Digital BW, The Print

As age begins to take over and I find myself pondering the question of life, I find it easier to ask completely absurd questions such as this one- What does a Black Only neutral curve really look like graphed in Excel? In theory if nothing else. In reality, I think it is impossible to achieve a truly compliant neutral curve because of the influence of the paper white and imperfections in the carbon inks.

However, as Lab L* progresses from 0 to 100, does Lab a* and Lab b* remain steady at 0? Wouldn't it require both a* AND b* to remain at the 0 axis to achieve a true neutral? A slippage of either a* or b* would induce warmth or coolness, yes?
 
If I were to graph this in Excel, Lab a* would be influenced by the paper color but would Lab b* remain on/near the 0 axis?

Phil

>>
However, as Lab L* progresses from 0 to 100, does Lab a* and Lab b* remain steady at 0? Wouldn't it require both a* AND b* to remain at the 0 axis to achieve a true neutral? A slippage of either a* or b* would induce warmth or coolness, yes?

Well, a* and b* don't lie exactly on the warm/cool axis, but b is closer to warm/cool, while a is now referred to as "tint"; tint being Adobe's choice of terms (I tried to argue Tom Knoll out of that abuse of the term, but that's history now) for the "other" axis, perpendicular to color temp. So b is yellow/blue, and a is red/green. 

C. D. Tobie
Global Product Technology Mngr.
Imaging Color Management
Datacolor.com
CDTobie@...

On Mar 24, 2011, at 3:59 PM, "grimmieoldfart" <grimmieoldfart@...> wrote:

> 
> However, as Lab L* progresses from 0 to 100, does Lab a* and Lab b* remain steady at 0? Wouldn't it require both a* AND b* to remain at the 0 axis to achieve a true neutral? A slippage of either a* or b* would induce warmth or coolness, yes?


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"grimmieoldfart" <grimmieoldfart@...> wrote:

> ... What does a Black Only neutral curve really look like graphed in Excel? 

>In theory if nothing else. In reality, I think it is impossible to achieve a truly compliant neutral curve because of the influence of the paper white and imperfections in the carbon inks.

True.  

 
> However, as Lab L* progresses from 0 to 100, does Lab a* and Lab b* remain steady at 0? Wouldn't it require both a* AND b* to remain at the 0 axis to achieve a true neutral?

As C. David noted, the warm-cool is mostly Lab B these days.  The more OBA's, the more negative (cooler) the Lab B will  be.  Natural paper will have a positive Lab B.

Lab A tends to be about +1 on my spectro.  It stays more constant across the density range than Lab B.

The Lab B will vary somewhat with the ink you're using.  They all, of  course, start at the  paper white.  The true carbon inks will all have some Lab B rise in the midtones, with Eboni being the least.  Then they'll get a bit more neutral or  cooler toward the 100% black.  Eboni might end up with a negative Lab B. 

The neutralized PK's vary depending on the amount of color they have mixed in.  HP PK will start quite neutral and have a cold shadow tone.  

MIS K4 PK, perhaps the warmest PK, on glossy  paper can have a Lab B rise over the paper white of 10 or  more.  On matte paper  it usually hits about Lab B = 8 at most.  Even this one, however, will head back toward a rather modest Lab B at the 100% black.

Epson has started to cool its PK and LK inks with what looks like cyan.  They will  have more modest Lab B's, but may stray very close to a negative Lab A -- too greenish for my tastes.

Paul
www.PaulRoark.com

I forgot to add, I published quite a few paper graphs with the 1800 3-MK write-up.
  
See http://www.paulroark.com/BW-Info/R1800-No-OBA-Paper.pdf for "natural" papers.

See http://www.paulroark.com/BW-Info/R1800-OBA-Papers.pdf for brightened papers.

Finding papers with the lowest Lab B increase was the challenge.

Paul
www.PaulRoark.com

Thanks for everyone's help & advise. Sometimes I feel as if I am getting wrapped 
around the axle and end up chasing an invisible tail not ever knowing if I am 
getting close or over shot the entire point. I guess the real challenge is 
understanding when a neutral is good enough. I spent some time over at hunter 
Labs reading a fe articles they have available on CIELab color space. The most 
important point I deoarted with was understanding the difference betwen 
technically acceptable an visually acceptable. Print gray charts, measuriong, 
and graphiong are super tools to work with. But what is the point of all of this 
effort if I am only surrounded by sheets full of "almost perfect" 21Step charts 
without ever printing a single photo. I suddenly find myself wrapped around the 
proverbial axle of tchnical greatness.

Paul, these documents will help alot as I work to master this art. Thank you and 
I did finally locate the other document (Split Toning ) I was looking for. It is 
from your 2006 7500_K4+ documented work. Great stuff.

The challenge I am currently struggling with is what I would like to think of as 
complete mastery of the tools. Ttrying to figure out how to pull a warm curve 
from a Lab b* +5 down to the x-axis. How to smooth a curve, extend the dmax of 
the 100% black, and how to manage the denisty spacing to an even 0.05 difference 
across all 21 steps. Somethings in life are acceptable as good enough while 
other notions will haunt us into the next life. Da Vinnci was on the History 
channel today...

Thanks for all of the help!

Phil


 



________________________________

From: Paul <roark.paul@...>
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Sent: Thu, March 24, 2011 5:55:06 PM
Subject: [Digital BW] Re: What does a BO Neutral Lab a + Lab b Curve look like?

  
I forgot to add, I published quite a few paper graphs with the 1800 3-MK 
write-up.

See http://www.paulroark.com/BW-Info/R1800-No-OBA-Paper.pdf for "natural" 
papers.

See http://www.paulroark.com/BW-Info/R1800-OBA-Papers.pdf for brightened papers.

Finding papers with the lowest Lab B increase was the challenge.

Paul
www.PaulRoark.com 





      

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