Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. Gamma correction is, in the simplest cases, defined by the following power-law expression:

${\displaystyle V_{\text{out}}=AV_{\text{in}}^{\gamma },}$

where the non-negative real input value ${\displaystyle V_{\text{in}}}$ is raised to the power ${\displaystyle \gamma }$ and multiplied by the constant A to get the output value ${\displaystyle V_{\text{out}}}$. In the common case of A = 1, inputs and outputs are typically in the range 0–1.

A gamma value ${\displaystyle \gamma <1}$ is sometimes called an encoding gamma, and the process of encoding with this compressive power-law nonlinearity is called gamma compression; conversely a gamma value ${\displaystyle \gamma >1}$ is called a decoding gamma, and the application of the expansive power-law nonlinearity is called gamma expansion.