Digital BW, The Print

>> but when those
>> conditions are
>> not met it would yield an inaccurate tone count. If I'm wrong
>> please explain
>> why.
> 
> You are absolutely right, and I'm happy that you have an understanding of
> this to make such an observation!  Bravo!

Thanks, and just think, it it only took you about 200 replies and a year of
your life to bring me to this point...
 
> This is where calculus comes into play.  It is a way of taking into account
> the variability of the noise throughout the system.  Here's the deal.  The
> noise "change" could be deterministic (possibly linear), which means it's
> predictable.  If that is true (and I believe it is), then taking some number
> of points (what ever are warranted by the type of equation that defines the
> noise over the range, and if the noise is a simple gain, as in it's linear,
> two points would do) in the "middle" will give you enough information to
> derive the dynamic range.  Let's not talk about what that "result" or
> equations would look like yet...

Okay, I'd be interested to see what you might come up with, because DyR as a
tone count has always been the hang-up in the whole conversation for me.

I fully appreciate that noise is an issue worthy of considering when
considering the ability to discern between tones in a system, and that IF a
system performs as expected you can make certain assumptions about the
capability of a print produced by that system.

BUT when assessing a print of unknown provenance, where we have no knowledge
of the capability of the system, wow, before you could compute a tone count
you'd need to assess the noise within virtually every tone within the DnR.

For instance, silver prints have characteristic curves which are non-linear,
and each brand and grade has it's own shape, which is further altered by
development...it'd be very difficult to make anything more than the most
general assumptions. Therefor to accurately determine the DyR of a "generic"
print of unknown origin the required measurements could be overwhelming.
Likewise for and inkjet print that contains mottling through some tones,
microbanding in others, etc. Plus all that is without the consideration of
the dynamic range of the
subject/material/file/negative/artistic-interpretation, the print is trying
to represent. Meaning not all prints are intended to be full toned and
linear!

Therefor, I find the concept of DyR much more useful for assessing the
CAPABILITY, of a well controlled system, but much less useful when assessing
singular prints. I look at it like this, you can pretty well assess the
dynamic range of a well behaved scanner, especially if it's linear across
the range of all the films on the market. But assessing the DyR of the same
scanner when there is an intermittent short in one or more of the
components, making for infinite variability between scans, would be much
harder. The infinite variability between scans represents the unknown
characteristics of a print of unknown origin.

I hope that made sense. ;-)

Todd