High-dynamic-range television


High-dynamic-range television is a technology that uses high dynamic range to improve the quality of display signals. It is contrasted with the retroactively-named standard dynamic range. 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.
HDR allows compatible displays to receive a higher-quality image source. It does not improve a display's intrinsic properties. Not all HDR displays have the same capabilities, and HDR content will look different depending on the display used, and the standards specify the required conversion depending on display capabilities.
HDR-TV is a part of HDR imaging, an end-to-end process of increasing the dynamic range of images and videos from their capture and creation to their storage, distribution and display. Often, HDR is used with wide color gamut technology. WCG increases the gamut and number of distinct colors available. HDR increases the range of luminance available for each color. HDR and WCG are separable but complementary technologies. Standards-compliant HDR display also has WCG capabilities, as mandated by Rec. 2100 and other common HDR specifications.
The use of HDR in television sets began in the late 2010s. By 2020, most high-end and mid-range TVs supported HDR, and some budget models did as well. HDR-TVs are now the standard for most new televisions.
There are a number of different HDR formats, including HDR10, HDR10+, Dolby Vision, and HLG. HDR10 is the most common format and is supported by all HDR TVs. Dolby Vision is a more advanced format that offers some additional features, such as scene-by-scene mastering. HDR10+ is a newer format that is similar to Dolby Vision but is royalty-free. HLG is a broadcast HDR format that is used by some TV broadcasters.

Description

Before HDR, improvements in display fidelity were typically achieved by increasing the pixel quantity, pixel density, and the display's frame rate. By contrast, HDR improves the perceived fidelity of the existing individual pixels. Standard dynamic range is still based on and limited by the characteristics of older cathode-ray tubes, despite the huge advances in screen and display technologies since CRT's obsolescence.
SDR formats are able to represent a maximum luminance level of around 100 nits. For HDR, this number increases to around 1,000–10,000 nits. HDR can represent darker black levels and more saturated colors. The most common SDR formats are limited to the Rec. 709/sRGB gamut, while common HDR formats use Rec. 2100, which is a wide color gamut.
In practice, HDR is not always used at its limits. HDR contents are often limited to a peak brightness of 1,000 or 4,000 nits and P3-D65 colors, even if they are stored in formats capable of more. Content creators can choose to what extent they make use of HDR capabilities. They can constrain themselves to the limits of SDR even if the content is delivered in an HDR format.
The benefits of HDR depend on the display capabilities, which vary. No current display is able to reproduce the maximal range of brightness and colors that can be represented in HDR formats.

Benefits

The highlights—the brightest parts of an image—can be brighter, more colorful, and more detailed. The larger capacity for brightness can be used to increase the brightness of small areas without increasing the overall image's brightness, resulting in, for example, bright reflections from shiny objects, bright stars in a dark night scene, and bright and colorful light-emissive objects.
The shadows or lowlights—the darkest parts of an image—can be darker and more detailed.
The colorful parts of the image can be even more colorful if a WCG is used.
The color dynamism and wider range of colors frequently attributed to HDR video is actually a consequence of a WCG. This has become a point of significant confusion among consumers, whereby HDR and WCG are either confused for each other or treated as interchangeable. While HDR displays typically have WCGs and displays with WCGs are usually capable of HDR, one does not imply the other; there are SDR displays with WCGs. Some HDR standards specify WCG as a prerequisite of compliance. Regardless, when a WCG is available on an HDR display, the image as a whole can be more colorful due to the wider range of colors.
More subjective, practical benefits of HDR video include more realistic luminance variation between scenes, better surface material identification, and better in-depth perception, even with 2D imagery.

Preservation of content creator intent

When a display’s capabilities are insufficient to reproduce all the brightness, contrast and colors that are represented in the HDR content, the image needs to be adjusted to fit the display’s capabilities. Some HDR formats allow the content creator to choose how the adjustment will be done. Other HDR formats, such as HDR10 and hybrid log–gamma, do not offer this possibility, so the content creator's intents are not ensured to be preserved on less capable displays.
For optimal quality, standards require video to be created and viewed in a relatively dark environment. Dolby Vision IQ and HDR10+ Adaptive adjust the content according to the ambient light.

Formats

Since 2014, multiple HDR formats have emerged including HDR10, HDR10+, Dolby Vision, and HLG. Some formats are royalty-free and others require a license. The formats vary in their capabilities.
Dolby Vision and HDR10+ include dynamic metadata while HDR10 and HLG do not. The dynamic metadata are used to improve image quality on limited displays that are not capable of reproducing an HDR video to its fullest intended extent. Dynamic metadata allows content creators to control and choose the way the image is adjusted.

HDR10

The HDR10 Media Profile, more commonly known as HDR10, is an open HDR standard announced on 27 August 2015 by the Consumer Technology Association. It is the most widespread of the HDR formats, and is not backward compatible with SDR displays. It is technically limited to a maximum peak brightness of 10,000 nits; however, HDR10 content is commonly mastered with a peak brightness between 1000 and 4000 nits.
HDR10 lacks dynamic metadata. On HDR10 displays that have lower color volume than the HDR10 content, the HDR10 metadata provides information to help the display adjust to the video. The metadata is static and constant with respect to each individual video and does not inform the display exactly how the content should be adjusted. The interaction between display capabilities, video metadata, and the ultimate output is mediated by the display, with the result that the original producer's intent may not be preserved.

Dolby Vision

Dolby Vision is an end-to-end ecosystem for HDR video, and covers content creation, distribution, and playback. It uses dynamic metadata and is capable of representing luminance levels of up to 10,000 nits. Dolby Vision certification requires displays for content creators to have a peak luminance of at least 1,000 nits.

HDR10+

HDR10+, also known as HDR10 Plus, is an HDR video format announced on 20 April 2017. It is the same as HDR10 but with the addition of a system of dynamic metadata developed by Samsung. It is free to use for content creators and has a maximum $10,000 annual license for some manufacturers. It has been positioned as an alternative to Dolby Vision without the same expenses.

HLG

HLG format is an HDR format that can be used for video and still images. It uses the HLG transfer function, Rec. 2020 color primaries, and a bit depth of 10 bits. The format is backwards compatible with SDR UHDTV, but not with older SDR displays that do not implement the Rec. 2020 color standards. It does not use metadata and is royalty-free.

PQ10 (PQ format)

, sometimes referred to as the PQ format, is an HDR format that can be used for video and still images. It is the same as the HDR10 format, except it lacks metadata. It uses the perceptual quantizer transfer function, Rec. 2020 color primaries and a bit depth of 10 bits.

HDR Vivid

HDR Vivid is an HDR format developed by the China Ultra HD Video Alliance and released in March 2021. It uses dynamic metadata standardized in CUVA 005-2020.

Other formats

  • Technicolor Advanced HDR: An HDR format which aims to be backward compatible with SDR. there is no commercial content available in this format. It is a global term for either SL-HDR1, SL-HDR2, SL-HDR3.
  • SL-HDR1 is an HDR standard that was jointly developed by STMicroelectronics, Philips International B.V., and Technicolor R&D France. It was standardised as ETSI TS 103 433 in August 2016. SL-HDR1 provides direct backward compatibility by using static and dynamic metadata to reconstruct an HDR signal from an SDR video stream that can be delivered using existing SDR distribution networks and services. SL-HDR1 allows for HDR rendering on HDR devices and SDR rendering on SDR devices using a single-layer video stream. The HDR reconstruction metadata can be added either to HEVC or AVC using a supplemental enhancement information message. Version 1.3.1 was published in March 2020. It is based on a gamma curve.
  • SL-HDR2 uses a PQ curve with dynamic metadata.
  • SL-HDR3 uses a HLG curve.
  • EclairColor HDR is an HDR format that is only used in a professional movie environment. It requires certified screens or projectors and the format is only rarely used. It is based on a gamma curve.

    Comparison of HDR formats

Displays

TV sets with enhanced dynamic range and upscaling of existing SDR/LDR video/broadcast content with reverse tone mapping have been anticipated since the early 2000s. In 2016, HDR conversion of SDR video was released to market as Samsung's HDR+ and Technicolor SA's HDR Intelligent Tone Management.
As of 2018, high-end consumer-grade HDR displays can achieve 1,000 cd/m2 of luminance, at least for a short duration or over a small portion of the screen, compared to 250-300 cd/m2 for a typical SDR display.
Video interfaces that support at least one HDR Format include HDMI 2.0a, which was released in April 2015 and DisplayPort 1.4, which was released in March 2016. On 12 December 2016, HDMI announced that HLG support had been added to the HDMI 2.0b standard. HDMI 2.1 was officially announced on 4 January 2017, and added support for Dynamic HDR, which is dynamic metadata that supports changes scene-by-scene or frame-by-frame.