Digital BW, The Print

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


--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale <stevekale@b...> 
wrote:
> Roy 
> 
> Thanks for the help.  Sorry I have been away and have only just come back to
> this.  Am I right in that one should determine the various ink limits (and I
> am quite happy to simply take your numbers for these) and that the
> partitioning should be determined with these inks limits in place?  As you
> can see from this thread I am getting quite different partitioning figures
> than Carl for the same ink/medium combination.  The lower partition for LK
> presumably means that the ink limits for LM and LC can be lower also (?).
> 
> The partitioning process makes intuitive sense to me but the final
> smoothing/curve math is way beyond me for the moment.  (Any reading material
> on this that does not require a physics degree?)
> 
> Cheers
> 
> Steve
> 
> 
> 
> 
> From: "Roy Harrington" <roy@h...>
> Reply-To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Date: Sun, 28 Dec 2003 05:21:27 -0000
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: Re: [Digital BW] QTR and Making Curves
> 
> 
> Hi Steve and Carl,
> 
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale <stevekale@=
> b...> 
> wrote:
> 
> 
> The 2200 ink limits were done a little more adhoc rather than strictly by
> my orginal 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.
> 
> > 
> > 
> 
> 
> 
> [Non-text portions of this message have been removed]