this occurs with any GFX100s 14 or 16 bit RAW with substantial shadow lift
to be visible, it needs an area of the image that is very dark (eg a cloudy night sky), which makes the banding obvious
settings for exposure, noise reduction, vignetting/lens-corrections etc modify the banding pattern but do not eliminate it
it is possible to see the banding with all corrections off except for exposure and a shadow lift
it is not affected by how the image processing is performed (GPU, CPU, etc)
This only happens with very large exposure corrections (typically 4 stops), but when it happens it is very visible in shadow areas. It does not happen with Adobe RAW or CaptureOne converters.
Normally, you would not push the exposures so much. But the GFX has essentially two sensitivities, at ISO100 and ISO500, and is otherwise fairly ISO invariant. This means that for high contrast night shots, rather than lifting ISO in camera, it is often better to deliberately under-expose and lift shadows in post-processing (thereby preserving highlight detail that would otherwise be lost). It only affects a small number of images where you are trying to process something with very high contrast, but when it does, it is very obvious.
My guess is that this is not a ‘bug’ in the usual sense, but instead a bottleneck in the DxO image processing pipeline. It looks as if there is a processing stage where data is being clipped to ~12 bits, which would explain why I do not see this with Olympus images (ie the Olympus RAWs are themselves only 12 bits).
I can post a raw file, but be aware that it is ~100MBytes in size. However, there is no image processing adjustment that will avoid the problem (you can turn all corrections off except for the exposure). It is something that needs to be looked at by DxO.
Weird then, because theoretically the pipeline has been entirely reworked for Wide Gamut to give more precision.
Frankly, on my Nikon bodies (D700 and Z6) I have never seen such artifacts, except ONCE when I was using a lens without DxO profile on PL3: I had used manual vignetting correction, and it gave somewhat similar results to what I am seeing here (but MUCH less severe, nonetheless).
It has to do with the fact that DxO rewrote the whole processing engine when they introduced Wide Gamut, and according to what they have explained, with that rewriting all the internal calculations are now done at 32 bit precision. So that makes it even more unexplainable.
In theory, a Wide Gamut would even be WORSE in terms of posterization than a restricted one like sRGB (=more colors to be represented with a limited number of bits). But at 32 bits it really shouldn’t matter.
J’avais régulièrement ces traces en auréoles sur des fonds unis (ciels bleus…) en traitant mes raw issus d’un Sony NEX7, je crois me souvenir qu’il s’agissait alors de PL5. Comme je voyais aussi parfois le même genre de traces sur des images vidéos reçues sur ma TV (Sony Bravia), j’en avais conclu que le problème se trouvait chez Sony et ses capteurs de format APS-C qui sont très courant chez les filmeurs documentaristes.
En tout cas je n’ai plus jamais eu ce problème avec mon Nikon Z plein format.
I am happy to put the RAW and DOP files online for DxO to take a look, but I can not upload a 100MB RAW file directly to this thread.
In any event, it is trivial to reproduce with the GFX100s - just under-expose and push the exposure. Maybe it is something specific to the RAW processing for that camera. But it is not a problem with the camera itself, because the same RAW file processed in other converters does not show the banding.
Re the lens profiles, this image is indeed one with a lens for which there is currently no profile. However, the problem occurs also with fully supported lenses. Enabling and disabling the lens vignetting and distortion changes the pattern of the bands. Disabling both corrections gives the same result as deliberately deleting the lens profile.