Selective Levels

Masks let you hide or reveal part of a layer, by painting black to hide or white to reveal. You can use them in combination with Adjustment Layers to selectively alter specific areas – like a contrast boost to the subject here. When using masks, highlight the mask thumbnail attached to the Levels layer so the mask is active. Once done, press Cmd/Ctrl+I to invert the mask to full black, then paint white to reveal the effect selectively.