[argyllcms] Re: Difficulty shaping Black ink curve for CMYK profile
- From: Samuel Chia <inksandpaper@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 18 Dec 2018 15:37:16 +0800
The primary constraint is that the color be correct. That forces a certain
combination
of inks.
Indeed that is true except that it would appear that the transitions need
not be so abrupt, and also, i1Profiler and is able to avoid such shapes and
still give correct colour, or perhaps I should say reasonably similar
colour in the extreme shadows for in-gamut source colours when mapped into
printer space. Although I am avoiding any i1Profiler profiles due to the
gamut mapping issues which we have discussed privately previously.
400% is a very high ink limit. Typically ink limits are around 300% at the
very most,
and some googling indicates Indigo presses typically run with a 280%
limit. So
are you sure that you are really getting 400%, and that the printer isn't
limiting it to less ? A downstream imposed limit will play havoc with the
profiling
process.
This is a common misunderstanding with Indigos. What you say is true for
traditional offset and perhaps several other types of digital offset
presses, but not Indigo. The Indigo blanket is able to take 1600% ink for a
single transfer to substrate, and it can make multiple passes on the same
sheet so several thousand % total is possible (raised ink effects) with
virtually no drying time needed. So 400% ink limit is nothing at all. For
sure the printer is not artificially limiting to less. The design of how
the Indigo Electroink technology works allows this to happen. The blanket
is heated so almost all the oil carriers in the ink are evaporated before
transfer to the substrate, the printed image on the blanket becomes more
like a film and is transferred to the substrate under high pressure and
that exits the printer dry.
There is another issue: the Indigo inks don't hit their potential for
dmax until a very high limit, about 350% or higher, depending. BTW Most
Indigo shops (here at least, and other places I've come to know about) also
advise their customers to use the generic Fogra39 CMYK profile, which
already has an ink limit of 330%, well over 280%. If they make their own
profiles limiting to 280%, perhaps they are trying to save ink, or for a
multitude of other reasons.
One other issue is also that the Indigo inks lose a lot of chroma when
calibrated to print at higher densities, so following the "XCMYK" method to
try and boost gamut with higher solid ink densities will not work. The
Indigo inks already exceed the gamut described by Fogra39 by a fair bit at
its default "glossy substrate densities" setting for light colours, so to
have more dark colour gamut and high dmax, it requires a very high ink
limit to fully max its potential without using additional ink hues (orange,
green, violet) or high chroma speciality inks.
Note that profiles can be somewhat inaccurate near black if the profile ink
limit
is at leas 10% less than that of the test chart. So even with a 400%
capable
device, a profile ink limit of 390% or less is recommended.
i1Profiler and Color Savvy RTKit were both able to build profiles for 350%
all the way to 400% ink limit with no discontinuities in the shadows, but
Argyll shows it even in this 350% profile (made from 400% ink limit target)
linked to earlier in this thread. Something is not right with Argyll's
profile calculation, because it affects both the perceptual and
colorimetric tables. In particular, the colorimetric table is totally
unusable. Please kindly have a quick look at the profile.
On Tue, 18 Dec 2018 at 13:13, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:
Samuel Chia wrote:
The insistence of the K curve to always be convex when approaching 100%
remains quite
strange to me, when it is happy to be concave or convex when approaching
0%.
The primary constraint is that the color be correct. That forces a certain
combination
of inks.
Unfortunately also, I am getting very strong discontinuities in smooth
gradients in the
shadows with Argyll making the CMYK profile using "-lp" for perceptual.
I'm not sure why
that is the case. When reducing the total ink limit to less than 400%,
the problem is
diminished, but still present and certainly visible in the output.
400% is a very high ink limit. Typically ink limits are around 300% at the
very most,
and some googling indicates Indigo presses typically run with a 280%
limit. So
are you sure that you are really getting 400%, and that the printer isn't
limiting it to less ? A downstream imposed limit will play havoc with the
profiling
process.
Note that profiles can be somewhat inaccurate near black if the profile
ink limit
is at leas 10% less than that of the test chart. So even with a 400%
capable
device, a profile ink limit of 390% or less is recommended.
Cheers,
Graeme Gill.
Other related posts:
