Standard-dynamic-range video

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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]

Contents

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:

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]

Related Research Articles

Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. Gamma correction is, in the simplest cases, defined by the following power-law expression:

<span class="mw-page-title-main">RGB color spaces</span> Any additive color space based on the RGB color model

An RGB color space is one of many specific additive colorimetric color spaces based on the RGB color model.

<span class="mw-page-title-main">Rec. 601</span> Standard from the International Telecommunication Union

ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601, is a standard originally issued in 1982 by the CCIR for encoding interlaced analog video signals in digital video form. It includes methods of encoding 525-line 60 Hz and 625-line 50 Hz signals, both with an active region covering 720 luminance samples and 360 chrominance samples per line. The color encoding system is known as YCbCr 4:2:2.

<span class="mw-page-title-main">Gamut</span> Color reproduction capability

In color reproduction and colorimetry, a gamut, or color gamut, is a convex set containing the colors that can be accurately represented, i.e. reproduced by an output device or measured by an input device. Devices with a larger gamut can represent more colors. Similarly, gamut may also refer to the colors within a defined color space, which is not linked to a specific device. A trichromatic gamut is often visualized as a color triangle. A less common usage defines gamut as the subset of colors contained within an image, scene or video.

sRGB Standard RGB color space

sRGB is a standard RGB color space that HP and Microsoft created cooperatively in 1996 to use on monitors, printers, and the World Wide Web. It was subsequently standardized by the International Electrotechnical Commission (IEC) as IEC 61966-2-1:1999. sRGB is the current defined standard colorspace for the web, and it is usually the assumed colorspace for images that are neither tagged for a colorspace nor have an embedded color profile.

High dynamic range (HDR), also known as wide dynamic range, extended dynamic range, or expanded dynamic range, is a dynamic range higher than usual.

xvYCC or extended-gamut YCbCr is a color space that can be used in the video electronics of television sets to support a gamut 1.8 times as large as that of the sRGB color space. xvYCC was proposed by Sony, specified by the IEC in October 2005 and published in January 2006 as IEC 61966-2-4. xvYCC extends the ITU-R BT.709 tone curve by defining over-ranged values. xvYCC-encoded video retains the same color primaries and white point as BT.709, and uses either a BT.601 or BT.709 RGB-to-YCC conversion matrix and encoding. This allows it to travel through existing digital limited range YCC data paths, and any colors within the normal gamut will be compatible. It works by allowing negative RGB inputs and expanding the output chroma. These are used to encode more saturated colors by using a greater part of the RGB values that can be encoded in the YCbCr signal compared with those used in Broadcast Safe Level. The extra-gamut colors can then be displayed by a device whose underlying technology is not limited by the standard primaries.

<span class="mw-page-title-main">Rec. 709</span> Standard for HDTV image encoding and signal characteristics

Rec. 709, also known as Rec.709, BT.709, and ITU 709, is a standard developed by ITU-R for image encoding and signal characteristics of high-definition television.

<span class="mw-page-title-main">Rec. 2020</span> ITU-R recommendation

ITU-R Recommendation BT.2020, more commonly known by the abbreviations Rec. 2020 or BT.2020, defines various aspects of ultra-high-definition television (UHDTV) with standard dynamic range (SDR) and wide color gamut (WCG), including picture resolutions, frame rates with progressive scan, bit depths, color primaries, RGB and luma-chroma color representations, chroma subsamplings, and an opto-electronic transfer function. The first version of Rec. 2020 was posted on the International Telecommunication Union (ITU) website on August 23, 2012, and two further editions have been published since then.

<span class="mw-page-title-main">Hybrid log–gamma</span> High dynamic range standard that was jointly developed by the BBC and NHK

The hybrid log–gamma (HLG) transfer function is a transfer function jointly developed by the BBC and NHK for high dynamic range (HDR) display. It's backward compatible with the transfer function of SDR. It was approved as ARIB STD-B67 by the Association of Radio Industries and Businesses (ARIB). It is also defined in ATSC 3.0, Digital Video Broadcasting (DVB) UHD-1 Phase 2, and International Telecommunication Union (ITU) Rec. 2100.

<span class="mw-page-title-main">HDR10</span> Open HDR standard

HDR10 Media Profile, more commonly known as HDR10, is an open high-dynamic-range video (HDR) standard announced on August 27, 2015, by the Consumer Technology Association. It is the most widespread HDR format.

<span class="mw-page-title-main">DCI-P3</span> RGB color space for digital movie projection from the American film industry

DCI-P3 is an RGB color space first defined in 2005 as part of the Digital Cinema Initiative, to be used for digital theatrical motion picture distribution (DCDM). Display P3 is a variant developed by Apple Inc. for wide-gamut displays.

<span class="mw-page-title-main">Ultra HD Forum</span> Organization

Ultra HD Forum is an organization whose goal is to help solve the real world hurdles in deploying Ultra HD video and thus to help promote UHD deployment. The Ultra HD Forum will help navigate amongst the standards related to high dynamic range (HDR), high frame rate (HFR), next generation audio (NGA), and wide color gamut (WCG). The Ultra HD Forum is an industry organisation that is complementary to the UHD Alliance, covering different aspects of the UHD ecosystem.

<i>ICtCp</i>

ICTCP, ICtCp, or ITP is a color representation format specified in the Rec. ITU-R BT.2100 standard that is used as a part of the color image pipeline in video and digital photography systems for high dynamic range (HDR) and wide color gamut (WCG) imagery. It was developed by Dolby Laboratories from the IPT color space by Ebner and Fairchild. The format is derived from an associated RGB color space by a coordinate transformation that includes two matrix transformations and an intermediate nonlinear transfer function that is informally known as gamma pre-correction. The transformation produces three signals called I, CT, and CP. The ICTCP transformation can be used with RGB signals derived from either the perceptual quantizer (PQ) or hybrid log–gamma (HLG) nonlinearity functions, but is most commonly associated with the PQ function.

ITU-R Recommendation BT.2100, more commonly known by the abbreviations Rec. 2100 or BT.2100, introduced high-dynamic-range television (HDR-TV) by recommending the use of the perceptual quantizer or hybrid log–gamma (HLG) transfer functions instead of the traditional "gamma" previously used for SDR-TV.

The perceptual quantizer (PQ), published by SMPTE as SMPTE ST 2084, is a transfer function that allows for HDR display by replacing the gamma curve used in SDR. It is capable of representing luminance level up to 10000 cd/m2 (nits) and down to 0.0001 nits. It has been developed by Dolby and standardized in 2014 by SMPTE and also in 2016 by ITU in Rec. 2100. ITU specifies the use of PQ or HLG as transfer functions for HDR-TV. PQ is the basis of HDR video formats and is also used for HDR still picture formats. PQ is not backward compatible with the BT.1886 EOTF, while HLG is compatible.

High-dynamic-range television (HDR-TV) is a technology that uses high dynamic range (HDR) to improve the quality of display signals. It is contrasted with the retroactively-named standard dynamic range (SDR). HDR changes the way the luminance and colors of videos and images are represented in the signal, and allows brighter and more detailed highlight representation, darker and more detailed shadows, and more intense colors.

Images and videos use specific transfer functions to describe the relationship between electrical signal, scene light and displayed light.

<span class="mw-page-title-main">EBU colour bars</span> Television test card

The EBU colour bars is a television test card used to check if a video signal has been altered by recording or transmission, and what adjustments must be made to bring it back to specification. It is also used for setting a television monitor or receiver to reproduce chrominance and luminance information correctly. The EBU bars are most commonly shown arranged side-by-side in a vertical manner, though some broadcasters – such as TVP in Poland, and Gabon Télévision in Gabon – were known to have aired a horizontal version of the EBU bars.

References

  1. 1 2 3 4 5 6 7 8 9 10 "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. 1 2 3 4 5 6 "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. 1 2 3 "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. 1 2 3 4 5 6 T. Borer; A. Cotton. "A "Display Independent" High Dynamic Range Television System" (PDF). BBC . Retrieved 2016-02-02.
  11. 1 2 "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.
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