FR: adapt initial exposure to embedded jpg

[MStraeten]

Is your feature request related to a problem? Please describe.
In discussions about darktables initial processing there are a lot of complaints about the image being too dark, don’t respect exposure compensation, far away from the embedded jpg…

Describe the solution you'd like
with #11142 darktable got the ability to match exposures between images of a series.
maybe that’s a solution to provide an option to match initial exposure to the exposure of the embedded jpg.
Since that’s just one way to get a proper initial exposure this behaviour could be controlled by a preference setting.

[ralfbrown]

One potential difficulty is the camera's lens distortion correction, which will have been applied to the JPEG but not the RAW. So patches won't exactly match up between the two except at dead center.

Might be worth looking at how RawTherapee handles this in its automatic tone curve matching.

[MStraeten]

maybe a patch containing the whole image is not perfect but good enough. And more than "good enough" won't be achieveable due to so fancy stuff like Canons Auto Lighting Optimizer ;)
It's not trying to get a tone curve matching, just exposure matching as an best guess for an initial exposure setting.

[elstoc]

The recent change to do exposure matching between images, by default, sets average image exposure to 50% lightness when you click the colour picker. You could map the picker to a shortcut.

[MStraeten]

You could map the picker to a shortcut.

Thats a misunderstanding of the requested feature - just follow some endless discussions on usage of exposure compensation - so having an option to match initial exposure to the embedded jpg is quite a different thing that setting something by manual using pickers.

The FR is based on the assumption: an exposure compensation in camera can be made with 2 different goals:

1. scene referred mindset: get the optimum raw file as a starting point for postprocessing
2. display referred mindset: get a proper exposed jpg file

For the 1st goal the scene referred default (with enabled compensation for exposure compensation) is fine, for the 2nd goal a pre-applied exposure mapping can be used.

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