Gamma

Gamma is the non-linear relationship between input signal values and output luminance in image encoding, originally derived from the response curve of cathode-ray tube displays and retained in modern digital workflows for perceptual efficiency. The human visual system perceives brightness logarithmically — small steps in dark areas are very visible while large steps in bright areas are barely noticed — so allocating more code values to shadows via a gamma curve produces images that look smooth at modest bit depths (8 or 10 bits). The Rec.709 broadcast standard specifies a camera-side OETF roughly equivalent to gamma 1/2.2 and a display-side EOTF of gamma 2.4 (formalized as BT.1886). DCI-P3 theatrical uses gamma 2.6 for the darker projection environment. sRGB uses a piecewise function approximating gamma 2.2 with a linear toe in shadows. Inside grading sessions, you choose a working space whose gamma matches the intent: log curves (ARRI Log C, Sony S-Log3, RED Log3G10) are gamma-like but stretch a much wider dynamic range; linear-light spaces (ACEScg, scene-linear EXR) have no gamma at all and are used for VFX compositing where mathematical operations like blur and additive compositing require linear data. Confusing gamma with the underlying transfer function or with the working space causes the most common color-pipeline bugs. Reference: ITU-R BT.1886 (display gamma) and the IEC 61966-2-1 sRGB specification.