Digital BW, The Print

Peter,

> I have just completed my first curve for Ilford Smooth Pearl, using 
> Lyson Fotonic ink printed on an Epson 2100. Quite an effort !! I 
> think I need to lie down for a week to recover. 

If you start from an existing profile, it should be a pretty quick 
process.  Of course, you are using a different inkset, so it would 
probably be a bit more effort.  Try starting with a profile that 
comes closest to your inkset and paper combination.  That should 
eliminate most of the work.

> However I would 
> appreciate some comments when evaluating the tone of a print and
> the corresponding Lab values, a and b. I have, I think a grasp on 
> how the inks vary these values, and the effect that the paper has. 
> However what do you look for when evaluating the figures ?

When evaluating a profile, I use my spectro to measure color (a* and 
b* values) at different points on the curve.  If I want a neutral 
profile, I try to get the a* abd b* values as close to "0" as 
possible.  I often read the color of the paper base before building 
my profile, and if it has a somewhat creamy or slightly yellow base 
color, I will often let that bias carry through from step 1 thru 26.  
But that is an artistic judgement call.  If you want all steps the be 
dead neutral, then that is another choice.  At any rate, if I measure 
my grayscale, and step 5 has a b* value of +2.5, but step 15 has a b* 
value of -3.2, then I have an obvious color shift going on.  If you 
don't want that color shift, it is time to adjust one or the other, 
or both.  Depending on the inks and curve shapes, you may be able to 
do this with ink limits, or more likely, by adjusting the curve 
shapes.  It's really pretty easy once you play with it a little.  
Make a tweak, print a new chart for linearization, then remeasure.  

I also try to get the densities for the various steps pretty close to 
the target values.  This way, the software applies smaller 
adjustments during the auto linearization process.  Most papers have 
a paper white L* reading of 97 to 99 (density of .01 to .03).  

Glossy papers have a Dmax that varies from L* 4 to 10 (density of 
2.35 to 1.95).  Matte papers have a lower Dmax, L* 15 to 20 (density 
of 1.72 to 1.52).  

If I am far from those numbers, I check to make sure I have a good 
Dmax and adjust the dark inks to get the best I can.  Once I have a 
good Dmax, you can enter the white and black points into the 
linearization screen, and IJC will give you targets for all the 26 
steps.  If a few spot measurements show I am way off, I will probably 
adjust my ink limits or curves to get closer.  If not, I just 
linearize.

This sounds like a lot of work, but once you have a good base 
profile, the others come very quickly.  If not, there is no way I 
could have created roughly 50 profiles in a month's period.  Once you 
have a good neutral profile for your ink and a matte paper, you can 
use that same profile as a starting point for other matte papers.  
Minor tweaks quickly deal with color casts and ink limits.  

Hope this helps.  Once you build a few profiles, it becomes pretty 
fast and easy.

Lou