Move the .cht definitions out of colorchecker.h to textfiles

[TutajITeraz]

Is your feature request related to a problem? Please describe.
I cannot add my own pigment-based checker card to darktable.

Describe the solution you'd like
Half solution:
Move the .cht definitions out of colorchecker.h to textfiles (as a csv, json or .cht file) so everyone could add own color calibration cards by adding new files to the folder.

Full solution:
Add GUI color checker card editor. It could be usefull for the darktable-chart too.

PLUS:
Add button to run darktable-chart from main darktable app. (Usefull for flatpack version).

Alternatives
Now i need to edit the src/common/colorchecker.h file manually and recompile darktable. It is not possible due to #17854 issue.

[Donatzsky]

Already proposed - and rejected - in #8705

[TutajITeraz]

Dear @Donatzsky this is not the same case.
I'm a painter and I'm using high quality pigments with known LAB values.
I have access to the official x-rite color card and calibration tools. This is not about cheap chinese replacements. I just want to calibrate to different pigments that are not present on the common used color cards.

[Jiyone]

It could be the same as the in/out color profiles, those added in the folder will be loaded in the module's profile list.
I use transparency IT8 charts for slide film and that could help.

[jenshannoschwalm]

It could be the same as the in/out color profiles, those added in the folder will be loaded in the module's profile list.
I use transparency IT8 charts for slide film and that could help.

Agreed. If someone does a working PR i would certainly support that.

[Jiyone]

I already tried to code something some years ago but my skills were not good enough 😅

[jenshannoschwalm]

Maybe they have improved ?

[jenshannoschwalm]

Maybe even some dev on some dt fork might be interested ?

[Jiyone]

Maybe they have improved

They have but this will still take time to code.

I don't know who might be interested, this is a feature for film photographer using an IT8 chart and they are a few.

Instead, I just added my own chart values hard-coded in the colorchart file.

[victoryforce]

They have but this will still take time to code.

Everyone will have to spend time coding. But others don't even have a personal interest.

I don't know who might be interested, this is a feature for film photographer using an IT8 chart and they are a few.

The code for implementing the functionality requested in this issue is fundamentally simple... the only problem is niche nature of this functionality. Therefore, active contributors will most likely not take on it, because they always have more priority tasks.

This is exactly the situation when the "scratch your own itch" principle applies.