Engineering:Standard-dynamic-range video

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Short description: Video with a dynamic range that was standard before high-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/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]

Technical details

Transfer function

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:

[math]\displaystyle{ E=\begin{cases} 4.500L & L \lt 0.018\\ 1.099 L^{0.45} - 0.099 & L \ge 0.018 \end{cases} }[/math]

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. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 "HDR (High Dynamic Range) on TVs explained". https://www.flatpanelshd.com/focus.php?subaction=showfull&id=1435052975. 
  2. ↑ "ITU-R Report BT.2390 - High dynamic range television for production and international programme exchange" (in en-US). https://www.itu.int:443/en/publications/ITU-R/Pages/publications.aspx. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 "BT.1886 : Reference electro-optical transfer function for flat panel displays used in HDTV studio production". https://www.itu.int/rec/R-REC-BT.1886-0-201103-I/en. 
  4. ↑ "15GP22 Color CRT". Early Television Museum. http://www.earlytelevision.org/15GP22.html. Retrieved 2016-02-02. 
  5. ↑ "Early Electronic Television". Early Television Museum. http://www.earlytelevision.org/telefunken.html. Retrieved 2016-02-02. 
  6. ↑ "CES 2014: Dolby Vision promises a brighter future for TV, Netflix and Xbox Video on board" (in en). https://www.expertreviews.co.uk/go/27453. 
  7. ↑ "BT.601: Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios". ITU. https://www.itu.int/rec/R-REC-BT.601/. 
  8. ↑ 8.0 8.1 8.2 "Study Group Report High-Dynamic-Range (HDR) Imaging Ecosystem". Society of Motion Picture and Television Engineers. https://www.smpte.org/standards/reports. Retrieved 2016-02-02. 
  9. ↑ "A Standard Default Color Space for the Internet – sRGB, Version 1.10". November 5, 1996. https://www.w3.org/Graphics/Color/sRGB.html. 
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 T. Borer; A. Cotton. "A "Display Independent" High Dynamic Range Television System". BBC. http://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP309.pdf. Retrieved 2016-02-02. 
  11. ↑ 11.0 11.1 "Dolby Vision White Paper". Dolby Laboratories. http://www.dolby.com/us/en/technologies/dolby-vision/dolby-vision-white-paper.pdf. Retrieved 2016-02-02. 
  12. ↑ "High Dynamic Range". European Broadcasting Union. https://tech.ebu.ch/docs/events/IBC2015/IBC_Fact_Sheet_HDR_Demo_Final.pdf. Retrieved 2015-11-01. 
  13. ↑ "BT.2100 : Image parameter values for high dynamic range television for use in production and international programme exchange". https://www.itu.int/rec/R-REC-BT.2100. 

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