Here’s the image:
Just looking at the masked image, I would not know that the histogram runs up the right side. If I try to reduce the exposure of the bright lights some, would I be missing out on the brightest pixels?
you are watching the mask, not the greyscale representation of the image and the histogram of the mask. The histogram tells you there’s a lot of dark stuff and also some brighter areas and even a few highlights in the mask.
So now the main question is: what do you want to brighten or darken in your original image?
if you want to darken the areas being displayed white in the mask you can do it directly in the image. Of course you can do it by moving the rightside points on the histogram but why trying to find the right node if you can do this at the right place in the image?
If you want to brighten the hoses right and left of the bus simply point there an scroll - the mask shows these are well separated from the dark areas behind the bus (even these are similar dark in the original image). And also her: no need to find the appropriate node in the histogram …
I think this is what I was getting at in my earlier comment…it would be nice to have those controls under the graphic display rather than in a separate tab. Sadly I am not clever enough to write the code for this but I would go to two tabs if I was clever enough to code this… I would keep the simple tab as is for the reasons mentioned above and then in advanced I would use the space where the current graph is displayed as display area where you could toggle the graph and the mask in that space and I would place the controls underneath that …thus you move controls and toggle between the mask histogram display and actual mask to evaluate…there may be too many technical challenges to achieve this…
I am still a relative beginner (about five months since I started seriously trying to learn darktable), and I will say that the Tone Equalizer module is one of few that I feel that I do have some understanding of how to use.
About 5 years ago ACDSee had a big discount on ACDSee Pro 9 so on a whim I bought it. I didn’t switch over to using it as my main program, but I played with it quite a lot and it had many very good points. I have it installed on another computer at another location, but I don’t have it on my current computer. One thing that was quite nice was what they call their Light EQ. As the name sounds, it is a tone equalizer that can be set to 2, 3, 5, 7, or 9 lighting zones or bands. Anyway, here is some good info I found about it:
Maximizing Dynamic Range with ACDSee
Using ACDSee Light EQ™ to Quickly and Effectively Edit Landscapes
ACDSee Light EQ™ Technology
When it comes to lighting adjustments, you have found yourself the right software. Not only does ACDSee have a range of lighting tools that allow you to approach your adjustments from a variety of angles, but we are also known for our patented lighting technology called Light EQ™.
Thanks for your response. I didn’t indicate that the image was a BW development. Are you referring to the histogram running up the right side? Is the only time a mask is no good is when the orange triangle appears?
I do everything else you describe now, e.g., using the scroll wheel. It’s just that since the beginning, I have understood from the videos and discussion that the histogram should be spread as wide as possible within the boundaries and centered as well as possible.
When I move the cursor into the bright areas in front of the bus, the histogram vertical line moves all the way to the right side. Since my interpretation is that the mask is clipping, something or somehow, I assume that I am missing out on adjusting some pixels.
I’m with Bill here. Martin your responses suggests the user wouldn’t want to adjust the whole range. But I don’t use tone eq on every image, and the only time I seem to use it is on high dynamic range image with bright highlights and dark shadows. In this case I definitely want the whole range to play with, to boost shadows and drop highlights, and its much more flexible doing this across the whole range, then across just a few ev. Often not even possible across just a few ev. So it is important to set the mask histogram properly to begin with. As others have suggested, this requires going back and forth between two tabs a lot, as the grey guide in masking tab can’t be trusted. Because it can’t be trusted, it is not very useful. Given this, having it all in one tab, with the mask exposure and contrast sliders underneath the mask histogram would be MUCH better for the user. Of course, I don’t know the complexity of coding this way. I assume there is a good reason it’s not already, and if that reason is performance speed, then it’s understandable. But to suggest users don’t need the mask histogram covering the whole range, limiting the tools capabilities, is the wrong answer, when often times we do - not because we are editing the histogram, but because the placement of the histogram allows for different results in our image.
My guts agree with yours, but it might be more familiar/obvious if the controls were flipped 90°.
Speaking of audio equalizers, if I may further muddy the opinion waters, a parametric EQ mode for the advanced tab would be superb, and an ideal solution for bringing more consistency across the contrast equalizer, denoise (profiled), and color zones modules as well.
A parametric EQ would provide more control, consistency and clarity IMO, but limited screen real estate would likely be an issue.
Thank you! Of course I did not have all this in my mind. Since I unfortunately did not spend enough time on it 
However I’m still hoping to contribute something by discussing some ideas.
So what about forgetting about absolute Values on the x axis (0, -1, … -8 EV)? After applying the eigf you get a mask which could be interpreted as an random lightness scale. Your x axis anchors in the advanced tab could just be evenly spread between some minimum and maximum value (e.g. 0%, 10%, 20%, … 100%).
Is this a useful thought?
Or do the values internally overflow?
Do outliers hinder this approach?
I just think that your software is great and should be used by more people. However many people wont have the endurance of adjusting masks that much. Therefore some slight simplifications would be really great 
I will try to just set the histogram of the mask and then use mouse scrolling but my attempts to get the masking to a way in which I feel that it is useful to me in a way that I am in control and directing it has evaded me. I do use it a lot for shadows…the relight preset is fantastic sometimes with no adjustments…or I will slide the exposure comp to shift the mask a bit or use some opacity or tweak the gaussian shaped curve it uses…this I can control when working with shadows its fantastic as for toning a whole image I am not there yet
Unfortunately, the mask display is affected by modules that come after it, so to be able to trust your eyes (for the mask) you need to disable them. Ideally, the mask should not be processed by the pipeline, but it seems not to be possible (tone equalizer: displayed exposure mask affected by iops coming later in the pipeline · Issue #3211 · darktable-org/darktable · GitHub)
An example: after enabling the mask and adjusting its exposure:
If I trusted my eyes, I’d think the mask was wrong.
The only way to display the real mask (so you can trust your eyes) is turning off both colour calibration(***) and filmic (plus any other modules coming after tone EQ in the pipeline, if you have them enabled):
(***) @anon41087856: I find it weird that turning off colour calibration (but not filmic) dramatically changes the mask display – compare with 1st screenshot (not that important from a usability point of view, as I usually use the mask histogram and then disable the mask; I never disable filmic and CAT to edit the mask, only did that to create this post):
The main question is: are the areas you want to adjust properly separated in the mask? You can’t get this information just from the histogram.
I don’t see any difference between the 2 screenshots.
example: after enabling the mask and adjusting its exposure:
turning off colour calibration (but not filmic):
Let me be clear, when I set the levels, I look at the image. I use a combination of scrolling the wheel. I also move the curve on the advanced tab and move the sliders on the simple tab. But I am watching the image. That said, besides what the manual says about setting up the histogram, IIRC, @anon41087856 said somewhere that it is better if the 0 point on the curve is not lower than the -1 point, and likewise, the -8 should not be higher than -7, and the curve should crossover at -4. So, I have always considered an ideal spread of the histogram to be from -7.5 to -0.5.
Maybe that’s not true, but that is what I have aimed at doing, and to get my ideal histogram, I find that I have to go back and forth multiple times between the masking and advanced tab. So, that is why I would like to see them combined. I am not a programmer, and if you said it’s a lot of work and not of a high enough priority, so be it.
2020-05-31_18-44-09_P1030264.RW2 (11.2 MB) 2020-05-31_18-44-09_P1030264.RW2.xmp (6.8 KB)
Try with these files: enable the mask in tone EQ, and toggle colour calibration.
Seems to be an issue with mask display:
Switch color calibration off: mask changes
In tone eq switch mask display off and on: old mask is back again.
Switch color calibration on: mask changes
In tone eq switch mask display off and on: old mask is back again.
…and so on.
dt 3.4.0 win
I got my instruction and methodology for this module from a Bruce Williams video. I turn on the mask and alternate between the Advanced and Masking tabs until I get the histogram spread from one node in to the left and one node in from the right (i.e., -7 to -1). Then, I turn the mask back off and use the cursor adjustment thingy to bring the shadows up and the highlights down.
But, then I saw a later Bruce Williams video where he said he hardly ever uses the Tone Equalizer. Who knows?
My issue comes when trying to evaluate the different norm models. They give completely different starting points. If you have something that is okay and just want to try one of the other norms everything changes dramatically and you have to start again moving sliders under that norm…if the norms could be useful it might help if there was not so much moving back and forth to check and see what kind of mask histogram is created but maybe that is again just a nuance I have not mastered. I was playing with it last night…under the defaults you get a histogram that looks a bit like a normal image histogram…likely why that can fool people but when I changed to a couple of the different norms to see what I would get I got a much different histogram with a series of spead out peaks …so maybe not so much for practical use but for troubleshooting or experimentation it might be nice to be able to visualize it all from one tab…in any case I have uses that I apply it for as I said the shadows but as for mastering getting an nice mask…I’m not in control of that at all…maybe just more practice…
If I remember right, the guide covers 80% of the graph, what if that was changed to 90% or 95%? It would then cover a larger spectrum and it would make it easier to identify, if the graph bumps into the end.
