Digital BW, The Print

Austin,

This is going to be a noisy/rambling post - I'm tired, I don't think I have
sufficient command of the jargon to express this as precisely as may be
required, and I'm having trouble to get my heed around some of this stuff.
But here goes, please bear with me and see what you can make of it.

Martin asked:
>> I do not see how you can directly "measure" the dynamic range of a print.
>> Perhaps in electronics you can.

Austin replied: 
> Very simply.  Print a completely solid tone, with as minimum detectable
> difference in density in the original as possible.  Print the darkest tone you
> can.  Measure the darkest tone, measure the paper, then take multiple
> measurements of the "patch" of your "test" tone.  The variance across the test
> tone is your noise, and yes, I know, you have to account for the original
> variances, as well as possible variances caused by the lense...but none the
> less, it does give you a basis for noise.  You get the "largest signal" in the
> dynamic range equation by your dMax - dMin, and you get your "smallest
> discernable signal" from the variance in your "patch".  There you have it.


Earlier in the thread you have said (I'm paraphrasing) that the dynamic
range of a print is an expression of how many tones that print contains.

I don't see how the simple test you suggest, which only differs from the
more common test for dynamic range (or what you call density range) is just
the additional step of measuring the variance across your test patch. I
don't see how that information tells you how many tones are in the print.
This would seem to be a case where, as you've said before, only 2 bits of
info is needed to establish dynamic range, no? But this then could suggest
the material is capable of a huge dynamic range, when in fact only three
tones are present.

Furthermore, what does it say about a scenario where ones printer/workflow
happens to produce a certain granularity/banding/mottling/artifacting
precisely in the tonal region of your test patch, but nowhere else; or
worse, the converse, everywhere but your patch?

And what of all this inkjet artifacting? I suppose it's debatable whether or
not it affects tonality, but surely it lowers dynamic range via the
inclusion of greater noise in the formula. Lets assume you can have
microbanding, which does not destroy the tonality of n area, while it does
heighten the noise of it. If dynamic range is a description of the number of
discrete tones in an image, but noise can reduce the dynamic range while at
the same time not reduce the number of tones, something is screwy in the
logic of the formula.

Furthermore, I agree that there needs to be some term to distinguish between
a litho-like substance, and a continuous tone substance, where the two could
conceivably have the same density range, while one is capable of far more
shades in between. But I wonder now if dynamic range IS that descriptor,
when in fact you could measure a three toned medium and presume it to have
the same number of tones and the continuous tone item, based upon that test
and calculation. So, at best dynamic range can provide a predictor of what a
medium is capable of, but it assumes a complete and linear set of tones
between the ends, which may or may not be so; at worst it could mislead one
wildly.

I need to explore this subject of linearity more fully as it pertains to
dynamic range. For instance, a print with an expansion of highlights and
contraction of shadows (= high contrast) will contain fewer tones than the
material is capable of, but your measure of dynamic range will not indicate
that has occurred. So, is dynamic range a measure of the number of tones an
item contains, or a measure of what the material is capable of if perfect
linearity is present?

Now I presume this instance of not exploiting the range of this material in
a linear fashion, in order to utilize the maximum number of tones the
material is capable of, is not a failing of the materials per se, but a
failing of the operator to utilize it in that way.

This has me wonder why you assume a Piezo print to have greater dynamic
range than a silver print given these considerations:

A) We know a well handled glossy fiber print is capable of a greater density
range than Piezo.

B) We know the source material of a silver print (negative) is capapble of
more tones (millions? billions?) than the source material for an inkjet
print (256? 65,000?).

C) Noise can go either way, depending on which papers are used in each
respective system, and other workflow considerations.

What else needs to be accounted for? Linearity. Admittedly this is the main
advantage of Piezo - it's easier (presumably) to acheive linearity in Piezo
than in silver, but that's not to say it's impossible to do it with silver.
Furthermore, there are several inkjet artifacts that can reduce the
linearity of Piezo, so it's not a guarantee.

I'm trying to get my head around my sense that the approach you advocate for
determining the dynamic range of a print is only marginally more informative
than the approach to determining density range (which is fine, you didn't
invent the formula <G>); that measuring the dynamic range of a print still
doesn't tell you how many tones it contains; that I see no logic that a
Piezo print is any more capable of greater dynamic range than silver, other
than the assumption that it is easier to maintain linearity - which with
banding, artifacting, mottling, hardware resolution limits, droplet size,
etc (all of which can raise noise if not tonality too), really isn't a
given.

I told you this would be noisy/rambling. ;-)

Your thoughts please.

Todd