This conversation has been merged. Please reference the main conversation: Lightroom: Ability to Invert Adjustment Brush Masks
In Camera Raw, I often control the luminosity of subjects vs. background using the adjustment brush. It would be useful to mask the background, adjust its luminosity, then invert the mask to apply a separate and different adjustment to the luminosity of the subjects. However, as of 3/21/2018, ACR has no facilities to invert an adjustment brush mask and make it available for a separate adjustment. So, my suggestion is to please design such a feature and incorporate it into an ACR update.