Standard-dynamic-range video

Standard-dynamic-range (SDR) video represents light intensity based on a CRT's brightness, contrast and color 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 intended to be watched on a display that has the same characteristics and limits as a CRT. However, it's technically possible to show them with higher brightness levels, deeper blacks and more saturated colors by adjusting the SDR image. This can, however, lead to quality issues: the content creator's intents can't be ensured and the display becomes out of calibration.

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:

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 as a 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. "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. "CES 2014: Dolby Vision promises a brighter future for TV, Netflix and Xbox Video on board". Expert Reviews. Retrieved 2021-04-24.
  5. "15GP22 Color CRT". Early Television Museum. Retrieved 2016-02-02.
  6. "Early Electronic Television". Early Television Museum. Retrieved 2016-02-02.
  7. "Study Group Report High-Dynamic-Range (HDR) Imaging Ecosystem". Society of Motion Picture and Television Engineers. Retrieved 2016-02-02.
  8. T. Borer; A. Cotton. "A "Display Independent" High Dynamic Range Television System" (PDF). BBC. Retrieved 2016-02-02.
  9. "Dolby Vision White Paper" (PDF). Dolby Laboratories. Retrieved 2016-02-02.
  10. "High Dynamic Range" (PDF). European Broadcasting Union. Retrieved 2015-11-01.
  11. "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.
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