High-dynamic-range video

In February and April 1990, Georges Cornuéjols introduced the first real-time HDR camera combining two successively[8] or simultaneously[9]-captured images.

In 1991, the first commercial video camera using consumer-grade sensors and cameras was introduced that performed real-time capturing of multiple images with different exposures, and producing an HDR video image, by Hymatom, licensee of Cornuéjols.

Also in 1991, Cornuéjols introduced the principle of non linear image accumulation HDR+ to increase the camera sensitivity:[10] in low-light environments, several successive images are accumulated, increasing the signal-to-noise ratio.

Later, in the early 2000s, several scholarly research efforts used consumer-grade sensors and cameras.[11] A few companies such as RED and Arri have been developing digital sensors capable of a higher dynamic range.[12][13] RED EPIC-X can capture time-sequential HDRx[14] images with a user-selectable 1–3 stops of additional highlight latitude in the "x" channel. The "x" channel can be merged with the normal channel in post production software. The Arri Alexa camera uses a dual gain architecture to generate an HDR image from two exposures captured at the same time.[15]

With the advent of low-cost consumer digital cameras, many amateurs began posting tone mapped HDR time-lapse videos on the Internet, essentially a sequence of still photographs in quick succession. In 2010, the independent studio Soviet Montage produced an example of HDR video from disparately exposed video streams using a beam splitter and consumer grade HD video cameras.[16] Similar methods have been described in the academic literature in 2001 and 2007.[17][18]

Modern movies have often been filmed with cameras featuring a higher dynamic range, and legacy movies can be converted even if manual intervention would be needed for some frames (as when black-and-white films are converted to color). Also, special effects, especially those that mix real and synthetic footage, require both HDR shooting and rendering. HDR video is also needed in applications that demand high accuracy for capturing temporal aspects of changes in the scene. This is important in monitoring of some industrial processes such as welding, in predictive driver assistance systems in automotive industry, in surveillance video systems, and other applications. HDR video can be also considered to speed image acquisition in applications that need a large number of static HDR images are, for example in image-based methods in computer graphics.

OpenEXR was created in 1999 by Industrial Light & Magic (ILM) and released in 2003 as an open source software library.[19][20] OpenEXR is used for film and television production.[20]

Display devices capable of greater dynamic range have been researched for decades, primarily with flat panel technologies like plasma, SED/FED and OLED.

TV sets with enhanced dynamic range and upscaling of existing SDR/LDR video/broadcast content with reverse tone mapping have been anticipated since early 2000s.[21][22] In 2016, HDR conversion of SDR video was released to market as Samsung's HDR+ (in LCD TV sets)[23] and Technicolor SA's HDR Intelligent Tone Management.[24]

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.[3]

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.[25][26] On 12 December 2016, HDMI announced that Hybrid Log-Gamma (HLG) support had been added to the HDMI 2.0b standard.[27][28][29] 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.[30][31]

Academy Color Encoding System (ACES) was created by the Academy of Motion Picture Arts and Sciences and released in December 2014.[32] ACES is a complete color and file management system that works with almost any professional workflow and it supports both HDR and wide color gamut. More information can be found at https://www.ACESCentral.com (WCG).[32]

The perceptual quantizer (PQ),[33][34] published by SMPTE as SMPTE ST 2084, is a transfer function that allows for the display of high dynamic range (HDR) video with a luminance level of up to 10,000 cd/m² and can be used with the Rec. 2020 color space.[35][36][37][38] PQ is a non-linear electro-optical transfer function (EOTF). On 18 April 2016, the Ultra HD Forum announced industry guidelines for UHD Phase A, which uses Hybrid Log-Gamma (HLG) and PQ transfer functions with a bit depth of 10-bits and the Rec. 2020 color space.[39] On 6 July 2016, the ITU announced Rec. 2100, which uses HLG or PQ as transfer functions with a Rec. 2020 color space.[6][40]

The PQ inverse EOTF is as follows:[6]

${\displaystyle V=\left({\frac {c_{1}+c_{2}\cdot L_{o}^{m_{1}}}{1+c_{3}\cdot L_{o}^{m_{1}}}}\right)^{m_{2}}}$

where

• ${\displaystyle V}$ is the signal value, with a range of ${\displaystyle \left[0,1\right]}$.
• ${\displaystyle L_{o}}$ is the normalized linear optical luminance, with ${\displaystyle L_{o}=1}$ representing the peak luminance of 10,000 cd/m² (minimal luminance[41] is 0.0001 cd/m²)
• ${\displaystyle c_{1}=c_{3}-c_{2}+1={\frac {107}{128}}=0.8359375}$
• ${\displaystyle c_{2}={\frac {2413}{128}}=18.8515625}$
• ${\displaystyle c_{3}={\frac {2392}{128}}=18.6875}$
• ${\displaystyle m_{1}={\frac {1305}{8192}}=0.1593017578125}$
• ${\displaystyle m_{2}={\frac {2523}{32}}=78.84375}$

Hybrid Log-Gamma (HLG) is a royalty-free[42][43] HDR standard jointly developed by the BBC and NHK.[42] HLG is designed to be better-suited for television broadcasting, where the metadata required for other HDR formats is not backward compatible with non-HDR displays, consumes additional bandwidth, and may also become out-of-sync or damaged in transmission. HLG defines a non-linear optical-electro transfer function, in which the lower half of the signal values use a gamma curve and the upper half of the signal values use a logarithmic curve.[1][44] In practice, the signal is interpreted as normal by standard-dynamic-range displays (albeit capable of displaying more detail in highlights), but HLG-compatible displays can correctly interpret the logarithmic portion of the signal curve to provide a wider dynamic range.[45][46][47] In contrast the other HDR formats it does not use metadata.[48]

HLG is defined in ATSC 3.0, Digital Video Broadcasting (DVB) UHD-1 Phase 2, and International Telecommunication Union (ITU) Rec. 2100.[6][49][50] HLG is supported by HDMI 2.0b, HEVC, VP9, and H.264/MPEG-4 AVC.[27][51][52][53] HLG is supported by video services such as the BBC iPlayer, DirecTV, Freeview Play, and YouTube.[54][55][56][57][58]

BT.1886 describes the transfer function of SDR content.[59]

For consumers displays that have limited color volume (i.e. do not provide peak brightness/contrast and color gamut required by the standards), SMPTE defines metadata for describing the scenes as they appear on the mastering display. SMPTE ST 2086 "Mastering Display Color Volume Metadata Supporting High Luminance and Wide Color Gamut Images" describes static data such as MaxFALL (Maximum Frame Average Light Level) and MaxCLL (Maximum Content Light Level).

The Society of Motion Picture and Television Engineers (SMPTE) created a standard for dynamic metadata: SMPTE ST 2094 or Dynamic Metadata for Color Volume Transform (DMCVT).[60] SMPTE ST 2094 was published in 2016 as six parts and includes four applications from Dolby, Philips, Samsung, and Technicolor.[60]

SMPTE ST 2094 "Content-Dependent Metadata for Color Volume Transformation of High Luminance and Wide Color Gamut Images" includes dynamic metadata that can change from scene to scene. This includes ST 2094-10 (Dolby Vision format), Colour Volume Reconstruction Information (CVRI) SMPTE ST 2094-20 (Philips format) and Colour Remapping Information (CRI) defined in ST 2094-30 (Technicolor format), and HDR10+ ST 2094-40 (Samsung format).

HDR10 Media Profile, more commonly known as HDR10, was announced on 27 August 2015, by the Consumer Technology Association and uses the wide-gamut Rec. 2020 color space, a bit depth of 10-bits, and the SMPTE ST 2084 (PQ) transfer function – a combination later also standardized in ITU-R BT.2100.[61]

It also uses SMPTE ST 2086 "Mastering Display Color Volume" static metadata to send color calibration data of the mastering display, such as MaxFALL (Maximum Frame Average Light Level) and MaxCLL (Maximum Content Light Level) static values, encoded as SEI messages within the video stream. HDR10 is an open standard supported by a wide variety of companies, which include monitor and TV manufacturers such as Dell, LG, Samsung, Sharp, VU, Sony, and Vizio,[62][63] as well as Sony Interactive Entertainment, Microsoft and Apple which support HDR10 on their PlayStation 4, Xbox One video game console and Apple TV platforms, respectively.[64][65][66] It is the most wide spread of the HDR formats.[48]

HDR10 generally is not the best looking HDR format. It is based on Static HDR.[67] In the Static HDR, metadata for Dynamic Range is provided to the display, and that setting remains constant for the entire video/movie. HDR10 has a single metadata for things like MaxFALL and MaxCLL applied across the entire video/content. This means the video cannot have specific settings for specific scenes. It isn’t the most wonderful scene every time, but it is far superior to SDR every time.

HDR10+, also known as HDR10 Plus, was announced on 20 April 2017, by Samsung and Amazon Video. HDR10+ updates HDR10 by adding dynamic metadata that can be used to more accurately adjust brightness levels up to 4,000 nits maximum brightness on a scene-by-scene or frame-by-frame basis and supports up to 10-bit colour depth and 8K resolution.[68][69][70][71] This function is based on Samsung application SMPTE ST 2094-40 Application #4.[72][60][73][69][70][71] HDR10+ is an open standard and is royalty-free; it is supported by Colorfront's Transkoder and MulticoreWare's x265.[69][70][71] A certification and logo program for HDR10+ device manufacturers will be made available with an annual administration fee and no per unit royalty.[74] An authorized test center conducts a certification program for HDR10+ devices.[74]

On 28 August 2017, Samsung, Panasonic, and 20th Century Fox created the HDR10+ Alliance[75] to promote the HDR10+ standard.[76] HDR10+ video started being offered by Amazon Video on 13 December 2017.[77] On 5 January 2018, Warner Bros. announced their support for the HDR10+ standard.[78] On 6 January 2018, Panasonic announced Ultra HD Blu-ray players with support for HDR10+.[79] On 4 April 2019, Universal Pictures Home Entertainment announced a technology collaboration with Samsung Electronics to release new titles mastered with HDR10+.[80] It is considered to have most of the advantages of Dolby Vision over HDR10, despite being fee free.[48]

Dolby Vision is an HDR format from Dolby Laboratories that can be optionally supported by Ultra HD Blu-ray discs and streaming video services.[81][82] Dolby Vision is a proprietary format and Dolby SVP of Business Giles Baker has stated that the royalty cost for Dolby Vision is less than $3 per TV.[83][84][85] Dolby Vision includes the Perceptual Quantizer (SMPTE ST 2084) electro-optical transfer function, up to 8K resolution, and a wide-gamut color space (ITU-R Rec. BT.2020 in YC_BC_R or IC_TC_P). Some Dolby Vision profiles allow for 12-bit color depth and 10,000 cd/m2 maximum brightness[86] (as of 2018, according to the Dolby Vision white paper, professional reference monitors, such as the Dolby Vision HDR reference monitor, are currently limited to 4,000 cd/m2 of peak brightness).[87] It can encode mastering display colorimetry information using static metadata (SMPTE ST 2086) but also provide dynamic metadata (SMPTE ST 2094-10, Dolby format) for each scene.[60]

Examples of Ultra HD (UHD) TVs that support Dolby Vision include LG, TCL, VU, Sony and Vizio.[88] MulticoreWare's x265 encoder supports Dolby Vision as of version 3.0.[89] Dolby Vision IQ is an update designed to optimise Dolby Vision content according to the ambient light.[90] It is considered to be future proof.[48]

This dynamic metadata or Dynamic HDR allows adjusting of brightness and contrast (in reality, the tone curve) on the scene by scene or even frame by frame bases as and when required and adjusts it many times during the video/movie.[67]

HLG10, commonly referred as HLG, is a video format using the HLG transfer function, a bit depth of 10-bits and the wide-gamut Rec. 2020 color space.[91] The HLG transfer function is backward compatible with SDR video[45][46][47] but the Rec. 2020 color space is not compatible with SDR color space (Rec.709).

A HDR format which aims to be backwards compatible with SDR.[48] As of 19 December 2020 there is no content in this format.[48]

SL-HDR1 (Single-Layer HDR system Part 1) is a HDR standard that was jointly developed by STMicroelectronics, Philips International B.V., and Technicolor R&D France.[92] It was standardised as ETSI TS 103 433 in August 2016.[93] SL-HDR1 provides direct backwards compatibility by using static (SMPTE ST 2086) and dynamic metadata (using SMPTE ST 2094-20 Philips and 2094-30 Technicolor formats) to reconstruct a HDR signal from a SDR video stream that can be delivered using SDR distribution networks and services already in place. SL-HDR1 allows for HDR rendering on HDR devices and SDR rendering on SDR devices using a single layer video stream.[93] The HDR reconstruction metadata can be added either to HEVC or AVC using a supplemental enhancement information (SEI) message.[93]

The below table gives a complete comparison for Dolby Vision vs HDR 10 vs HDR 10+ vs HLG vs AHDR.[94]

AV1 Image File Format (AVIF) is an image file format compatible with HDR.[95]

Rec. 2100 is a technical recommendation by ITU-R for production and distribution of HDR content using 1080p or UHD resolution, 10-bit or 12-bit color, HLG or PQ transfer functions, the Rec. 2020 wide color gamut and YC_BC_R or IC_TC_P as color space.[6][40]

UHD Phase A are guidelines from the Ultra HD Forum for distribution of SDR and HDR content using Full HD 1080p and 4K UHD resolutions. It requires color depth of 10-bits per sample, a color gamut of Rec. 709 or Rec. 2020, a frame rate of up to 60 fps, a display resolution of 1080p or 2160p, and either standard dynamic range (SDR) or high dynamic range that uses Hybrid Log-Gamma (HLG) or Perceptual Quantizer (PQ) transfer functions.[96] UHD Phase A defines HDR as having a dynamic range of at least 13 stops (2¹³=8192:1) and WCG as a color gamut that is wider than Rec. 709.[96] UHD Phase A consumer devices are compatible with HDR10 requirements and can process Rec. 2020 color space and HLG or PQ at 10 bits.

The DisplayHDR standard from VESA is an attempt to make the differences in HDR specifications easier to understand for consumers, with standards mainly used in computer monitors and laptops. VESA defines a set of HDR levels; all of them must support HDR10, but not all are required to support 10-bit displays.[97] DisplayHDR is not an HDR format, but a tool to verify HDR formats and their performance on a given monitor. The most recent standard is DisplayHDR 1400 which was introduced in September 2019, with monitors supporting it released in 2020.[98][99] DisplayHDR 1000 and DisplayHDR 1400 are primarily used in professional work like video editing. Monitors with DisplayHDR 500 or DisplayHDR 600 certification provide a noticeable improvement over SDR displays, and are more often used for general computing and gaming.[100]

*Wide Color Gamut

Ultra HD Premium is a certification from the UHD Alliance.[101]

Mobile HDR Premium is a certification from the UHD Alliance for mobile devices.[101][102]