How is Active D-Lighting in Nikon DSLRs handled in dt?

Software darktable
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I recently purchased a used Nikon D610 (*). In reading about Active D-Lighting, I find a recommendation to turn this feature off if the post processor is other than Nikon NX Studio, other wise the shot will be underexposed, requiring more tonal correction in the chosen post-processor. This underexposure, is it suggested, might also lead to a noisier image.

Does dt take any notice of ADL data in the metadata?

In an earlier post on this topic (Nov 2018) s7habo says “darktable can achieve much better results than with nikon’s Active D lightning”. Does this suggest I ought to set it to ‘off’? What effect will there be in dt if I set ADL to anything other than ‘off’'?

(*) Camera purchased for DSLR scanning only, with AF Micro-Nikkor 60mm f/2.8D.

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None, ADL applies to JPEGs only

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If I remember correctly, it does affect the exposure as it may underexpose a bit to protect highlights (so for raw shooters it is often recommend to set it to “auto”). This is then automatically adjusted in the camera JPGs. I think darktable does not do this adjusted automatically but you can simply raise exposure a bit as needed.

This of course means a bit more noise in the shadows but at the benefit of less clipping in the highlights.

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Active D Lighting is equivalent to DR400 in Fuji: under-expose the raw by one stop to gain more highlight headroom, and compensate with a tone curve in the JPEG, so midtones stays properly exposed.

The way I deal with that in Fuji should also work for Nikon: a lua script reads the EXIF info to ascertain whether ADL is active, and if so, apply a style that activates an appropriate tone curve.

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Hmm, that appears to contradict a lot of what I read on-line and also in the NX Studio software, which supports ADL on NEFs, by automatically applying information contained in metadata. But what do I know? If I knew I wouldn’t be asking the question.

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is that a Lua script that you wrote for yourself or is it in the lua script ‘library’ ?

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I bought a Nikon and was very excited by D-lighting at first but really all it is doing is what any software like photoshop, Gimp, darktable, Lightroom etc would do with the shadow and highlights tools. I disabled it on my Nikon and reserve that fix for the computer. Of course if you want to continue using it you would need to create a style to apply to raw files that simulates the d-lighting effect. That is possible.

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Some of my code was added to the lua library at some point. I don’t remember which.

At any rate, the script is available at GitHub - bastibe/Fujifilm-Auto-Settings-for-Darktable: Automatically apply Fujifilm film simulation LUTs, crop, and DR correction when importing images in Darktable · GitHub. Obviously, it would need some changes to read Nikon’s ADL EXIF tag instead of Fuji’s DR tag.

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I think it’s recognised and applied in exposure

highlight preservation mode (manual mode)
Some cameras underexpose the raw file in specific modes such as HDR, dynamic range expansion, highlight tone priority, HLG or AutoLightingOptimizer to protect the highlights. When enabled, it restores the withheld exposure (the amount, in EV, is shown on the button). This control appears only when such a mode is detected in the image’s Exif data.
(darktable user manual - exposure)

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With my Canon R7 just sometimes in the exposure module highlights preservation is activated. It brightens the exposure by 0.5 EV extra and in my case I have always the need to turn it off to get the exposure looking how I expected.

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If anyone is interested, the EXIF tags being checked can be found here:

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