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:

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

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

According to ITU, for a better match, [math]\displaystyle{ L_B }[/math] 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