Re: Fogra 51 and 52
Re: Fogra 51 and 52
- Subject: Re: Fogra 51 and 52
- From: Refik Telhan via colorsync-users <email@hidden>
- Date: Sat, 22 Jun 2019 22:50:25 +0300
- Thread-topic: Fogra 51 and 52
Hi Graeme,
>> 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.
In the real-life scenario, the paper is "not" significantly different, it is
"identical" in both FOGRA39 and FOGRA51-based print runs. This also true for
FOGRA47 and FOGRA52 print tests. I have used the following papers:
COATED
Sappi Magno Satin
M0 - Lab: 95.05, 0.93, -4.24
M1 - Lab: 95.17, 1.28, -5.99
M2 - Lab: 94.87, -0.42, 0.48
UNCOATED
Sappi Magno Natural
M0 - Lab: 94.10, 2.14, -6.96
M1 - Lab: 94.27, 2.57, -9.32
M2 - Lab: 93.84, 0.28, -0.35
Hence, when the printing conditions are almost the same (FOGRA39 -> FOGRA51), I
expect to have similar separations that would end up with a visually related
prints in both worlds. Knocking down the yellow channel on "colorimetric"
grounds produces an unpleasantly cold appearance from the standpoint of the
print buyer.
>> 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.
Then I must ask the question:- which measurement mode should we use, M0, M1 or
M2?
When M1 (or even M0) is used on moderate or high OBA papers, yellow ink appears
to be more yellow than what it really is, and black ink appears to contain a
strong yellowing power in comparison to the excessive blueness of the paper.
Hence, when color values are captured in M1 mode, the correspondence to
appearance is different from that of M0 or M2.
For building the perceptual and relative colorimetric B-to-A tables of an ICC
profile, what we really need is the paper-agnostic color data. M1 data (or even
M0 data) contains the color of the paper as well as the blue radiation of the
OBAs. This secondary radiation can be seen through the full tonal range under
magenta and cyan inks, but as yellow and black inks progressively block the UV
component of the spectrometer, this blueness quickly diminishes towards end of
the tonal range. And for this very reason, yellow and black ink become "more
yellow" than what they really are.
This is why I have been proposing M2 as the measurement mode to grab data for
building the ICC profiles for color conversion. In M2 mode, as the OBAs in the
paper are not even triggered, the data can be stripped off the paper color
quite cleanly and the color separations made by the profiles created from this
data have a full body yellow that we see in the profiles of the ISO
12647-2:2004(AMD 2007) era. The reference papers had low OBA levels and the
relatively low power of the UV content of spectrometers in M0 mode, gave us a
better CMY balance in the separations.
M1 data is still needed for proofing/verification work. With M1, you can
"measure-as-you-see" to properly verify that your proof and your print is
compliant to the standard. For proofing, you can use this M1-data-based profile
in absolute colorimetric mode and print on a proof substrate that may have a
different OBA level or in relative colorimetric mode and print on a proofing
substrate that exactly matches the OBA level of the print.
As we all know, the paper whites of FOGRA39 or a FOGRA47-certified proofs
(being made on proof substrates with b* value of -2 for the sake of being
compliant to the standard) appear to be more yellow when viewed next to the
prints made on commercially available coated and uncoated papers under ISO
3664:2009-compliant lights. What many printers have done on the way from
FOGRA39 to FOGRA51 is to use a FOGRA51-compliant proofing substrate to simulate
a FOGRA39 separation printed on a moderate OBA print stock. By doing the final
simulation in relative colorimetric mode or in absolute colorimetric mode with
no paper white simulation, they now have a proof that typically "fails" the
FOGRA39 verification test but that serves as a better visual reference to both
the print-buyer and the machine operator.
The printers have been using the above mentioned papers in the past under ISO
12647-2:2004 (Amd 2007) related printing conditions, are using it now under ISO
12647-2:2013 related printing conditions and will also be using them under
future revisions. This I why I am trying to focus my efforts not on reference
papers that are picked by technical considerations but on real ones that will
go on using in the future.
>> 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.
Surrond? It is the same light booth with side panels. The FOGRA39 and FOGRA51
prints are made on the "same" paper (see above) in their respective printing
conditions and they have been viewed side by side in this light booth confined
with side panels.
>> But have they dealt with proofing on FWA papers ?
Yes, they have. They all have full FOGRA39 and FOGRA51 verified proofing
workflows. And they can also do proofs on FOGRA51-certified proofing substrates
that provide a better visual match to prints made on commercially available
printing papers from FOGRA39 color conversions. Their proofing substrate
library is quite extensive to cover a wide range of OBA levels as they also do
proofing for custom profiles.
>> 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.
When colorimetrically verifying a proof or a print, the numbers should
definitely correspond to the appearance. And by measuring as-you-see, M1
measurement mode does that. But profiles based on M1 data have a strong
tendency to suppress the yellow channel. I have recently tested three
commercial profiling packages with M0-M1-M2 data. They are quite different from
each other in terms of overall behaviour, but one thing is common: they all
produce weaker yellow separations when they are using the M1 data. And this is
why I have been proposing M2 for profiles to do the color conversions and M1
for profiles to do the proofing/verifying.
>> 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.
The balance of CMY, on whatever paper it is being used, should always be
maintained. The success of FOGRA39 (or FOGRA47) lies in the fact that it was
created from a dataset grabbed from a low OBA paper in legacy M0 mode. The CMY
ink-film is quite neutral itself and thus can be be used on papers with
different levels of OBA. And all "appear" neutral, relative to whatever paper
it is printed on. K channel is approx. (16,0,0) in "all" measurement modes.
Solid Black and Yellow patches return almost the same values in M0-M1-M2 modes.
When building the gray axis, the neturality of the CMY ink-film should always
be observed. You should not be relying on the neutralizing power of black.
Black is the first ink that goes on the paper, when you print a CMY gray -with
a weak yellow- on top (and yellow is the topmost layer), the result is visually
cold on whatever paper you are using. The balance of the CMY gray should even
be maintained when you are targeting higher GCR settings for ink saving or for
other purposes. In summary, a netural ink-film works on "all" papers. Knocking
down yellow destroys the neutrality of the CMY ink-film and black barely
compensates this shift to blue.
>> No, I don't see that at all. From the profile data I see that they are both
>> neutral separation
>> produced from distinctly different CMYK values due to the action of the FWA
>> and the shifted
>> observer adaptation point.
You are looking at profile data and the print buyers are looking at the prints.
They do see the shift to blue in the rich blacks and they don't like it.
>> Maybe. But the natural light won't change, and M1 is based on a natural
>> light assumption.
Color-critical work where color management really matters does not rely on
natural light. M1 is there to answer OBA-related issues. And OBAs have probably
become this important when the paper industry rightly moved away from the
environmentally harmful bleaching agents used to whiten the cellulose fibers.
With the imminent extinction of UV from artifical light, OBAs will sooner or
later become irrelevant.
All who have the means can do the test. Pick a high OBA uncoated paper. Define
a printing condition along the TVI or G7 line. Measure the chart simultaneously
in M0-M1-M2 modes. Create a profile from each dataset. Make separations with
each profile and print them. And judge them yourselves.
Thanks and regards,
Refik
On 22.06.2019 04:44, "colorsync-users on behalf of Graeme Gill via
colorsync-users" <colorsync-users-bounces+rtelhan=email@hidden on
behalf of email@hidden> wrote:
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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