Higher frame rates may be as important as more pixels for improving the quality of television. The Broadcast Technology Futures group of the European Broadcasting Union is testing the significance of higher frame rates, up to 240 frames per second. While the industry is still considering the implications of increasing spatial resolution for the next generation of television and video systems, it seems there are other fundamental factors to be reviewed.
The current recommendation for Ultra HD production and programme exchange allows for a maximum rate of 120 frames a second in addition to rates currently used for film and television, but researchers are also considering other frame rates.
The EBU is co-ordinating work being conducted by the research labs of the BBC, IRT, RAI and NHK.
One of the open questions is whether observers will appreciate higher frame rates and whether there is a practical upper limit. It could be that the basic recommendations so far adopted for UHDTV could be too restrictive.
Tests at IRT in Munich have been designed to evaluate frame rates up to 240 frames per second with different genres of material.
Early results provide a clear indication that observers appreciate higher frames rates to a significantly greater extent than increased resolution.
The BTF group and the Beyond HD strategic programme of the EBU will consider the detailed results, together with other technical parameters including higher dynamic range and extended colour space.
While manufacturers may be keen to promote a new range of 4K displays, there is growing evidence that spatial resolution is not the only dimension that needs to be addressed by next generation television and video services.
Many flat panel screens are already capable of refresh rates of 120, 240Hz or higher. They typically use interpolation to generate additional frames in an attempt to smooth the motion, with variable results.
Most high-definition television is still broadcast at 50 or 60 interlaced fields a second, representing just 25 or 30 frames a second. Most movies are still shot at 24 frames a second, although some are now being shot at 48fps. Ironically, some people still seem to prefer the softer ‘film look’ that has characterised cinema since its inception, together with various motion effects that viewers currently consider normal.
The rate of 24 frames per second was originally selected because it is around the critical fusion frequency at which an intermittently displayed image appears continuous to the average human, although this depends on many factors.
The frame rates of television systems were chosen to accommodate this and were related to the mains electricity frequencies in use, resulting in incompatible systems in different regions.
While scenes may be recorded at various frame rates, for instance to enable super smooth slow motion, it is only relatively recently that serious consideration has been given to transmission of television at higher frame rates.
Many consumer cameras can now record at 50 or 60 full frames per second, while many computer games are designed to work at such frequencies.
Given the practical limitations for screen sizes in many homes, it may well be that higher temporal resolution could have a more significant effect than simply increasing the spatial resolution.
It may be harder to justify and explain the advantages to consumers, who generally just want bigger screens with more pixels, but issues such as frame rate may be more subjectively important to the overall perception of the quality of the viewing experience.
William Cooper of informitv will be chairing The Great Quality Debate at the IBC Conference in Amsterdam on 14 September 2013, moderating teams of speaker responding to the question: Do we really need to go beyond HD?