Luminosity Mask
A mask generated from the image's own brightness values, restricting an adjustment to a specific tonal range.
In depth
Because the mask follows the image's actual tones, its edges align perfectly with every boundary in the picture — no hand-painted selection can match that precision on complex subjects like foliage against sky. Masks can be narrowed by intersecting them repeatedly to target very specific ranges such as the brightest two per cent.
Examples in practice
A highlights luminosity mask lets a warming adjustment fall only on sunlit rooftops and nowhere else.