I copied the following response to the scanner list.
> I am making raw 48 bit scans
> and gamma correcting them for a 2.2 gamma in the Silverfast software, and
> then exporting them to Photoshop 6 (depending on the image I am doing the 48
> bit editing in either Photoshop or Silverfast HDR). Another problem I am
> noticing with my raw, profiled scans is that the blackest blacks and whitest
> whites are clipped in the raw 48 bit, profile-corrected, scan. My darkest
> shadow areas never get below "20" on the Photoshop histogram and the whitest
> highlighs never above "235."
Your private email wasn't as detailed as the above explanation and so my
answer probably didn't address all your concerns. Sorry about that.
Your highlights and shadows are not being clipped. If the scanner (any
scanner) outputs in linear raw (no gamma correction) all the data will be
stacked towards the shadow end, but with a scanner such as the SS120 or the
Nikon 4000/8000 you shouldn't find that it is tight up against the Level 0
buffer (maybe level 1). When we apply the gamma curve the data will be
stretched out across the histogram. With gamma 2.2 you are finding it starts
about level 20 and finishes at level 235. Changing the gamma to 1.8 will
certainly bring it down to about level 8/10, but level 0 requires gamma 1.
If your images stop at level 235 they don't have any real bright highlights.
I have scanned a few images that go from level 15 to level 250 (in gamma
2.2). Since you are outputting the image without SilverFast applying any
other edits; the end points will rarely if ever stretch from end to end and
they shouldn't or you have just wastes $3000plus on a scanner that has
limited dynamic range. I would be surprised if any of the 14bit units
produced end to end data for a "linear raw" scan. The only way that could be
achieved is if the software forced to clip to highlight and shadow and I'd
want my money back from the outfit who wrote that software and worry about
the guys who made the scanner. What do they not want me to see?
I followed Ian Lyon's tutorial religiously in
> calibrating the scanner with Silverfast; is losing the blackest blacks and
> brightest whites a result of using a 2.2 gamma (as opposed to say 1.8
> gamma)? Is there some easy way to retrieve these more extreme values? I
> can of course increase the contrast in Silverfast HDR or Photoshop 48 bit
> editing (for example by moving in sliders on the "Levels" command), but then
> this has other effects as well. . . .
Fortunately, you haven't lost anything; the data in your shadows is all
there to be extracted. True clipping is when the data ends in a cliff at
level 0 or 255 and nothing exists at either of those points, it's gone
forever. Going to gamma 1.8 means the image will be darker and will
therefore require more editing to get it to the brightness level you want.
You can set SilverFast HDR to clip the end points quite easily - just set
the Auto threshold for highlight and shadow to about 7 or 8 % and you'll get
what you want. I suggest you don't, but you feel that something's needs to
be done then choose 4 or 5% (you'll need some headroom for later). see Page
9 of the HDR tutorial for the screen garab off the dilaog box
>> Photoshop has excellent masking tools, which Silverfast does not (while not
>> available in 48 bit mode, you can save a duplicate of the file to 24 bit
>> mode, mask in 24 bit mode, and then, reopening the 48 bit file, use the
>> masks created in the 24 bit mode on the 48 bit file). To be fair,
>> Silverfast's automatic correction tool with manual override is a nice
>> feature, but is it worth $300?
Whilst not being as effective as the more powerful masking tools found in
Photoshop, which you rightly point out are only available in 8bit mode,
SilverFast does indeed have two masking in tools (see the selective colour
toolbox). You'll find a freehand and Polygon lasso tool that is actually
quite useful at times. When you combine the selection tools with the
selective colour tool you have an extremely powerful editing facility.
You haven't wasted your money. I think there is a lot to SilverFast that you
haven't quite discovered yet. That's said LaserSoft don't make life easy for
the user with their poor documentation for version 5.
I hope the above helps a tad more than my earlier response