[filmscanners] RE: scanner dmax discussion

["Austin Franklin" <austin@darkroom.com>]

Chuck,

> This is true in a philosophical and theoretical sense, but I believe we
> would have a difficult time pointing to any scanner which has an
> electronic
> circuit doing anything explicit with samples of an identifiable spatial
> frequency function.

Fact is, it takes a certain sensor element pitch to replicate a particular
spatial frequency, and that is what a scanner does.  It may simply be a
"spec" to you, but it IS recreating spatial frequencies.

> The scanner does simplistic electronic time sampling of the CCD's data
> stream,

Correct, and I've not said anything different...

> which is only a set of x values, row by row, in fixed
> format for the
> frame.

Row by row, fixed format or not does not effect how the CCD/AFE/AD
work...the AFE/AD don't know a thing about anything except voltage...

> The output file presented to the coumputer doesn't "know"
> or "say" it
> is an image: it is just an ordered set of pixel values with at most some
> simple pixel-by-pixel corrections.

Exactly, and this was my point that the scanner doesn't know squat about
"film noise", which you've yet to explain...

> As I mentioned to Austin, we're way off the deep end on this
> topic and need
> a way to get back to clear relevance for scanners and their
> explicit active
> functions.

The WHOLE subject was number of bits that the A/D is in a scanner, and how
that is determined.  I've stated how it's done, you've disagreed.  OK, so
here is an exercise for you.  The CCD has an output voltage of 0-2.5V, with
a noise of .001V.  How many bits do you need to "sample" the data with such
that the entire dynamic range available from the CCD data is captured, and
why?

Regards,

Austin

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