RGB Curve: Area picker misbehaves (multiple versions).

Is there an existing issue for this?

• I checked and did not find my issue in the already reported ones

Describe the bug

It is no longer possible to use the area picker in RGB independent channels mode.

The curve misbehaves (mainly shown in the shadows part) and the nodes are no longer connected to the shown curve.

Steps to reproduce

1. open any raw file
2. activate the RGB curve module, set the method to RGB, Independent channels.
3. click on the area picker (no need to actually select a part of the image)

See the malformed curve

Try to set a node and see it is no longer connected to the curve.

Expected behavior

It should work as the point picker.

Logfile | Screenshot | Screencast

Result of the above mentioned steps:

Commit

Don't know. Just noticed it the previous dev version but haven't used the area picker for a while (5.4.1 is ok)

Where did you obtain darktable from?

darktable.org / GitHub release

darktable version

5.5.0+348~g98b939b7c8

What OS are you using?

Linux

What is the version of your OS?

Debian 13 (latest + all updates)

Describe your system

X11
libgtk 3.24.49-3

Compile options:
Bit depth -> 64 bit
Exiv2 -> 0.28.5
Lensfun -> 0.3.4
Debug -> DISABLED
SSE2 optimizations -> ENABLED
OpenMP -> ENABLED
OpenCL -> ENABLED
Lua -> ENABLED - API version 9.6.0
Colord -> ENABLED
gPhoto2 -> ENABLED
OSMGpsMap -> ENABLED - map view is available
GMIC -> ENABLED - Compressed LUTs are supported
GraphicsMagick -> ENABLED
ImageMagick -> DISABLED
libavif -> ENABLED
libheif -> ENABLED
libjxl -> ENABLED
LibRaw -> ENABLED - Version 0.22.0-Release
OpenJPEG -> ENABLED
OpenEXR -> ENABLED
WebP -> ENABLED

32Gb ram

Are you using OpenCL GPU in darktable?

Yes, but this is not opencl related. Same behaviour is seen when opencl is turned off.

If yes, what is the GPU card and driver?

Nvidia GeForce RTX 2060 SUPER + propriety driver version 550.163.01-2

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

This behaviour is not shown with the latest stable version (5.4.1).

• It does not matter which workflow you use,
• Other modules do not seem to be the problem.
• Not brand specific (tried a nef, cr3 and cr2).
• Interpolation method used also does not matter.

Additional info:

Something more nuanced than mentioned in the above steps to reproduce seems to be going on here.

Yes, those steps end up, initially, with a malformed and non functioning curve and using the window in the RGB Curve module to set/drag nodes does no longer work. But....

If that happens and you then select a portion of the image in the main window the curve and nodes "reset" and it works again.

So, the initialisation of the area picker in combination with RGB, Independent channels goes wrong, which gives the impression that this functionality no longer works.

rgbc.nuances-2026-02-22_08.15.41.mp4

I'll try to bisect this one later on, which might take a while (only good starting point I have is the 5.4.1 stable self compiled version.

[pehar1]

I'll try to bisect this one later on, which might take a while (only good starting point I have is the 5.4.1

I still have a few 5.5.x versions available. 5.5.0+261~g8b6ade32f6 does not exhibit the bug, but I can reproduce it with 5.5.0+295~gc3debd7c8e. So the critical commit must be somewhere in between.

I was not able to get a reliable result using bisect. Every run I tried, oldest being 5.4.1, came up with a different culprit. That might point to an older issue and, after more testing, that seems to be the case.

I can actually reproduce this behaviour on 5.5.0-352-gffad91568b, 5.4.1, 5.2.1 and 4.8.1. It also isn't exclusively linked to the RGB independent channels mode.

Development and 5.4.1 - These two react as described above if the histogram shown in the RGB Curve module shows overexposure.

5.2.1 and 4.8.1 - These two also show it if: You reset the RGB Curve module and the select area mode picker for both independent and linked modes (even if the histogram show a "correct" exposure).

---

I'm not a developer but I'm guessing that it might be quite a challenge to, after all these versions, trace the underlying issue.

There's a workaround (extra step if you like) that makes the initial issue go away:

When you sees this issue after selecting the area picker: Select an area on the actual image. This "resets" the window in the RGB Curve module and now you can use the nodes there to manipulate the curve.

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@TurboGit

I'm not sure if I need to close this one. I'll leave that up to you.

[jenshannoschwalm]

I'm not sure if I need to close this one.

I'd leave it open as a pending bug. It's probably something we could solve if someone get's interested :-) (Haven't used that module at all "for ages")

[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.