Editing Gamma correction (section)

==Terminology==
The term [[luminous exitance|intensity]] refers strictly to the amount of light that is emitted per unit of time and per unit of surface, in units of [[lux]]. Note, however, that in many fields of science this quantity is called [[luminous exitance]], as opposed to [[luminous intensity]], which is a different quantity. These distinctions, however, are largely irrelevant to gamma compression, which is applicable to any sort of normalized linear intensity-like scale.

"Luminance" can mean several things even within the context of video and imaging:
* ''[[luminance]]'' is the photometric brightness of an object (in units of [[candela|cd]]/m<sup>2</sup>), taking into account the wavelength-dependent sensitivity of the human eye (the [[Photopic vision|photopic curve]]);
* ''[[relative luminance]]'' is the luminance relative to a white level, used in a color-space encoding;
* ''[[Luma (video)|luma]]'' is the encoded video brightness signal, i.e., similar to the signal voltage ''V''<sub>''S''</sub>.

One contrasts relative luminance in the sense of color (no gamma compression) with luma in the sense of video (with gamma compression), and denote relative luminance by ''Y'' and luma by ''Y''′, the prime symbol (′) denoting gamma compression.<ref>Engineering Guideline EG 28, "Annotated Glossary of Essential Terms for Electronic Production," SMPTE, 1993.</ref>
Note that luma is not directly calculated from luminance, it is the (somewhat arbitrary) weighted sum of gamma compressed RGB components.<ref name=poynton/>

Likewise, ''[[brightness]]'' is sometimes applied to various measures, including light levels, though it more properly applies to a subjective visual attribute.

Gamma correction is a type of [[power law]] function whose exponent is the [[Greek letter]] [[gamma]] (''γ''). It should not be confused with the mathematical [[Gamma function]]. The lower case gamma, ''γ'', is a [[parameter]] of the former; the upper case letter, Γ, is the name of (and symbol used for) the latter (as in Γ(''x'')). To use the word "function" in conjunction with gamma correction, one may avoid confusion by saying "generalized power law function".

Without context, a value labeled gamma might be either the encoding or the decoding value. Caution must be taken to correctly interpret the value as that to be applied-to-compensate or to be compensated-by-applying its inverse. In common parlance, in many occasions the decoding value (as 2.2) is employed as if it were the encoding value, instead of its inverse (1/2.2 in this case), which is the ''real'' value that must be applied to encode gamma.