Re: Fogra 51 and 52
Re: Fogra 51 and 52
- Subject: Re: Fogra 51 and 52
- From: Graeme Gill via colorsync-users <email@hidden>
- Date: Sat, 22 Jun 2019 11:44:12 +1000
Refik Telhan wrote:
Hi,
In this case CMYK "structures" are relevant. The printing conditions for
FOGRA39 and
FOGRA51 are very closely related. In real life they are printed with the same
inks on
the same coated papers with almost identical primaries and very slightly
different TVI
curves (CMY balance is unchanged). Hence, the kind of structural change that is
taking
place is causing a "visible" yellow-deficient appearance.
Sorry, this makes no sense. The "structural changes" are a result of the color
data.
The color data tells you in an objective way how it will look. Just because the
ink
and printing conditions are the same doesn't imply that the separation will be
similar
if the paper is significantly different. And it is different - it has FWA in it.
Shaving off a hefty amount of
yellow from the rich blacks is causing a change in the apparent color.
Core question :- do the measured color values correspond to the appearance
or not ?
If not, then the profile is useless. To make use of the profile you would
have to get the appearance and measured values into alignment.
(And appearance match needs to take into account the state of
observer adaptation. Checking FWA paper under M1 with a neutral
surround is asking for trouble if the relative colorimetric
separation makes the default assumption that the observer is adapted
to the color of the paper white.)
If the measured values do correspond to appearance, then trust the numbers
and ignore the "structure".
This is the core aspect you need to face up to, rather than going
around in circles.
Evaluation is always done under the same ISO 3664:2009-compliant light sources.
The
comparison has physically been made in the same light booth.
What sort of surround ? If the surround doesn't have matching FWA response
to the M1, then the observer will be in a compromised state of white
adaptation.
All those who tried their hands at FOGRA51 and FOGRA52 are competent printers
who know
what they are doing.
But have they dealt with proofing on FWA papers ?
All have the tools to create and maintain the relevant printing
conditions. The apparent coldness of the FOGRA51 and FOFRA52 separations starts
with
the initial conversion, before the files reach printers.
You can't have it both ways. If the numbers don't correspond to the
appearance, then tackle that. If they do, trust the numbers.
It is same black ink and the same printing stock that are being used for
FOGRA39 or
FOGRA51. Measuring it in M1 mode does not make black ink any more yellow than
the same
black ink measured in M0 mode.
Yes it does! Look at the numbers. CMY is cold because the FWA is kicking in.
K is relatively warm because FWA is not having an affect.
While what you say can be seen as
"colorimetrically" correct, this cannot be used as an excuse to shave off
yellow in the
rich blacks.
Yes of course it can. That's the whole point of measuring the color.
Yellow ink is more than a colorant; it carries waxes and varnishes that
add rub-resistance and gloss respectively. Hence, you cannot freely replace it
black on
the basis of "colorimetric correctness". This decision is up to the printer and
more
importantly to do print buyer. There is one more subtle problem here. Yellow
ink is
"last" ink in the print sequence. Hence, when any reduction takes place, it is
distinctly "visible". But during the buildup of the rich black in a
FOGRA51-certified
proof, all the inks are finely mixed up. Hence, the proof both measures and
appears
"correct" but the print definitely shows the yellow is missing in comparison to
its
FOGR39 counterpart. We all know that colorimetric sameness does not guarantee
common/consistent color apperance. As much as proof of the pudding is in the
eating,
proof of the printing is in the "seeing". Print buyers only come back to you
when they
like what they see.
I've suggested a few ways of increasing yellow if you need it for other
purposes. But given other tradeoffs (level of black desired, type of
black ink), then perhaps that's the reality of printing on Fogra 51/2 paper.
I disagrre. The amount of yellow is very relevant. Comparative work done on
more than
occasion has confirmed that the new set of profiles are producing cooler/colder
ink-films, that is highly visible. And print buyers do not like that.
Why isn't it reflected in the color measurement then ?
You can't have it both ways. You can't say that it looks cooler,
and that the profile says it's not, and that the measurements accurately
reflect the appearance. You need to resolve these contradictions.
This neutrality, I would say,is only mathematical,
It shouldn't be mathematical. If the profile is to be any use
the measurement values need to reflect the appearance.
When you transpose a FOGRA51
separation of a CIELAB-neutral RGB image to FOGRA39 by assignment, you will see
that
this separation is relatively colder what the FOGRA39 does from the same image
file.
The coldness of the FOGRA51/52 separations relative to the FOGRA39/47
separations is a
real issue.
No, I don't see that at all. From the profile data I see that they are both
neutral separations produced from distinctly different CMYK values due to
the action of the FWA and the shifted observer adaptation point.
Sooner or later all artificial lighting will lose the UV component.
Maybe. But the natural light won't change, and M1 is based on
a natural light assumption.
Cheers,
Graeme Gill.
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