Moving to HD Videoconferencing
Apr 1, 2008 12:00 PM, By Jay Ankeney
As broadcast evolves into high-end HD, conferencing systems are following close behind.
Although the perception of high definition is in the eye of the beholder, HD has rapidly become associated by most people as the highest level of video presentation commonly available today. In reality, many applications — especially in the medical and scientific field — are already reaching far beyond the resolution of HD, and professional postproduction editors who are working in the 2K realm to approach film resolutions consider HD to be a scratch track, or “offline” resolution used for down-and-dirty editorial decision making.
When the Advanced Television Systems Committee (ATSC) was asked to come up with standards to support the FCC mandate for domestic broadcasters to change over to digital broadcasting by an end date of Feb. 17, 2009, they came up with 18 or 36 formats for HD television, depending on how they are measured. The only points they share are that the HD image for broadcasters has to be widescreen (16:9), and it must be encoded using MPEG-2.
The two HD formats most widely adopted have been 720p (1280×720) scanned progressively 60 times a second, and 1080i (1920×1080) with an interlaced scan also at 60Hz. In the United States, 720p has been adopted by Fox, ABC, and ESPN, among others. 1080i proponents include NBC, CBS, CNN, and HBO.
It is important to note that the FCC mandate is for digital broadcasting, not specifically HD, and many networks are already drooling over the potential of dividing their newly allocated 6MHz digital channels into several 4:3 standard-definition programming streams. That would give them untapped potential for narrow-casting up to six specialized programming channels over that single government-guaranteed part of the frequency spectrum.
However, videoconferencing systems are not constrained by FCC regulations, and the term “HD” has become such an enticing sales tool that many companies are playing loosely with the definition of the high-definition signals they are sending to their screens. Although it is generally agreed that the ubiquitous term “telepresence” (used for the most immersive videoconferencing installations) should rely upon reality-emulating HD images, many systems are using lower frame rates than broadcasters. So although an advertised 720p system may indeed have 1280×720 pixels on the screen, they may be presented as low as 15fps to save on bandwidth.
There are even some companies presenting images in 1080p, which is 1920×1080 scanned progressively. It takes a very golden eye to tell the difference between 1080i and 1080p when presenting human faces, but the difference may pay off in graphic details or CAD drawings — and it is always good to shoot for the highest possible quality if your bandwidth can support it. Because the European Union is considering standardizing on 1080p for terrestrial HD transmission, this format may just be coming into its own.
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