Digital BW, The Print

----- Original Message -----
From: "Austin Franklin" <darkroom@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Friday, March 29, 2002 2:07 AM
Subject: RE: [Digital BW] Dynamic Range Definitions and Print Tones


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

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

Yes but values that are lost below the noise floor are of no interest and
including them as the lower limit of the range would not be helpful.
>
> > > 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. 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.
> >
> > 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.

Okay, what would be a reasonable number of samples and which tones should we
look at first?
>
> > 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.

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

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
>
(snip)

> > 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.
>
(snip)
> >
> > 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 am just saying that is we can only work with the information we have or
are able to obtain. From that we have to make the best choice we can. If you
can't determine a value for noise to use in your dynamic range equation then
all we may have left are the density or reflectance values.

(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.
>
(snip)
> >
> > 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.

Then add into my statement above ..or our ability to discern tones with an
instrument
>
> > 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.

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

What would the equation look like then?
>
(snip)
>
> 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.

How who is being vague? <G>
>
(snip)
> >
> > 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.

Perhaps this is analogous to stepping outside the limits of the range.
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?

Best,
Martin