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I just have observed a strange behavior in Darktable (Fedora 32, darktable-3.2.1-1.fc32.x86_64): when looking at the image with 'fit screen', it is much darker than the 100% view. After saving the image in 16bit TIFF and opening it with GIMP, I can see that the 100% view is much closer to what GIMP shows.

More: in Darktable, going from 100% to fit screen gradually, I can see the image getting darker and darker.

Why is this? Mabye a config thing? A Bug?

Here you can see screenshots with the two views of Darktable, and the 16 bit Tiff opened with GIMP (or with Darktable itself!):

enter image description here

EDIT: Just filled a Bug report.

EDIT2: The problem is MUCH more serious than I thought, and it is not related to zooming the view: Darktable saves an image that is underexposed with respect to the one shown at the screen. This does not happen with TIFF files, but do happen with my RAW files.

EDIT3: As you can check it by yourself, Darktable team was extremely rude and closed the bug report without a reason. So do not expect this to be fixed anytime soon. I'm glad that I use RawTherapee!

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    What is the format of the file you're looking at in darktable – is it RAW? What happens if you view the TIFF in darktable at 100%?
    – Kahovius
    Aug 22, 2020 at 19:03
  • The file is an Olympus RAW (.ORF) file. If I save it as tiff and open it with darktable it looks dark, with blocked shadows. So the only different is viewing the RAW at 100% in darktable.
    – Luis A. Florit
    Aug 23, 2020 at 0:30

1 Answer 1

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Two options come to mind.

1).
Darktable is showing you a representation of the RAW data, processed through it's own 'pipeline' - a series of computations that converts that data into something you can see on screen. One of the early stages is de-mosaicing where the sensors data is converted into RGB values for each pixel. This can be complex and slow so Darktable allows the user to set the quality of display for different sizes of display.

eg.

8.1.2. Lighttable
don't use embedded preview JPEG but half-size raw
Check this option to not use the embedded JPEG from the raw file but process the raw data. This is slower. (default off).
high quality thumb processing from size
If the thumbnails size is greater than this value, it will be processed using the full quality rendering path which is better but slower (default 720p).

8.2.1. Quality
demosaicing for zoomed out darkroom mode
Interpolation when not viewing 1:1 in darkroom mode: “always bilinear (fast)” is fastest, but not as sharp. “at most ppg (reasonable)” is using ppg + interpolation modes specified below, “full (possibly slow)” will use exactly the settings for full-size export (default “at most ppg (reasonable)”).

2). Darktable has lots of settings for colour management and applying icc profiles. The Colour Management System (CMS) uses the profile to make the display of the RGB values appear the same across different pieces of software and device. For Gimp and Darktable to display the image the same they must both be using the same icc profile and display intent. Both software's try to use the system display settings but it may be worthwhile checking what the setup is.

see 3.2.6. Color management in the Darktable manual.

and Chapter 11. Color Management with GIMP and 1.3. Color Management in the GIMP manual

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  • Tried fiddling with the suggestions above without any luck. I don't think it has anything to do with color management since the fit-screen views are equal. In fact, it has nothing to do with GIMP: the 100% view of the saved TIFF has blocked shadows where the 100% view of the preprocessed RAW does not, even when seen through Darktable. It seems a bug to me.
    – Luis A. Florit
    Aug 23, 2020 at 13:34
  • Fair enough. At least it gives you a bit of background for your report. Darktable 3.2.1 is new and unusual in that it is a major summer release rather than the usual Christmas update. I haven't had the chance to try it much myself, but hopefully you can help to find a solution and post an update here.
    – dmkonlinux
    Aug 23, 2020 at 15:54
  • I will. I posted 5 more ScreenShots in my bug report showing the comparison with rawtherapee. It seems to me that there is a bug in the RAW conversion. I hope this only affects ORF files.
    – Luis A. Florit
    Aug 23, 2020 at 17:58
  • As you can check it by yourself, Darktable team was extremely rude and closed the bug report without a reason. So do not expect this to be fixed anytime soon. I'm glad that I use RawTherapee!
    – Luis A. Florit
    Aug 23, 2020 at 19:40

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