I have a Canon CR2 that I’ve been editing in darktable 4.6. I used the duplicate manager to create two duplicates of this image. When editing the second copy of the image, suddenly when changing settings in a module (in this case it was raw denoise but I don’t think the specific module matters), a line of banding appeared at the bottom of the image as seen below.
Since both of these are being rendered from the same RAW file, it’s puzzling that this would occur on one of the duplicates but not the other. Now that this has occurred, I can’t seem to get rid of it (e.g. going back in the history stack or disabling modules has no effect on the banding). I’ve noticed this effect on other photos I’ve edited in the past too (I thought it was some corruption in the RAW file until I just saw it happen before my eyes while editing). Has anyone seen this before and if so what can I do to get rid of it? Thanks!
I noticed that the “crop” isn’t quite the same in the two versions: the zone that shows the vertical banding is absent from the first image (very visible at the darker area just right of the black “crack”).
I agree with @rvietor and also on some of my CR2 files from my Canon G16 I get a similar issue that the borders sometimes have a dark fringe and it seems that DT is showing more than what is in the JPG version and this is some minor edge artefact. Ultimately I just crop it away.
EDIT: I opened the same image in Art and it is cropping so much more in from the edge of the frame. Maybe DT is just not cropping correctly for your CR2 file.
Are you saying that you have made two duplicates… and both have the same edit but look different after you changed one module and then changed it back?? You mention raw denoise…you have to be very gentle with that … I was just not 100% clear as one example shown is darker. They are the same physical size in your snippets but much different in file size so in any case I am wondering if you can look at the xmp files again to be sure they are equivalent…or copy it to a new file and see if the problems follow it…
Good idea. I did have it on but turning it off doesn’t seem to make a difference. If I copy the CR2 to a new folder where there are no XMPs present and open it with darktable --library ':memory:' --configdir /tmp/ then it opens fine without the banding on the bottom.
You’re right! Here’s a comparison of the original CR2 (opened with the command above) compared to the version with the banding:
I tried just enabling crop (it was disabled in both of these duplicates) and cropping away those few pixels at the bottom, but when I do that, the resulting image’s height is 3125px, but the other copy of the duplicate (the one which doesn’t show this distortion) has an export height of 3158px, so it seems like something legitimate is getting lost (e.g. the whole image is shifted up when this banding appears).
Two duplicates with different edits and using a different set of modules. I just happened to be using raw denoise on the second duplicate when the problem occurred, but I don’t think it has anything to do with that module itself (e.g. disabling it, resetting the module, etc makes no difference).
If you duplicate the corrupt duplicate is it corrupted as well and or if you load the sidecar from it onto a fresh original duplicate image does that also show the issue…
Copying the corrupt XMP to a new folder with a copy of the RAW still causes the banding to appear. Duplicating via the “duplicate” button causes the newly created duplicate to still have the banding. Duplicating via the “original” button does NOT reproduce the banding.
I got it! It was bad values in lens correction:
bad values:
good values (after I manually re-selected the lens):
After I re-selected the lens, the banding has disappeared. Thank you for the help solving this!
