Re: filmscanners: Re: bit depth and dynamic range

["shAf" <michael@shaffer.net>]

Paul Patton writes ...

> I've just been reading some Nikon literature about their new
scanners, and
> I have some questions about the terminology.  The ad states that the
> coolscan IV ED yeilds 48 bit images (48 bits per pixel?).  Later, it
> states that the scanner has a color bit depth of 24 or 36 bits.
What does
> this refer to?

    Good question!  A 48bit file probably refers to the common file
depths being 24bit (8bits/channel RGB) and 48bit (16bits/channel).
Altho the Nikon scans with 12bits/channel resolution (or precision),
it needs to write to the common file formats.

>  It also states that the scanner has a dynamic range of
> 3.6.  What is a scanner's dynamic range?  Can anyone suggest an
article
> somewhere on the web or elsewhere that explains all this?

    Dynamic range refers (supposedly, sometimes, generally) the
ability for a pixel value to truely and significantly represent a
"shade" of film exposure.  I have my own hard time understanding how
this refers to both negative and positive films (i.e., "optical
density" vs "exposure latitude"), but 3.6 should represent 12 f/stops
of exposure, ... although the shadows (slides) and highlights (negs)
do sometimes contain "unadvertised" and objectionable amounts of noise
(sometimes minimizable with nikon capable multi-pass scanning).

    Tony's wwwsite is a very good source for these explanations, as is
www.scantips.com.

shAf  :o)