Digital BW, The Print

Austin

I think I'm winding down here on my participation in this thread, so I'm
taking stock of where we stand at this point. I'm curious after all that's
been discussed on this topic, what is your position on the usefulness of a
calculation of dynamic range on an "existing print of unknown origin", at
least with regard to giving an indication of how many tones THAT print
contains.

Lets face it DyR might be a useful measure of a SYSTEM, where you know the
values of a range you put through it, and you compare it to the values that
come out. That's how you test the DyR of a scanner right? You scan a target
of known values and you measure how the noise and non-linearity of the
system distorts those values upon output? I don't know, I'm asking. For a
print system you'd print a target of known values, measure those values at
the print, and compare?

If so, it's a comparison of input to output values that is relevant; or
calculations based upon assumed linearity, and if the system is linear, and
you can measure the noise, you can make an assumption or calculation of tone
count.

But in the case of a print of unknown origin, the only way to count the
tones present would be to do a full "pixel count" along the lines of a
Photoshop histogram calculation. I can see no way that a few well chosen
samples will get you there. Not without have a great understanding of the
materials underlying the process, but a print of unknown origin rules that
out.

Furthermore, tones will either be present or they will not, but how many are
present almost certainly be based upon far more powerful determinants than
"noise". For instance, the number of tones present in the original file or
negative - or the printmakers intent!

So really, what do you think?

Now this part I don't expect an answer on (though feel free), but I'm tying
my thoughts in with Martin's, just to summarize what I've taken from this
extremely thorough and enlightening discussion.

It seems to me that the formula you site for dynamic range may well be
useful in some small measure WRT a print, or large measure when speaking to
a SYSTEM'S CAPABILITY. But I think it's been shorthanded by the printmakers
to dmax - dmin, not because they are too ignorant to know better ,though
surely that plays it's part, but because they have found that given the
strong tonal manipulations they have control over, and the ability to place
tones as desired within a density range, they consider the "noise" in their
"system" something they have control over, while having a measure of the
minor issue of "noise" at the print surface, (like a bit of tooth to the
paper), is insignificant in scale, and moot to their concerns, and thus
assigned a value near zero and dropped.

Furthermore, as we see in inkjet prints, you can have microbanding,
mottling, etc, (i.e. noise) and still perceive a tone. It's really a
function of the amount of noise relative to the geometric dimensions of a
tone; or the amount of noise of the system relative to the detail of the
print. (I know that's vague, but it's very tangential, so I'll leave it at
that.)

IOW, it's about perception, and the photographer feels that within the
density range of his print s/he can place the tones where they need be, and
if there is noise enough that it becomes visibly distracting, they know it
without a spectro or densitometer. And if they can't perceive it they don't
mind?

Obviously materials designers and engineers will feel otherwise, and take a
different approach. In that scenario a controlled test would be set up,
input/output values would be compared, and your formula would be
appropriately applied.

Now to be fair to you, you never said photographers should make DyR
measurements, you were just explaining how the dynamic range formula you
know so well is applied, and making the distinction between it and density
range. You did a great job with that. I know I will be more careful how I
use those terms in the future. I will consider strongly the dynamic range of
a "printing system", but honestly, I don't expect to refer to the dynamic
range of a "print" much - density range speaks more solidly to my concern
there. Furthermore, I think other descriptive terms, like tonal separation,
linearity, microbanding, tooth, refraction, etc, - and their negative
counterparts - are much more useful and less nebulous than a measurement of
"noise".

Thanks,
Todd