By Carlos Medina, Audiovisual Technology Expert and Advisor

Most professionals in the audiovisual broadcast sector already know -in one way or another- what HDR is. Firstly, because the world of photography, smartphone capture and fixed-image retouching techniques have accelerated the use and enjoyment of this type of technology; secondly, because manufacturers of audiovisual equipment, both for professionals and consumers, have made this term popular in their promotional and marketing campaigns.

But, at what point is HDR on Broadcast TV? We will learn through this article how HDR is gradually conquering the current landscape of professional audiovisuals.

Every time a technology is developed there are many factors that determine its level of success and implementation. In the image/video scene, we have been experiencing many changes in recent years. Some, with greater luck, have been accepted, used and seen feedback of high satisfaction among users/viewers, such as, for example, the resolution of images/videos. In a very short time we have gone from SD (PAL= 720 × 576; NTSC= 720 × 480) to FHD (1,920 x 1,080 pixels), 2K (2,048 x 1,080 pixels), UHD (3,840 x 2,160 pixels), 4K (4,096 x 2,160 pixels), or even 8K (7,680 x 4,320 pixels) throughout all phases of the audiovisual process, from capture to reception, distribution and broadcast of contents.

Surely, resolution is a notion that is easier to understand, or at least to assume. This is one of the main reasons for its success. So then, what’s going on with HDR?

The first thing is to know what we are talking about. HDR stands for High Dynamic Range. It is a technology that is harder to understand since it involves knowing and grasping other technical parameters. Simply put, HDR allows for greater tonal richness between illuminated and dark areas in an image/video in terms of exposure.

The purpose behind this technology is to provide greater realism to the image being viewed. Therefore, we want to improve the recording and playback of the maximum values/levels for white, gray and black (what we usually refer to as brightness or luminance). When we watch HDR videos, our assessment is usually conveyed through such popular expressions as “such a good quality”, “everything looks so good”, “how vibrant the images are” or “what a strength”, among others.

Brightness or luminance is measured in “nits”, or candelas per square meter (cd/m2); thus there are variations from very dark values -0.00005 nits- to very bright values -about 10,000 nits or more. Therefore, HDR involves working with images with greater nit ranges as compared to SDR (Standard Dynamic Range), that is, it works with a range that goes from the maximum level of brightness, which corresponds to pure white, to the minimum level, black.

For example, a TV whose maximum brightness capacity is 100 nits and a lowest value of 0.1 nits has a contrast ratio of 100/0.1 i.e. 1000:1 (standard in HD TV). If the maximum brightness is increased up to 400 nits while keeping the black level at 0.1 nits, we will get a contrast ratio of 4000:1. That is, the contrast ratio and therefore the dynamic range have been increased. Thus, we get a new visual experience in the perception of images/videos and come a little closer to what happens with human vision when looking directly at reality. *Thus, the viewing experience increasingly comes closer to the direct perception of reality by the human eye.

The implementation of HDR means having control of this technology during all phases of audiovisual production. A clear improvement as compared to the use of SDR, where the result of an image showed “high areas -white level- that were burned” and/or “pasted in blacks or dark areas”.

The HDR format involves in some way reinventing the TV or, at least, changing the rules of the game for production of SDR (Standard Dynamic Range) content. FHD/UHD images feature some modifications in issues such as:

-The improvement in capture devices, both regarding sensitivity of the sensors and in the way of processing images using the different logarithmic gamma curves existing in the audiovisual market.

-Full image standardization with a color depth (bits per pixel – bpp) below 10 bits or greater.

-Working with new color spaces that are wider under ITU-R BT.709, ITU-R BT.2020 and/or DCI-P3 standards.

-Knowledge and practice of illuminating with logarithmic gamma curves and raw images.

-The final finishing process of the image and color-grading in the visual content.

-Implementation of codecs that allow the dissemination of HDR for different deliveries.

-Using SDR/HDR and HDR/SDR production workflows in parallel.

-Marketing of HDR-compatible viewing devices, i.e. monitors, video projectors and consumer televisions (whatever the technology used: Full LED, Nanocell, OLED, OLED+, QLED…).

All broadcast organizations are strongly committing on UHDTV and HDR production, as recommended by the International Telecommunication Union (ITU), the American Society of Film and Television Engineers (SMPTE), the Consumer Technology Association (CTA, the former Consumer Electronics Goods Association – CEA), the Moving Image Expert Group (MPEG), the Blu-Ray Optical Discs Association (BDA), and even VESA (Video Electronics Standards Association).

The HDR TV standard reminds us of some situations experienced in the past when implementing a new technology, that is, the appearance of several solutions and denominations in a short period of time, for example:

HDR10

In August 2015, the Consumer Technology Association (CTA) announced this open standard (no need to pay license fees) for the adoption of HDR, supported by most manufacturers, distributors and content creators, including Sony, Samsung, LG, Sharp, Vizio, Hisense.

Its main features are the use of the Electro-Optical Transfer Function (EOTF) in the SMPTE ST 2084 standard, a Rec. 2020 color space, color luminance up to a maximum of 1,000 nits, color depth of 10 bits and global image instructions in addition to a single layer of content with static metadata and a minimal interface to GET signal – HDMI 2.0a.

This system has no backward compatibility with SDR TVs, although it is the most widespread standard, and even mandatory on UHD Blu-Rays.

In April, 2016 the UHD Alliance (a partnership made up of different industry sector, including major movie studios, manufacturers of consumer electronics and technology companies as well as content distributors) established the Ultra HD Premium certification to ensure a correct HDR10 implementation with the following resolution features: 3,840 x 2,160, color depth of at least 10 bits, BT.2020 color space, maximum luminance of more than 1,000 nits, black level of less than 0.03 nits and implementation of the SMPTE ST 2084-EOTF standard.

The main creators and distributors of HDR10 content are Netflix, Amazon Prime Video, VUDU, HBO, Google Chromecast Ultra, Playstation 4 PRO, Xbox One, Vimeo, You Tube. And the Hollywood studios: Fox, Warner Bros., Paramount, Sony, Lionsgate.

HDR10+

2017 saw the updating of the HDR10 format, thanks to the cooperation between Samsung, 20th Century Fox and Panasonic which has Amazon Prime Video as the major streaming service provider.

The great novelty is that it features dynamic metadata, which allows to adjust the settings of the scene parameters frame by frame. This new functionality is called Dynamic Tone Mapping; it integrates the HEVC x265 codec, an HDMI 2.0 connection and is supported by UHD Blu-Ray.

DOLBY VISION (DV)

This is a reference and a standard in HDR, which draws on the conclusions obtained from a series of experiments with viewers so as to determine how much dynamic range human vision needs. The result was that a satisfactory level (90%) is reached by playing back within a range of 0 to 10,000 nits.

Dolby labs have determined to use the BT.2020 SMPTE ST-2084 standard, color luminance up to a maximum of 10,000 nits, 12-bit color depth (allows to use 68 billion colors) and partial metadata instructions per individual frame.

It features backward compatibility with SDR TVs and is -optionally- HDR10 compatible TVs. It is also optional on UHD Blu-Rays. This standard has an added cost that usually affects consumers, due to the need to pay for a special Dolby Vision chip, a certification process and playback licenses.

The main creators and distributors of HDR Dolby Vision content are Netflix, Warner, Universal Pictures, Amazon Prime Video, VUDU, Google Chromecast Ultra…The Hollywood studios: MGM, Sony, Warner Bros. Universal.

HLG

Hybrid Log-Gamma (HLG) is a standard sponsored by British public broadcasters BBC and Japan’s NHK. One of its great successes for implementation is the compatibility in SDR/HDR environments with REC 709 for terrestrial, cable and satellite television transmissions. It is an open standard (no need for license fees). It uses a hybrid logarithmic gamma (HLG) Electro-Optical Transfer Function (EOTF) with   no metadata and 10-bit color depth.

Its distinguishing factor is that it is mainly geared towards live content, on television or sports broadcasts, for example, during the 2020 Tokyo Olympics.

Advanced HDR

This is the proposal from one of the technological giants directly associated with cinema, Technicolor (HDR Technicolor), and for the time being it has not caused any impact, although it relies on the support of content creators. Since CES 2016, Philips became its great ally, and this resulted in the SL-HDR1 format (formerly Prime Single).

It is backward compatible with SDR televisions, through an external decoder device. It uses the Electro-Optical Transfer Function (EOTF) of the SMPTE ST 2084 standard and includes a single layer of content with static and dynamic metadata; as usual, it is also optional in UHD Blu-Ray.

HDR Converter

It is not an HDR standard as such, but a technology developed by LG for its televisions that allows converting and scaling a content from SDR to HDR by emulation, in which basically some settings are retouched, such as contrast, to give the image an HDR feel.

VESA DisplayHDR

It is simply a certification for proper HDR compliance within the field of monitors. VESA’s DisplayHDR and DisplayHDR True Black specifications provide an important benefit for the screens industry and end consumers.

It consists of an open industry standard to determine the quality of HDR viewing on monitors so as to determine what is the image quality that we will have on each screen.

There are three levels of certification: DisplayHDR 400 (low range), designed for laptops, DisplayHDR 600, for mid-range laptops and monitors, and DisplayHDR 1000, for high-end equipment.

The path is not being easy due to a myriad of solutions that are being proposed, which in many cases can confuse both professionals when generating content or marketing HDR images and videos, and end users when it comes to buying a television set, updating the technical equipment or enjoying audiovisual proposals on their screens.

Even in the field of consumer products, many manufacturers use proprietary names that continue to cause confusion: Samsung with SUHD Precision Black Pro; Panasonic under Dynamic Range Remaster; LG with Wide Color Led; Sony with X-tended Dynamic Range; Philips by naming it Bright Premium and Micro Dimming Premium, among others.

However, it is necessary to highlight the effort that these manufacturers of TV sets and video projectors are making to introduce the HDR ecosystem in our homes with screen devices capable of showing 1,000 nits of brightness at color depths of 10 bits or even with 17 bits, although Dolby continues to recommend reaching 4,000 nits to achieve incredible images.

In the broadcast TV sector, the International Telecommunication Union published recommendation ITU-R HDR-TV, BT.2100-0, so professionals are under two standards worldwide: Hybrid Log-Gamma (HLG) and Perceptual Quantizer (PQ), which are then translated into the different above-mentioned denominations.

Finally, when producing and marketing in a broadcast environment, it is essential to determine whether we want to maintain compatibility between an SDR/HDR stream or also use static or dynamic metadata.

And, regarding standards, there are releases that already support the assurances provided by HDR production for the professional sector:

-ARIB STD-B67 Essential Parameter Values for the Extended Image Dynamic Range Television (EIDRTV) System for Programme Production.

-EBU Tech 3320 User Requirements for Video Monitors in Television Production. Version 4.1 (9/2019).

-ETSI TS 103 433-1 High-Performance Single Layer High Dynamic Range (HDR) System for use in consumer electronic devices.

-SID ICDM IDMS 1.1 SID International Committee for Display Metrology (ICDM) Information Display Measurements Standard v1.1.

-ITU-R Rec. BT.601-7 Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios. ITU-R. March 2011.

-ITU-R Rec. BT.709-6 Parameter values for the HDTV standards for production and international programme exchange. ITU-R. June 2015.

-ITU-R Rec. BT.1886 Reference electro-optical transfer function for flat panel displays used in HDTV studio production. ITU-R. March 2011.

-ITU-R Rec. BT.2020-2 Parameter values for ultra-high definition television systems for production and international programme exchange. Oct. 2015.

-ITU-R Rec. BT.2035 A reference viewing environment for evaluation of HDTV program material or completed programs.

-ITU-R Rec. BT.2020-2 Image parameter values for high-dynamc range television for use in production and international programme exchange. July 2018.

-ITU-R Rec BT.2390-11 (03/2023) High dynamic range television for production and international program exchange.

-ITU-R Rec. BT.2124 Objective metric for the assessment of the potential visibility of colour differences in television. ITU-R. Jan. 2019.

-ITU-R Rec. BT.2408-0 Operational practices in HDR television production. ITU-R. Oct. 2017.

-ITU-R Rec. H.273 Coding-independent code points for video signal type identification, 2016.

-ITU-R BT.2381-0 (07/2015): Requirements for High Dynamic Range Television (HDR-TV) Systems.

-ITU-R BT.2077 Real time serial digital interfaces for UHDTV signals.

-OpenEXR High-dynamic-range scene-linear image data and associated metadata format. www.openexr.com.

-SMPTE ST 2036 1 Ultra High Definition Television Image.

-SMPTE ST 0196-2003 Motion-Picture Film – Indoor Theater and Review Room Projection – Screen Luminance & Viewing Conditions.

-SMPTE ST 0431-1-2006 D-Cinema Quality – Screen Luminance Level, Chromaticity and Uniformity.

-SMPTE RP 0431-2-2007 D-Cinema Quality – Reference Projector and Environment.

-SMPTE ST 2084:2014 and CEA-861.3-A-2016: High Dynamic Range (PQ) Electro-Optical Transfer Function of Mastering Reference Displays. SMPTE 2014.

-SMPTE ST 2086:2018 Mastering Display Color Volume Metadata Supporting High Luminance and Wide Color Gamut Images.

-SMPTE ST 2094-0:2017 and CEA-861-G: Overview Document – Dynamic Metadata for Color Volume Transformation. DOI: 10.5594/-SMPTE.OV2094-0.2017.

– SMPTE ST 2048-1 2048×1080 and 4096×2160 Digital Cinematography Production Image Formats FS/709.

-SMPTE ST 2065 4:2013 ACES Image Container File Layout. HDR Production File Format.

-SMPTE ST 268-2 DPX format extensions for high dynamic range and wide color gamut pictures.

-VESA DisplayHDR: VESA High-performance Monitor and Display Compliance Test Specification (DisplayHDR CTS). Rev. 1.1 (2019).

-ARIB STD-B67 (2015, Japanese standardization agency): Hybrid Log Gamma (HLG) Essential Parameter Values for the Extended Image Dynamic Range Television System.

The Advanced Television Systems Committee (ATSC), under the ATSC 3.0 terrestrial transmission, the MPEG Committee under the HEVC standard, DVB Europe and the Society of Cable and Telecommunications Engineers (SCTE) are already working on the preparation of HDR standards for dissemination of this type of content.

Any professional in the audiovisual sector, both in the broadcast field and in digital cinematography, must be clear that HDR is a technology that has to be taken care of throughout the entire work process (HDR Workflow): from origin and development of the project (Project Development), through pre-production, contribution (production, recording/ shooting and post-production), delivery  (distribution, broadcast and/or retransmission) and, of course, up to the displays or image output devices used by end users or viewers (monitors, televisions, tablets, cell phones…).

The HDR standard has very important implications in regard to all the decisions that have to be made to obtain quality broadcast content. At present, we must continue to promote HDR content versus SDR content, given the level of satisfaction generated by their enjoyment. However, this is a boost that still needs collaboration between the players involved in the technology (developers, engineering, equipment manufacturers…) and those who promote visual creativity (producers, directors, photographers, camera operators, post-production and color grading technicians…).

The success of HDR means that technology and creativity shpuld go along hand in hand, a conversational dynamic between the research drive of new image quality options and the requirements of increasingly demanding viewers.