Digital BW, The Print

Alesandro-

To stay in keeping with the other scanning threads I really should 
start with some cutting or insulting statement  ...  nahhh ...

>
> I rely on numbers, i.e. open Photoshop levels and press AUTO. You can
> configure this tool not to clip anything, so that only values with no 
> data
> are excluded. This way you're sure to keep all information from the 
> scan,
> and are free, later, if you feel like, to clip at either end of the
> histogram.

Yes, that's another way to do it.  As you say, the clipping point 
defaults can be adjusted.

> Considering that changing exposure affects the raw (unprocessed) scan, 
> I'd
> say it's a hardware thing.

It's hard to say for sure how raw raw is.  It is software dependent.

>
>> Do you know if the Epson 3200 can change the intensity of the light 
>> source
> or the duration of the time the CCD is capturing info? From memory the 
> RGB
> exposure is a multiplier not like the analog gain in some of the Nikon
> scanners that actually change the exposure time.
>
> I expect all scanners to be able to change either of these parameters. 
> My
> gut feeling is that what changes is time rather than intensity, and I'm
> pretty sure this is what Vuescan's RGB exposure does. It shouldn't be 
> hard
> to verify, though: just see how long it takes to scan the same image 
> with
> different values. If it's just a multiplier (I assume you mean a 
> software
> transformation of data from the raw range [x, y] to [n*x, n*y]) it 
> should
> take about the same time.

Actually I think this is not available on many scanners.  I know it was 
available on the Nikon LS2000, and I know it is not available on the 
Polaroid ss120 or ss4000 or any flatbed scanner I have looked at (which 
doesn't include the 2450 or 3200).

On the nikon LS2000 which does have this feature adjusting the gain 
only moves the data right or left.  In that case at leas the only 
result of changing the exposure was to change the position of the 
histogram, not its shape or width. I remember spending a couple of days 
fooling around with this trying to figure out exactly how it worked.

In abstract I think the scanning process contains the following major 
steps:

1. The scanners hardware captures the film density as a set of A/D 
readings.
2. A white point and black point are set.
3. The Gamma is adjusted.
4. A curve is/may be applied to get the contrast you want
5. Manipulate according to preference.

Step 1 has to be done in the scanner.

Step 2,3, and 4 can be done in the scanners software or in photoshop 
(or some other software).  The choice of where  to make these changes 
depends on your confidence in the scanner/software combination and 
personal preference.  Some scanner software is better than others.  For 
me, I usually perform steps 2 and 3 in vuescan unless I don't like the 
results then I may try something else until I get what I want.


--
Kevin Gulstene
http://www.dockwalker.com