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Digital BW, The Print

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How to adjust the tone to look neutral when the paper isn't neutral

2007-10-30 by etlblbt

Hello,
      I have an Epson 2400 using the C,M,Y,K,LC,LM,LK,LLK inkset from 
Lyson.  I am initially trying to profile it to print a neutral black 
and white print and have the benefit of an eye-one to help me do it.

I started using quadtone RIP, which was great for linearising the 
greys, but I found overly complicated for adjusting the tone, so I am 
now giving the Epson Advanced black and white mode a try.  I found 
the linearisation pretty good with no adjustment when I used 
the 'darker' setting but I am again faced with the problem of 
adjusting the tone to neutral.

Then I realised my fundamental problem.  I am trying to acheive Lab 
values of 0 for both 'a' and 'b' throughout as much of the range as 
possible.  However my paper stock is obviously quite blue because I 
am getting a 'b' reading of about -9.5 from the paper base itself, 
with no ink applied.

Thus although with a bit of adjustment I can get the 'b' reading to 
be approximately 0 throughout the midtones and shadows, I can never 
get it correct in the highlights because there simply isn't enough 
ink on the page to overpower the 'blueness' of the paper base, and if 
I add more ink then I am increasing the density which I don't want to 
do in the highlights.

But then I thought that since the eye/brain combination of the viewer 
will adjust the perceived whitepoint to match the paper-white anyway, 
perhaps I shouldn't be aiming to get the 'a' and 'b' values to zero 
throughout the range, but should be aiming for a smooth linear 
progression from the paper-base values at 0 density to zero at 100% 
density.

Does anyone know the theory of what will look neutral to an observer 
when the base paper is not neutral itself?

Regards, Bill

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