ITU-R BT.1886

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).

Definition

BT.1886 EOTF is as follows:

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

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

According to ITU, for a better match, $L_B$ 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).

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

See also

• Gamma correction
• Transfer functions in imaging

References

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