Home Analysis UHD standards bodies work together to harmonize High Dynamic Range

UHD standards bodies work together to harmonize High Dynamic Range

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By Bülent Çelebi, Chairman and Co-Founder, AirTies Wireless Networks

As the Ultra HD TV era looms it has become ever clearer that picture quality is about much more than pixel density but also a host of other factors including color range and frame rate, with continuing debate over how much to increase the latter. But recently another key measure, dynamic range, has raced up the agenda, largely because it appears to have the greatest impact on picture quality of all. Dynamic range in the context of UHD defines the spread of light intensity that a TV can give, in essence the ratio in luminance between the darkest and lightest pixels. HDR TVs were one of the highlights of the recent CES (Consumer Electronics Show) in Las Vegas, standing out from other supposedly UHD models. The greater contrast between blacks, whites and shades in between was quite dramatic, not just looking better but also revealing details otherwise washed out by the lack of range. 

The drive for HDR began in still photography in the 19th century in order to capture areas of high brightness in strong sunshine for example and at the same time very dark images such as star nebulae. The human eye can resolve all of these both by almost immediately varying the diameter of the pupil to change the amount of light admitted and then over a longer period up to 30 seconds by altering retinal chemistry. Taken together these give the human eye a contrast ratio of 100 and give it a phenomenal dynamic range of 214. But when viewing images the eye makes no adjustment and so the picture has in effect to exaggerate light and dark to appear more “natural”. This can only be done by simulating the effect of the human eye’s adaptation to light in the camera by superimposing on a single image or frame several exposures taken at different apertures and also sometimes different wavelengths. 

For video there is the additional challenge of synchronizing the different exposures accurately between successive frames after compression, in order to avoid artefacts appearing. Clearly in order for HDR to work effectively across the whole UHD ecosystem the video processing has to be done in a standard way. Unfortunately some TV makers, after seeing what a great impact HDR has, have decided to make this a point of differentiation, as was evident at CES. They have almost regarded HDR as an optional extra beyond the main UHD standard, in the zone reserved for competitive added value and even have adopted their own terminology. 

The ITU, EBU alongside DVB, SMPTE and MPEG have all been defining what to add to the existing syntax for HDR, expecting to conclude this process sometime around July 2015. Blu-ray is finalizing its HDR specification in coordination with MPEG and SMPTE, hoping to freeze it mid-2015 in time to launch services for Christmas 2015. 

Such a timescale looks wildly optimistic and there is a clear need for an overarching standards body to crash heads together and converge on a common set of specifications all parties will adhere to. Fortunately such a standards body now exists, or more precisely two. But they are at least fully coordinating their efforts and concentrating on complementary areas of standardization.  

One is the Ultra HD Alliance, comprising around 10 companies, including Disney, Fox and Warner Bros on the studio side, Samsung, Sony, Panasonic, and Sharp for CE makers, Dolby and Technicolor on the technical front and then Netflix and DirecTV representing operators. This powerful lobby is taking an evangelizing role, seeking to harmonize terminology as much as technology, but also aiming to overcome obstacles in defining clear standards for HDR output.

Then a group of about 40 companies led by Ericsson, Dolby and Harmonic have proposed forming a new body called the Ultra HD Forum to address the complete end to end UHD ecosystem from camera to consumer device and all the infrastructure in between. Aware that there may be skepticism over the creation of yet another standards body, this embryonic Ultra HD Forum has emphasized that it will dovetail its efforts closely with the Ultra HD Alliance. There is growing hope and expectation that this duumvirate will establish order across the UHD ecosystem and enable HDR to shine.

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