Curves
A tonal adjustment that maps input brightness values to output values along a freely shaped line.
Formula / rule
Output = f(Input)
Measured in
levels
In depth
Curves is the most precise tonal tool available because it can raise one range while lowering another — a gentle S-curve adds contrast by steepening midtones and compressing both ends. Steeper sections increase contrast and flatter sections reduce it, so the shape is literally a map of where contrast is being spent.
Examples in practice
Lifting the curve's lowest point off the axis creates a faded, matte black that mimics a film print.