Does anyone have a method to batch auto-level a collection? I am finding myself doing this action to each image 
and it is taking forever.
I’ve also tried picking this action from history, but what that does is only remember the actual measurement on that particular photo and apply it to the new one. DT doesn’t really know that it’s supposed to auto-level levels.
Thank you & happy holidays everyone!
This is not a common thing as you would not normally do this for scene referred edits but it should be possible using a Lua script…
Thanks for taking a look, Todd. Unfortunately, I’m unfamiliar with Lua scripts, and what is a ‘scene-referred’ edit?
It may not be common for you, but it’s definitely a feature that’s growing on my continued use of DT 
Hi Mike!
I’m not very good at explaining this sort of thing… best I can do is point here: darktable 4.6 user manual - process
It’s definitly better than my attempt 
Edit: just discovered that @pehar beat me to it with a link to a more detailed bit in the manual 
You can speed up the process a little by setting up a shortcut.
I have the letter “k” assigned to “toggle the button” for the “white relative exposure button” in filmic.
You might need to delve into the depths of the shortcut process, but it does work well
Others have provided links but in short DT is designed to do scene referred edits. The goal is to preserve as best you can the scene lighting. Levels won’t clip data but the UI is using a 0 to 100 scaling of the data. Doing scene referred edits it is best to set exposure in the image or for a portion of the image to expose well the midtones so essentially setting middle grey as your anchor. Then you use something like filmic to map the dynamic range around that point. The added exposure until that point will likely push the data past 100 percent so levels cannot control it. What you are doing with levels I think you would normally do by setting white relative and black relative with filmic to handle dynamic range…If you do use levels be sure to use RGB levels…
Can I ask what you are using auto levels for and what you are hoping to achieve with using auto levels? The reason I ask is that there may be a better way or module to achieve what you want.
A point I think is that plain ‘levels’ comes after filmic/sigmoid/base curve by default, so I don’t think it’s neccessarily a ‘bad’ idea to use it for fine tuning in that position? Of course, this is assuming one is using one of the 3 tone mappers… and of course RGB levels can be moved… just think there’s a few possibilities here
I just prefer it as it avoids a trip into LAB processing…perhaps not such a big deal but with both versions why not. I likely would always use it post tone mapping I think if I was going to …I guess to stretch the DNR if there was still room but to that end I tried on purpose to add too much white relative and then stretch it with auto levels and then set relative white correctly . There was not much benefit if any to the look that I could see…maybe a quick and dirty way to tweak the midtone slider for a final small adjustment??
It would be interesting to see exactly how people are using levels. I think for me I would just be using rgb curves to do anything that might be done with levels??
Yup… I have used RGB levels, but not often, and I can’t remember what for. But I don’t think I have ever used Levels.
I have done a midtone adjustment this way, post filmic, a few times, mostly when I’d spent a while getting everything else just right, and only wanted a minor adjustment.
Still, I’m sure it has it’s place in certain workflows - I say this because I’ve thought before “nobody would ever use that” and then discover that there’s a very good use case!