There has been some concern amongst the production community that Digital Europe’s ‘Beyond HD’ recommendation that their minimum standard for 4K/Ultra-HD displays should be set at an 8-bit depth for colour is simply not adequate. There was considerable argument at IBC over the proposal, with a general consensus that a colour bit-depth of 10-bit should be the industry minimum for Ultra-HD displays, or else the consumer would not experience the “wow” effect of 4K.
Now Dolby Labs has entered the debate, saying that many display manufacturers are adopting a 10-bit minimum, and which permits a wider colour gamut and higher luminance. But Dolby says it can put even more “icing on the Ultra-HD” cake by the industry adopting a higher standard than that proposed by the ITU and DigitalEurope.
The Dolby proposal recognises that higher frame rates should be available to minimise motion blur, as well as so-called “better pixels” which address colour gamut and luminance. Key to these elements, says Dolby, are “nits”. “Nits” are not head-lice but a measurement of light sources and reflection. For example, the sun’s direct light output is measured at 1.6 billion nits, while starlight is expressed as 0.0001 nits. The reflection of light on a car might produce around 300,000 nits, while the reflection of light from green foliage might only be 40 nits.
The problem with a typical TV display is that they are only capable of resolving at up to about 500-600 nits for the brightest white, while a movie can barely manage 48 nits. Most TV sets comfortably manage 120-300 nits in a typical dimly lit room, although good quality computer screens are said to easily handle up to 300 nits but tend to be used at lower levels because their ‘always on’ brightness can hurt the eyes.
Dolby’s idea is to see this limit – for TV displays – to be upped to 4000 nits, and that any future standard should be set as a requirement for 4K to be 10,000 nits, and perhaps as high as 20,000 nits and that the higher levels are achievable, and could be 200 times brighter than are visible today on displays. Dolby has produced a prototype reference display monitor which it will showcase at CES and NAB. A recent Dolby demonstration showed a significantly improved end result over and above its existing reference monitor (PRM4200).
Dolby Labs recognises that more work needs to be done, on movie and TV production as well as on TV displays, but Dolby says it is developing technology that will aid the production community in these goals.