By Craig K. Tanner, Consultant to CBS Corporation
CBS, BBC, NHK and others now have years of high-end production experience utilizing the Hybrid Log Gamma (HLG) format for live high dynamic range (HDR) production of premier news and sporting events. They are enthusiastic supporters of HLG for production, and for its use as a distribution format interrestrial broadcasting and for its subsequent retransmission by multichannel video programming distributors (MVPDs), as well as for transmission of non-broadcast linear cable channels. The goal of this presentation is to explain why HLG is the best format to streamline and optimize deployment of HDR for both broadcast and cable systems.
HLG was invented by two of the world’s leading broadcasters: the BBC and NHK (Japan Broadcasting Corporation). They developed HLG specifically to provide high quality HDR video, and to allow an easy migration to live HDR production and distribution. Whether in the home or outside, Hybrid Log-Gamma provides consistent results on TV screens and devices, because it is optimized for the human visual system in all TV viewing environments.
High dynamic range television is destined to be an important service type for broadcasters and cable operators because it delivers more natural and beautiful images. HDR video is an imaging system that provides a greater contrast ratio; in other words, it provides a higher variation in displayed luminance values with respect to its average luminance. This provides brighter highlights and specular reflections, extends visible detail in shadow and dark parts of the picture, and also gives a greater impression of sharpness. Coupled with the wide color gamut used in HDR formats, this greater contrast ratio provides a video experience that is far more lifelike and compelling.
HDR has become possible because the contrast capabilities of today’s video cameras and displays far exceed what can be represented by the limited signal standards for traditional video. To enable delivery of these improved imaging characteristics, two HDR video signal types have been developed and standardized, known as Perceptual Quantization (PQ) and Hybrid Log-Gamma (HLG) – both with the ability to convey greatly improved shadow detail at the dark end of the tone scale, and extended highlights at the bright end.