BBC HD TV: Winding Down from Wimbledon
Wimbledon was the BBC's first ever 3D TV transmission. Andy Quested writes about the technical details of BBC HD encoders going back to 2D mode.
This morning after a very successful 3D trial the BBC HD Channel encoders reverted back to their “2D” mode. As a last word on the Wimbledon 3D trials, I am trying to get a series of blogs together from everyone involved, so hopefully more over the coming weeks.
From your comments I know the topic of 1920 transmission is something some of you feel very strongly about. So I thought this would be a good opportunity to do a post about it. The whole topic is not straightforward or we would have been 1920 from the start of the HD Channel. Although technology has matured the debate still moves between the science, the technology to produce it, the ability to deliver it and the impact when you see it at home.
As trevorjharris pointed out in the Gearing up to Deliver Wimbledon 3D blog post, the BBC’s HD strategy states we fully support the 1920 x 1080 standard for programme making. This position has not changed but even though all programmes are delivered this way, not that many are yet made 1920.
In the BBC HD Channel promo for example there are only two programmes acquired and post produced in 1920 and during the time the encoders were set to 1920, the majority of programmes shown were not made in 1920.
One thing to remember is, two of the current primary production formats are not 1920. Sony’s HDCam tape format is a 1440 3:1:1 format at around 140Mbs and DVCPro100 (DVCPro HD) well – that’s slightly more difficult to define. It depends on the camera and whether it’s being used as a tape or a file codec. As a tape codec it is often used in the Panasonic Varicam where it’s used to record 1280 x 720.
The Varicam is one of the very few 720 cameras we allow – its “CV” goes back as far as Planet Earth and Galapagos and it’s still being used for stunning Natural History programmes. This was one the points I made during the picture quality debates last year.
During the trial we did take the opportunity to look closely at some of the differences on each platform and how some devices handled the change. I will report back on the findings as we get more information.
We’re also looking at the impact of the different scaling technologies used. Good scaling is vitally important, especially when it’s used during programme making.
If we don’t do it well it can cause aliasing – this was something we had to guard against when we made the Side-by-Side image for 3D. Similarly up-scaling from 1440 to 1920 in domestic equipment, can also soften the images or a add edge ringing (or both!). The degree of softening or ringing depends upon the interpolating filters which perform the up-scaling.
We are working on other improvements to the programme and transmission chain including more use of 1920 and hope to have news later in the year.
I will keep you up to date on the work as often as possible.