Re: [ECI-EN] Fastest way to find densities for ISO 12647-2 implementation?
25 Aug
2004
25 Aug
'04
1:12 p.m.
Yann,
that's exactly what we advise, and what other people are doing, too. Use
a "skewed" density setting on the press - not necessarily the Altona job
- in a short press run, measure wet densities, and later dry
colorimetric values. Then you can relate one to the other and determine
the optimal densities.
As a byproduct, you get an idea how your dot gain depends on density,
and you can adjust your platesetter curves to get standard dot gains for
your optimum density. Only when this is done, proceed to print the
Altona uniformly across the sheet, at your optimum densities.
However, going up to a density of 2.0 overdoes it a bit, I'd say... (but
then I have also seen Cyan densities of 2.4 and even above in so-called
"normal" jobs :-)
Cheers,
Hanno
---
Dr. Johannes Hoffstadt
Color Solutions Software
Yann Bouckaert wrote:
Hello,
I would like to know what would be the fastest way to find the correct
wet densities on a printing press to match the solid primary colours
as stated in ISO 12647-2.
What I learned from the documentation that accompanies the Altona Test
Suite, you start with underinking, measure the solids in L*a*b* and
continue to rise the densities until the originally falling delta E's
start rising again.
I'm in the middle of implementing this standard on one sheedfed and
two web presses. To find correct densities, I started off with asking
the printer his normal working densities (eg. C 1.40, M 1.35, Y 1.20,
K 1.70), took 0.2 off (C 1.20, M 1.15 etc) and let him continue to
print until about 0.3 higher than normal with intervals of + 0.05. The
layout of the sheet was the normal one I use to profile a press; it
has solid tone bars at the bottom. I asked them to try to print the
sheet with the same density with a minimum deviation of 0.05 across
the sheet. Because the printer did not have some sort of automatic
density control, it took them almost two hours to finish the series on
one paper type. At 40.000 sheets per hour a lot of paper was wasted.
The result was that I could indicate per ink what density gives solid
colours what are within ISO standard, but I'm not sure if the route I
took was the most efficient. I was thinking if it would be wiser to
print sheets with low densities on one side, and gradually rising the
ink level going to the right side of the sheet? At the left then you
would have eg. CMYK = density 1.0 and then smoothly going to the right
where the densities for CMYK are 2.0? Of course right after picking a
sheet you would have to measure the wet densities and write them down
for as many zones as you can.
I tried to find anything on this matter on the internet, but found
nothing. If there is something to find, or people are giving training
on this matter, please let me know. Willing to travel :-)
Any help is very welcome, and thanks for reading this long letter.
Cheers,
Yann Bouckaert
Sagam NV
Drongen, Belgium
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