Digital BW, The Print

John,

I had the same question, and here is how I resolved it along with my 
reasoning. 

I use L* readings from my Eye One instead of using density units.  L* 
readings, which are plotted on a linear scale, should show roughly 
the  same difference between steps on a linear profile.  If a glossy 
paper has a paper white of L* 95, and deepest black of L* 6, then 
there is a total difference of 89 L* units.  Divide this by 26 (the 
number of steps in the IJC linearization routine) and each step 
should be differ by about 3.4 L* units.  That helps me better put it 
into quantitative terms.  

When step 25 and 26 both look the same by eye, I take readings with 
my EyeOne.  If step 26 reads 6.0 and step 25 reads 6.3 or 6.4, they 
are so close as to be nearly indistinguisable both by eye and by L* 
readings.  They are both essential black, and looking at a desired 
difference of 3.42 helps me put it into perspective.  In this case, I 
will select 25 as my ink limit.  My reasoning is that if I use 26, 
there is essentially no tonal separation between 25 and 26, which 
forces IJC to make more extreme adjustments to give me a linear tone 
scale.  Getting closer to being linear before asking IJC to do its 
math will give me smaller adjustments.  I seem to get a better 
profile that way and don't notice any loss of black.

If step 26 reads L* 6.0 and step 25 reads 7.0, tonal separation is 
more substantial (even if it may still be tough to see by eye) and I 
would probably choose 26 as my ink limit.  If the difference is 1 or 
greater, I always go with the darker test patch.

Maybe not totally scientific, but it seems to make sense and works 
for me.

Lou

--- In 
DigitalBlackandWhiteThePrint@yahoogroups.com, "johndavidgill2003" 
<jdgill@l...> wrote:
> 
> I'm really impressed (and getting more impressed by the day) with 
> IJC/OPM - thanks to Joe and Richard for their help and also for the 
> new tutorial.
> 
> One question though; When I print the target for linearisation my 
> densitometer reads step 26 darker than step 25 but to the eye there 
> is no difference whatsoever. If I linearise using the readings am I 
> in effect wasting shadow detail by having step 25 and 26 identical 
to 
> the eye even though step 26 is "densitometer darker"? Would I be 
> better tweaking the inks or the sliders to get a visible difference 
> between 25 and 26 before completing the profile?
> 
> Thanks in advance.