Standard-dynamic-range video

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/m^2, a black level around 0.1 cd/m^2 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]

Technical details

Transfer function

Conventional gamma curves:

• Opto-electronic transfer function (OETF):
  • Rec. 601 (analog video signals in SD-TV digital video form)[7][8]
  • Rec. 709 (HD-TV)[8]
  • Rec. 2020 (UHD-TV)
  • sRGB
• Electro-optical transfer function (EOTF):
  • ITU-R BT.1886 (SDR-TV)[3]
  • sRGB (monitors, printers, World Wide Web)[9]

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:

${\displaystyle E={\begin{cases}4.500L&L<0.018\\1.099L^{0.45}-0.099&L\geq 0.018\end{cases}}}$

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]

A transfer 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]

Color gamut

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. 2020 or DCI-P3 color primaries.[1][13]

Dynamic range

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]

Displaying SDR video on modern displays

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]

References

1. "HDR (High Dynamic Range) on TVs explained". FlatpanelsHD. Retrieved 2021-04-25.
2. "ITU-R Report BT.2390 - High dynamic range television for production and international programme exchange". ITU. Retrieved 2021-04-29.
3. "BT.1886 : Reference electro-optical transfer function for flat panel displays used in HDTV studio production". www.itu.int. Retrieved 2021-04-24.
4. "15GP22 Color CRT". Early Television Museum. Retrieved 2016-02-02.
5. "Early Electronic Television". Early Television Museum. Retrieved 2016-02-02.
6. "CES 2014: Dolby Vision promises a brighter future for TV, Netflix and Xbox Video on board". Expert Reviews. 6 January 2014. Retrieved 2021-04-24.
7. "BT.601: Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios". ITU.
8. "Study Group Report High-Dynamic-Range (HDR) Imaging Ecosystem". Society of Motion Picture and Television Engineers. Retrieved 2016-02-02.
9. Michael Stokes; Matthew Anderson; Srinivasan Chandrasekar; Ricardo Motta (November 5, 1996). "A Standard Default Color Space for the Internet – sRGB, Version 1.10".
10. T. Borer; A. Cotton. "A "Display Independent" High Dynamic Range Television System" (PDF). BBC. Retrieved 2016-02-02.
11. "Dolby Vision White Paper" (PDF). Dolby Laboratories. Retrieved 2016-02-02.
12. "High Dynamic Range" (PDF). European Broadcasting Union. Retrieved 2015-11-01.
13. "BT.2100 : Image parameter values for high dynamic range television for use in production and international programme exchange". www.itu.int. Retrieved 2021-04-25.

External links

• ITU-R Recommendation BT.1886