[filmscanners] RE: Density vs Dynamic range>AUSTIN (2a)

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

Anthony,

> > The signals for a scanner (and audio) are
> > sampled DC signals at an instant in time.
>
> But samples are not signals, and DC is not a signal.  A current or voltage
> that does not vary (i.e., DC) carries no information, and is thus not a
> signal.  All signals are AC.  More precisely, all signals vary
> over time; DC
> does not vary over time; therefore DC and signals are mutually exclusive.

That has absolutely nothing to do with the discussion.

> Confusion probably arises because signals can be imposed on carriers, and
> these carriers can be either DC or AC, depending on how they are defined.
> The signal itself, however, must always vary over time.

Again, that isn't pertinent to the discussion.

> > For audio, yes, but not for imaging.
>
> In images, the signal variation is spatial, not temporal.  But
> the variation
> is still required.

No one said it wasn't, but again, that has absolutely nothing to do with the
discussion.

> > The CCD does not output an analog AC signal.
>
> The signal varies in the spatial domain.  From an information-theory
> standpoint, this amounts to the same thing as a temporal variation.

Again, that has nothing to do with the discussion.

The CCD, analog front end, A/D etc. do not care a wit about the A/C nature
of the signal.  They simply sample a DC voltage (or current) at a single
point in time.

Austin

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