[filmscanners] RE: Density vs Dynamic range

["Austin Franklin" <darkroom@ix.netcom.com>]

> Austin,
>
> One cause of the disagreement has been your use of terms that have had an
> agreed understanding in the engineering world since long before scanners
> in a non-standard way. I realise that you may have been "encouraged" into
> this usage by the scanner industry, but it doesn't make it any less
> confusing to the rest of us.

I know that is not the case, as I've been doing this long before there was a
"scanner industry" and certainly long before commercial scanners.

> In engineering terms you are confusing dynamic range with signal-to-noise
> ratio.

Absolutely not the case.  Being that I've also designed a LOT of audio
equipment, I know the difference.  They are SIMILAR, but not the same,
except at one point, when the SNR is at it's highest, it is the same as
dynamic range.  SNR also is an RMS based measurements, and RMS doesn't apply
to dynamic range.

> I will make one final comment. In the post, to which this is a reply, you
> said:
>
> >
> > So, where on earth did you get the idea that I believe that I fail to
> > understand that "increasing the number of bits from the AtoD does not
> > necessarily increase the dynamic range of the scanner"????????
> > OBVIOUSLY
> > from my four clips above, and ESPECIALLY the last one it should be
> > bloody
> > obvious that I completely understand what you believe I do not.
>
> However, at 10:32 yesterday, you said:
>
> > > However my point is that if you can reduce the noise level then you
> > > can
> > > increase the number of steps (by halving the step size) with real
> > > benefit, but without altering the range.
> >
> > Correct, but that INCREASES the dynamic range.
>
> Does not the first clip say "no increase of dynamic range" and the second
> say "increases the dynamic range"?

The first one SPECIFICALLY says no increase in dynamic range NECESSARILY.
If the number of bits is insufficient TO represent the full dynamic range of
the CCD/analog front end, then adding bits WILL increase the dynamic range
of the scanner.  If the number of bits already is sufficient, then adding
bits will NOT increase the dynamic range.

The second one SPECIFICALLY says that if you DO reduce the noise (in the
CCD/analog front end), THEN adding bits DOES increase the dynamic range.

BOTH statements do NOT say the same thing, and they are BOTH correct.  The
first is keeping the noise in the CCD/front end the SAME and the second,
DECREASING the noise in the CCD/front end.

> I rest my case m'lud.

BIG SIGH.  You need to read what I wrote, and not what you THINK I wrote.
Please, READ IT CAREFULLY.  Both statements are different, and BOTH are
correct.

Even the ISO proposal agrees with me on what the equation for dynamic range
is, except they make ONE assumption that I don't like, and that's that the
lowest measurable signal is the same as the noise.

Austin

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