Digital BW, The Print

Hi Roy

I am hoping to get back to ³making curves² this weekend for my 2100 (and
from there to the soft proofing profiles).  With regard to ink limits, where
do you suggest I start?  Below are the ink limits that Carl used in his cool
and warm EEM descriptor files, respectively:

N_OF_INKS=7
DEFAULT_INK_LIMIT=75

LIMIT_K=
BOOST_K=90
LIMIT_C=0
LIMIT_M=0
LIMIT_Y=0
LIMIT_LC=27
LIMIT_LM=27
LIMIT_LK=56

N_OF_INKS=7
DEFAULT_INK_LIMIT=75

LIMIT_K=
BOOST_K=90
LIMIT_C=0
LIMIT_M=0
LIMIT_Y=0
LIMIT_LC=0
LIMIT_LM=0
LIMIT_LK=60

As I noted earlier, if I adopt these ink limits I get quite different
partitioning values than those used by Carl.  Maybe this is something I am
doing wrong but I intend to start from scratch again in the morning.  I hope
to get curves done for EEM and HPR ­ adjusting for the effects of spraying
with Lyson Print Guard ­ over the weekend.

>The other plus is that UC_NEUTRALIZER feeds the exact same curve shape into
>LK LC and LM so no matter how you change curve shapes and ink limits
>the 3 inks are always used in the same proportion which avoids color
>crossover problem.

So effectively in the above cool scenario LK is limited to 27 anyway?  Sorry
I am confused by this and your next sentence:

>So the ink limit values i.e. ratios for LK,LC,LM determine
>the color tone of the output.

Do you mean they are used increasingly together but always in the proportion
of 27/110, 27/110, 56/110?  So this ink ³mix² (an equal dose of LC and LM
applied to LK ­ a virtual mix) is that which is deemed to take the LK from
warm to cold?  Ie if I could print a 100% patch of this combo it would look
cold? 

And this combo of limits is deemed to give good coverage for a 100% patch in
the same way that 75 was deemed enough for K?   I am surprised that both
27/27/56 and 0/0/60 are deemed to each give good coverage. Wouldn¹t one have
a lot more ink laid down than the other?
  
If this is the case then how is K cooled, if at all (I suspect it is not)?
I ask because, although when I look at the Ink Pattern Page printed using
calibration mode it seems that K is quite neutral, at least vs LK.  However,
I have been puzzled by the comments in the BO discussion which note (quite
clearly from the examples given) that BO prints with Epson UC K  are very
warm vs their BO Eboni counterparts.  Am I right in understanding that with
BO printing ONLY K is used (ie no LK is used) or is the warmth of BO UC due
in part to LK?  

Thanks again for your help and generosity

Steve

From: "Roy Harrington" <roy@...>
Reply-To: DigitalBlackandWhiteThePrint@yahoogroups.com
Date: Wed, 14 Jan 2004 20:08:23 -0000
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: Re: [Digital BW] QTR and Making Curves


Hi Steve,

You're right that you ought to come up with the ink limits before deciding
on
the partitioning values.  I'm not positive exactly how Carl did his curves
--
it's somewhat difficult since ideally you should be partitioning the
LK,LC,LM
combination rather that just the LK.   Fortunately, it's not a big problem
because the final linearization smoothes out the step wedge very well.  The
other plus is that UC_NEUTRALIZER feeds the exact same curve shape into
LK LC and LM so no matter how you change curve shapes and ink limits
the 3 inks are always used in the same proportion which avoids color
crossover problem.  So the ink limit values i.e. ratios for LK,LC,LM
determine 
the color tone of the output.

The linearization or "final smoothing" is really not that complicated in
concept.  Smoothness is actually built into the partitioning and mixing of
the inks -- there are only smooth changes to all the inkjets.  The main
necessity is that it's always increasing as you go from light to dark.
Once that is true, it's a matter of a correction curve that puts the
densities
in the "right place".   You can think of it as first plotting densities
versus
input step values -- a bunch of (x,y) or (input,output) points.  The
correction
curve is just the mirror image: x and y swapped.  If you go into Photoshop
and design a custom dot gain curve you are doing exactly the same thing.
There are some hairy looking formulas for converting between density,
luminosity and other units.  If you want more reading, Adobe has some
info buried deep in their website.   Here's a website that has some
pretty technical info, but your eyes may start to glaze over.
http://www.brucelindbloom.com/

Roy

> The 2200 ink limits were done a little more ad hoc rather than strictly by
> my original documents.  The idea for cool 2200 prints is to have a
> combination of LK,LC,LM play the role of one light black ink. (Basically,
> instead of mixing the inks manually to get a neutral gray, the idea is
> to mix them using software curves).  However the difference is that you
> now have 3 inkjets delivering ink so it made sense to lower the individual
> limits to make sure we don't flood the paper.




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