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Standard Dynamic Range (color representation)

Topic: Engineering

 From HandWiki - Reading time: 3 min

Standard Dynamic Range (SDR) is a way of representing light that is based on CRT's brightness, contrast and colors characteristics and limits.[1] It's 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 transfer function.[1][3] SDR videos and image are supposed to be watched on a display that have the same characteristics and limit than CRT. However, it's technically possible to show them with higher brightness levels, deeper blacks and more saturated colors by adjusting the SDR image.[citation needed] This can however lead to quality issues, the content creator's intents can't be ensured and the display becomes out of calibration.[citation needed]

HDR is a new way of representing light that emerged in 2014 to overcome SDR's limits.[1][4]

The first CRT television sets were manufactured in 1934 and the first color CRT television sets were manufactured in 1954.[5][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.[7] 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.[8] HDR standards such as Hybrid Log-Gamma (HLG) and SMPTE ST 2084 allow for a larger dynamic range by using a different transfer function.[8][9] HLG is compatible with SDR displays.[10]

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][11]

Dynamic range

The dynamic range that can be perceived by the human eye in a single image is around 14 stops.[8] 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.[8] 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.[8]

Limitations

While conventional gamma curves are useful for low light and are compatible with CRT displays, they can only represent a limited dynamic range.[8][9] Standards require SDR to be viewed on a display with same characteristics than CRT (i.e. 100 nits peak brightness, gamma curve, Rec. 709 color primaries).[1][3] However, current displays are often way more capable than CRT's limits.[1] On such display, 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]

See also

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. ↑ "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. 
  5. ↑ "15GP22 Color CRT". Early Television Museum. http://www.earlytelevision.org/15GP22.html. Retrieved 2016-02-02. 
  6. ↑ "Early Electronic Television". Early Television Museum. http://www.earlytelevision.org/telefunken.html. Retrieved 2016-02-02. 
  7. ↑ 7.0 7.1 7.2 "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. 
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 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. 
  9. ↑ 9.0 9.1 "Dolby Vision White Paper". Dolby Laboratories. http://www.dolby.com/us/en/technologies/dolby-vision/dolby-vision-white-paper.pdf. Retrieved 2016-02-02. 
  10. ↑ "High Dynamic Range". European Broadcasting Union. https://tech.ebu.ch/docs/events/IBC2015/IBC_Fact_Sheet_HDR_Demo_Final.pdf. Retrieved 2015-11-01. 
  11. ↑ "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. 

External links




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