[filmscanners] Re: scanner dmax discussion

["Berry Ives" <yvesberia@earthlink.net>]

on 7/18/03 4:24 PM, Austin Franklin at austin@darkroom.com wrote:

>
> 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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12?

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