Digital BW, The Print

> > I never said it was a "law of physics", but it IS a specific
> measurement,
> > and as I said, it IS defined by a fixed, non-negotiable (except
> different
> > systems have some different multipliers, but the basic equation, and
> > meaning, is the same) equation with defined relationships.
>
> It is only good if those relationship exist or exist to a
> meaningful degree
> in a system.

Yeah.  I don't know that you can quantify the dynamic range of a pizza.

> > What does that have to do with dynamic range?  I'm missing your point
> here.
> > For "largest", of course you need to measure the darkest black
> and whitest
> > white and "largest" is the difference of the two...which is the same as
> > density range...but to derive dynamic range from that, you
> divide that by
> > the "smallest discernable signal".
>
> In photography the dynamic range has been takes as the density range

Since when?  By people who don't understand what the real meaning of dynamic
range is, perhaps...

> which
> happens to be the reflectance ratio and fulfills the general definition of
> dynamic range as the ratio of the min and max signals for a photographic
> system.

It depends on what you mean by "min" and "max".

> This is not a sophisticated enough definition to define dynamic
> range for digital imaging where your equation is appropriate.

The equation is system independent.

> First the definition for dynamic range is not a constant and have
> different
> meaning for different fields.

It does not, except for using different multiplication factors for other
reasons, but it is ALWAYS based on (largest signal divided by smallest
discernable signal).  Always.

> I understand that you don't agree with this
> and see it as a universal concept. What I am saying here is let's
> apply your
> equation to a photographic print and see if the values help us understand
> what we see.

Well, I have and it does ;-)

> In order to do that we need to have a definition of
> what would
> be the noise in a photograph and a value for it.

I've given a method for doing so.

> > > > Well, then what do YOU believe is "dynamic" in dynamic
> range?  That is
> a
> > > > very important question.
> > >
> > > The ability to change tone.
> >
> > OK, then how does only using dMax and dMin give you anything dynamic?
>
> They tell you the size tonal space you can change tones in and
> they tell you
> the size of the largest change you can make.

That is density range, not dynamic range.  Why on earth does the equation
for dynamic range (the ONE AND ONLY one that anyone has presented, and given
a succinct reference for, namely the one I provided) clearly base dynamic
range on smallest discernable signal?

> And no I do not believe that
> there are a finite number of steps between them so I don't need an
> expression to calculate what isn't there.

Yes, I know.  This is like trying to get Newtonian physicists to understand
Einsteinen physics...it goes against everything they based their beliefs on.

> > > What tonal value do you print for your test patch and how do you know
> that
> > > the variation at this single tone will be representative of all
> > > the tones in
> > > the range?
> >
> > You can do various samples.
>
> Okay, what would be a reasonable number of samples and which
> tones should we
> look at first?

This is completely irrelevant to the overall discussion.  This is purely an
implementation issue.

> > OK, now I feel like we are getting somewhere ;-)

I take that back ;-(

> > I believe so, but I haven't thought about that at all.  I'm
> just trying to
> > lay down the foundation for that part of the discussion.
>
> Well since you have arrived at a possible concept for noise in a print,
> design an experiment to determine a value. I have a Spectrocam
> photospectrometer on order and I could try some readings across monotone
> patches. I think that probably the variation may be much less that it can
> measure but it can't hurt to check.

That sounds like a plan ;-)  What are the specs for the unit?

> I also hope to have a Howtek D4000
> scanner soon. Would that give higher resolution or be usable to
> attempt such
> a measurement?

No, I don't believe so.  I would just create a test pattern with darkest
black and a probably 4 or so different solid test patches in PS and print
that.  It's as "pure" as you're going to get!

> > Those definitions only work for density range, not dynamic
> range.  min and
> > max mean something different in the dynamic range equation.
>
> Now I am confused again. So what attribute of the print would you use to
> determine min and max if not the whitest white and blackest black

Good!  Confusion IS good...  Seriously.  OK, in the density range equation,
"max" IS simply the maximum density value you can measure by direct
measurement, and "min" IS simply the minimum density value you can measure
by direct measurement.  Simply put, measure the darkest patch, get your max
value, measure the paper, get your min value.

For dynamic range, take dMax (from your density range measurement) and
subtract your dMin (from your density range measurement), and that gives you
"max" for the dynamic range equation.  "min", basically, will be the
variance across the patch that I've suggested above.

> (snip)
> > >
> > > From my own experience with a MacBeth densitometer the ability to
> discern
> > > tonal differences declined steadily as you increased print density
> > > especially above 2 and stopped around 2.4. I was doing a lot
> of contact
> > > exposures with a Stouffer step wedge to measure the different
> brands of
> > > silver paper and the effects of different developers and toning
> processes.
> > > Why do you say 3?
> >
> > X-Rite 810 manual ;-)
>
> Can you quote what they say or is it too lengthy? I'm curious because it
> really is at odds with my own experience.

Be happy to.

Quoted from X-Rite 810 Operator's Manual, p. 51, section 6.0
SPECIFICATIONS/6.1 Instrument Specifications

REFLECTION SPECIFICATIONS

Measuring Range: 0-2.5D
Accuracy: +- .02D
Repeatability: +- .01D

TRANSMISSION SPECIFICATION

Measuring Range: 0-4.0D
Accuracy: +- .02D (0-3.50D)
          +-   1% (3.1D-3.5D)
          +-   3% (3.6D-4.0D)
Repeatability: +- .01D

Note, I was quoting the reflection specs, but note the transmission specs
show it consistent across the entire range, up to the max of 2.5D.

> Doesn't that suggest that the ability for the eye to discern tones is a
> function of the tonal density?

Of course it is...but I don't see how that applies.

> > > Well if you are going to do the division in your equation you
> > > need to choose
> > > a value. So if it varies what do you use? Yes but long ago
> and far away.
> >
> > You can integrate it very easily.  This is not a problem.  Your
> > concern/point is entirely valid, but it can easily be dealt with.
>
> What would the equation look like then?

Don't know, I'd have to work it out...but as I've said, this is a red
herring and completely irrelevant to the overall discussion.  It is merely
an implementation detail.

> > > Well give me a rough estimate of the number of tones you think
> > > there are in
> > > an inkjet and silver prints.
> >
> > It depends on the print, of course!  Inkjet, using the Cone
> system is over
> > 100.  Silver I have not "counted", but I can easily tell when one print
> has
> > "more" than another.  The same negative printed in a wet darkroom, that
> has
> > a high dynamic range (many tones ;-) shows more tones on the
> inkjet print
> > than the wet print.
>
> How who is being vague? <G>

Not me.  I am simply relating my direct experience.  It's not scientific,
but it IS my experience.

> Severe over exposure or over development would be similar to
> pushing an amp
> signal to the point of high distortion.
> >
> > > I sure do
> > > want to know the DR of my scanners though!
> >
> > Get a high range target and scan it ;-)
>
> What target do you use?

Q-60...but also check with Edmund's or Stoffers.  Your sensitometer might
come with one.  Some scanners do too...

Regards,

Austin