At 22:36 23-9-2007 -0400, Roger wrote:
This process
is successful due to the gray balance and tone shape
approach to
offset lithography.
Gery (Gerlach), does it make sense to say that the G7 method results on
lower midtone
densities as opposed to traditional TVI methods of press calibration?
I recently conducted G7 calibration on #3 grade of coated paper in a web
heatset process and got 5% less TVI on CMY ay 50% as compared to the "old"
method.
Roger Breton
Hi Roger,
Yes that seems the major advantage of the G7 calibration.
Up to the 50% midtone all processes would have an identical
tone reproduction curve.
In the regular ISO 12647-2 and 12647-3 procedures one has
different TVI curves for different paper groups and processes.
There is even a difference between ISO 1247-2 for heatset web offset
and ISO 12647-3 for coldset if you compare the difference in curves
for CMY and K and the differences in slopes between heatset and coldset.
In ISO 12647-3 CMY and K curves are identical.
Not in the TVI curves as proposed in Process Standard Offset and 12647-2.
By using tone curves with an identical slope up to 50 percent one
generates a specified difference between the old curves and the G7 curves.
And of course also a difference between the ISO 12647-3 curve and the G7
curve if used for coldset applications.
The question is, what output condition (characterization data) and what kind
of TVI was used to generate those prints?
As long as the TVI for CMY and K are identical (as in ISO 12647-3)
the difference is only in tone, not gray balance.
That however also depends on the amount of GCR used in the color
separations for coldset.
Regards, Henk