only applied<br />
occasionally, calibrating <strong>and</strong> profiling with coating is usually adequate for both conditions.<br />
6.2 Print to nominal solid ink values<br />
Run <strong>the</strong> press up to <strong>the</strong> nominal solid ink colorimetric values (L*a*b*) or densities (SIDs) for <strong>the</strong> process<br />
being calibrated. Approximate ink CIELab values for commercial printing on coated paper are given in<br />
<strong>the</strong> table below, along with equivalent Status T densities. Devices with o<strong>the</strong>r Status readings can also<br />
be used in <strong>the</strong> G7 process, but will require using that device in conjunction with a spectrophotometer to<br />
determine <strong>the</strong> wet densities which produces <strong>the</strong> closest Lab value found in <strong>the</strong> table below.<br />
NOTE: The relationship between status T ink density <strong>and</strong> Lab values shown below may not match your<br />
device, due to ink metamerism or instrument filtration. When in doubt, <strong>the</strong> Lab values take priority.<br />
L* a* b*<br />
Approximate<br />
Density (T)<br />
Tolerance<br />
(Density)<br />
C 55 -37 -50 1.45 +/- 0.10<br />
M 48 74 -3 1.45 +/- 0.10<br />
Y 89 -5 93 1.0 +/- 0.07<br />
*K 16 0 0 1.7 + 0.2 – 0.05<br />
Colorimetric Values <strong>and</strong> Approximate Equivalent Status T (non-polarized) densities on a number 1<br />
sheet (ISO paper type 1 & 2) measured with white backing<br />
*NOTE: Lower L* (e.g. 12) or higher K density (e.g. 1.9) are acceptable if <strong>the</strong> k NPDC is correct.<br />
6.3 Check CMYK TVI<br />
Check individual CMYK TVI values. The CMY<br />
TVIs should be within about +/- 3% of each o<strong>the</strong>r,<br />
with black typically about 3 – 6% higher. If<br />
possible, plot TVI curves for each ink <strong>and</strong> look for<br />
a similar curve SHAPE for each, as shown here.<br />
NOTE: TVI values are NOT important but all inks<br />
should have relatively smooth curves.<br />
Right: One of many possible TVI curve sets of a<br />
healthy but un-calibrated CtP press. (NOTE:<br />
These curves are calculated <strong>by</strong> CIEXYZ <strong>and</strong> may<br />
be different from density-based TVI curves.)<br />
21 Copyright © International Digital Enterprise Alliance, Inc. [IDEAlliance] (2006). All Rights Reserved.