Levels

cmd ⌘ + L
Use Levels to adjust shadows, mid-tones, and highlights in the image, selection or layer.

Choose Image ‣ Levels

The levels tool can move and stretch brightness levels in a histogram using three main components: a black point, white point and midtone slider. The position of the black and white point sliders redefine the histogram's black and white points respectively, whereas the midtone slider redefines the location of middle gray (128). Each slider is shown below:

Black point slider.

Midtone slider.

White point slider.

Click to reset values.