Standard-dynamic-range video (SDR video) is a

video Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...

technology which represents light intensity based on the

brightness Brightness is an attribute of visual perception in which a source appears to be radiating/reflecting light. In other words, brightness is the perception dictated by the luminance of a visual target. The perception is not linear to luminance, and ...

, contrast and

color Color (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...

characteristics and limitations of a

cathode ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms on an oscilloscope, a ...

(CRT) display. SDR video is able to represent a video or picture's colors with a maximum

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...

around 100 cd/m², a black level around 0.1 cd/m² and Rec.709 /

sRGB sRGB (standard RGB) is a colorspace, for use on monitors, printers, and the World Wide Web. It was initially proposed by HP and Microsoft in 1996 and became an official standard of the International Electrotechnical Commission (IEC) as IEC 6 ...

color gamut. It uses the gamma curve as its electro-optical transfer function. The first CRT

television set A television set or television receiver (more commonly called TV, TV set, television, telly, or tele) is an electronic device for viewing and hearing television broadcasts, or as a computer monitor. It combines a tuner, display, and loudspeake ...

s were manufactured in 1934 and the first color CRT television sets were manufactured in 1954. The term "standard-dynamic-range video" was adopted to distinguish SDR video from

high-dynamic-range video High dynamic range (HDR), also known as wide dynamic range, extended dynamic range, or expanded dynamic range, is a signal with a higher dynamic range than usual. The term is often used in discussing the dynamic ranges of images, videos, audio or ...

(HDR video), a new technology that was developed in the 2010s to overcome SDR's limits.

Technical details

Transfer function

Conventional gamma curves: * Opto-electronic transfer function (OETF): ** Rec. 601 (

analog video Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...

signals in SD-TV

digital video Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises ...

form) ** Rec. 709 ( HD-TV) ** Rec. 2020 ( UHD-TV) **

* Electro-optical transfer function (EOTF): **

ITU-R BT.1886 ITU-R BT.1886 is the reference EOTF of SDR-TV. It is a gamma 2.4 transfer function (a power law with a 2.4 exponent) considered as a satisfactory approximation of the response characteristic of CRT to electrical signal. It has been standardized ...

(SDR-TV) **

(monitors, printers,

World Wide Web The World Wide Web (WWW or simply the Web) is an information system that enables Content (media), content sharing over the Internet through user-friendly ways meant to appeal to users beyond Information technology, IT specialists and hobbyis ...

) 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 High dynamic range (HDR), also known as wide dynamic range, extended dynamic range, or expanded dynamic range, is a signal with a higher dynamic range than usual. The term is often used in discussing the dynamic ranges of images, videos, audio o ...

(HDR) cameras. An example of a conventional gamma curve would be Rec. 601:

E=\begin
4.500L & L < 0.018\\
1.099 L^ - 0.099 & L \ge 0.018
\end

ITU-R Recommendation BT.1886 describe the reference

EOTF Images and videos use specific transfer functions to describe the relationship between electrical signal, scene light and displayed light. Definition The opto-electronic transfer function (OETF) is the transfer function having the scene light as ...

of SDR. It's a gamma curve representing the response of

CRT CRT or Crt most commonly refers to: * Cathode-ray tube, a display * Critical race theory, an academic framework of analysis CRT may also refer to: Law * Charitable remainder trust, United States * Civil Resolution Tribunal, Canada * Columbia ...

to video signal. It has been published by ITU in 2011. A

transfer function In engineering, a transfer function (also known as system function or network function) of a system, sub-system, or component is a function (mathematics), mathematical function that mathematical model, models the system's output for each possible ...

that is closer to Weber's law allows for a larger dynamic range, at the same bit depth, than a conventional gamma curve. HDR standards such as

hybrid log–gamma 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 is backward compatible with the transfer function of SDR (the gamma curve). It was approved as ARIB ...

(HLG) and SMPTE ST 2084 allow for a larger dynamic range by using a different

. HLG is compatible with SDR displays.

Color gamut

In some cases the term SDR is also used with a meaning including the standard color gamut (i.e. Rec.709 /

color primaries). HDR uses wide color gamut (WCG) such as Rec. 2020 or DCI-P3 color primaries.

Dynamic range

The

dynamic range Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' " power") or dynamic may refer to: Physics and engineering * Dynamics (mechanics), the study of forces and their effect on motion Brands and ent ...

that can be perceived by the

human eye The human eye is a sensory organ in the visual system that reacts to light, visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and Balance (ability), keeping balance. The eye can be considered as a living ...

in a single image is around 14 stops. 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. 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.

Displaying SDR video on modern displays

While conventional gamma curves are useful for low light and are compatible with

displays, they can only represent a limited

. Standards require SDR to be viewed on a display with the same characteristics as a CRT (i.e. 100 nits peak

, gamma curve, Rec. 709 color primaries). However, current displays are often far more capable than CRT's limits. On such displays, higher brightness and wider color gamut can be displayed by adjusting and trying to enhance the SDR picture. HDR is however required for the creative intents to be preserved.

References

External links

ITU-R Recommendation BT.1886
{{Dynamic range color representation Display technology Television technology Color High dynamic range