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ITU-R BT.1886 is the reference EOTF of SDR-TV. It is a gamma 2.4 transfer function (a power law with a 2.4 exponent) considered as a satisfactory approximation of the response characteristic of CRT to electrical signal. It has been standardized by ITU in March 2011. It is used for Rec. 709 ( HD-TV) and Rec. 2020 ( UHD-TV). ^{[1] [2]}

Definition

BT.1886 EOTF is as follows: ^[1]

${\displaystyle L=a(\max[(V+b),0])^{\gamma }}$where

• ${\displaystyle L}$ is the screen luminance, in cd/m².
• ${\displaystyle V}$ is the input video signal level, in the range ${\displaystyle \left[0,1\right]}$.
• ${\displaystyle \gamma }$ is the exponent of the power function and equal to 2.4
• ${\displaystyle a=({L_{W}}^{1/\gamma }-{L_{B}}^{1/\gamma })^{\gamma }}$ is the variable for user gain (legacy “contrast” control)
• ${\displaystyle b={\frac {{L_{B}}^{1/\gamma }}{{L_{W}}^{1/\gamma }-{L_{B}}^{1/\gamma }}}}$ is the variable for user black level lift (legacy “brightness” control)
• ${\displaystyle L_{W}}$ is the screen luminance for white, in cd/m².
• ${\displaystyle L_{B}}$ is the screen luminance for black, in cd/m².

According to ITU, for a better match, ${\displaystyle L_{B}}$ can be set to 0.1 for moderate black level settings (e.g. 0.1 cd/m²) or to 0 for lower black levels (e.g. 0.01 cd/m²). ^[1]

An alternative EOTF has also been provided by ITU for the cases a more precise match of CRT characteristics is required. ^[1]

See also

• Gamma correction
• Transfer functions in imaging

References