From your graphs, basICColor CMYKick is using a delayed
black start so
uses CMY in the highlights instead of K while Heidelberg PrintOpen is
not
doing that. This is not good nor bad but a user preference trading off
graininess vs. gray balance locking. It is not true that "high light is
not neutral" just because one uses CMY in place of K and from the graph it
appears that the CMY are in the proper relationship to still produce a
gray. That is, the two profiles may be producing the same colorimetric
result in the highlights.
The gray balance using CMY may be less stable to process variation, but
that is the tradeoff for deferring the introduction of black. The black
(K) dots are of higher contrast and more visible to the naked eye.
Whether this results in graininess depends on factors such as the
resolution or more specifically the minimum dot size for the particular
screening being used (i.e. how many spots make up the smallest halftone
dot), at least for the extreme highlights. C and M dots have roughly half
the visual density of black dots and yellow has hardly any visual density
so CMY combinations spread out this contrast and have it be less visible.
In the shadow area for the darkest color there does seem to be a mismatch
between the profiles where the Heidelberg PrintOpen reduces yellow, but
here again this is something of a user preference because as was explained
by Florian the Yellow can end up lightening instead of darkening in which
case there is a choice of whether to keep darkening but get bluer or to
flatten out (reversal would be bad) and maintain gray balance. If I look
at FOGRA39L characterization data I find the following for black alone,
with CM, and with CMY:
1347 0 0 0 100 2.02 2.10 1.73 16.00 0.00 0.00 Black (K) only
darkest point
1273 40 40 40 100 1.38 1.41 1.10 12.03 0.55 0.87
1286 100 100 100 100 0.93 0.97 0.69 8.71 -0.07 2.06 Darkest neutral
point
1268 100 100 0 100 0.99 0.87 1.08 7.88 5.79 -5.94 Darkest point,
but bluish
Remember that with 300% TAC the 400% above is really 66 66 66 100 so I
show 40 40 40 100 above for comparison. Note how the L* gets larger
(lighter) when yellow is added to the darkest blue. So you can see the
trade-off decision between going to the darkest point that is bluish vs.
maintaining gray but not quite hitting the darkest point. There isn't a
"right" answer here since we are talking about trade-offs. Personally
given how close the dark neutral is to the darkest point that is bluish, I
would prefer to stay neutral when an a*=b*=0 neutral is requested, but
that's a personal preference.
The bottom line is that there are 3 degrees of freedom going into the B2A1
profile tag based on the tristimulus values corresponding to human vision
while there are 4 degrees of freedom going out of the profile to the CMYK
process colorants. So the black vs. CMY relationship is an extra degree
of freedom profile makers have and therefore you may see differences
between profiles regarding black start, GCR level, and choice of darkest
point. This does not mean there is a different colorimetric result -- in
general there isn't except for the darkest black choice.
On 10/31/14, 7:55 AM, "Michael Sartakov" <msartakov(a)gmail.com> wrote:
Hello Dietmar!
Yhank You!
I was interested in colorimetric rendering course - table B2A1
(Lab->CMYK) in colorseparation profiles. Relative and absolute are
described in the profiles of a single table - colorimetric rendering.
Noncolorimetric tables B2A0 (perceptual) and B2A2 (saturation) are not
interesting in comparison, each developer is free to do what it wants,
but colorimetric table is strictly based on the characterisation data
(fogra39 in examples). However comparable profiles give different
colorimetric result in print, and I just showed it in the
screenshots.
Best regards
Michael Sartakov
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