12.21.2005 04:07 PM
The New Continuum: Why HDTV Is Not A Great Adjective
‘Tis the season to get presents. Why not an HDTV set from Sony, America’s number-one-selling TV brand, according to the NPD Group?
What does the adjective HDTV suggest? Might it indicate an ability to receive HDTV signals directly from broadcasts or cable TV? Sony’s MFM-HT95 HDTV LCD TV set can do neither. Does HDTV then mean a wide aspect ratio? The MFM-HT95’s is 1.25:1, narrower than an ordinary TV’s. How about a large screen? The MFM-HT95 is 19-inch, and, when displaying HDTV, offers images the same height as those of an ordinary 14-inch set. What about a resolution of 1920 x 1080? The MFM-HT95, in 16:9 mode, can display just 1280 x 720.
Sony’s website lists 30 HDTV models. They come in 1.25:1, 1.33:1, 1.67:1 and 1.78:1 aspect ratios; sizes from 17- to 80-inch (plus two projectors); vertical resolutions of 720, 768, 1024 and 1080; and horizontal resolutions of 1024 (less than even the 1280 of the 720p standard), 1280, 1366 and 1920.
It’s not just Sony. Toshiba is NPD’s number-three TV brand. Tell its web-based Television Buyer’s Guide that HDTV compatibility is important, and it narrows choices from 102 models to just 44, including the 4:3 (1.33:1), 640 x 480 14DLV75. Each of the websites of NPD’s top-five U.S. TV brands calls at least one 4:3 TV HDTV.
It’s not just consumer TVs. Looking for an HDTV camcorder? Sony models offer one or three imaging chips; 6-mm, 8-mm, and 11-mm image diagonals; and horizontal imager pixel counts of 960, 1440 or 1920 per line. Again, it’s not just Sony. If all professional HDTV camcorders are considered, chip sizes range from 6 mm to 27.5 mm, horizontal pixel counts from 960 to 5760 and vertical from 540 to 2160.
That’s the camera sections. Sony’s recorder sections, alone, use MPEG-2, MPEG-4, or proprietary compression systems. They use either intraframe or interframe coding. They capture 1440 or 1920 samples per line of luma; 480, 720, 960 or 1920 samples per line of color information; and 540 or 1080 lines of color information per frame. They record 18, 25, 35, 140, 440 or 880 million bits per second. Add other manufacturers, and there are several more compression systems, several more bit rates, and recorded luma samples as low as 960 per line. Grass Valley’s Infinity camcorder, alone, can capture 720p or 1080i HDTV at a variety of frame rates, compressed using MPEG-2 or JPEG2000, and be recorded on two different types of removable media (neither one of them tape); the same unit will also capture standard definition using different forms of DV compression.
None of this is a problem in the grand scheme of things. For much of the history of videography, there has been a broad range of quality in lenses, cameras, recorders and displays—but not for all of the history.
There was a period when some equipment was categorized as being of “broadcast quality.” It began at a time when a sync generator could occupy much of a room. Expensive broadcast cameras, making use of such equipment, were properly interlaced; relatively inexpensive cameras were initially of “random interlace.” Then sync generators became small and inexpensive, and even broadcasters began making use of what previously had been considered non-broadcast-quality.
Something similar was true in the early days of HDTV. Virtually all cameras were expensive and built to the same exacting standard. Similarly expensive recorders captured uncompressed signals. The adjective HDTV denoted a unique form of video: widescreen, very high resolution, intended to be seen on a large display.
Today, HDTV is still generally better than ordinary television, but it represents a broad continuum of quality. The adjective is no longer very useful in defining a specific class of imagery. It is going the way of “broadcast quality.”
There are some HDTV cameras with 960 x 540 imagers; many non-HDTV imagers have more resolution. HDTV is sometimes recorded at 18 Mbps; most digital standard-definition recorders use a higher data rate. And, as was noted at the beginning of this piece, some displays labeled HDTV actually have narrower aspect ratios than ordinary television.
No one would assume that an equipment rack is of higher quality because it is labeled HDTV. The time has come to apply a similar critical analysis to anything using the adjective.
Mark Schubin is an engineering consultant with a diverse range of clients, from the Metropolitan Opera to Sesame Workshop.