QTR-Quadtone RIP

I'm making a curve for printing from on R1800 with MIS Ultrachrome inks onto an HP glossy paper.  I only print B/W occasionally for personal use, so I don't want to go the K, LK, LLK, toners route.  I acquired a large quantity of this heavyweight glossy paper in roll form, and have a question (more probably to follow) about how to correct the tonality of the MIS Photo Black ink on this paper.  The paper itself is a bit on the cool side (L*a*b values of  93.25 -0.39 -1.15).  I plan to use the colored inks (C, M, Y, and possibly Blue & Red) to counteract the warm tonality of the MIS PK ink by using the "a" and "b" values I measure from printing the 51 step random file (measured with a ColorMunki) as curves for the respective inks.  I've gone through the first steps of ink optimization and linearization with fairly good results.

My question has to do with how to offset the "a" and "b" values to achieve "truly" neutral grays.  My initial thought was to add Cyan ink to offset the positive "a" values since cyan is the "opposite" of red, but the "a" axis in the L*a*b space is a red - green axis.  Should I, instead, be using a combination of Cyan and Yellow (= Green).  Likewise for the "b" offset.  Most of the "b" values are positive (yellow), but should I use the Blue ink to correct, or would it be better to use Cyan + Magenta (= Blue).

My first round of correction (using Cyan and Blue inks) seemed to help a lot with the lighter grays (<40%) but not so well with the darker grays, which brings up a second question.  Should I be adding proportionally more of the correcting colors as the base ink density (from Photo Black) increases?  Is it reasonable to assume that the more PK that is laid down, the more tone correction ink is needed to bring the grays back to neutrality?

I've only had QTR for a week, so haven't had much experience, but I'ld like to develop a purely empirical approach to generating ink/paper "profiles" by using the ColorMunki, gray patches, and statistical tools.

On 05/30/2012 03:24 PM, wolverinemsu wrote:
> I'm making a curve for printing from on R1800 with MIS Ultrachrome inks
> onto an HP glossy paper. I only print B/W occasionally for personal use,
> so I don't want to go the K, LK, LLK, toners route. I acquired a large
> quantity of this heavyweight glossy paper in roll form, and have a
> question (more probably to follow) about how to correct the tonality of
> the MIS Photo Black ink on this paper. The paper itself is a bit on the

I am intrigued, was that paper ever meant for an HP dry minilab ?


-- 
Met vriendelijke groet, Ernst

Dinkla Grafische Techniek
Quad, pi\ufffdzografie, gicl\ufffde
www.pigment-print.com

Actually it was meant for one of the HP large-format printers that we use in the department for printing posters.  I got the better portion of a 100-foot roll of 42-inch wide paper that I cut down into 13" rolls.  I also got some leftovers of another type of glossy paper and some HP heavyweight matte paper.  Most users have now opted for posters printed on fabric because they're easier to transport to scientific meetings than the paper ones (fold 'em up and pack in the suitcase instead of carrying in a large tube).

wolverinemsu <bowlby@...> wrote:

> **
>
>
> ... R1800 with MIS Ultrachrome inks ...
>


> My question has to do with how to offset the "a" and "b" values to achieve
> "truly" neutral grays. ...
>

If I were profiling that printer, I'd make a good carbon core or backbone
profile first.  Then to cool the carbon, I'd use C and M in equal parts to
pull the Lab B into place first.  Then for Lab A  I'd use C and M in
offsetting moves.  THat is, if I wanted higher Lab A I'd increase M one
unit and decrease C one unit.

That is basically how I profile with the dilute carbon core and LM & LC in
this inkset: http://www.paulroark.com/BW-Info/4000-6K-Plus.pdf    The
approach works well and is actually rather easy.

Once you get into the other colors, things will get more complicated.  I
can't help you there.  I'd recommend you take the easiest route first.

Paul
www.PaulRoark.com


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