Clicking the two colour pickers under the masking tab usually does the job for me.
What I find myself looking for is having those controls or a subset on the actual advance graph display so you can adjust it without going back and forth…I know there is a sliding bar display but it really only indicates the span and central locations approximately it would be nice to be able to shift and expand the histogram on the same tab…
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Thank you for making this point. It would be extremely helpful for everyone. This drives me crazy every time I use the tone equalizer. I spend many minutes moving the mask exposure compensation and mask contrast compensation sliders around repeatedly going back and forth between them trying to fill the bar with no orange at either end. I usually never get it right so I give up with orange on one end or the other or the ends not filling the space. 
Every time I do this I think to myself: This sort of thing is exactly what computers are good at doing for me. Why isn’t there a button to click that will expand them properly? Or, why isn’t it done automatically when I turn on tone equalizer? Are there cases when I may want the histogram in tone equalizer bunched up on the graph? I haven’t thought of any, but maybe there are.
I tried that, but it doesn’t seem to work. I ended up with the left end orange and the right end pretty far from the end.
If this automatic function doesn’t work fine, why do you think it would be fine if done automatically everytime even without clicking the pickers?
In cases with orange areas its worth to activate the mask view to see what you‘re doing. If the masked areas are well spread it doesn‘t matter if there’re orange areas that aren’t relevant for correction …
I wonder why bothering about numbers or ranges where having a look on the image/mask can give more value…
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And if that was possible, I would have done it already. But if you can predict the amount of contrast compression that results from a local convolution with built-in variance thresholding, I would be happy to hear it.
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Here are the maths :
That sounds so easy when you talk about it, I bet you will derivate a contrast compression formula depending on \epsilon and r in no time. Then, I will code your auto-mask-exposure the next day, I promise you.
Until then, I can’t code a software solution to a maths problem for which maths themselves have no solution.
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Because I read the manual and saw that it says:
To avoid having to switch back and forth between the advanced tab and the masking tab, under the “mask post processing” label there is a grey bar which shows a representation of the middle 80% of the histogram. By using the controls mentioned below to centre and spread out this grey bar, you can then expect to have a nicely shaped histogram when you return to the “advanced” tab. If you see orange at either end of the grey bar, it means too much of the histogram has moved off the edge of the screen, and you need to bring it back to centre and/or compress it a bit more.
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Okay. From reading the manual it wasn’t clear what was involved. Sorry.
I have just one suggestion: put the masking underneath the advanced tab, like with the drawn or parametric masking on other modules. Now, I’m an old engineer, so take that into account when I say the interface seems perfectly intuitive to me. Thank you, @anon41087856!
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Of course this can be done by looping over possible values on both sliders, to find the best combination. But then don’t complain on a laggy interface since this has to be done on each mouse event on a slider earlier in the pipe that triggers an update of the preview …
The UI could be easier to use if the histogram was visible when the mask exposure compensation and the contrast are adjusted. Would moving those two sliders to the ‘advanced’ tab be a big task?
You can see the area the histogram covers on the slider. It’s more useful to enable display of the mask to see how the areas are spread over the image.
You’re editing an image, not an histogram;)
Maybe it’s just me, but I find it hard to distinguish between -6EV and -8EV on my display, when simply looking at the mask. One should make sure the mask is well spread out, without much clipping, as far as I know.
I adjust the mask exposure compensation and contrast sliders to get the bar moved to a central spot and spread out, but when I look at the histogram, I see that it is not as central as I thought, or not as spread out, or has also frequently happens, it’s too close to the left end, and I see the histogram running up the left side. So I go back to the masking tab and adjust, and go back to the advanced tab, and am still not happy. Rinse. Repeat. How about combining the two tabs as I suggested?
Why do you want to edit the histogram instead of the image?
Turn on the mask, have a look if the areas that needs more or less exposure are properly separated, adjust the sliders until it seems to be ok and then adjust these by scolling the mousewheel while pointing in these areas.
It’s no rocket science - just trust your eyes
From the instructions in the manual about the advanced tab:
" If the histogram is too bunched up, it means your mask doesn’t have a good spread of intensity levels, which makes it harder to independently control the brightness of different parts of your image. It is therefore recommended that the histogram is adjusted so that it extends the entire range, and covers as many control points as possible, thereby providing you with maximum flexibility. You can adjust the mask using the controls in the masking tab."
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What if I do that and the histogram is running up the right or left side; what does that mean? Do I need to readjust or just go with it?
Go with it. If you don‘t need to adjust these areas then they don’t need to be taken into account. You need to spread the range of intensity over the areas you want to adjust.
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Here’s the image:
Masking:
The histogram:
Mask on:
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 …