[filmscanners] RE: scanner dmax discussion

["Chuck Cole" <cncole@earthlink.net>]

> -----Original Message-----
> From: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Austin Franklin
> Sent: Wednesday, July 16, 2003 8:29 AM
> To: cncole@earthlink.net
> Subject: [filmscanners] RE: scanner dmax discussion
>
>
> Chuck,
>
> > The "steps" mentioned above have nothing to do with intrinsic
> > properties of sensor chips and I doubt that anyone tries to
> size an A/D's
> > lsb to some rms noise level
>
> But that is EXACTLY how the A/D is sized in analog to digital systems.  It
> isn't sized less, then you aren't getting all the data that is available,
> and if you size it more, then you simply throw the bits away as they are
> noise.

au contraire:  the Shannon waveform sampling theorem would be that
criterion, and that says the steps must be smaller by a factor of about 3 or
more.  An 11 bit A/D exceeds that for the signal characteristics of films.
The case of sampling the ccd (vs a staring array of detectors) is a bit
simpler because the ccd itself is a sample-and-hold front end system.  An
A/D past 10 bits in a scanner is primarily for spec gamemanship alone: film
info isn't quite that good.  The A/D is scaled to keep the min to max signal
range between just a few bits and below full house, as was said before (by
you?).  The size of the lsb is just not relevant nor is it significant (as
for frame-to-frame waveform analysis/synthesis) in these scanner systems.

>
> > Is/was there a point to this technical thread I stumbled into?
>
> Possibly, but I don't remember what it was.
>
> Regards,
>
> Austin


Clearly, we've lost aim and relevance for this techie minutia.


Regards,

Chuck


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