On Wed, Aug 12, 2020, at 23:34, Timur Irikovich Davletshin wrote:
> I believe white balance is nothing to worry about.
The role of the white balance module is explained here:
https://discuss.pixls.us/t/inverting-photos-of-color-negatives-with-darktable/9140/44
How much that step actually matters in practice probably depends on the
specific camera/color matrix being used, I guess.
> Anyway you adjust channels individually in negadoctor module without any
> reference to the bulb type. The only thing you should worry about is to get
> no clipping in individual channels of your "scan".
Avoiding clipping is the most important thing, but also having some data to
work with is important, too. :-)
When you capture a scene under 2700K lighting, you're capturing very little
information in the blue channel. Using digital white balance adjustment to
"correct" this capture so that white objects display as white is similar to
boosting a very underexposed capture with respect to the blue channel. This is
something that people try to avoid by exposing correctly, for good reason. Now,
when using this 2700K source to backlight an orange-masked color negative, you
are compounding this problem - there's a lot of red spectrum hitting the
sensor, and very little of the blue (you can see it in the histogram).
Film scanners get around this by exposing each channel for as long as needed
for a "good" exposure, but you can't do that with a camera. What you *can* do
is adjust the spectrum of the light source to balance the orange mask, just
like in an analog darkroom. The good news is that you don't have to get it
"right", because you can do that digitally later... but if you can get it
"better", that's better, and probably especially so if your "scanner" is a
15-year-old sensor with a base ISO of 200.
--
jys
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