I've been scanning some 20-year-old Kodachromes for 3 days now with my
LS4000 and Nikon Scan 4, and it's a royal pain in the neck. Besides
being generally underexposed, the balance between the RGB channels shifts
drastically, and the only luck I have had fixing this involves increasing
the analog gain on the red channel (a lot) and the green channel (some)
while knocking down the gamma on the blue channel. But this leads to
spiky histograms unless I do it in 14 bit mode. Yesterday I only got the
spiky histograms in the blue channel (due to using curves in NikonScan);
today I get them in all channels if I even touch the gain. If someone knows
of a solution for this (other than buying Silverfast--I do have VueScan
but haven't tried it for this), I'd love to know about it.
If you think that's bad you should try it with an LS-30!!! If you look
around this newsgroup you'll see lots of pulled hair on the floor and
numerous climbing scratchmarks on the walls... That's all mine! ;o)
But seriously, Kodachromes on Nikons are a nightmare although I was
under the impression that newer scanners - like the LS4000 - do a
pretty good job.
I've been trying to streamline the process because tweaking each slide
individually is just plain excruciating, as you've discovered. And
there just isn't enough time in this Universe to do the job properly.
My approach in broad strokes (still "work in progress") is to try and
get the maximum out of the scanner without any software adjustments in
Nikon Scan (no curves, brightness, etc). I leave all post-processing
to Photoshop. In particular this means:
1. Turn off Nikon Color Management! Very important! NCM just makes
matters *much* worse i.e. it *amplifies* blue!!!
2. Turn off Auto Exposure! Nikon Scan has a "random exposure
generator" ;o) which (at least in my setup) out of the blue (sic)
would produce diametrically different back to back scans without any
change in parameters. Even when it works, it creates a different color
balance in each scan which makes streamlining cast removal impossible.
3. To get rid of spiky histograms (I called them "weird" histograms
a.k.a. "comb" histograms - there's a thread on it in the archives) the
workaround is to set Interpolation to Bilinear and fix cropping. Once
spikes are gone stick with the same cropping. (Without going into too
much detail the spikes are the result of gamma conversion.)
I also have to do contrast masking but your scanner has sufficient
dynamic range so that's not applicable in your case.
I have no definitive suggestions on streamlining color cast removal
but the consensus (at least for difficult, very dark slides) seems to
be: assuming blue is level (0), boost red by about 1 Analog Gain and
green by about 0.2. (I know, the "about" bit really bothers me too.)
Another automatic approach (similar to Auto Levels) is to boost Analog
Gain until all three channels bump up against the right histogram
edge. This will give you a good color balance in most cases. However,
just like Auto Levels, in some cases (depending on image content) this
may actually introduce a color cast, but at least you will be getting
the maximum dynamic range.
Of course, like auto exposure, this will also create a different color
balance with each scan which makes streamlining (any residual) cast
removal later impossible.
That's where I'm at right now, still chasing my tail and cursing
Nikon... ;o)
As for VueScan, I for one am not exactly a fan... Even forgetting its
"interesting" user interface, its lack of controls (no individual
channel Analog Gain adjustment) makes it totally unsuitable for the
task.
In regard to color balance, VueScan is like a throwaway Instamatic
camera. Point and shoot. When it works, it works well, but when you
get a difficult situation (e.g. a very dark Kodachrome) you end up
with something looking like a false color image. Totally unacceptable
(for me, anyway, although many differ).
One VueScan plus is the ability to boost exposure more than NikonScan
(which is effectively limited to 4 AG). However, instead of using
Analog Gain i.e., EV values, VueScan insists on its own unique
"interesting" scale... :-/ And, of course, you still can't adjust
individual channel AG which renders this advantage meaningless.
Don.
