[filmscanners] Original Vs Edited

["Jack Jansen" <jackjansen@bwn.net>]

Hi People,

I've been lurking for a couple of months, but I've just ordered a Sprint
Scan 4000 from ecost.com and UPS tells me it's scheduled to be delivered on
Jan 11.  I'm confused about the function of scanning software such as Ed
Hamrick's VueScan.

When I expose and develop B&W film, for example, I strive to compress or
expand the dynamic range of the subject to best exploit the dynamic range of
the film.  For a high-contrast subject, I compress by overexposing to bring
up the shadows, and by underdeveloping to keep down the highlights.  For a
low-contrast subject, I expand by underexposing to darken the dark areas,
and by overdeveloping to raise the light areas.

I have the impression that the scanning software has a similar function
between the film and the file.  The software permits the user to compress or
expand, and to center, the dynamic range of the image on the film to best
exploit the dynamic range of the file.  For eight-bit color, this dynamic
range of the file is 256 levels in each of three channels.  If the image on
the film is carefully fit to the dynamic range of the file, then that file
becomes an optimum archival representation of the image, within the limits
imposed by the number of bits per pixel and the number of pixels scanned per
inch.  Is this correct?

But here's my confusion:  If the three channels are individually,
independently compressed or expanded from film to file, then it seems to me
that in general, when the file is viewed, it won't look like the original
subject.  Image-editing software is then used to produce another file which
looks right when viewed on the monitor or when printed.  Is this correct?
(Ignore, for the purposes of this discussion, any editing to produce special
effects).

But if carefully scanning the image produces an optimum exploitation of the
range of the digital word size, then the edited file is NOT an optimum
representation.  Are both files saved as archives, (twice as much storage
required), or has the process of carefully scanning the image served its
purpose, and only the edited file that looks right when viewed is saved?

Jack Jansen

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