[filmscanners] RE: Density vs Dynamic range

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

Wire,

> >> Julian wrote:
> >> There it is in your agreed formula.
> >
> > Yes, we are agreed as to the WORDING of the formula, but I do
> NOT agree with
> > your misuse of the term "smallest discernable signal".  PLEASE
> go look up
> > the meaning of the word "discern(able)".
> >
>
> Austin,
>
> I looked up "discernible" in the closest handy dictionary
> (American Heritage
> Dictionary; a popular and reputable book in the States) and the definition
> supports Julian's usage, as much as yours.

It depends on WHICH of Julian's usages you are referring to, and without
more of the context of his usage, I can't say.

> ...the use of the word discernible as the smallest signal that by
> Julian makes sense in the context of the DR discussion.

It's "smallest signal" that is ambiguous, not "smallest discernable signal".
Smallest signal could be either "smallest discernable signal", OR, could be
"smallest signal level".  The main point is, the terms he's using are
ambiguous.  BOTH "interpretations" are valid for DR discussions, as both can
be used in a DR equation.

> And a sensible
> reader will take the ambiguity into account, so there no point in
> hammering
> away about this. Your story is not made clearer by your position.

I think you might be missing the point then...see the last paragraph I
wrote.

> BTW--you misspelled discernible. But I'm sure that Julian knows what you
> mean :)

Not according to my spell checker, and to "dictionary.com", and both say
that "discernAble" is correct.  "discernIble" is a synonym for
"discernAble", BTW.  Either is acceptAble ;-)

> As a side topic, I could use some more explanation of the term
> noise in this
> DR context. Is the noise level an absolute level at which signal can no
> longer be discerned?

Possibly, but not necessarily.  Noise MAY limit discernability, but
discernability may be limited by other things.

> Or a level below which there is some
> uncertainty as to
> the the signal.

Yes.  In the case of film scanners, "noise" is the limiting factor to
"smallest discernable signal".

> I've heard of a technique of using dither to
> allow recovery
> of a signal below the noise level...

There are noise reduction techniques, but dithering is typically actually
adding noise TO the signal...  Since you're good with dictionaries ;-), look
up dither...

Regards,

Austin

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