Digital BW, The Print

Peter,

To me, numbers are simply a means to a desired end.  The measured 
numbers help me to quantify what is truly neutral, what color is 
causing a problem (e.g., is it a yellow or green cast), or where 
crossovers occur.  I let my eye be the final judge, but I do look at 
the results under a variety of lighting sources to be sure I don't 
have any weird shifts occuring due to metamerism.

For me personally, I design my "neutral" profiles to be a little cool 
for cool papers, and a little warm on naturally warm papers.  That's 
my judgement call and is what I like.  

Also, I tend to be a little less concerned about the deep blacks if 
they measure with a color cast, since I have a hard time seeing it.  
I try to keep it in line with the overall tone of the profile, but I 
don't obsess about it.  Having said that, my profiles are pretty 
close.

In Lab, positive a* values are more magenta, and negative a* values 
are more green.  Positive b* values are yellowish and negative b* 
values are more bluish.  Lab space isn't particularly intuitive, but 
you get used to it if you work with it for awhile.  So, you readings 
of Ilford Smooth Pearl (96, -0.15 and -5.36) show a very cool paper 
white.  My tendency would be to keep the b* value cool.  

For the a* value, if you are happy with the look of the print in 
various lighting situations, I'd leave it alone.  It is easy to get 
carried away with the numbers and forget that the final result we are 
after is a great print.  If you like it, it's done.

Lou

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "bwbonkers" 
<PeterDLevis@a...> wrote:
> 
> Lou
> 
> First of all thanks for such an informative reply. The design of 
the 
> Black and Light Black curves was pretty easy because as you pointed 
> out I based them on the UC ink curves for the paper that I was 
> profiling. I used the EyeOne to measure the L values and adjusted 
the 
> shape and ink limits to get a nice smooth curve. That was the easy 
> bit. The harder bit was tonning. Understanding the relationship 
> between a and b values, and the fact that there were no suitable 
> curves to use. The Fotonic inks are cooler than the Epson inks. 
> Initially I tried to get both a/b values zero, but after a check 
> print decided that the result was too warm, yellow for my taste. I 
> guess this is because of the base colour of the paper. Ilford 
Smooth 
> Pearl gives me values of 96, -0.15 and -5.36. So I cooled things 
down 
> a bit with b values averaging -6. I have no postive to negative 
> shifts in values. The values do increase slightly. The bigest 
> increase is from steps 24 to 26. The b values are pretty constant 
> ranging from step 5 -6.02 to step 23 - 6.86. The a values are not 
as 
> good they range from 0.15 to 2.97.
> 
> Do these values look sensible to you. Would you tweak the a values ?
> 
> The print looks darn good. The best I have achieved yet. I really 
do 
> like OPM/IJC. The more I work with the program and try to 
understand 
> it the more I like it.
> 
> Once again Lou many thanks.
> 
> Peter.