Calibrating, Printing and Proofing by the G7™ Method

Calibrating, Printing and Proofing by the G7 Method Version 6, August 2006
NOTE: If your automated press control system or digital press does NOT permit some form of graybalanced
control, ask the supplier how this can be achieved, or add separate gray balance (HR)
patches alongside the bar for manual measurement.
5.3.2 Minimum G7-compliant control bars
To make a basic press bar G7-compliant, add a mid-tone gray balance patch (HR patch) of 50c, 40m,
40y – ideally at ink-key intervals. The HR patch can replace one RGB or 50 CMY patch at each ink key.
If your press control bar already has gray balance patches with slightly different values (e.g. 50c, 41m,
41y), see 5.3.4 – Bars with non-G7 gray patches.
Minimum G7-compliant press control bar – layout may vary – (HR_cmy patches are notched)
5.3.3 Optimum G7-compliant control bars
For maximum G7 compliance, add at least one SC (shadow contrast patch) of 75c, 66m, 66y, and at
least one HC (Highlight Contrast) patch of 25C, 19M, 19Y. These patches can be added less often than
the HR patch. For example after placing SID CMYK and HR patches at each ink-key, use the remaining
spaces to repeat a sequence of R, G, B, 50c, 50m, 50y, SC, HC, as shown below.
Optimum G7 press control bar – layout may vary – (note SC and HC patches repeat less often than HR)
5.3.4 Bars with non-G7 gray patches
Some existing color bars already contain gray balance patches with slightly different values. For
example the Brunner System Instrument Flight Colorbar uses a gray balance ratio of 50c, 41m, 41y.
These control bars can be used with the G7 method so long as the target CIELab values (or target CMY
density values) are modified to produce the same gray balance as if the patches were the official
GRACoL 7 balance. The new target values can be determined by balancing the press on a true G7
gray patch, then measuring the non-G7 gray patch and recording it’s actual CIELab or density values.
5.4 Set up the RIP
Set up the plate making RIP exactly as you would for a normal job, but clear out any values in the
current calibration table, or begin with a new, empty table. The first press run is best made with ‘uncalibrated’
plates – i.e. no calibration values in the RIP.
IMPORTANT: Do NOT linearize the plate-setter so that measured dot values on plate exactly match
original file percentages. Contrary to common belief, this may reduce accuracy of subsequent steps.
5.4.1 Screening
For commercial work, halftone screen ruling should be at least 150 lines/inch and nominally 175
lines/inch. Common screen angles are 15 C, 75 M, 0 Y, and 45 K (symmetrical dot) or 15 C, 75 M, 0 Y,
and 135 K (asymmetrical dot) with K and M interchangeable.
For other printing systems check the relevant standard for suggested screen conditions.
Note that unlike TVI-based calibration, the G7 method is perfectly compatible with ANY screening
system (e.g. FM or ‘stochastic’) without change to target values.
5.5 Check plate-making system
Check that plate-making hardware, chemistry, and RIP are within manufacturer’s specs.
19 Copyright © International Digital Enterprise Alliance, Inc. [IDEAlliance] (2006). All Rights Reserved.