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: Mon, 24 Jun 2019 13:46:16 +1000
Refik Telhan wrote:
Hi,
>>> 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.
Not according to Fogra:
<https://www.fogra.org/index.php?menuid=48&downloadid=1100&reporeid=0>
"(FOGRA39:) This is mostly due to the paper white point (CIELAB (M0, wb)=95 1
-2),
which does not reflect typical paper shades having higher amounts of optical
brightener agents (OBA)."
> 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
Looking at the Fogra profile data:
Fogra39:
xicclu -ff -ia Fogra39L.icm
0.000000 0.000000 0.000000 0.000000 [CMYK] -> Lut -> 95.021551 0.001909
-1.997379 [Lab]
Fogra51:
xicclu -ff -ia Fogra51.icm
0.000000 0.000000 0.000000 0.000000 [CMYK] -> Lut -> 95.037647 1.505190
-6.102197 [Lab]
Under the different measurement conditions, the Fogra51 is noticeably more blue
(delta b* -4.1), indicating greater FWA activity.
> 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.
"colormetric" should be exactly the same as visual appearance.
If it's not, then the profile is not appropriate.
> 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.
Use a measurement mode that corresponds to your evaluation conditions. Ideally
you would measure you evaluation conditions and use that.
> 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.
Conceptually this is possible, but the maths is not simple when FWA is part
of the mix, nor when you want accuracy, since the print process needs
to be modeled in some detail. i.e. you can't simply subtract one paper white
and add in another.
But I strongly suspect that viewing conditions are also an issue. Placing
a paper with FWA in an M1 viewing booth with spectrally flat surround
is asking for problems due to the different white points of the surround
and the paper.
> 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.
You may well be right that such a profile is more portable (i.e. less
sensitive to the paper type) than one that takes the paper effect
into account. i.e. use of relative colorimetric intent effectively
strips out the paper background in a simple way, and the printing
process itself adds it in again. If the physical recombining
is sufficiently close in effect to a simple addition, or if any
errors tend to be in a direction that is visually acceptable,
then the overall result may be acceptable.
>>> 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.
Right, but does the light booth have spectrally flat grey side panels ?
Because this is a source of white point reference for the observer that is
going to be noticeably warmer than the paper substrate under M1, and
so is at risk of giving a misleading impression of the color compared
to real world viewing conditions.
> 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.
You simply can't have it both ways. Suppressing the yellow is what the
data says has to happen.
> The balance of CMY, on whatever paper it is being used, should always be
> maintained.
The CMY should be whatever is needed to produce the correct
color. That's what the profile does for you. If you want to set CMY
by hand, then you aren't color managing.
> 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.
You have an obvious contradiction that you keep talking about, but do not
seem to be trying to resolve.
> 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.
Then fix the profiles!!!! You can't keep using profiles that don't correspond
to appearance and then complain that the profiles produce separations that
don't give the correct appearance. Of course this is so, by definition.
Cheers,
Graeme Gill.
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