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

["Anthony Atkielski" <anthony@atkielski.com>]

Austin writes:

> 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.

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.

> For audio, yes, but not for imaging.

In images, the signal variation is spatial, not temporal.  But the variation
is still required.

> 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.



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