Digital BW, The Print

----- Original Message -----
From: "Austin Franklin" <darkroom@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Wednesday, January 08, 2003 7:23 PM
Subject: RE: [Digital BW] Scanning and Zone Sys Development.


>
> > > > The Nikon 8000 has analog gain control. I presume that it works
> > > > the same way
> > > > as you describe it otherwise why call it "analog gain" control.
> > > > It will show
> > > > more noise in the shadows when set to a maximum
> > >
> > > Actually, I believe it's misnamed.  This has been discussed with Ed
> > Hamrick
> > > and should be in the archives.  It does not change the actual
> > gain between
> > > the CCD and the A/D, but the exposure time.  To quote from Ed
> > Hamrick (who
> > > wrote ViewScan) from the rec.photo.digital newsgroup:
> > >
> > > "The "Analog gain" in the Nikon is a bit misleading.  It's actually
> > > just the exposure time for each of red, green, blue, and infrared."
> > >
> > > Austin
> >
> > In what way can one compare both methods ? Is there a difference in the
> > results ?
>
> Hi Ernst,
>
> Yes, there is a MARKED difference in the results.  The "analog gain" that
> Nikon has merely shifts the tones up or down the "scale".  Example:
>
>         -
>       - - -   - -   - -
>     - - - - - - - - - - -
> 0 1 2 3 4 5 6 7 8 9101112131415
>
> now shift that up:
>
>           -
>         - - -   - -   - -
>       - - - - - - - - - - -
> 0 1 2 3 4 5 6 7 8 9101112131415
>
> Same curve, just different "values", but all relative values are
maintained.
> What it's useful for is getting your entire tonal range within the range
of
> the scanner...but other scanners do that as well with their exposure
> setting.
>
> If the scanner is designed such that it has actual analog gain between the
> CCD and A/D, you would EXPAND your analog data, and actually get MORE
tones:
>
>     - - -
>   - - - - -   - - -     - - -
> - - - - - - - - - - - - - - - -
> 0 1 2 3 4 5 6 7 8 9101112131415
>
> The limit, of course, is our vision (and noise in the CCD/analog
> circuitry/AD).  As long as you can get 256 tones out of your data, and you
> have tonal "separation" between tones you want to show tonal separation
> between...more tones in the image data wouldn't necessarily do you any
good.
> Again, I understand the Piezo driver claims to give more tones beyond what
> you give it for data, to smooth the tonal transitions.
>
> Regards,
>
> Austin

Austin, Kevin,

After some excercises with NikonScan and an IT8 slide I'm not so certain
that it is just a false name for an exposure strength variation.
When I crop the scan to a small part of the greystep in that image, change
the analog gain setting so I can get the histogram in the middle,
then the histogram is stretched to the density range. Of course it still can
be a digital stretching that is performed and not an A/D stretching but it
isn't a simple exposure change either. Still a false term if it is not done
at the A/D stage.

What is interesting though is that it will not stretch any crop and with
"positive" negative scanning the redraw button will more often (but not
always) initiate a new reading scan instead of picking the data from the
preview. That could mean that NikonScan is behaving more intelligent than
expected. My guess is that it could use true analog gain but checks what it
actually has to offer in dynamic range to make that worthwhile. That makes
this function less transparent but still very useful. It also has the logic
of the comments I made before on the usefulness of analoge gain in CCD film
scanners, most of the time there's not enough dynamic range.

What I write is based on 'dry' scans, I didn't measure the RGB values in
scanned images etc, just looking at the histogram changes.
Disappointment is still possible.

Ernst