Standard-dynamic-range video (SDR video) is a video technology which represents light intensity based on the brightness, contrast and color characteristics and limitations of a cathode ray tube (CRT) display.[1] SDR video is able to represent a video or picture's colors with a maximum luminance around 100 cd/m2, a black level around 0.1 cd/m2 and Rec.709 / sRGB color gamut.[1][2] It uses the gamma curve as its electro-optical transfer function.[1][3]
The first CRT television sets were manufactured in 1934 and the first color CRT television sets were manufactured in 1954.[4][5] The term "standard-dynamic-range video" was adopted to distinguish SDR video from high-dynamic-range video (HDR video), a new technology that was developed in the 2010s to overcome SDR's limits.[1][6]
Conventional gamma curves:
The linear part of the conventional gamma curve was used to limit camera noise in low light video but is no longer needed with high dynamic range (HDR) cameras.[8] An example of a conventional gamma curve would be Rec. 601:
ITU-R Recommendation BT.1886 describe the reference EOTF of SDR.[3] It's a gamma curve representing the response of CRT to video signal.[3] It has been published by ITU in 2011.[3]
Atransfer function that is closer to Weber's law allows for a larger dynamic range, at the same bit depth, than a conventional gamma curve.[10] HDR standards such as hybrid log–gamma (HLG) and SMPTE ST 2084 allow for a larger dynamic range by using a different transfer function.[10][11] HLG is compatible with SDR displays.[12]
In some cases the term SDR is also used with a meaning including the standard color gamut (i.e. Rec.709 / sRGB color primaries).[1] HDR uses wide color gamut (WCG) such as Rec. 2020orDCI-P3 color primaries.[1][13]
The dynamic range that can be perceived by the human eye in a single image is around 14 stops.[10] SDR video with a conventional gamma curve and a bit depth of 8-bits per sample has a dynamic range of about 6 stops, assuming a luminance quantisation threshold of 5% is used.[10] A threshold of 5% is used in the paper (instead of the standard 2% threshold) to allow for the typical display being dimmer than ideal. Professional SDR video with a bit depth of 10-bits per sample has a dynamic range of about 10 stops.[10]
While conventional gamma curves are useful for low light and are compatible with CRT displays, they can only represent a limited dynamic range.[10][11] Standards require SDR to be viewed on a display with the same characteristics as a CRT (i.e. 100 nits peak brightness, gamma curve, Rec. 709 color primaries).[1][3] However, current displays are often far more capable than CRT's limits.[1] On such displays, higher brightness and wider color gamut can be displayed by adjusting and trying to enhance the SDR picture.[1] HDR is however required for the creative intents to be preserved.[1]
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Standard- and high-dynamic-range color representation
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