Hi,
thanks -- seems that I'm lost a little :-(
talking about writing a module / is it possible to write a module in lua?
Am 19.03.2015 um 10:12 schrieb johannes hanika:
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 <mailto: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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