HD: What is it?
The term HD (Hi-Definition) could apply broadly to all video formats with a resolution greater than that of Standard Definition video, whether it be analogue or digital.
In reality the term HD refers to two distinct forms of digital video, each with different resolutions, but both sharing an aspect ratio of 16:9. They are commonly referred to as '720' and '1080', each term representing the number of vertical lines of resolution in their respective signal.
Due to the need of describing these formats in computer parlance, they are often described by their respective pixel resolutions, for which '720' contains 1280 (horizontal) pixels by 720 (vertical) pixels, and likewise '1080' contains 1920 x 1080 pixels.
Furthermore, HD may be captured either in interlaced (i) or progressive (p) form, based on how the resultant video will be displayed on screen.
Using the Interlaced method, lines are displayed in two separate fields (phases) where the odd numbered lines (upper field) are displayed first followed by the even numbered lines (lower field). The two fields combine to form one full frame of video.
Progressive scan on the other hand denotes video which is displayed one full frame at a time, similar to film which provides 24 frames per second (fps), and as a result appears to flicker slightly.
Thus when describing an HD format, one might say '1080i' or '720p' where the i or p denotes interlaced or progressive.
Various flavours of HD also support a number of different frame rates, including 24fps (similar to film), 25fps (similar to PAL) and 29.97 (similar to NTSC).
These figures, denoting frame rate, are often added to the description. In the case of a progressive HD signal this figure represents the number of frames per second, e.g 24, thereby allowing one to fully describe progressive video with a resolution of 720 at 24fps, as simply '720p24'.
In the case of an interlaced signal, the last figure pertains to the number of fields per second (where two fields combine to make up one image frame). '1080i60' for instance represents interlaced video with a vertical resolution of 1080 at 60 fields every second.
So what is it?
In terms of viewing, the only event in the history of broadcasting which compares to the introduction of High Definition television, was the introduction of colour TV in the early fifties.
This will only become apparent when you've had the opportunity to spend time leisurely watching HDTV. No facts or quantitive data can describe the experience of watching moving images closely resembling the resolution of the human eye.
To the consumer then, HDTV is an exciting leap forward in the quality and clarity of their viewing experience, but what will it mean for those who have a more commercial interest in the roll-out of HD?
Clearly to manufacturers of televisions, players, and computer monitors HD is the next big technology wave. 2005 will see the release of more sensibly priced HDTV televisions, decoders and the 'trojan horse' of HD - the HD-DVD or Blu-Ray player. This last device will support HD-DVD or Blu-Ray film releases which closely resemble the resolution, quality and colour of film. And truly impressive they will look too!
To broadcasters, HD presents both a challenge and an opportunity; roll-out will require new investment but providing new HD services will provide new channels of revenue.
Clearly HDTV roll-out is happening at a different pace depending on where you are in the world.
In November 2001 the American FCC announced that all TV stations would be HD capable by 2006, and Japan has the widest HDTV roll-out with broadcaster NHK leading the way. Here in Europe on the other hand, we've been slower to adopt HDTV, although that is clearly changing.
HD1 (formerly named Euro 1080) started broadcasting on January 1st 2004 and became Europe's first HDTV channel.
TPS, the French pay-TV channel, have announced plans to launch HD versions of their film and sports channels in 2005 - one year earlier than BskyB in the UK. French terrestrial Channels TF1 and M6 are also anticipating their own HD service. Ultimately all six terrestrial channels in France, as well as Canal + and TPS Star, may be broadcasting HD as soon as early 2006.
HDTV, then, is a global revolution, and it's happening from all sides. And with most HDTV channels throughout the world showing a mixture of HD and upconverted SD content, the world is crying out for more HD programming.
Capturing HD
There are many flavours of HD based on the offerings of each of the manufacturers. Most of these still use magnetic tape on which to record the video signal, but high end solutions include cameras such as the Thompson Viper which can write uncompressed video data to hard disc recorders, eliminating the use of tape.
More cost effectively, Sony HDCAM and Panasonic DVC ProHD are the two primary flavours of HD, each supported by a range of cameras, and each using their own brand of cassette.
Sony HDCAM and Sony HDCAM SR:
It's almost a certainty that Sony HDCAM will become the preferred format for shooting content for quality mainstream television, and will therefore take over the mantle from Digital Betacam.
The pace at which this occurs will depend on the roll-out schedule of HDTV broadcast channels throughout the world, and be fuelled by the inevitable demand for HD content.
Sony certainly have no intention of placing unsurmountable cost barriers in the way of HD's natural progress. With the introduction of both the HDW-730S and HDW-750P Sony have produced affordable HD cameras with four times the quality of Digital Betacam, both based on the all singing, all dancing HDW-900, Sony's top of the range HD-CAM.
Technically speaking, Sony HDCAM records to tape 8-bit progressive or interlaced video with a sampling ratio of 3:1:1 and 1440x1080 pixels. Resultant file sizes are around the order of 22MB/sec.
The HDCAM format supports multiple frame rates including 25p, 50i, 60i, and 30p, Not all cameras support all frame rates however, and as with everything HD, the producer must select a format applicable to their target broadcast platform.
HDCAM camera specs are included in our document 'Camera Packages'. Click to download. (Adobe Acrobat Required)
Sony HDCAM SR records to tape 10-bit progressive or interlaced video, with a sampling ratio of up to 4:4:4, whilst retaining the full 1920 x 1080 pixels. This is a less compressed HD format.
Panasonic's DVCPRO HD:
DVCPRO HD supports 720i, 720p and 1080i standards.
720 DVC PRO HD video is recorded in 8 bit 960 x 720 with a 4:2:2 colourspace, resulting in file sizes of around 5.5 MB/sec.
1080 DVCPRO HD video is recorded in 8 bit 1280 x 1080 with a 4:2:2 colourspace resulting in file sizes of approx 14MB/sec.
Why produce in HD?
HD offers vastly superior picture quality over Standard Definition. If viewed on an HD monitor or HD television, colours are vivid and don't bleed, and detail looks stunning, right throughout the impressive luminance range.
Probably the greatest economic argument for shooting HD is that you are futureproofing your content; content which may ultimately be destined for HD broadcast or HD-DVD/Blu Ray media, or indeed future HD platforms.
Certainly producers of documentaries and ads, or any other program or content which has a shelf life of over one year, should, in our view, be working in HD.
HD too offers compatibility with formats which share a 16:9 aspect ratio. For instance finished HD edits can be downconverted and printed to Digibeta or DVCAM, allowing you to create a SD version of your final show for broadcast in the short term.
HD Post Production
Editing HD literally requires a greater attention to detail. A skin blemish, an insect or a written sign in the background, which would normally have been visible but blurred, is super-defined in HD.
All of that extra detail has an overhead. Datarates and, consequently, file sizes are relatively vast. And, in turn, NLE systems and hardware which efficiently handle the heavy throughput of data are costly, necessitating superfast processors and terrabytes of storage.
In 2005 we're going to be hearing much about downconverting HD material to SD before onlining/conforming with the originally shot footage. Or indeed creating SD versions of shows whilst keeping the HD version 'in the bank' for future broadcast.
Happily, a piece shot and edited in HD can be treated in the same way as SD for distribution purposes. The finished piece can be compressed in MPEG2 for DVD, or compressed for the web, or indeed downconverted to SD if required.
Curious about HD? You'll find more in our Resources section.