It will be a while before 4K TV broadcasts hit our screens but Sky, the BBC and other members of the DTG’s UK UHD Forum are hard at work making sure everything’s right before launch.
At the DTG (Digital TV Group) annual summit in London, Recombu was able to witness test footage shot by Sky, delivered to a Panasonic TX-L65WT600 by a Broadcom BCM7445 set-top box.
This was the UK’s first live public demonstration of 4K Ultra HD content at 50 frames per second (50Hz) with 10 bits of colour depth, using HEVC (H.265) compression. So what does this mean in plain English and what did we think?
4K Ultra HD will eventually replace 1080p Full HD as the cutting edge of high definition, bringing a photo-realistic fourfold increase in the amount of detail on screen. HEVC (or H.265) has emerged as the preferred codec for 4K transmissions, replacing the H.264 codec used for today’s HD TV.
Testing 4K out before it’s ready for broadcast has involved experimenting with different frame rates, one of which is 50fps.
Many commentators in the past have warned that 50fps isn’t high enough for live sports broadcasts and after seeing the test footage ourselves we’re inclined to agree.
While the picture was incredibly sharp – at times you could make out individual blades of grass on the pitch – whenever the camera panned sharply to follow the action, the footage, particularly the crowd and the stands, looked incredibly blurry.
The shots below are 4000 x 3000 – click to enlarge.
Admittedly when you’re watching a match, you tend not to spend a great deal of looking at the crowd, but the motion blur was prominent enough to spoil our enjoyment of the game.
Contrast issues also plagued the test video. The game was shot during the middle of the day and one half of the pitch was brightly lit by sunlight, with the stands throwing a looming shadow across the other.
Action in the brighter areas of the pitch wasn’t as distinct and focussed as it was in the darker areas. It was harder to discern action in the darker areas of the pitch from a distance. This could cause problems if you’d bought a big 65-inch TV and you were watching the game from the other side of the room.
Simon Gauntlett, chief technology officer for the DTG, said that broadcasters have found that modern lighting is a major cause of problems for 4K TV at 50fps.
Gauntlett said: “Lighting sources have caused the most issues for sports broadcasting. The BBC has done a lot of tests with 120fps footage and found that flicker, caused by high rate LED stadium floodlights, is a problem.”
Footage shot at 100fps hasn’t suffered as much from flickering effects and reportedly doesn’t suffer as much from blurred motion. Gauntlett said that to get hardware capable of handling 100fps will take time and it’s not there yet. The long-awaited HDMI 2.0 spec can only handle frame rates of up to 60fps so support for 100fps will need to be built in to future editions of HDMI.
It could be next year before we start to see 4K hardware capable of handling 100fps transmissions, dashing the hopes of anyone expecting to see the BBC showing the World Cup in 4K. FIFA and Sony are, however, planning to screen some matches in cinemas around the world and produce a 4K film of tournament highlights.
Gauntlett also echoed comments made by David Wood, chairman of the ITU (International Telecommunication Union)’s standards group for Ultra HD, saying that a higher range of colours will help iron out issues with lighting and contrast.
Testing of several proposals for 4K Ultra HD with HDR (High Dynamic Range) is ongoing but the ITU hopes to reach its conclusions by next spring.