The following is taken from the PanoTools list at yahoogroups.com from a
discussion originating over extending dynamic range of digital and film
images. VueScan users in particular will find this interesting since
there are links to an incomplete VueScan user's guide written by Eric
Krause.
Chuck Norcutt
-----------------------------------
<snip> I am able to extract
the complete dynamic range with my LS 40 as well using vuescan and
some special settings. See http://www.erik-krause.de/cn_hdr for some
early examples.
Although the dynamic range of negative film is pretty high (up to 15
f-stops) the density range is pretty low. Compared to slides it is
relatively easy to scan the whole dynamic range without need for
scanner exposure bracketing and similar tricks even with a not top
level scanner.
The problem starts because there are severe color shifts in the
extremes. This might be partly due to non-linearity of the CCD but
mostly due to differences in the film sensitivity curves in the
extremes. This is "corrected" in the usual scan software by applying
a white point clipping below this extreme region.
Vuescan gives me the controls to scan without any clipping, but then
I have to correct for very pink highlights. This can of course be
done manually, but that introduces color shifts for other parts of
the histogram.
The best would be an IT8-profiling using the whole dynamic range.
Wolf Faust still works on calibrating his machines to expose
negatives, but he told me the negative targets are to be expected
this summer.
The second is to use a correction curve. I've started to write a
tutorial on this but never finished (lack of time). If you are
interested in the draft (complete text, no images) have a look at
http://www.erik-krause.de/tutorial/part1.htm
http://www.erik-krause.de/tutorial/part2.htm
http://www.erik-krause.de/tutorial/part3.htm
(If you prefer reading german replace 'part' by 'teil')...
best regards
-- Erik Krause Ressources, not only for panorama creation:
http://www.erik-krause.de/ Read panotools at GMane:
http://news.gmane.org/gmane.comp.graphics.panotools
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