Digital BW, The Print

>
> > But the equation for dynamic range does not allow YOU to select the
> > "meaningful" definition of smallest and largest as YOU understand them.
> > They are defined by the equation.
>
> Austin,
>
> You write the equations to reflect the meaningful relationships
> in what you
> are examining. The dynamic range equation is an engineering expression for
> certain systems, not a law of physics.

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.

> > They you are missing the entire concept.  What I have shown, quite
> clearly,
> > is that there are AMBIGUOUS definitions of both largest and smallest.  I
> > have also shown what the two ambiguous definitions are.
>
> In a print you can choose to start at either end of the scale but the two
> values are the darkest black and the whitest white. The usual
> description is
> Density calculated from reflectance.

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".

> Your equation is fine and works very well in electronic and
> digital imaging
> but since you have not defined or quantified the noise of a
> static print, I
> don't see how it can be aplied.

OK.  I'm confused.  At first you said density range was the same as dynamic
range, and that dynamic range didn't require noise...are you now agreeing
that density range and dynamic range ARE different, and that dynamic range
does require noise?

> > > I agree with this as part of the
> > > process of determining the min and max.
> >
> > I don't follow you there.
>
> Knowing the noise floor and/or ceiling is part of determining the
> usable min
> and max.

Not at all.  Noise floor and min are two entirely different things.  I've
given examples of that being true.  Noise "ceiling" has nothing to do with
max either...  I'm not getting your point here.

> > 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?

> > > "Discernable difference"
> > > is very important when you are talking about systems where
> the input and
> > > output are changing with time
> >
> > Time has nothing to do with it.  You do not need time to discern change,
> but
> > you do need change to discern time (off topic, but it's true
> anyway).  Two
> > things can have a discernable difference at the exact same time!
>
> True but time is not a factor in a print.

I'm happy to take the "true" admission, and work on the application to a
print at another time ;-)

> I am sorry. I misunderstood you to mean that you could take a single
> measurement to get a value for dynamic range. So you are taking multiple
> measurements and getting the DR by calculation. Your idea for determining
> the noise is an interestin one and similar to what John suggested earlier
> regarding using variations in the paper at Dmin.

Oh, oh...is this a breakthrough?

> 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.

> From a practical point of view I think that this will be difficult to
> measure, at least with the densitometers I have seen but it
> certainly could
> be done in some fashion.

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

> There is also the issue of what is
> contributing to
> this variation and to what degree. Variation in the paper, the ink or the
> way the ink is laid down. This could give you multiple noise sources that
> contribute differently at each end of the range.

Absolutely agree.

> Finally what do you conclude if this turned out to be a very small number?
> Would your concept of dynamic range still be of value in comparing two
> different print media?

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.

> > As I've said countless times, min and max WHAT?  What does min and max
> mean?
> > They are incomplete terms.
>
> Whitest white and blackest black.

Those definitions only work for density range, not dynamic range.  min and
max mean something different in the dynamic range equation.

> >
> >  This does not seem to account for the values in
> > > between or
> > > they assumed a continuously variable system.
> >
> > Min and Max does if you take max to mean the maximum signal and min to
> mean
> > the minimum discernable signal ;-)
>
> I agree, but we have not clarified what the minmum discernable
> signal might
> be or if it is of significant magnitude.

That's OK for now.

> >
> > > > What's the dynamic range?  Well, we don't know what the smallest
> > > discernable
> > > > signal is, now do we?  Nor do we really know the largest that the
> > > > paper/system can attain either.  This makes for a quandary.
> > >
> > > Not really because you are interested in the meaningful or
> useful values
> > > which may simply be the only the values you do know.
> >
> > Sorry, I have no idea what you mean by that...
>
> That you may have to describe a reationship based upon the values you do
> know and neglect those that cannot be determined. In other words if you
> cannot determine your "minimum discernable signal" you would need to
> describe the density relationship in some other fashion.

But minimum discernable signal only applies to dynamic range, not to density
range/relationship...

> > > I agree that you may be able to discern a change of 0.01 density
> > > near Dmin.
> > > The problem is that as you approach Dmax the density change you
> > > can discern
> > > decreases.
> >
> > You're right, but only if you're above 3!!!  It's also not
> relevant to the
> > discussion, but is a noted point.
>
> 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 ;-)

> > > The discernable difference is not a constant in this
> > > system which
> > > is why I object to using this in a dynamic range calculation for this
> > > system.
> >
> > That's the first you've said that!  But...as I said, your claim is only
> good
> > for density values above 3, below 3, they are quite constant...and since
> > this IS a B&W list...and as we all know, B&W doesn't go above
> 2...I think
> > we're safe ;-)
>
> Yes it is the first time I have said that. But remember I do not believe
> that our ability to discern tones has anything to do with the number of
> tones present.

No, not OUR ability to discern tones, but some methodology for discerning
tones.

> Well I would appreciate where the density of three comes in
> and I assure that silver prints do go up to 2.6 from my own
> measurements and
> others have reported as high as 2.8. I am not convinced that it
> is constant
> since I personally can easily detect the difference between a density of
> 0.02 and 0.04 but not so easily between 2.36 and 2.40. I believe we can
> differentiate the highlights easier than the shadows.

I completely agree with you on this.

> >
> > > From your earlier diagram you indicated
> > > that the discernable difference was constant across the entire range.
> That
> > > is not the case here.
> >
> > Well, it is the case, but even if it weren't, it's not
> relevant.  Did you
> > ever take Differential Equations?
>
> 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.


> > > I believe I did. From the definition the dynamic range is the ratio of
> the
> > > maximum divided by the minimum.
> >
> > That's NOT an equation.  AND maximum and minimum are left undefined.
>
> Why is the lightest and darkest points on a print so vague?

They aren't, but "maximum" and "minimum" are vague...and as I've pointed
out, each can mean one of two things.

> And yes the
> dynamic range of the reflectance is the density range.

Sigh ;-(

> 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.

> > I have
> > done the same print that has very bad tonality, there aren't many
> > discernable tones, and I have re-printed the exact same image
> and managed
> to
> > get a heck of a lot more tones out of that same image...via development
> > time/exposure.
>
> Same here, but is this meaningful information about the materials or about
> our skills?

Understood.

>   Similarly with film, I have film that has the blacks so
> > blocked up, and some that has them nice and open...and that was based on
> > development/exposure too ;-)  Dynamic range is VERY important
> to me, as I
> > want full tonality in my specific prints.  Density range isn't as
> important
> > to me, for reasons that have been mentioned by you and others.
>
> Here it seems you are talking about zone placement with expanded and
> contracted development. This is an issue of how do you map the real world
> tones you want to capture onto your film. Whether you do this
> well or badly
> the film will still go from base fog + film density to totaly blocked and
> contain every tone in between. You do not add or subtract the number of
> tones in the negative by adjusting your exposure or or development,
> (assuming you are at least in the ballpark and took your lens cap off and
> remembered to put the dark slide back in) you are adjusting which specific
> tones in the scene wind up in the usable range of the negative.

Not true!  I have negatives that are completely blocked up, and almost look
like litho film!  The fact that there IS litho film backs up my statement.
It doesn't necessarily have to do with Zone etc, but can be only related to
development...trust me!  I've done some lousy development in the past.

> I sure do
> want to know the DR of my scanners though!

Get a high range target and scan it ;-)

Regards,

Austin