I understand the reason to get a raw scan--to get the maximum amount of
information possible in the scan itself, instaead of using the scanner s/w
to decide what part of it you are going to get. I'm still wondering about
exposure, insofar as I assume that in some cases the dynamic range of the
film is going to exceed the dynamic range of the scanner.
Yes, and then you have to employ various other methods like
multi-scanning or contrast blending to get the full dynamic range.
However, if you at the same time let scanner software adjust color,
contrast, etc. this will just get in the way and generally interfere -
if you're trying to get the most out of the scanner.
Similarly doesn't the exposure of the scanner play a role in the amount of
information and which information is finally included in the digital scan?
Yes, and this is far too important to leave it to the scanner because
the scanner can only blindly follow simple rules (such as black and
white clipping). This may work in some (even many) cases but can't be
relied upon if your goal is to get the most out of the scanner.
Is it not the job of the scanner s/w to determine the correct amount of
exposure for a given piece of film, considering its maximum density and
contrast range?
Actually, it's not. It's the job of the operator to determine the
correct amount of exposure. The scanner can assist by guessing, but
that's all it is: a guess and a suggestion.
It's just the same as taking pictures. I mean, you wouldn't say it's
the job of the camera to determine exposure. The camera can assist by
guessing, but that's all it is: a guess and a suggestion. In the end
it's the photographer who decides.
!!!
This is actually a very interesting point. People often think their
"work" is done after taking the picture. Scanning, to many of them (me
too when I started!), is supposed to be a mechanical, automated
procedure of converting this photo into the digital domain.
The truth is, however, that scanning is just as complex and difficult
as taking the photo in the first place. One could maybe even argue
more so, because while a photographer works with first-hand data (the
reality) the scanner operator works with second-hand data (a photo of
that reality).
!!!
When you talk about a raw scan, how is the exposure determined? Do you
sometimes tweak the analog gain if, for instance, you wish to try to get
better tonal separation in the shadows, or is this just a function of the D
max of the scanner--a set quantity--and changing the analog gain will have
no effect on getting better tonal separation on the other side of the D max
floor?
I personally tweak Analog Gain all the time. I explained how I, for
one, determine exposure in the other message so I won't be repeating
it here.
My current "obsession" is trying to eliminate noise in dark areas and
bring out the detail. This was torture on LS-30 (a 10-bit scanner) but
after running many tests on the LS-50 (a 14-bit scanner) I'm starting
to think Dmax is really just another theoretical number divorced from
reality... According to my preliminary tests I'd really need a 20 or
even 24-bit scanner to get the full Kodachrome range without noise and
with maximum detail - which is what I'm currently wrestling with.
Even though LS-50 doesn't support single-pass multi-scanning, I ran 18
scans, lined them up *perfectly* with sub-pixel alignment and then
blended them.
The result was underwhelming. While this masked random noise it did
not bring out any more *detail* in shadows. Indeed, comparable results
to multi-scanning can be achieved by simply selecting dark areas
(about 32 Threshold) and then applying 0.3 Gaussian Blur to the
shadows.
A simple scan with Analog Gain boosted by 1 or 2 clicks revealed
gradients in shadows which multi-scan failed to bring out at nominal
exposure. Of course, boosting Analog Gain by 1 or 2 steps blows
highlights big time!
So, the fun continues...
Don.