[filmscanners] Re: Dynamic range

["Julian Robinson" <jrobinso@pcug.org.au>]

Austin,

> > I have never read whatever paper you are talking about, but I
> > GUARANTEE you
> > it does not SAY that dynamic range is a resolution.  I am sure that you,
> > Austin, INTERPRET it to say that, but it will not actually say that.
>
>You probably should have read the paper before commenting...

But no, that is the point. I am confident that I don't need to look at the
paper, because I know that no paper will say what you believe.  You are
mistaken in what you say and still, to this date, after buckets of wasted
electrons and keyboard hours, you have still not produced a single
reference that says what you say.  So I was giving you a FREE KICK - a
totally unsupported challenge which gave you absolutely every chance to
smother me in extracts from this paper with quotes that agree with
you.  The fact that you have not done so I think proves the point.

Now as for the rest of the post, I am in a bind.  If I respond to all of
yours, you and others will accuse me of being interminable.  If I only
respond to what I think are relevant points, you will accuse me of being
selective.  So I am going to be selective.  But I have written a complete
response at some cost, and if you want the rest please tell me.
...
> > ***In this case DR = 30 dB
> > ***Resolution is still 36dB if you stick with your formula = max/noise, or
> > 30dB as it obviously is in fact, given you have a digital step size of
> > 1/1024 or 30dB.
>
>Well, here you go again, Julian...and this is why I get pissy with you.  You
>take things out of context and apply them to something else.  I NEVER said
>the MDS was ALWAYS noise.  In the case of the ORIGINAL SIGNAL, it is noise,
>in the case of the digitized signal, it is NOT noise.

Well let me quote one of many interminable exchanges where I was tearing my
hair out because you were insisting that MDS was noise.  Please note
carefully the contradiction, clear and unambiguous between statement A and
the statements B1,2,3 :

A)  "I NEVER said the MDS was ALWAYS noise. " - from this post

B1) "The "smallest discernable signal" IS noise." - from post in June

B2) "This is a misunderstanding of the concept of dynamic range. It is ALWAYS
based on noise." - post in June

B3) "Noise and "smallest discernable signal" are EXACTLY the same thing." -
post in June.

I have struggled for months to get you to agree that noise and MDS are not
the same thing, and now you tell me you have always thought this!!  I am
pleased that you are coming round, but flabbergasted at the same time.

Here is the exchange for the record so you don't accuse me of taking you
out of context:
------start of exchange last June--------------
Julian:
 > iii) How can you tell me that "smallest discernable signal" is not the
 > correct term!?

Austin:
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.
-----------end of exchange----------------------------

IN fact, noise and digitised step size are the two things that limit MDS in
a scanner, as I have always said.  Whichever one predominates determines
MDS and thus the bottom half of DyR..

...
> > : max signal / MDS. This time, MDS is determined by the noise level,
> > because noise level is higher (4 times higher) than the bit size.  MDS =
> > noise level = 1/4096. So the DR of this scanner is 36dB again.  You could
> > have any number of bits over 12, and it would not change the dynamic range
> > one iota.
> >
> > ***In this case DR = 36dB.
> > ***Resolution is --- 36dB by your formula = max/noise (correct this time),
> > or 42 dB if you just consider digital bit numbers and step size.
>
>I really don't know what your point is here.

My point was to demonstrate in agonising detail that your unambiguously
applied formula for DR (of the system) as "something/noise" is not always
correct, and your unambiguously applied formula that DR is determined by
the number of bits is not always correct.  We may even agree on this, but
in past discussions you have blasted people with these as absolute truths
when they are not.  The ONLY absolute in dynamic range that is true all the
time is: DR =  max signal / MDS.  Max signal and MDS are what determines
DR, and it pays to keep this in mind when making absolute statements like
the erroneous ones of yours I quoted above.  It is precisely these kinds of
statements that causes muddy waters and very confused people.

...
>Of course, the number of bits LIMITS the dynamic range, I've always said
>that...but BTW, that contradicts Roy's last round, as he claims that 8 bits
>has the same dynamic range as 16 bits...

Yes, I don't agree with Roy on this point.

Julian

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