Digital BW, The Print

Kevin,
 
it's really amazing how some people can turn technical issues in ego wars.
They will be disappointed to read that I agree with your statements :-)
What I actually meant about scanners capability to change exposure time is
that I think they have it at least internally, i.e. they can adapt to
different images: whether or not this setting can be modified by the user is
another matter (BTW it would be interesting to see how Vuescan behaves with
such scanners that do not let the user change exposure time: is the "lock
exposure" checkbox still visible? How does it affect scans?).
As for the question "How raw raw scans are?" (we're getting philosophical
here :-), I assume it is the result of step 1 in the scanning process you
defined. Of course, depending on the scanner model it may or may not imply
some software intervention, but from the practical point of view it's enough
for me to know that it's as raw as it can get (i.e. that there's no loss of
information from what the scanner extracted from the film), as this is the
problem with most scanning software. For instance, if I use my Canon 4000
own s/w to scan B&W I get less detail, as it uses all three color channels
rather than only one, and often clipped highlights.
 
Austin promised to give these matters a thought, but I'm afraid he's still
on the "Digital, film, scanning" battlefield :-)
 
alex

-----Original Message-----
From: Kevin Gulstene [mailto:kevin@...]
Sent: Wednesday, May 28, 2003 20:47
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: Re: [Digital BW] Re: Scanning


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 <http://www.dockwalker.com> 





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