Digital BW, The Print

> > > Now the big question is "What's the signal?".
> >
> > Very simply, for a photographic image, it is the density value.
>
> This is precisely what I'm trying to say.   Let's take the
> original definition
> equation and substitute "density value" for "signal".  We have:
>
> Dynamic Range = log10 (largest signal/smallest discernable signal)
>             =  log10 (largest density value/smallest discernable
> density value)
>
> Isn't that precisely the same as: dMax - dMin  as I derived last post?

Well, no, you're taking a "leap" here to arrive where you did.  As I've said
a dozen times, "largest" is an ambiguous term, as well as "smallest".  It is
open to interpretation if left undefined.  The equation for dynamic range
clearly uses largest to mean the "absolute value of the maximum detectible
signal", in other words, the amplitude...dMax - dMin, as opposed to just the
single measurement for dMax...

> It not that time or space figure into the calculation, its just that they
> built into the properties that we are interested in.

That's my point, they don't.  You can take a measurement in and of it self,
and you don't have to relate it at all to time and/or space.  They aren't
part of the dynamic range equation at all.

> You say I can figure the dynamic range of whatever property I want.
> Well I want the dynamic range of the density of the print!

But that's what this entire discussion has been about, hasn't it?

> It seems that you are insisting that I can only calculate (i.e. have) the
> dynamic range of the contrasts of the print.

Contrast (in out case) simply means delta density, right?  In order to
distinguish density, you MUST have contrast.

> > I disagree with your use of the term "mapping".  Again, you pick the
> > property you want to figure out the dynamic range of...note the dynamic
> > range equation does NOT use any units for largest/smallest...they simply
> > have to be on the same scale, of the same unit.
>
> Right.  And I want the property "density".

That's no different than we have been talking about.  Contrast merely means
there is a difference, and as far as the discussion goes, density is the
same as contrast.  High contrast means large distinguishable difference, low
contrast means small distinguishable difference.

> > > For pictures, what's the basic perception?  It seems you've picked
> > > contrast --  so the ratio is (highest contrast/lowest contrast).
> >
> > Yes, since contrast (as in delta change) is all that distinguishes tones
> > from one another.
> >
> > > Why not the more basic perception: darkness versus lightness?
> >
> > What, exactly, do you mean by "darkness" and "lightness"?
>
> Can't you go with: darkness = high density, lightness = low density??
>
> >
> > > The ratio would be (darkest/lightest). I guess you can see
> > > where this is going->> it reduces the whole thing to
> > > Density Range.
> > >
> > > DynRange = log10 (darkest/lightest)
> > >          = log10 (darkest) - log10 (lightest)
> > >          = dMax - dMin
> > >          = Density Range
> >
> > But you have now removed, arbitrarily from what I can tell, the smallest
> > discernable signal from the equation, that above, you agreed
> was part of the
> > equation.  Why?  This seems like one of those Gary Larson "and
> then magic
> > happened" on the chalk board...
>
> I figured dMin = smallest discernable density  = smallest
> discernable signal
> I haven't any problem keeping the word "discernable" throughout.

Yeah, but that's wrong.  dMin is merely the smallest signal level that has
been measured, and has nothing to do with the ability to discern anything.
You could have a dMin of 2...but your ability to distinguish a signal could
be much smaller, like .01.  dMin and smallest discernable signal are
entirely different.  This goes back to my statement that smallest is
ambiguous in the definitions given, except mine ;-) which included a diagram
that showed what was meant by smallest...

> > > I doubt that you're ready to switch definitions but intuitively
> > > using "dynamic range" to means "number of tones" rather
> > > than some "range" of values seems weird.
> >
> > Not at all, my guess is it really means dynamic OVER THE particular
> > range...but I do not know the history of the term.  It isn't
> really A range,
> > but it describes a property OF the given range.  Density range
> isn't a range
> > either, but it does describe the width OF the range of density.
>
> "Range" as commonly used in math is used to describe the set of possible
> values.  Density range given by dMax and dMin entirely describes the
> possible density values i.e. they all have to lie between dMax and dMin.

No, not at all.  It describes the MAXIMUM and MINIMUM value, but not the
resolution of values in between.  Counting from 0-100, you could count by
10's or 5's or 1's, you have the same range, but different number of steps.


> I'll acknowledge that you didn't make up the definition taken
> from the Higgins
> book, but I've yet to see corroborating info for your interpretation of
> "signal" in the equation.

Signal means nothing but some distinguishable quality.

> Higgins most definitely does NOT
> address how to
> apply the equation to the photographic prints, so I'm assuming you
> decided how to do that.

I didn't have to decide on anything.  Density values are "signals", as they
signal a quality of the density.  Though signal is commonly used in
electronics, that doesn't preclude other things from being considered a
signal.  In fact, dynamic range is commonly used with simple numbers, like
number of bits has a particular dynamic range...and there is no electronics
involved in that!

> As you say below there's lots of info about.
> I'd like to see more supporting your  interpretation.

I don't believe this is something that people write down, it's just an
inherent understanding.  There is no book on how to count from 2 to 3 that I
know of, or someone substantiating that you can count trees with integer
values....  Hum.  I'll have to think about that.

I guess if you understand the concept of dynamic range, it should be obvious
how it can be applied to photographic prints with no problem...I mean, even
Martin said dynamic range has been spoken about with respect to photography
for a long time, so did Ansel Adams...so others apparently believe dynamic
range applies to chemical photographic prints...  As far as interpretation
goes, well, as I've said, I didn't make up the dynamic range equation, so
it's not up to me to interpret it.  The use and definitions I've given to it
are common amongst any engineers I know of who understand dynamic range...
So I am on very firm ground I've gotten the equations and definitions of
terms used in the equation correct, and others have agreed dynamic range
applies to chemical prints...so I don't know what more I can substantiate.

Another thing is dynamic range does in fact describe a unique
property...that is NOT defined by density range.  If dynamic range were
simply the same thing as density range, they there probably would not be two
distinct terms, but there are.  Density range does not describe the same
thing that dynamic range does, and that is why dynamic range exists...

Austin