Description

While workflows for 4K will be front and centre for many exhibitors at IBC2012, advances in higher resolution technology are pulling higher dynamic range (HDR) video in its wake. HDR is claimed by some to be as much a step change in our viewing experience as the move from black and white to colour.

Developments are swift. A prototype (by GoHDR) of a HDR TV demonstration from capture to display was premiered in the Future Zone at IBC2011 and a year on it is being primed for commercial deployment. Camera manufacturers are heading toward HDR with ever more sensitive sensors. The Sony F65 and Arri Alexa offer 14 f-stops of latitude, Canon’s C500 delivers 12 f-stops and Blackmagic Design vouches 13 for its camera. Red claims its new Dragon sensor affords 15+ HDR and has sensors with even higher dynamic range in the works.

Why does it matter? Essentially HDR is a means of capturing more information per pixel about a scene so that the viewable detail approximates that which the human eye can see at any one time. Camera technology has been limited in its ability to do that with detail in shadows and bright lights particularly susceptible to being clipped or bleached, resulting in under - or over-exposure.

Capturing the range of luminance depends on exposure and f-stop setting. Film stock, for example, is rated between 15-16 stops of dynamic range. The science is debated but, in general, ratings above 8 are considered to be of high dynamic range but to achieve anything like the 1,000,000:1 contrast ratio of human vision, around 20 stops are necessary. The problem is that digital sensors that reach (or surpass) the latitude of film rely on proprietary raw formats and log encoding tricks to make use of the results. From a colourist’s point of view increased dynamic range is the most important factor to obtaining the desired image, or to recover footage or detail that would otherwise be lost. The more detail you have will only serve to make the picture richer and more engaging.

Cinematographers like International Cinematographers Guild President Steven Poster, ASC see the potential: “We don’t necessarily need to show 25-30 stops of dynamic range on screen but we can use it in post to pull things in that could never be shown before,” he says. In visual effects HDR imagery is already the established standard for recording scene reference and lighting information. This 'canned scene light' is then used to light CG objects, so they integrate seamlessly into a plate.

HDR could benefit sports broadcasts, for example, by enabling golf or footballs to be clearly tracked from areas of shadow to sunlight. Other broadcast examples include a simple interview with someone backlit against a window: a conventional camera might struggle to record the details of the person and the details outside the window whereas, it’s argued, HDR-enabled video would not.

At 20 f-stops each colour channel (red, green, blue) would use 32 bits of information, producing single frames of 24MB making the storage let alone manipulation of HDR video impossible without compression. A number of compression schemes have been proposed with that of GoHDR, a venture formed out of research from Warwick University, among the most advanced. It claims to preserve the full dynamic range emanating from a camera capable of 20 f-stops of video by compressing it up to 150 times.

The final link in the chain is the display, without which all the advantages of HDR content are redundant. Displays with a wide dynamic range have begun to emerge in professional monitors and the functionality is being incorporated into many LCD TVs with LED backlight technology available in the high street today. There is even an attempt to define common interface standards for HDR content. This is being co-ordinated under the European Cooperation in Science and Technology (COST) framework, across 22 countries, aiming to establish Europe firmly as the world leader in the field.

Filmmakers are not achieving as much as they could from HDR at the moment but as workflows become more seamless and cameras get more sensitive to light this is an area of fast moving change.

It also dovetails with the trend toward heightened realism in the moving image which developments like Higher Frame Rates, stereo 3D and higher resolution capture and display are bringing to the fore.

You can find more on all these topics at the IBC Conference, notably at the free to attend “EDCF/SMPTE: Cinema Workshop” on Sunday 9 September.