Hello, (sorry to re-up) I think I’am getting it !
I have explored the code and yes, Rawtherapee does the average but it takes the metadata of the first frame in the batch. This is why it is displaying one image name when checking the ‘auto select’ checkbox.
As an experiment :
Load a random black image from the set.
Crank up the exposure to see what is happening.
Go to Dark-Frame filter, check the “auto select” checkbox, see the modification in the graphic view and note the file name.
Then uncheck the “auto select” checkbox and choose in your dark frames folder the image that correspond to the name you noted before.
See the result is not the same proving it’s indeed averaging the images using the template (49 shots, 1 template).
Now the question is :
How to export this template and delete all the shot to make some space on the HDD ?(making a fake dng with Siril + ImageMagick + Exiftool is not working at all for me).
Edit :
I finally found a fast workflow for generating master bias/dark frames and flat fields [SOLVED] Workflow for creating master bias for Rawtherapee - #4 by Florian_BEAULIEU