hi,
depends what you mean by `possible'. you can't currently dial in your
values in spectral directly. if you want to do it without coding, i would
do the wrong thing and convert your spectral transmission to camera rgb (by
integrating the colour matching functions to obtain XYZ and applying the
XYZ to camera rgb matrix) and then use the tristimulus values in the white
balance module.
that's wrong because light transport is clearly happening in spectral in
the real world. so if you want to simulate transmission more accurately,
you might get better results by coding a new module which upsamples XYZ
values of your image to spectral representation, then multiplies your
spectral data and converts back, again using the cmf.
that second approach is of course flawed, too, since the upsampling is an
ill posed problem and you'll get random spectra instead of the one that
really created your colour.
in case you want to use any cmf, use the 2deg 1931 5nm step ones (the 1964
or whenever the newer ones were measured result in a different XYZ than
what we're using in darktable). abridged or full wavelength scale probably
doesn't matter for the precision we need here. also keep in mind that
darktable's Lab is D50 and XYZ is natively illuminant E if you multiply the
cmf to your spectra.
cheers,
jo
On Wed, Mar 18, 2015 at 10:16 PM, Dr. Johannes Zellner <johan...@zellner.org
> wrote:
> Hi,
>
> I'd like to apply a wavelength-dependent attenuation function to an image.
> Suppose I've discrete transmission data like this
>
> nm transmission
> 400 0.9
> 410 0.91
> 420 0.912
> ...
> 650 0.98
>
> is it possible to make this with darktable?
>
> best regards,
>
> --
> Johannes
>
>
>
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