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[filmscanners] RE: Density vs Dynamic range



> Morning Austin,

Morning (actually afternoon by the time I got this)!

> >JULIAN....oh, JULIAN... (R that is...)
>
> >Julian said: > The term "dynamic range" is simply defined for ANY system
> >as the ratio of
> > > the largest possible signal to the smallest possible signal
> which can be
> > > handled without changing system parameters (usually smallest
> is determined
> > > by "noise" or some equivalent).
>
> >Austin said:
> >Above, you CLEARLY say dynamic range is based on noise...
>
> No!!!!!   I don't!!!!!  Please read.  I say it is "usually" determined by
> noise, because noise is what USUALLY determines the smallest possible
> signal.  WHat  I actually say is dynamic range is based on
> largest possible
> signal and smallest possible signal.  I thought that was pretty
> straightforward.  Sheesh.

OK, your clarification straightened me out...that your belief is still not
right...darn, I thought we were getting somewhere ;-)

> > >Julian:  This example system for some reason has a noise of
> 1V, a smallest
> > >discernable signal of 2V and a largest signal of 10V.
> >
> > > I'll do it here:
> > > DR = largest signal/smallest discernable signal
> > >          = 10/2
> > >          = 5
> > >
> > > That is, the dynamic range of our example system is 5.
> >
> > > 7) If you agree they are different, then this explains why you say the
> > > example dynamic range is 8 and the definition that is used by
> everybody
> > > else uses gives a dynamic range of 5.
>
> Austin:
> >OK, your point 7) here makes me believe YOU believe the DR of the above
> >example is 5, YET YOUR use of the terms for that equation
> clearly shows that
> >equation is NOT based on "noise", but on the smallest signal
> LEVEL, and in
> >the example you CLEARLY show that noise is different than smallest signal
> >level (which you are mistakenly calling "smallest discernable
> signal", which
> >is not the correct term).
>
> i) Yes, the DR here IS 5.  Correct, so if you believe that I believe that,
> then we have a small success!

I DO believe that you believe the DR is 5, and the problem is, your
understanding and use of terms is incorrect, and that the DR is NOT 5 in
your example...

> ii) You are correct - my use of the terms DOES show that in this example
> the equation is not based on noise.  That is because the noise IN THIS
> EXAMPLE is not the determinant of smallest discernable signal.

But that is not how dynamic range works.  YOUR belief as to what the meaning
of the terms mean/what the equation is, is simply wrong.  You use/belief is
entirely contrary to ISO, my reference material, and the web reference
posted.

> The
> smallest discernable signal here does NOT equal noise.

NO.  "smallest discernable signal" means noise.  "smallest signal level" is
what you believe "smallest discernable signal" means, and it does not.
Discernable means the smallest perceptible difference...and the smallest
signal level may be WELL above the smallest perceptible difference.

> And dynamic range
> is measured based on smallest discernable signal.

Yes it is, but "smallest discernable signal" means NOISE...again "smallest
perceptible difference", and that has NOTHING to do with smallest signal
level.  See the diagram I so thoughtfully provided that CLEARLY shows what
"smallest" and "largest" mean with respect to the dynamic range equation.

> There it is in your
> agreed formula.

Yes, we are agreed as to the WORDING of the formula, but I do NOT agree with
your misuse of the term "smallest discernable signal".  PLEASE go look up
the meaning of the word "discern(able)".

> Have a look, there it is on the bottom -  "smallest
> discernable signal".  It doesn't say "noise", it says "smallest
> discernable
> signal" .  Heck, what more do you want?

Well, as I said, YOU are using the incorrect interpretation of "smallest
discernable signal"...and is IS ABSOLUTELY WITHOUT QUESTION is the same
thing as noise in it's use in the dynamic range equation.

> I *define* the smallest
> discernable signal is 2V,

No, that is the "smallest signal level", the "smallest discernable signal"
in your example, I believe, was 1.  And 1, in your example, is the smallest
signal change that can be discerned...NOT the smallest level of the signal.

> the equation calls for smallest discernable
> signal, so I put 2V in there.

Yes, it does call for the "smallest discernable signal", but again, you are
using it like it means the smallest signal level, and it does not mean that.

> This means that in THIS EXAMPLE,
> the dynamic
> range is not determined by noise,

ALL dynamic range is determined by noise, period.  Why on earth would the
"inventors"/users of the dynamic range equation not simply leave the term
"noise" (or any derivation you want of this term) out of the equation, it
was not part of the equation, and simply say "largest signal level -
smallest signal level" and NEVER say noise...because as you say, noise can
be the same as smallest signal level?????  Well, because, though it IS based
on largest signal level and smallest signal level, it is ALSO required to
use noise in the equation.  It JUST SO HAPPENS that "most" of the time,
smallest signal level and noise have the same value, and the two terms
"largest signal level" and "smallest signal level" give a derived value for
the top of the equation.

> The
> dynamic range is NOT what you think it is.

But...I KNOW dynamic range is what I KNOW it is...I don't have to think
about it.  Again, EVERY "respectable" reference agrees with me on this.

> But dynamic range is NOT that - rather, it is the ratio of the
> largest signal to the smallest signal.

NO, to the smallest DISCERNABLE signal.  That is a different term than
smallest signal (level)...though, in some cases they may have the same
value.

> iii) How can you tell me that  "smallest discernable signal" is not the
> correct term!?

It IS the correct term, but you are using the wrong definition for it!  The
"smallest discernable signal" IS noise.

>   I don't say it IS determined by noise, I say that most of the time it
> is.  Because MOST of the time, the "smallest discernable signal" is
> determined by noise, so MOST of the time dynamic range is determined by
> noise.

This is a misunderstanding of the concept of dynamic range.  It is ALWAYS
based on noise.

> The importance of this semantic juggling is twofold, first, it is
> important to understand the DEFINITION of dynamic range, and the fact that
> it is NOT defined in terms of noise, it IS defined in terms of "smallest
> discernable signal".

Noise and "smallest discernable signal" are EXACTLY the same thing.

> Second, on those odd occasions when "smallest
> discernable signal" is NOT determined by noise, then you need to make sure
> that noise is NOT in the equation!  (which is one reason why your equation
> has a problem).

So, you are saying that my reference material is entirely incorrect?  I KNOW
that isn't the case.

> Once again, if you want me to describe such a box where the "smallest
> discernable signal" is NOT determined by noise, just say so .

But that would be a mis-use of terminology.  Again, for the 100th time,
"smallest signal level" is NOT the same as "smallest discernable signal".
"Smallest discernable signal" IS noise, and as my references have defined
it.

> I don't
> want to spend the time on this unless there is some point.

Well, me either!  My point is to try to get you to understand that you are
mis-using terms, and are missing the concept of dynamic range.  It is
reasonably clear to me that you want to believe what you believe...and don't
want to change your belief.  Of course, that's your choice.  I know you
aren't going to convince me your understandings are right, I have too much
reference material, too many people and too many years of experience with
this subject to be convinced that everyone, every reference and every bit of
work I've done on this for 20+ years is simply wrong.  So, unless you are
willing to accept the terms and concepts that the reference material
provides (and I have been using and trying to explain), I don't believe we
can go any further.

Regards,

Austin

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