For directors of photography (DP), HDR poses significant challenges, and while most cameras today can output the 10 to 11 stops of dynamic range required to produce good HDR, there are still serious areas of concern for those of us struggling to preserve the integrity of our images from capture through the long journey downstream.

Fundamentally, there are two ways of transmitting and receiving an HDR signal. For over-the-air (OTA) broadcasters, HDR can be  particularly problematic. Beyond the exigences of a 10-bit signal, most TVs today (older legacy models) do not support HDR and can’t differentiate an SDR signal from an HDR one. This means some kind of new or modified consumer demultiplexer box and coding system are required. Beyond that, the old ATSC 1.0 and DVB MPEG-2 standards from 20 years ago is still in use in many parts of the world, creating an even greater complication for those of us with a dog in the fight. Truth is, giving up even a tiny amount of bandwidth to accommodate 10-bit HDR signals can be a hard sell to broadcasters contending already with highly constrained legacy systems.

The Ambient Light Problem

For DPs and content creators, the most significant shortcoming of HDR is the current inability of displays to adjust for the ambient light level in the viewing environment. From the outset, Dolby Laboratories has worked diligently with content creators to develop a PQ display-referred system, the intent being to ensure the displayed image intensity matches perfectly the reference monitor picture in the color correction and grading suite. This had the consequence of eliminating the adjustment knobs in consumer TVs, but did little to address the greater challenge, how TVs may display the PQ signal in the absence of some kind of automatic ambient light compensation. In February 2018 at the HPA Conference in Palm Desert, Dolby explored ways to address this very issue. Suffice it to say, Dolby (and others) are working on it!

Finding a Way Forward

Bryce Button, director of marketing at AJA, sees the many HDR challenges as ultimately self-resolving, pointing out HDR is already practical and functioning well in smartphones and tablets. Button notes we will likely see millions more HDR TVs entering the consumer space in 2018¹, and so we will be hard pressed to find any new TVs on the market now without HDR capability. Still, given the large number of non-HDR TVs in use, it behooves broadcasters in the more traditional arena to figure out a way through the various legacy issues, and identify approaches that will serve both HDR and SDR requirements. 

Some cable service providers like Comcast's Xfinity encourage customers to utilize the wired full-bandwidth connection to ramp up the bandwidth available compared to OTA – allowing choice of resolution, HDR, and SDR, to coexist amicably in the same framework.

This is a good starting point. Shooters and DPs can also do our part by paying closer attention to potential clipping of highlights on set, and shooting the cleanest images possible, free of noise and artifacts, utilizing proper high-performance optics. At NAB Show 2018, Fujifilm and Canon introduced new 4K lenses, designed with advanced coatings and improved mechanical precision for optimal downstream HDR processing.

Fixing HDR, however, will require more than a wired connection into the home and the diligent application of good craft by DPs. HDR’s imperfect workflow must also be addressed, as maintaining good HDR without any kind of metadata support moving in and out of SDR can be ruinous to the quality of our images. On many projects, as we know, we must utilize a range of ENG and broadcast cameras, and dubious IP sources of varying resolution, dynamic range, and color space – all of which must somehow be made to conform seamlessly and elegantly to a single output signal.

At NAB Show 2018, AJA introduced new firmware for the FS-HDR frame converter to address, among other things, the multiple-source workflow conundrum. The FS-HDR wide color gamut (WCG) real-time converter and frame synchronizer utilizes the Colorfront engine to minimize latency and processing issues for UHD/4K and HD/2K workflows. The FS-HDR also serves as a single-channel UHD 4K cross-converter, or 4-channel HD/2K converter, with HDR transforms, scaling, color correction, and deinterlacing.
The Colorfront engine, developed for the most stringent cine applications, provides complete input signal support for ARRI Log C, Canon Log 2/3, Panasonic V-Log, RED Log3G10/Wide Gamut, and Sony S-Gamut3. Notably for many of us, Sony’s S-Log3 compatibility is critical for integration into our existing workflow systems; the range of log formats can be reproduced and converted directly from the NLE timeline to HDR and/or simultaneous SDR output.

One Workflow for HDR/SDR

Given the many HDR challenges, it is simply not cost effective for broadcasters to pursue separate HDR-SDR workflows. Instead, for most applications, broadcasters are advised to adopt a single mastering format which can then be converted as needed to HDR and/or SDR for distribution. The FS-HDR’s real-time built-in capabilities can be the key to adopting a single master approach, regardless of the ultimate HDR or hybrid log gamma (HLG) flavor demanded. In the UK, BBC facilities are obliged to accommodate both HDR and SDR, a tall order supported seamlessly and elegantly in the FS-HDR converter, given the range of BBC HLG LUTs to address particular needs and tastes. Technologically speaking, this is a significant achievement, given the simultaneous, conflicting demands, of multiple SDR and HDR outputs. Citing just one example in sports, the typical replay box does not currently support HDR; the FS-HDR frame converter then can be used to simultaneously output 1080p HDR with a 720p SDR signal. An easy solution to a vexing problem!

For DPs of live TV programming and sports, direct HLG capture in-camera makes sense, as this can simplify the workflow and eliminate the need for any type of converter. For all other non-live production, DOPs would do best to shoot in log (S-log3 in Sony cameras) in order to capture the widest range possible data set with a reasonable-size data load. Of course, some DOPs with a more impractical streak will opt for RAW capture, this offering the greatest flexibility for color and density correction in post.

¹ 4K UHD Sales Set To Surge Worldwide, by Adam Jacobson, Radio+Television Business Report