[filmscanners] LS-2000 and Kodachrome

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

I came up against the dreaded blue cast when attempting to scan some
Kodachrome in my LS-2000. On Usenet, people have been fighting with this,
trying to find some easy tweak to the controls the controls to fix this. I
decided to buy a Kodachrome IT8 target and just profile the damn thing. I
found the slide at B&H, and the data file on the Kodak FTP site, and built a
profile.

When I assigned the new profile to the scan of the IT8 target, it looked
very nice, but I was surprised to see that there was still a blue cast in
the light grays. After puzzling over this for a while, I decided to actually
look at the slide, and saw to my surprise that it actually had a visible
blue cast in that area. So the profile works.

I also tried boosting the master analog gain on a dark slide, and comparing
the result to boosting the levels using PS Curves. I was relieved to find
that, while the former produced a cleaner result, the colors were identical.
In other words, the scanner is linear enough that the you don't need
different profiles for different master analog gain settings.

If you want to correct for the blue cast without profiling, you can't do it
with the analog gain controls, because the problem is that the scanner is
misreading the density of the yellow dye, and there is no yellow dye left in
white areas. So if you cut back on the blue, whites will turn yellow. There
is no alternative but to apply some sort of curve. But of course, that's
what a profile does.

By the way, I was doing all my tests with NikonScan. I'm now trying to
figure out how to build a profile that works with VueScan. The built-in
profiling in VueScan is very primitive, producing a profile that only has
some primary colors and simple curves--it's not a complete 3D profile. So
I'm trying to figure out how to make a real profile that has the right
response to work with VueScan. If anyone has done this, I'd appreciate any
suggestions.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com

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