[filmscanners] Re: Density vs Dynamic range

["" <peter@softwell.co.uk>]

>
> Yes, it is my web site, and I did put that diagram there.  It is
> straight
> out of Higgins book "Digital Signal Processing in VLSI".
>
That explains a lot.  That diagram (and some of the other things you have
written) describe the situation with respect to digital signals only.  As
I've said before, for digital signals the noise is +/- half the step size
- or one step size.  On that basis your statement that 5000 values are
required to represent a 5000:1 range is correct, as is the formula you
quote as the noise is equivalent to one bit.

But that is only half the story - there is a further analogue noise figure
that you seem to disregard which, to me, is the far more important figure.
You can always increase the digital dynamic range (or lower the noise
figure - same thing) by using a higher resolution AtoD.

> But Peter, I am the definitive source ;-)  If you want me to pull out my
> qualifications, I am more than happy to.  But seriously, please, take my
> word that what I am describing and talking about I am entirely correct.

I'm sorry, as an engineer I take nobody's word for anything.  If you want
to convince me you will have to produce a water-tight explanation.

> Please try to understand it....and once you understand it, you will see
> why
> I am correct...and how useful what I am trying to get you to understand
> is.
> And, that will be one more person who can stop the proliferation of
> misunderstanding on this subject.  Your comment above makes me believe
> that
> we have a good chance of that.
>

I agree that there is a proliferation of misunderstanding on this, but I
don't think it's all mine.

What you have called "Dynamic range" is really only the range of possible
values on the digital side.  This may or may not bear any relationship to
the capabilities of the CCD. Manufacturers can give us more digital bits,
but if the bottom 10% are all in the analogue noise region and the top 10%
represent values beyond the saturation point of the CCD then quoting a
"dynamic range" based on the digital capabilities of the AtoD are
nonsense.

> I will refrain from answering you rather prolific prior response and see
> where you go with this...
>

That is your prerogative,


Peter, Nr Clonakilty, Co Cork, Ireland

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