Doctor Who Christmas special to be offered in 4K HDR on iPlayer

The BBC is to screen Doctor Who's Christmas special in 4K resolution and high dynamic range (HDR) colour via iPlayer.

When the programme is broadcast, viewers will be prompted to switch to the higher quality streamed version by pressing the red button.

US video platforms including Disney+, Netflix, Apple TV+ and Amazon Prime Video commonly offer content in this format.

But it is more rare on the BBC and Sky.

To take advantage of the facility, households will need a compatible TV and a relatively fast internet connection.

The BBC recommends a minimum 24 megabits per second (Mbps) connection.

By contrast, regular 1080p high definition (HD) programmes require a 6.3Mbps connection, and standard definition (SD) content 1.1Mbps.

More vivid

Ultra-High Definition (UHD) - the other name given to 4K on TVs - delivers four times as many pixels as HD video.

The benefits are that images can appear sharper and more detailed, although this is not always apparent if the screen is not large enough or viewers are sitting too far away.

For many people it is HDR that delivers the most notable difference.

Pictures typically appear to be more vivid and colourful.

It takes advantage of the fact screens can go brighter and/or darker than they used to be able to, providing a greater dynamic range.

As a result, the shadows of an image can be made less murky while the highlights - including sparks from special effects - can have more impact.

The BBC first publicly tested 4K HDR on iPlayer in 2016 when it offered four minutes from its Planet Earth II series.

This simulated image from Blue Planet II shows - on the right-hand side - the advantage of using high dynamic range

It has subsequently offered a limited range of full-length programmes including Dynasties; His Dark Materials; and Dracula, as well as sport including Wimbledon and Fifa World Cup 2018 matches.

But despite pioneering related technologies - such as developing the hybrid-log gamma format used to stream live action simultaneously in both HDR and normal TV - it has been resistant to deploy it widely.

This had led to odd situations such as Peaky Blinders being offered in HDR on the UK's Netflix service but only Standard Dynamic Range (SDR) on iPlayer.

The BBC is, however, also providing further shows in 4K HDR over the coming days including:

• the Queen's Christmas Broadcast

• the drama series Black Narcissus

• the natural history documentaries Meerkat: A Dynasties Special, and A Perfect Planet

A documentary about meerkats will benefit from the 4K HDR treatment

A spokesman for the corporation added that there would be further content in the new year.

"Many factors are taken into account when we're deciding what content to make available in UHD," he said.

"We've made a range of drama, factual and natural history programmes available for iPlayer viewers to watch in UHD, as well as some of the biggest live events, and we'll continue to look at these as well as other areas as we explore UHD on iPlayer in the future."

The announcement comes a month after Sky announced it was boosting its library of 4K HDR movies for Christmas, including adding all the Harry Potter films in the format.

However, at present it is limiting this to its  Sky Q satellite service and not its Now TV streaming platform, which is still broadcast in 1080p.