Gamma correction

The effect of gamma correction on an image: the original image was taken to varying powers, showing that powers larger than 1 make the shadows darker, while powers smaller than 1 make dark regions lighter. This is not the actual gamma the picture has, though.

Gamma correction or gamma is a nonlinear operation used to encode and decode luminance in video or images.

Gamma correction is, in the simplest cases, defined by the following power-law expression:

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

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

A gamma value $\gamma <1$ 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 $\gamma >1$ is called a decoding gamma, and the application of the expansive power-law nonlinearity is called gamma expansion.