The Exposure module has a parameter “clipping threshold”, which as documented in the dt manual:
darktable can calculate correct black level and exposure values for your image based on the content of a rectangular area. The adjustment slider lets you define what percentage of bright values are to be clipped out in the calculation. Pressing the icon starts the calculation and lets you draw a rectangular area of your choice using your mouse. This feature is only available in “manual” mode.
You can indeed draw different rectangles on the image to affect the calculation, and use the clipping threshold slider to alter the result. What you cannot do is turn it off, unless you reset the Exposure module to its defaults or throw away the results of the Exposure module by clicking the previous item in your history stack. You can click the color picker, and it toggles between highlighted and non-highlighted states, but it has not effect on the result…once it’s on it’s on.
Is it the intended behavior of the tool that once it’s on it’s irrevocably on?
- Ubuntu 18.04 LTS
- dt 3.2.1 from http://ppa.launchpad.net/ubuntuhandbook1/darktable/ubuntu