[filmscanners] RE: Density vs Dynamic range

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

Hi Peter,

> > In my view, despite your (Austin's) statement to the contrary, the
> > dynamic
> > range is PRECISELY the measurable density range, in our context.
>
> This is almost my understanding.

Understood...and I'm trying to explain to you why that understanding is
wrong.

> I believe what Austin is trying to say is
> that to increase the number of bits to the point where the step size is
> lower than the noise value gives no more information.

That is correct.

> There is some
> justification in this view, however, there are methods, in particular
> multiple scans, where more information can be recovered by reducing the
> contribution of the noise.

You do not need to increase the number of bits that you scan at to do
multiple scans ;-)

> My main point of disagreement is in the definitions of the terms. In my
> view the DYNAMIC range of the scanner is determined by the CCD, the optics
> (in terms of the contrast available, the digital noise created by the AtoD
> (roughly half the step size) and other noise generated in the circuitry.

It's incomplete, but correct.  Dynamic range is simply based solely on the
overall range the scanner puts out (say, .01V to 3V) and the noise (say, +-
.01V).  If you measure the range into the A/D as well as the noise, that's
all you need to give dynamic range.

> What Austin defines as the dynamic range could be taken as the "goodness"
> of the device, by I believe you can have a scanner with a high dynamic
> range but may or may not be noisy.

I don't understand a word of what you said here...  There's ALWAYS noise.

I am not bringing film into this, as I believe it simply defocuses the
actual discussion at hand.

Austin

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