Professional shooters have long hoped for the day when what we see with our eye matches what we see on our home TVs. The dream may have seemed elusive or impossible in the past but today, given the latest HDR advances, the dream of 1:1 capture and display is not only realistic, but is already here.
With many cameras offering log recording and 14+ stops of dynamic range, the arrival of HDR consumer TVs has major implications for shooters; the robustly textured highlights we so diligently capture and fret over on set can now finally be integrated into the final grade. It’s not all peaches and cream given the limitations (still) of the latest HDR displays, but the vastly improved highlights reproducible on an ever-increasing number of sets is a cause for serious celebration.
HDR is the real deal. With a 4000:1 contrast ratio and colors that no longer clip at 100% but at 1000%, even the most unsophisticated viewer can see and appreciate the three to four stops of additional highlight detail evident on HDR displays.
Simulation of HDR vs. SDR image.
Samsung
If some veteran shooters harbor an anti-HDR bias, that’s understandable. It’s hard to forget the dreadful Red implementation from a decade ago that utilized a crude form of bracketing with multiple frame exposures. This technique of merged data sets and blending of frames may have worked okay for still photography (the iPhone is an excellent case in point) but it worked horribly for motion video applications, especially at night — shooting fireworks displays, for example. Suffice it to say, the blurring inside the frame and softening of the image only got worse after compression downstream over IP or cable.
Your smartphone’s camera with its minuscule sensor needs plenty of light to produce good HDR images. Don’t expect your phone to replace your large-format camcorder any time soon!
Dynamic Range: What You Captured vs. What Viewers Saw
The dynamic range of standard television, implemented decades ago, has long been constrained by the limitations of 1950s-era CRTs, which offered a scant 6.8 stops of exposure latitude and a 100:1 dynamic range. For shooters seeking to reproduce smooth, flattering flesh tones and realistic, well-textured highlights, the NTSC/PAL television systems were the source of never-ending consternation. The 601 (SD) and later 709 (HD) output gamma limited displayed images to +2 stops above and -4 stops below 18% reference gray. Highlight values beyond +2 stops were subject to ugly clipping, while values below -4 stops sank into the murk, never to be seen again.
For this reason, many shooter-filmmakers for years opted to originate on film, which offered greater dynamic range. With a contrast ratio of 4000:1 and 12 stops of latitude, shooters reveled in the four- to five-stop advantage over electronic origination. The thrill didn’t last long, however, as those happy shooters faced the ultimate misery later, cramming and shoehorning the high dynamic range filmed images into the crippled 8-bit 601/709 output reference in the telecine suite.
Just the facts, ma’am: The 8-bit 709 gamma curve, based on a 1953 standard, can display less than seven stops of dynamic range. This limitation persists today on non-HDR displays.
Most current HDR TVs can only display 10-11 stops of dynamic range, so some clipping of highlights may still be evident even in the latest generation sets.
Samsung
I recall spending hours peering into the film negative and squishing my once-glorious highlights into the knee of the output signal. The advent of a knee control in electronic cameras significantly reduced the risk of clipping during image capture, but the limited-range 100-nit CRTs continued to be the overarching problem.
By the year 2000, electronic cameras had improved and could capture over 10 stops of latitude with enhanced highlight control and tonality. The Panasonic VariCam, introduced in 2004, employed a clever, low-contrast Film-Rec curve to expand dynamic range. The camera, amazing for its time, offered a stunning 10.8 stops of latitude and 1500:1 dynamic range in Film-Rec mode.
Consigning Rec. 709 to the Dustbin
By 2007, home TVs had grown brighter. Plasma sets ran 200-250 nits and LCD TVs fitted with more powerful backlights output 250 nits or more. So while displays were brighter and cameras were able to capture more dynamic range than ever, the 709 gamma reference, limiting output to 6.8 stops, remained very much the elephant in most viewers’ homes.
Today, thanks to log recording, most mid- and high-end cameras can capture 14 stops of latitude without clipping, and home LED and OLED displays may exceed 1000 nits. Without HDR, however, the brighter displays only exacerbate the problem, as the shortcomings of Rec. 709 appear even more egregious on the more luminous screens. Clearly, the once-venerable 601/709 signal, introduced in 1953 as a byproduct of NTSC and CRTs, needed to go away.
For shooters, the benefits of HDR are compelling, with current implementations accommodating 1000% more headroom than the old 601/709 reference. Derived from human response studies pioneered by Dolby, HDR is capable of producing markedly improved images on consumer displays that are approaching, and in some cases, exceeding 1000 nits.
Rainy Montmartre at night. With the advent of HDR, for shooters, close attention to exposure in-camera is more critical than ever.
The ABCs of HDR: EOTF, HDR10, PQ, and HLG Explained
HDR utilizes an Electrical Optical Transfer Function (EOTF) to determine how a video signal is displayed on the home TV. Dolby’s Perceptual Quantizer (PQ) system (SMPTE 2084) is popular with filmmakers and large studios, owing to its precise assignment of values for gray scale and luminance. But PQ also poses significant challenges, especially for broadcasters, whose live productions require tweaking and matching of multiple cameras, and whose business model demands good compatibility with the many millions of Rec. 709 non-HDR displays still in use.
HLG curve. While shooters of digital cinema will likely utilize Dolby’s PQ system for HDR grading, Hybrid Log Gamma (HLG) will be the more popular choice for most broadcast and cable applications, given the many millions of legacy 709 TVs, and the inclination of most broadcasters like the BBC and NHK to continue to support them.
For broadcasters like the BBC and NHK, the HDR system Hybrid Log Gamma (HLG) offers critical compatibility with non-HDR sets, with a supplemental log curve applied at 50% and above to accommodate the more robust highlights captured in today’s cameras. Setting the white reference at 50%, HLG provides more than sufficient contrast and dynamic range for satisfactory viewing of programs on a traditional SDR TV. The non-HDR set simply displays the compressed, slightly yellow highlights we’ve grown accustomed to over the years since the advent of knee processing. On an HDR HLG display, however, the upper log portion of the signal is expanded to accommodate the greater contrast and dynamic range. With peak levels on new TVs in the range of 600-800 nits, the image is noticeably brighter, with three to four additional stops of dynamic range. For even the most unsophisticated viewer, the improved highlights and quality of the picture are immediately apparent. And for shooters, the implications are profound: We no longer have to jettison critical highlight detail in the grade!
While HLG is a hybrid system and offers good compatibility with non-HDR sets, it complicates the transcoding process to other profiles like PQ. For broadcasters and shooters of sports and news magazine programs in particular, it seems likely that manufacturers like Sony and Panasonic will soon offer an HLG output option in future cameras to avoid the necessity of transcoding HDR profiles downstream.
On home TVs, there are a few HDR variations to contend with. HDR10, a subset of PQ, utilizes Rec. 2020 color space at 10 bits and limits the screen intensity to 1000 nits — a reasonable compromise, all things considered, given that Blu-ray and most movies are graded for 1000 nits.
HDR10+, advocated by Samsung, Amazon, and others, employs a dynamic metadata stream to manipulate scene-by-scene and frame-to-frame adjustment of screen brightness. Today, most HDR TVs support HDR10 and HLG. Dolby Vision PQ, despite its superior technology, is not as widely supported, most likely due to the licensing fees imposed on TV manufacturers, who prefer the open-source HLG system for this reason. In theory, an HDR-enabled TV reads a flag contained in the signal metadata and displays the proper HDR flavor.
Even though HDR10, a 10-bit system, specifies a maximum screen brightness of 1000 nits, most viewers prefer a more comfortable 300-400 nits for general viewing. Many new HDR TVs feature a maximum screen brightness of 500-600 nits, while cheaper non-HDR sets currently average around 200-250 nits.
Samsung
A Brighter Future
For shooters of broadcast and cable television, HDR is transforming how the public views our images. To be effective, HDR requires at least 12 stops of latitude in-camera. Fortunately, most modern cameras are capable of this or more. One small problem remains, however: most HDR TVs can display only 10 to 11 stops (at 500-600 nits), so some clipping of highlights may still occur even on the latest-generation HDR displays.
Shooting proper HDR requires a lot of light, so large-format Super 35 cameras like the Panasonic VariCam, fitted with five-micron pixel sensors, are particularly well suited, while small-format 1/3- and 2/3-type cameras are at a disadvantage, with inherently finer pixels that struggle to capture sufficient highlight detail in low light. The video from most smartphones suffers horribly for this very reason — the phones’ sensors with their minuscule pixels are barely able to reproduce even eight stops of dynamic range.
For shooters, HDR represents a quantum leap forward in how we light, capture, and grade our images. Abandoning 8-bit 709 gamma and the resultant clipping of highlights in home TVs, HDR means we shooters can keep more of what we make. We have remarkable, fabulous cameras now that can record log with wide dynamic range, and now, finally, we have the system and displays at home to take ample advantage of our cameras’ capabilities. The richly detailed highlights that form our most compelling images can finally be delivered to our viewers.
