Can you set the base film color manually in negadoctor?
I have a Nikon FH-3 film holder that leaves often no film base in the frame. It should be convenient to copy and paste the film base RGB or HEX as all images on a give roll will have the same base color.
Or how to handle base-less negatives?
Yes,
Thanks!
One off subject topic question:
For negative processing you start with the scene-referred preset or with none?
I always start with “none”.
After a bit of try and fail…
When I switch on negadoctor in immediately inverts the negative - before I set the base film color. Of course that looks pretty wrong.
I use the film base picker - it chooses nearly the whole image. That seem to be wrong either, we want the edge, right?
So I select a edge area anyway, which is now black - and the picker picks up, well, black.
OK, back to square one, delete everything. Negadoctor not enabled. I use the left side are picker. The color is 101,63,52 - I switch on negadoctor, double click the film base color area - I go to customs - I can input a custom color - but in Hex and not in RGB.
I can see when people say it’s not intuitive 
Using this module since it’s appearance in git master, having processed hundrets of negatives, I can assure: this is a fantastic peace of software!
Aurelien Pierre (the author) published a video (inverting photos of color negatives with darktable - #75 by anon41087856) about the module. It is strongly recommended to watch this video first.
You have to enter the RGB values in hexadecimal coding : #RRGGBB. To convert from decimal to hexadecimal you may want to use Decimal to Hexadecimal Converter
The film base also appears in translucent areas, meaning black parts in the inverted image, or white parts before inversion. If you have no such naked film part, then the last option is to tweak this color by eye until it looks good. Or maybe just take a test frame with shifted film to profile the film base once for all. But that part needs to be done carefully, 80% of the final result depends on it.
You can also post a raw so I can get a look.
Thanks. I am just starting with the right setup. Finding film base color somewhere is no problem. I think having an RGB setting option would be a good thing as the value from the left panel picker is in RGB. Currently I lack quality negative material that’s not too degraded. Any RAW donation (with a bit of base) is welcome!
More questions after I watched your video 3 times.
I make ‘a scan’ from a piece of unexposed film. I use that to set the base color in negadoctor. Then I save (or update) a preset, and use that preset for all frames from the same roll (and I always keep exposure the same across a roll ).
There are RGB settings : Dmin red/gree/blue components
Dmin is film base color (https://www.kodak.com/uploadedfiles/motion/US_plugins_acrobat_en_motion_education_sensitometry_workbook.pdf).