The Opto-Electronic-Transfer-Function (OETF) is a correction function that compensates for the human perception of brightness and the nonlinearities ofimage sensors.
Since the conversion of the brightness signals falling on the image sensors generates a nonlinear electrical voltage, the OETF function compensates for these nonlinearities between brightness and generated voltage. In analog imaging, this effect is called gamma distortion. For display purposes, the corrected images are subjected to a further compensation in which the voltage for the image pixels is adapted to the human perception of brightness, the gamma correction. This is called Electro-Optical Transfer Function( EOTF) in the display.
The OETF and EOTF functions are part of the BT.709 for HDTV and BT.2020 for UHDTV standards. The compensation functions can be according to different nonlinear or logrithmic curves. Perceptual Quantization( PQ) and Hybrid Log Gamma( HLG) are specified in the SMPTE standardST.2084.