Hello Happy Pierre, nice to hear from you again! We were missing you
last spring in Paris. :-)
Thank you for this interesting and well-documented question.
To be fair, I don't know if darktable/lensfun support that. (I'm using
Nikon bodies and lenses FYI.)
From a technical standpoint, that looks like having code that would
read parameters from picture metadata data instead of a lensfun profile.
Depending on lensfun stance on it, either :
* darktable would have to decode camera manufacturer data into something
suitable for lensfun.
* or darktable would hand raw parameters over to lensfun for it do decode
Additionally, in recent years I thought about lens design shifting
because of pervasive electronic post-processing. AFAIK recent Nikon
bodies perform some lens correction by default (hinted I guess by the
different resolution and cropping of RAW vs "full-res" JPEG).
Intellectually this looks good, because it relieves the design process
from some constraints, which means opportunity to optimize other
parameters, like bulk (reference
<http://www.dpreview.com/articles/5653763779/a-distorted-view-in-camera-distortion-correction%20on%20that%20topic.>
with rather impressive examples) or perhaps (or not?) after-correction
chromatic aberrations, sharpness, focus range, maximum aperture, or ...?
I'm wondering if chromatic aberrations are included in this trick (that
is, design a lens that may have wild chromatic aberrations, but which
are precisely known in all (focus distance)*(aperture)*(focal length) so
that they can be finely compensated.
There is interesting information about this on
http://www.dpreview.com/articles/5653763779/a-distorted-view-in-camera-distortion-correction
. Vignetting correction is good. Sometimes the software-corrected 4/3
yields better sharpness (in grass).
Have you got any pointers on the metadata format? Is it standardized or
vendor-specific? Reference above suggests that it is not except in DNG (
Also for swappable lens cameras, does the lens tell its parameters to
the body? It the protocol standardized?
What happens then for independent (not camera maker) lens vendors ?
I'd like enlightenment from anyone who knows!
Le 10/02/2016 14:11, Pierre Gérard a écrit :
Hi,
I'm reluctant to ask such a question on a mailing list rather than on
forum, but the darktable forum has to be replaced soon and does not
generate much activity, so here am I. And sorry if I do spam. That
beeing said...
As a long term Lightroom user, fed up with Adobe policy and silly
functionalities and forever growing hardware requirements, I'm
thinking about trying Darktable, and switching to Linux as well, since
LR is in fact the only software that keeps me using Windows.
As a Micro 43 user, I use a system where algorithmic lens correction
is part of the system : lenses are designed with a subsequent
electronic correction in mind. This "philosophy" is very different
from the Canon or Nikon way of thinking, but it makes Micro 43 users
very careful to lense correction.
Among my current lenses (and former ones for which I can't perform a
custom calibration by my own), many have lensfun profiles, but without
vignetting corrections. There comes my question ...
With Darktable, are profiles mandatory to perform lens correction ?
Because AFAIK, raw data include manufacturer parameters to correct
geometry and vignetting, and LR does typically not need a profile to
correct that.
Best,
Pierre.
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