Digital BW, The Print

----- Original Message -----
From: "Austin Franklin" <darkroom@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Thursday, March 28, 2002 7:19 PM
Subject: RE: [Digital BW] Dynamic Range Definitions and Print Tones


(snip)

> 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.
>
(snip)
> >
> > For the most part I feel you are simply substituting synonyms.
>
> 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.
>
> > The point
> > where we collide is over "discernable."
>
> But it's clearly defined by the equation and what dynamic range is there
to
> measure.  As I've said time and time again, you are arguing over a very
> clear concept/definition/equation that I did not come up with.  I am
merely
> trying to get you to understand what it really is, and how your
> understanding of it is flawed.  Unfortunately, for what ever reason I do
not
> know, it isn't working.

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. If there is no noise or if the noise is so
low it can be ignored then the relationship you are showing would not have
any relevance.
>
> > 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.
>
> > You move on into the idea of
> > "discernable difference" over the entire tonal range and I think that
this
> > is not covered by the general concept of dynamic.
>
> Well, then what do YOU believe is "dynamic" in dynamic range?  That is a
> very important question.

The ability to change tone.
>
> > "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 do not see how you can directly "measure" the
> > dynamic range of a print. Perhaps in electronics you can.
>
> 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.

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.

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?

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. 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.

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?
>
(snip)
>
> 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.
>
>  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.
>
> > > 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.
>
> > 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?
>
> > 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. 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.
>
> > 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.
>
(snip)
> >
> > 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?
>
> > Dynamic Range of the Reflectance = (maximum reflectance of the brightest
> > visually discernable white)/(minimum reflectance of the darkest visually
> > discernable black)
>
> Yeah, but that's wrong.  You have just given an equation for DENSITY
range,
> not dynamic range.

Not according to most of the definitions I posted earlier. And yes the
dynamic range of the reflectance is the density range. Remeber the
difference of two logs express a ratio.
>
> > My thought is that the dynamic range of a print may not be a
particularly
> > useful expression for us. The simple range or knowing the lightest and
> > darkest shades of gray of a medium are what is of importance to
> > us.
>
> But it is so obvious that some images may have NO tones between black and
> white, and some may have a LOT of tones between black and white.  That is
> why dynamic range IS important.

Well that is an artistic decision by whoever made the print and not a result
of the dynamic range of the materials unless they were specifically designed
that way like litho film.
>
> > We also
> > tend to overly focus on getting the deepest black where in
> > reality you gain
> > more by increasing the brightness white.
>
> I very much so agree with that!

Wow! Austin and I agreed on something! Where's the champaign? <G>
>
> > I understand that you are trying to give us an expression that says
> > something about the number of discernable tones that a media or system
can
> > create but I don't think that this can be done here because I do not see
> > that there are a finite number of tones.
>
> And I do see a finite number of tones, or at least a "range" of the number
> of tones.  I can certainly say one has more or less than another!

Well give me a rough estimate of the number of tones you think there are in
an inkjet and silver prints.

> 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?

  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.
>
> You seem to be shifting a bit here...more to an argument that dynamic
range,
> what ever we believe it is, isn't really that important...  Just a note.

In general, I think that knowing the Dmin, Dmax and the contrast grade of a
particular silver paper is adequate and for inkjet just the Dmin and Dmax
since the software seems to give us control over the contrast. I sure do
want to know the DR of my scanners though!

Best,
Martin