When using the “haze removal” module I get “haze removal could not calculate ambient light due to image content” and there is no change to the image.
Darktable 5.2.0
Ubuntu 24.10
Are you able to share the faulty image and xmp file. I can’t see anything wrong with the haze removal module, but I am on Windows DT 5.3.
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Seems to be specific to certain images, all are shot on the same camera. Is there anyway I can share the image and XMP file with you privately?
EDIT: I should have also said welcome to the forum.
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I would like to ask you three questions for possible changes to improve the user experience:
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Have you ever read the tooltip for a module?
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Do you have an expectation that this module should make changes (like “removing haze”) to ALL images regardless of their content?
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Would adding an explanation to the failure message that the dehaze algorithm is not applicable to this image dispel your impression that this is some kind of bug in the program?
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Not that anyone reads it, but it would probably be a good idea to have something in the manual to explain it.
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I would think that an app can only calculate “ambient light” if appropriate exif is available.
For example, if “ambient light” means ‘Light Value’ (Ev - see Exposure value - Wikipedia ) then your image’s exif should at least have f/number (N) and shutter speed (t) - because Ev=log2(N^2/t).
If f/number is 5.6 and shutter speed is 1/1000 then Ev=15 = a nice sunny day outside.
P.S. I have no idea what “distance_max” is, so the above may not apply. It would be odd if, in a series of pictures, some would have exif and some not!
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I wouldn’t say I have an expectation for the Dehaze module specifically, but I often use Darktable modules for creative effects beyond their intended use. So, I do have an expectation that they do something when I use them, regardless of the image.
Incidentally, I have used negative values of Dehaze to add haze on occasion.
I read it. I might be the only one. But I have it bookmarked and refer to it as my first source of troubleshooting.
One module I use for sort of dehazing is the local contrast module applied with some sort of mask which could include a gradient mask. It helps sometimes when I get a spot of crap or water on my lens that causes very localized haze.
I’m interested to hear from a user who considers the current behavior and message from the module to be a possible bug, what could be improved so that it is clear for him from the UI that a particular image simply cannot be “dehazed”.
Well, I think this doesn’t apply to all processing modules. For example, I don’t think you have such an expectation from the “hot pixels” module. 
Sorry, maybe I didn’t understand your original question then. I don’t recall seeing any messages from the module recently, and I haven’t found any bugs with it.
Well, I simply said I expect modules to “do something” when I use them, i.e. have a non-null effect. All I meant was that I expect something to happen when I use a module. If the module can’t do anything, for whatever reason, I would expect a message to tell me why.
But yes, some modules are for very simple operations and I wouldn’t expect more of them, like the Hot Pixels module and other corrective modules.
The OP got a message:
It’s also mentioned in the release notes:
Reduced haze removal visible difference between exports and HQ darkroom processing. For some images the algorithm fails to calculate correction parameters, this is reported via control log.