GRACoL7 – A Brief Overview

Background
GRACoL7 is the seventh edition of the specification for the General Requirements for
Applications in Commercial Offset Lithography. “G7” is the calibration methodology
used to make a digital printer or press conform to the GRACol7 specification. Though
the word “Offset” appears in the GRACoL title, in fact the G7 methodology can be
applied to a variety of printing condition, including traditional and inkjet proofers, to
ensure consistent performance throughout the entire print production workflow.

G7 Benefits to the Print Buyer
By encouraging print providers to adopt G7, print buyers can expect consistent results
across multiple print providers. G7 also helps achieve more consistent results across an
individual print run, so there is a potential improvement with an individual press as well
as multiple providers.

In addition, printing to G7 specifications can lead to prints with greater saturation and
density. The Adobe CS default CMYK working space, and default industry standard, is
SWOPv2 (Specification for Web Offset Printing). This space has a smaller gamut than
GRACoL7 (see below) and a relatively dim/yellow white point not consistent with most
high quality sheetfed stocks.

So, RGB images that are separated to the default SWOP, or CMYK designs and layouts
created in SWOP, can lose some of the saturation and density that is well within the
reach of a typical sheetfed press. Separating and printing to G7 addresses this issue.

Benefits to Print Producers
G7 also provides substantial benefits to the print producer. Unlike previous standards,
G7 focuses on producing neutral grays through the entire tonal range, yielding a visually
more pleasing result that is more easily maintained over time. This is primarily achieved
by creating a Neutral Print Density Curve (NPDC) that yields similar lightness (the L of
Lab) results between 3-color (CMY) gray and single-color black (K) throughout the entire
tonal range.

Once the G7 process is in place, printers can more quickly get a job up to color since
they need to measure fewer patches, thus saving time and making each job more
profitable. In addition, G7 provides a methodology that can help ensure consistency
across multiple presses, providing printers the flexibility to assign jobs to the most
readily available press and the confidence that the job will come out right.

In addition, G7’s focus on gray balance means that fewer patches need to be measured
to ensure consistency during a given run. And if measurement is not feasible, a visual
inspection of the three-color gray vs the K patch allows for superior results compared to
what would otherwise be possible.

Lastly, if you are doing trade printing, or just occasionally need to match jobs printed at
another location, it will put your customers at ease if they know you are conforming to
industry standards.

Overview of Methodology
The G7 methodology is described in great detail in the G7 How To Training Guide found
at http://www.gracol.org/. In brief, for each press/stock/line screen combination the
following will be done:

1. Evaluate press and make sure it is printing to manufacturer’s specifications
2. Print a calibration target to characterize current state of platesetter/press.
3. Compare current state to G7 NPDC values
4. Apply correction to platesetter curves to achieve desired NPDC values
5. Print calibration chart on press again to ensure that desired results have been
achieved. Make refinements if needed.
6. Review quality control methods to ensure consistent results over time
7. Calibrate proofer to ensure it is matching newly calibrated press

What It Takes to Get G7 Calibrated
In conjunction with a qualified G7 Expert Consultant like Spectraflow, a printing plant
can get G7 calibrated in a relatively short amount of time, assuming the presses are in
good operating condition. In a typical environment, a printer may want to calibrate two
presses, two stocks (maybe house coated and matte), and one line screen (maybe 175
lsi). This would represent a total of 8 combinations. In a single day, it’s usually feasible
to perform 2 press runs along with the required analysis and adjustments to the plate
curves. Add a day for proofer calibration, and the entire G7 calibration can be typically
performed in a single week or less for a single press.

Call Spectraflow at 415-382-8681 for more information about G7 calibration.