[filmscanners] Re: Dynamic range

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

Roy wrote that Austin and David have a mental block with ranges and ratios.

I can't make out this mental block either.  Here is some parts of previous
post of mine which was studiously ignored but covered much of the ground
now being discussed, again.  It was addressed to Austin about the formula
for DR in the ISO standard:

-------------------------------------
Austin... In your last sentence, you seem to think that Dmax is a
range.  It is not, it is a value.  This single unarguable conceptual error
should put the rest of your assertions to rest, but ... I guess not.
...
In some cases it may be reasonable to assume that a VALUE implies a range
with respect to some understood reference value, but that is not how it is
being used in this equation.  Dmax in this equation is the top end (or
bottom end, depending on your point of view) of the range in question - the
range in question being from Dmax to Dmin.  Dmax does NOT itself in this
context represent an implied range from 0 to Dmax, it is just a value, Dmax.

The range that IS mentioned in the quoted equation (taken from the
standard) is the range between Dmin and Dmax - now THAT is a range.  It is
the range between the smallest density and the largest. Or the largest and
the smallest, no matter.  This range is quantified here as a ratio, which
is a very good way of quantifying a range.  In fact it is the ONLY way of
quantifying a range so that the resulting number is independent of gain and
other irrelevant things.  That is why it is used for the definition of
dynamic range -  range = Dmax/Dmin.  Or if we express the densities in log
terms (whether Bels, or decibels or purple turtle doves, it doesn't matter
and I won't insult you by giving you a lesson on Basic Logarithms for
Beginners) it is Dmax - Dmin.  That is a quantification of the range.  A
ratio is the ONLY way you can quantify a range so that it is independent of
irrelevant things.

...  It is not hard to understand - 1dB is a small range (about 1.26 to 1),
100dB is a big range (10000000000 to 1). The range we are discussing is the
range from MDS to max signal, which in scanner case is Dmax to Dmin.

Is that so hard to comprehend?

Julian

Roy wrote:
>David,
>
>I can't figure out why you and Austin have such a mental block about
>ranges and ratios.  In all the situations we're talking about, they are
>just plain one and the same.  Dynamic Range is a ratio AND its a range --
>that's why they call it a range!  Similarly, Dmax - Dmin is a ratio and
>its also a range -- looks like a density range (a range as well and its
>a ratio).  They are ALL the same kind of animal.
>
>Todd is reading and interpreting the ISO standard and that audio paper
>entirely correctly.  Listen to him.


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