[filmscanners] RE: Density vs Dynamic range

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

> > Woah, Peter...what non-engineering standards are you talking about?
> > What I
> > specifically quoted as the formula for dynamic range is straight out of
> > an
> > engineering Bible for signal processing.  I've also been an engineer in
> > this
> > VERY field for more than 20 years, so I don't understand why you believe
> > anything I've said is not in "adherence to ... non-engineering
> > standards".
> > In fact, the equation below is exactly the same as I've been saying all
> > along, and meets with every aspect of what I've said.
>
> I was going to say no more, but I can't let this one through.
> Your diagram, as you have said, is taken from a document on DIGITAL signal
> processing.

Peter,

It is a diagram of an ANALOG signal, and is used in a description of ANALOG
dynamic range...  We really haven't been discussing digital dynamic range as
the primary topic (except as a periphery TO what you do to represent an
analog dynamic range digitally).  Digital dynamic range is simply (in dB)
log2**n where n is the number of bits.

> It is only valid in the real (analogue) world when the A/D
> step size is approximately the same as the noise level in the analogue
> system.

How's that?  That diagram has NOTHING to do with A/Ds.  It is a diagram that
visually shows the terms "largest" and "smallest discernable signal" as used
in the dynamic range equation.

> My understanding is that the current performance of CCDs is better than
> that.

Huh?  CCD performance better than what?  Where was it compared it TO
anything?  What are you saying it is better than?

It's a simple diagram...again, showing what the terms "largest" and
"smallest discernable signal" mean WRT the dynamic range equation:

DR (dB) = 10log10(largest/smallest discernable signal)

plain and simple.  Smallest is the noise, and largest is the absolute range
(which I have also stated as max-min at times).  Min is not the same as
smallest, though that doesn't mean they couldn't be in some cases.

Austin

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