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[filmscanners] RE: IV ED dynamic range... DYNAMIC RANGE!




> At 11:57 08/08/02, Austin wrote:
> >Density range is merely the extents that it
> >can capture density...but dynamic range is the resolution within that
> >density range.
>
> aaaaaaaaaaaaaaaaagh!!!!

Yes, ARGH!  Not again, Julian.  More misinformation about dynamic range!

> NO!

Well, yes.  What I said is absolutely correct.  Even the ISO spec agrees
with this, as well as all the resources I've posted.

> DENSITY RANGE is the maximum range of densities that the scanner can deal
> with / capture - using any available settings.

That is correct, and exactly what I said.

> You will in
> general have to
> modify gain and maybe other settings and do two different scans to capture
> the minimum density and the maximum density that the scanner can record,
> but the range between them is the Density Range.

And yes, correct.

> DYNAMIC RANGE on the other hand, is the smaller range within the Density
> Range that the scanner can capture AT ONE TIME i.e. dynamically i.e in one
> scan.  It is the instantaneous range the scanner can handle.

Absolutely not correct.  Where on earth did you get that?  Please please
provide any credible source that says anything to the such.  The ISO spec
doesn't define dynamic range that way...nor do any of the resources I have
seen.

> It is a simple enough concept.  Most explicitly, dynamic RANGE is
> ***not***
> the RESOLUTION,

Yes it absolutely is.

> and there is no book or standard that has ever said
> this.

Well, the ISO spec shows clearly it is exactly what I've said it is, as well
as every other resource I've posted on this subject before.  I simply don't
understand where you get the resources for your misguided understanding of
it.  YOU HAVE NO RESOURCES THAT SUPPORT YOUR BELIEF.

> Let me rephrase my first definitions, hoping for clarity -

You can't reach "clarity" when you are stating something incorrectly.

> The ***dynamic range*** is the range of densities that the
> scanner can scan
> or discern at one time, which means in practice in a single pass.

Absolutely incorrect.  Dynamic range is absolutely NOT a "range" as you
believe it is.  It is what happens WITHIN "A" RANGE...or it would not
contain the word "dynamic".  A range is simply a range.  I'll repeat that
again.  IT IS NOT A RANGE.  Dynamic means "change" basically, and it is the
amount of changes that can be discerned WITHIN a particular range.  Plain
and simple.

> The ***Density Range***  is a larger range than the dynamic range

The two are NOT related.  They do NOT represent the same thing at all, and
therefore can NOT be compared.  Anything can be represented logarithmically,
so simply because they can be represented logarithmically does NOT mean you
can compare them.  Your claim of "larger" is like saying 100 volts is larger
than 100 pounds.

You can have a density range of .1D units, and have a dynamic range of
100dB.  You can also have a density range of 4.0, and a dynamic range of 10
dB.  Clearly you can not say the Density Range is larger than Dynamic Range
simply by association, as this example shows your statement to not be true.

> PRACTICAL EXAMPLE
> *************************

A scanner that can capture 14 bits of valid data has a higher dynamic range
than a scanner that can only capture 12 bits of valid data.  The equation
for dynamic range is exceptionally simple for bits.  It is log10(2**n) and
has absolutely NO bearing on the density range, they are NOT related, except
that with a larger density range, your "resolution" or steps represent a
larger density per unit.

A 12 bit scanner with a Density Range of 4 has a resolution of 0.0009765625
density units, and with a dynamic range of 3.6.  A 12 bit scanner with a
Density Range of 3 has a resolution of 0.000732421875, but STILL has the
same dynamic range of 3.6.

A 14 bit scanner with a Density Range of 4 has a resolution of
0.000244140625 density units, and with a dynamic range of 4.2.

Obviously, the scanner with 14 bits has a higher resolution over the same
range than the 12 bit unit, and it also has a higher dynamic range, but the
same density range.

To make this REALLY simple.  14 bits has a higher dynamic range than 12
bits, that's undisputable...as the dynamic range that can be represented by
14 bits is 4.2, and of 12 bits is 3.6...and the last time I checked, 4.2 IS
larger than 3.6.  The resolution that can be represented by 12 bits is LESS
resolution than can be represented by 14 bits, that's undisputable...as
16,384 data points is FAR more than 4096...therefore, it's plain and simple
that dynamic range does in fact represent the resolution.  A higher dynamic
range of 4.2 has higher resolution than the lower dynamic range of 3.6 over
the same density range, as clearly shown above.

Austin

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