Levels
A tonal adjustment that sets the black point, white point and midtone gamma of an image or channel.
Measured in
levels (0-255)
In depth
Levels is the simplest way to establish the tonal endpoints: dragging the input sliders to where the histogram data begins ensures the full range is used. Its midpoint slider adjusts gamma rather than adding a shaped curve, so it lightens or darkens midtones without changing the endpoints.
Examples in practice
Pulling the black input slider to the left edge of the histogram data restores a proper black to a flat, hazy scan.