Video is currently going through an exciting revolution that holds great promise for creative expression – one that aims to deliver richer, more realistic pictures. And best of all you won’t have to don a pair of multi-coloured, multicoated specs to enjoy it.
High dynamic range imaging (HDRI) is well known in photography and VFX. Typically, it’s used to gain extra detail in the lightest and darkest areas of an image, which are created by combining multiple versions of a shot taken at different exposure levels.
However, when the term HDR is applied to video, people are generally talking about video at any point in the production, post or distribution process that has detail pulled out from the deepest darkest shadows to the brightest highlights. This allows for brighter pictures, greater contrast and gradations in shade, the ability for more scenes to be naturally-lit; all in short offering a far wider palette for cinematographers to a work with and audiences to enjoy. See also: How to capture and edit HDR video.
The recent spread of high-end video cameras that can capture the wider exposure range required means that creatives are already experimenting with HDR, delivering gorgeous results. HDR boosts specular highlights, with shiny metallic objects and light-reflections in eyes being especially noticeable. The aim is to create films and TV with a similar range of luminance to that which we experience in the real world.
Sports broadcasters are taking note too, with HDR being especially helpful in displaying a golf ball flying through the sky, or tracking the action in naturally lit sports stadium as the play moves quickly from light to shadowed areas.
The move to bring immersive audio to the cinema and home entertainment systems is seen as a perfect complement to the quest for higher dynamic range TV and movies. HDR-capable televisions, carried on the Ultra HD technology wave, are already on the market, and premium large format (PLF) cinemas are being equipped with ultra-bright digital projectors capable of high dynamic range. Films are being mastered in higher dynamic range too – Disney/Pixar for example has released an HDR version of Inside Out (above).
Make no mistake, HDR video will soon be as familiar a term to consumers as HD video or IMAX, bringing with it a dramatic leap in content creation.
So what’s the holdup? Why aren’t we all using this across the board already? The reason you’re not seeing Strictly or Doctor Who broadcast in glorious HDR at the moment is that there’s still a big debate in the broadcast industry about what HDR actually ‘means’.
What is HDR?
In essence HDR is video that’s captured at such a wide exposure range (measured in stops) that the resulting footage – and subsequently displayed content – has bright images with high contrast ratio enough to retain detail in both highlight and shadow areas. The current aim is for a higher dynamic range that results in a viewing experience closer to reality, and hence of greater impact or immersion. HDR also increases the subjective sharpness of images and so provides a double benefit.
There are at least four technologies striving to become the worldwide standard for HDR, from Dolby, Philips, Technicolor and a combined effort from Japan's national broadcaster NHK and the BBC. The shared aim is to offer a ‘display independent signal that can produce high quality images, which maintain the director’s artistic intent on a wide range of displays in diverse viewing environments’
They’re under consideration by the International Telecommunication Union(ITU) which has already defined various aspects of Ultra HDTV in the recommendation BT.2020, more commonly known as Rec.2020 standard (current broadcast TV signals, Blu-ray and DVD adhere to the Rec. 709 standard). HDR is thus seen as another complementary aspect of this next-generation video standard.
Rec.2020 also concerns the wider range of colours, or gamut, that can be displayed by Ultra HD devices. The standard stipulates 10-bit (supporting one billion colours) or 12-bit (68 billion colours) devices. HDR and wide colour gamut (WCG) are thus often linked in the quest for immersive imaging.
HDR on TV (and streaming services)
Just recently an HDR roadmap was published by film industry group SMPTE, based on contributions from over 170 industry experts. It predicts that HDR will be adopted rapidly alongside 4K Ultra HD, but identifies the challenges ‘for creating harmonised and standardised technologies that will be needed to produce HDR content in real time’.
The BBC and NHK might have an answer to this. Both state broadcasters agreed to merge their proposals to the ITU in a solution called Hybrid Log-Gamma. This aims to ensure that precisely the same signal can be viewed in a controlled production suite, a home cinema, an ordinary living room, or on a laptop or mobile device. Furthermore, the signal can be displayed on a conventional display with a standard dynamic range (SDR) to provide a high-quality ‘compatible’ image. Its main appeal then is that footage does not need to be specially graded for the screen it will be shown on, thus being suited to real-time content. It can also offer end-to-end broadcast utilising a single distribution signal which can be decoded on both HDR receivers and legacy SDR receivers.
BT Sport, which currently films and broadcasts live sports in 4K Ultra HD (3840×2160) has been trialling HDR, with the most recent tests favouring the Hybrid Log-Gamma approach.
Dolby’s rival technology is already certified as SMPTE PQ or SMPTE 2084. Dolby said it also offers an end-to-end solution that starts with the creation of content and carries on through to distribution and playback. The Dolby Vision format for HDR is being supported by various movie companies as well as the UHD Alliance and the US Consumer Electronics Association (CEA), which announced its ‘industry definition’ for HDR-compatible video displays only recently.
Warner Bros. is remastering 4K Ultra HD titles with Dolby Vision, and to date 15 titles from Hollywood studios have been announced in the format, including Star Wars: The Force Awakens.
“Dolby Cinema technology is an epic, premium way to go to the movies,” JJ Abrams – the writer, producer, and director of Star Wars: The Force Awakens – is quoted as saying in a press release for Dolby. “I am honoured to be a part of the continuation of the Star Wars saga, and can’t wait for people to see The Force Awakens through the power of the Dolby experience.”
Among the streaming fraternity, Amazon was first to bring HDR content to its Prime Instant Video service with original series like Mozart in the Jungle andRed Oaks. Netflix is using Dolby Vision for its original series Marco Polo. In the US, VUDU, Walmart’s video-on-demand service, is currently distributing 4K, Ultra HD Dolby Vision titles from Warner Bros.
We’re likely to see two HDR ‘standards’ emerge, possibly SMPTE PQ for cinema, streaming movies and Blu-ray, with Hybrid Log-Gamma for broadcast TV, particularly sports. Choose your next TV with care.
HDR for non-broadcast projects
So what do you need if you want to use HDR in experiential projects, digital art or museum installations? For display purposes you could use a digital cinema projector such as those by Christie, or digital signage screens, which could provide adequate brightness for HDR (measured in cd/m2 or ‘nits’). Then there are OLED production monitors, or the new range of HDR TVs from a host of manufacturers getting ready to deliver on the promise of HDR. Top models include the Samsung JS9500 SUHD 4K TV (below) which offers 1,000 nits, or the 800 nit Reference Series 4K Dolby Vision display from Vizio (above), bearing in mind the certified industry standard for consumer TV is a lowly 100 nits.
The key is the setting, as the ambient lighting in the environment in which the content is viewed can have a big effect on the perception of blacks and contrast. The darker the setting, the less bright the display device needs to be to show higher dynamic range.
Want to capture and edit HDR video, see our guide to HDR video-capable cameras and editing software.