Support for external flatfield files

[progo]

Is your feature request related to a problem? Please describe.

Some lens/sensor combinations can exhibit radial color shifts towards the edges of the frame, including so-called "Italian flag syndrome". This is very difficult to correct using standard color correction modules.

Describe the solution you'd like

To correct the Italian flag problem, the best practice is to maintain a collection of flatfiles, stored as raw files. Such a flatfile can be loaded to any old raw file to compensate the color shift and vignette. This is how rawtherapee and ART implement it.

Darktable 4.2.0 has some flatfield support but it doesn't support reading external raw files as input data. And I am not quite sure if the implemented functionality does exactly what the ART equivalent does.

Alternatives

Additional context

Related issues include at least these two: #8728, #1963

[github-actions]

This issue has been marked as stale due to inactivity for the last 60 days. It will be automatically closed in 300 days if no update occurs. Please check if the master branch has fixed it and report again or close the issue.

[github-actions]

This issue has been marked as stale due to inactivity for the last 60 days. It will be automatically closed in 300 days if no update occurs. Please check if the master branch has fixed it and report again or close the issue.

[PeterWem]

I have the same issue with Canon EF 800/5.6 IS USM. Especially when taking pictures of something with a blue sky in the background.

[github-actions]

This issue has been marked as stale due to inactivity for the last 60 days. It will be automatically closed in 300 days if no update occurs. Please check if the master branch has fixed it and report again or close the issue.