I use this workflow
https://web.archive.org/web/20080421211129/http://privat.albicker.org/foto-tutorials/foto-tut-neg-en.html
-Bernhard-
Steven Fosdick schrieb am 17.11.2014 um 19:18:
I have been using Darktable for some now for digital pictures but I
recently borrowed a slide/negative scanner and used it to scan some
old negatives I had. While searching I also discovered a couple of
rolls of undeveloped film from years back which I got developed.
Looking at the colours from the negatives they seemed a little odd but
when I got the recently discovered films back from developing complete
with CD scans from the developer these have turned out to have very
different colours from those I get if I scan the same negatives myself.
Here an example:
http://s16.postimg.org/tchwpmfwh/img22highres.jpg
This is the scan that came back from the people developing the film.
http://s16.postimg.org/l5pwy1ptt/img22raw.jpg
This is what I get if I scan the film myself.
I also have an example where water is a very obvious purple. As I
have already scanned quite a few images and had to return the scanner,
at least for the time being, I am wondering if can work out a colour
correction to be applied to the images from the scanner I borrowed.
Moving the sliders in the white balance or colour balance modules to
search for useful settings does not seem to work very well. Taking
samples from patches of what should be the same colour on each of the
scan from the developers and the scan from the scanner I borrowed,
working out the ratio for each colour and then setting that as the
gain in the colour balance module works but only for that patch, i.e.
that patch then becomes the same colour in the corrected version from
my borrowed scanner and the scan from the developers but the rest of
the picture retains noticeably incorrectly coloured.
So this suggests to me that the film or some aspect of the scanner
does not respond linearly and the extent of the non-linearity is
different for each colour. This is presumably what the other sliders
in the colour balance module are intended to correct but again moving
them around whilst visually checking is not very productive.
I know there is a step in adding a new camera to produce a colour
matrix which can be done given an IT8 target where there are various
shades of exactly known colours but I can't see a way to do that in
this case. IT8 targets do not seem to be available on negative film
and the films I have been scanning are old so even buying an IT8
target, finding a film camera and a similar roll of new film,
photographing the target, developing the film and then running the new
camera colour matrix tool on the resulting scan would not necessarily
yield the right results as the film formulation may have changed in
the intervening years (20 or more, in some cases).
Could a similar process work for multiple patches where for each patch
a sample (r,g,b) is taken from the desired colour and another (r,g,b)
for the uncorrected colour picking, for example, both strong colours
and neutral areas, shadows and highlights? Does anyone know of a tool
that would be able to process these to work out the parameters for
colour balance (or as a colour matrix to add as if it was a new camera)?
If not what other approach would you use?
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