Opinion: getting heads around HDR2 May 2017
High dynamic range represents a major advance in image quality, but it comes with challenges, says Ken Eagle, director of field training and technical sales at Atlona.
HDR is a very exciting development for the AV industry. It provides information about brightness and colour across a much wider range than standard dynamic range (SDR). The result is greater detail, due to enhanced contrast levels and more vibrant images created from a wider colour gamut throughout the image, from the very brightest to the very darkest objects. Rather than simply ‘brighter’ and ‘darker’ that viewers have been used to with SDR for many years, HDR shows that level of brightness or darkness in the differences in colour and detail.
Even with HDR content on lower-resolution displays, viewers tend to choose HDR as the better picture. But while the pictures speak for themselves, there is a lot of information in circulation that is both incomplete and confusing.
In video, ‘high resolution’ is frequently used as a way of saying ‘better’. But higher resolution is not the most important factor to the human eye when evaluating image quality. Colour and contrast are what make a picture really stand out, what make it seem more ‘real’. This is what HDR delivers, through increasing both the contrast spectrum (dynamic range) of every pixel and the colour range (gamut) that each is capable of reproducing. (HDR refers both to the technology used to capture moving images and that used to display them.)
HDR is a standard feature of cinema and TV cameras. With AV displays that can accommodate and display the extra image information, the industry now has to develop the signal transfer infrastructure to handle HDR transmissions.
One of the primary issues that integrators need to consider is bandwidth. Handling HDR data requires more than 11 Gbps (up to 18Gbps), so only AV equipment compatible with HDMI 2.0 has enough headroom. But this comes with severe limits of just a few metres on transmission distances. Even then, only equipment meeting the recent HDMI 2.0a or 2.0b specs supports HDR metadata, making the correct choice of source, display and components in between absolutely critical. AV equipment will also need to support HDCP 2.2, the current protection scheme on most content.
One such solution is the new Atlona Centum 301 CEA, which utilises HDBaseT. Using VESA Display Stream Compression (DSC), a visually lossless technology, it applies extremely light compression (1.5:1 or less) to the 18Gb HDR signal, allowing transmission of HDR over a single category cable up to 100m, while ensuring pristine image quality.
HDR ‘format wars’
Another challenge facing integrators is that HDR is not a universal format; there are currently four standards. The two best established are the proprietary Dolby Vision and the more open-platform HDR10. The main differences? Dolby Vision supports up to 10,000 nits peak brightness, with a current peak brightness target of 4,000 nits, and 12-bit colour depth; while HDR10 supports up to 4,000 nits peak brightness, with a current peak brightness target of 1,000 nits, and 10-bit colour depth. In short, Dolby Vision currently has slightly (and potentially considerably) higher video quality.
Alongside Dolby Vision and HDR10 are the newer Hybrid-Log Gamma (HLG), developed mainly as an HDR format for live video, and Advanced HDR, aimed at broadcast media and upscaling SDR video.
However, while integrators need to be aware of the different formats and to match the correct AV components for their clients, manufacturers are producing equipment that embraces a number of formats, although Dolby Vision requires a playback device with the Dolby Vision hardware chip.
Currently, quality HDR content is still fairly thin on the ground, making the increased cost in hardware and cabling more difficult to justify. HDR media players, Blu-ray players and gaming consoles are helping to the bridge the gap, but it will take quality streaming HDR content to really get purchasers embracing the medium.
Although HDR currently presents challenges for integrators, it brings significant benefits – including the potential for increased revenue that HDR’s easily demonstrable qualities offer. Integrators who are prepared to face the technological challenges of selling, installing and supporting HDR now can differentiate themselves from the competition and have a head start with this exciting new technology.
The biggest drawback to HDR really is that, once you see it, you won’t want to go back.