Gamma correction

Gamma correction is a nonlinear transformation of signal values that compensates for display response and human visual sensitivity. It is used to encode image values for storage or transmission and to decode them for display.

Transfer function: A mathematical function that maps input values to output values in a system. Gamma correction is defined by the nonlinear transfer function applied to signal values.
sRGB: A standard RGB color space with a piecewise nonlinear encoding curve for display and image exchange. Its familiar curve approximates a power law but includes a linear segment near black.
Cathode-ray tube: An electronic display device that produces images by steering an electron beam onto a phosphor-coated screen. Its nonlinear luminance response helped motivate early gamma-encoding practice.
Gamma value: An exponent that characterizes a power-law relationship between signal level and output intensity. The exponent is a parameter of some curves, not a complete description of every encoding.
Quantization: The mapping of a continuous or finely sampled range of values to a finite set of discrete levels. Nonlinear encoding allocates more code values to darker tones, where visual sensitivity is greater.
Power law: A function in which an output is proportional to an input raised to a fixed exponent. A power law is the common mathematical form of gamma encoding and decoding.
Rec. 709: An ITU-R standard defining image parameters for high-definition television, including a nonlinear signal encoding. Its camera encoding curve is often treated as gamma 2.4, though the exact function is piecewise.
Herbert E. Ives: An American physicist and engineer who studied visual perception, color, and image transmission. His work helped establish the relationship between image-signal encoding and visual response.
Logarithmic encoding: A mapping that represents values using a logarithm to compress a wide range of magnitudes. Logarithmic encoding compresses dynamic range differently from gamma's usual power-law mappings.
Color banding: Visible discrete steps in a smooth image gradient caused by limited tonal precision or processing. Quantization after nonlinear encoding can still produce banding when precision is insufficient.

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