As Screens Grow, HD Will Suffer, Says Noland

Katie Noland

Katie Noland is an R&D technologist at the BBC. She spoke about a survey undertaken last year, investigating average viewing distances in the UK.

A small but growing number of people are sitting in a position where they will see a difference between HD and UltraHD. This isn’t because people have started sitting closer – it’s because TVs have grown large enough to show pixels on an HD image from an average viewing distance! The same factor means that SD is now starting to look “ropey”.

The question, ‘how many pixels are enough’ depends on viewing distance. For SD, people must be sitting six times the height of their screen (6H) away in order to not perceive pixels; for HD, it is 3H; for UltraHD, 1.5H; and for 8k, 0.75H. Of course, most people don’t set up their TV and sofa to be at the optimal viewing distance. “Well, there’s probably a few at BBC R&D”, noted Noland.

Results from the survey (which asked about screen size, typical viewing distance, ideal screen size, and more) showed that 58.5% of the population are viewing from 6H or closer; 10.2% from 3H or closer; 1.5% from 1.5H or closer. The median was 5.5H.

When considering ideal screen sizes (most people want a TV that is just a bit bigger than what they have now), these numbers change a little. Relative viewing distances would fall, so 76.3% would be at 6H or closer; 22.9% from 3H or closer; and 4.8% from 1.5H or closer. The results show that a small but growing number of people would benefit from upgrading to UltraHD TVs. Additional enhancement including HDR and WCG would benefit all viewers, regardless of viewing distance.

BBC Ideal screen size viewing distanceThe chart shows relative viewing distances if people had their ideal-size TV. The chart has a much sharper slope on the left side when considering peoples’ existing TVsNoland said that the distance to view pixels is also the distance at which people can see artefacts on an image, so more than half can already see artefacts on SD services.

Hewlett asked if there are diminishing returns as resolution climbs. Noland said absolutely – two independent tests, by the EBU and Orange Labs, show that there is a big jump in visual quality when moving from SD to HD, and a significant but much smaller jump from HD to UltraHD.

The trials did not use any additional enhancements like HDR, Noland repeated comments made by Gauntlett: the most striking enhancement will depend on the content being watched. She said that it is about offering different options to producers. In an ideal world, TVs would support them all (HFR, HDR, WCG, etc) and convert content streams as necessary.

Noland feels sure that UltraHD will be taken up as a standard. While it is possible to enhance HD content with enhancements like HDR – and some broadcasters in Europe are looking into this – the BBC’s focus for now is on UltraHD resolution.