Hi everyone,
I made a new iop module designed for removing fringes that come from
longitudinal chromatic aberration. This means CA that is evenly
distributed across the picture and not a geometrically centered
distortion - so something that can not be solved with lens profiles.
Often it is seen as "purple fringing" but can also be red/green.
However, the approach works phenomenologically, doing a kind of
edge-detection on high-saturated edges (A+B channels in Lab space),
similar to what RAW Therapee does, but with some enhancements and
options - this should be tuned for LCA however, as TCA can also be
removed with auto CA removal ("chromatic abberations") or lens profile
based ("lens correction").
I am still not entirely sure about it, as there are still some issues:
1. speed (some things can be optimized, but not sure how much they will
help)
2. how effectively it is in reducing LCA and at the same time not
modifying other parts of the image
So for that I need some of you guys, hope some of you can try it on
their pictures *which can not be corrected with lens profiles or auto CA
correction*. I know that defringe can also work on "geometrical CA"
(TCA), but it should be optimized for LCA, as there is currently no
module optimized for that in dt.
Please use either of those modules and after that check how to remove
the remaining CA/fringes with the defringe module.
Here is the branch: https://github.com/bluesceada/darktable/tree/defringe
and my pull request: https://github.com/darktable-org/darktable/pull/326
I am interested in possible issues for your picture examples, and some
ideas for "sane defaults". If you read the code and have some ideas for
improvements directly on that level, that would also help me!
Thanks for trying and any useful feedback!
Dennis
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