Digital BW, The Print

Antonis-

Thanks for another thoughtful answer.
  
> > 1. Does this gamma or ramp rate change depending on Dmax?  The rate at
> > which denisyt changes near the Dmax point needs to be steeper with a
> > larger Dmax - I think?
> 
> 
> That's the reason IJC made the linearization gama variable. It's an
easy way
> to compensate for high dmax media and inks. With profiles that result in
> dmax around 1.6 the slider is set to -6. However if you profile
something
> with a dmax of 2.4, you will inevitably have an overall darker scale
if you
> leave the slider at -6.  As you go down to -11 or -12, you are in
essence
> lightening the mid tones. This is much like lightening the mid tones
in Photoshop: 
> it decreases contrast in the highlights and increases it in the
shadows (as you
> note above). 
> 

Thanks for the guideline numbers.  I had adopted -6 for the HPR and my
3000 with piezotones.  I got a 2200 the other day and looking at the
curves you and others had produced for ISP I wanted to understand
where the slider should be for larger DMax combinations and what the
slider actually meant.

I made some graphs yesterday and interestingly (to me anyway), when
the slider is at -6 for Dmax of 1.65(ish) this makes the luminance
values more or less a straight line. When the DMax is 2.3(ish) the
luminance is a linear straight line when the slider is at -10.

In the end, as long as you're close and consistenet I guess it's still
a 'salt to taste' issue.


> > 
> > 2. Is it possible to create a gamma or ramp rate which matches a
> > hardware calibrated monitor at some specific gamma (1.8 or 2.2 or
> > whatever)?  Is that undesirable for some reason?
> 
> I'm sure it is possible, and rather desirable, but that's not how IJC is
> set up.  It so happpens that with the Lin. slider set to -6 and dmaxes
> in the 1.6-1.8 range it comes pretty close to gamma 1.8 (except the
shadows
> look a little too light). To really match to a monitor you'd have to
> linearize by hand (trial and error) with the present version. If we are
> lucky enough to have a future version where you can control the
> aims, it would be a matter of writing a set of aims of your choice
> to which IJC will linearize your profile. That would be far more
> desirable than the simple pull of the midtone we have now.
>

Hmm.. I've been calibrating to a gamma of 2.2 and using a 2.2 working
space.  If it is closer to a gamma of 1.8 maybe it's worth the effort
to change for future images.  I know it's just fiddling with the fine
tuning dial but ...

> 
> > 
> > 3. Is there a "formula" based on human perception that can be used to
> > determine what an optimal greyscale ramp would look like?
> 
> There may be, but I don't know it. Kodak literature has densities for
> optimal grayscales as they apply to their instruments and that became
> the basis for the aims in IJC. But I am sure the committees who wrote
> ICC specs and gammas etc for color management have arrived at
> optimal grayscales in lots of other ways. There is also the old prepress
> school of dot percent where 50% means half the dot is black and
> half is paper-white. 
> 
> 
> Hope this is helpful....

Yes, thanks.