With Atomos announcing their Flame series of video monitors/recorders at NAB 2016, HDR is the talk of the town. Most photographers, be it professional or amateur, will know what the acronym HDR stands for: high dynamic range. Dynamic range is defined as the ratio of the largest value of a signal to the lowest measurable value. The dynamic range of luminance in real-world scenes can be 100,000 : 1, while our computer screen or TV set is limited by technology to a ratio of 400 : 1 or even less. With HDR rendering, bright things can be really bright, dark things can be really dark, and details can be seen in both 1.
High-dynamic-range imaging (HDRI or HDR) is a technique used in imaging and photography to reproduce a greater dynamic range of luminosity than is possible with standard digital imaging or photographic techniques. The aim is to present the human eye with a similar range of luminance as that which, through the visual system, is familiar in everyday life 2.
Our eyes adjust constantly to the broad dynamic changes in our environment. The brain continuously interprets this information so that most of us can see in a wide range of light conditions. Few cameras and lenses know how to mimic that trick. However, acquiring an HDR image is only half the story. You must also be able to display the results. The method of rendering an HDR image to a standard monitor — or printing device when we’re talking still images — is called tone mapping.
Tone mapping reduces the overall contrast of an HDR image to allow for display on devices or printouts with lower dynamic range. It can be applied to produce images with preserved or exaggerated local contrast for artistic effect.
To give you an idea of the dynamic range of some devices and why you need trickery to display HDR images on those devices:
- Dynamic range of a LCD screen: 9.5 EV (f-stops)
- Negative film (Kodak VISION3): 13
- Human eye (static): 10–14
- High-end DSLR camera (Nikon D810): 14.8
- Human eye (dynamic): 20
An increasing number of image sensors now have high dynamic range capabilities. As display devices are not evolving at the same speed, HDRI or HDR software is increasingly important. To create HDR images, you’ll need software such as Photomatix or Aurora HDR to blend the differently exposed images together and create the HDR image from which you can tone map to a version that can be displayed on a common monitor.
HDR for Video
A few companies such as RED and Arri have been developing digital sensors capable of a higher dynamic range. Already, some movies have been filmed with cameras featuring a higher dynamic range. In essence, every video camera capable of shooting in Log, shoots in HDR video.
In 2015, the Consumer Electronics Association announced their definition for HDR compatible displays. These will have to be able to process “HDR10 Media Profile video”. This type uses the Rec.2020 colour space, SMPTE ST 2084 or Dolby Perceptual Quantizer (PQ). It allows for the display of HDR video with a luminance level of up to 10,000 cd/m2, and a bit depth of 10 bits.
On the video/TV side, the goal of HDR is essentially the same as in photography: to capture and reproduce all of the subtle nuances of the image, from its finest black/shadow details to its brightest white/colour elements.
A HDR display must have a high brightness and a low black level. Today’s LED/LCD TVs are capable of about 300 to 500 NITS (or candelas per square metre). HDR video requires a significant increase in peak brightness and enough local dimming to keep the black level at its minimum. The top-shelf HDR-enabled TVs on display at CES (from Samsung, Sony, and Panasonic) use full-array LED backlighting systems with local dimming. (Source: Home Theatre Review).
HDR video: how quickly will the newest hype be forgotten?
HDR for video is most probably here to stay — more so even than 4K or 8K video. More pixels is nice, but better colour and luminance definition is nicer as it really improves the viewing experience. Choosing a HDR TV set may still prove to be a challenge as some manufacturers will try to sell you bright TVs as HDR (See: Consumer Reports).
According to a press release dated October 2015, IHS forecasts that unit shipments of HDR TVs globally will grow from 2.9 million in 2016 to 32.6 million in 2019. According to the Quarterly TV Design and Features Report from IHS Technology, HDR will start to gain a toehold in the market beginning in 2016, but the start of rapid growth won’t occur until 2017 when 12.5 million HDR TV are expected to ship.
Are video monitor/recorder developers ready?
Not all video recorders are capable of displaying HDR for video. While all cameras that record in Log are in essence HDR ready, the monitors used by camera men are not. As a result, Log footage on monitors looks washed out and often the operator has to make assumptions about what the footage will actually look like or have an expert understanding of curves, parades and levels when recording.
The good news is that Atomos have just announced its new range of video monitor/recorders. Atomos is taking a risk. They rely on the HDR market picking up quickly and are offering the new Shogun and Ninja Flame with screens that are capable of 1,500 NITS (!). These new recorders, of which the Shogun will be released later this month, offer a nice upgrade path into the future — now.
Even if HDR wouldn’t become a mainstream technology, the Atomos Shogun Flame and Ninja Flame will deliver a brighter screen to their operators so these new models are definitely worth buying. An additional reason why they’re an interesting buy is that they once again come with all the accessories of the pre-Assassin models, as well as having been built to stronger specs, with incorporated bumpers.
In order to process Log video correctly to a HDR TV set or HDR capable screen, Atomos has developed its own HDR engine: AtomHDR. The engine processes the Log output and displays it on the Shogun or Ninja Flame, giving you the opportunity to see exactly how it will render on a HDR TV.
- Green S., Cebenoyan C.: “High Dynamic Range Rendering on the GeForce 6800.” ↩︎
- Wikipedia, “High Dynamic Range Imaging”. ↩︎