Gamma Correction

This effect lightens or darkens a clip without substantially changing the shadows and highlights. It does this by changing the brightness levels of the midtones (the middle-gray levels), while leaving the dark and light areas unaffected. The default gamma setting is 1.0. In the effect's Settings dialog box, you can adjust the gamma from 0.1 to 2.9.

Applying Effects > Video effects included with Premiere > Gamma Correction