Twenty-five years ago, at the SMPTE Winter Conference in San Francisco, the modern form of HDTV was introduced to the United States. Not quite 20 years ago, the FCC began an inquiry into how to transmit it. Ten years ago, the nation’s first HDTV stations went on the air. Do we have to go through everything again?
The issue is not flaws in HDTV encoding, transmission, reception or decoding systems. It’s not about bit starvation when terrestrial or satellite broadcasters or cable operators squeeze too hard to cram too much into their distribution systems. It’s not about digital rights management. No, the issue is the fundamental nature of HDTV itself.
The HDTV system shown at SMPTE in 1981 had 1125 total scanning lines; so does the one called 1080i that we have today. It was vastly superior to the 525-total-lines system it was to replace. But was it necessary?
In Japan, perhaps it was. In small rooms, Japanese families sat close to their TV screens. Close up, the scanning lines of 525-line television become annoyingly visible. HDTV solves that problem.
In the U.S., however, the average size of TV sets sold to dealers didn’t exceed 25 inches until sometime in 2001. A viewer with 20/20 vision watching a 25-inch TV set from a distance of nine feet (found in the early 1980s to be the average American viewing distance) cannot perceive more than standard-definition resolution.
The same viewer at the same distance would need a 70-inch screen before running out of 1080-line HDTV resolution. In 2005, the average size of a TV screen sold to U.S. dealers was just over 27-inch, so it would seem that the agony of the current transition shouldn’t have to be repeated for quite some time to come.
Alas, that might not be the case. Most of the TV sets sold in 2005 were picture tube based. The biggest picture tube ever made was just 43 inches, and it came and went quickly due to implosion concerns. But Panasonic is currently selling a 103-inch plasma TV, and LG.Philips has shown a 100-inch LCD and JVC a 110-inch D-ILA rear-projection display. At such large sizes, viewers watching from nine feet will be able to perceive individual rows and columns of picture elements of 1125-line HDTV, the same problem that viewers in Japan had with standard-definition TV.
There are also issues beyond mere resolution. A properly filtered HDTV system cannot display any contrast at its finest resolution, i.e., the contrast ratio of a 1080-line display at 1080 lines is zero. But the contrast ratio of a 2160-line display at 1080 lines is about 64% of maximum if a sin x/x filter is used.
A 2160-line display? Yes. Chi Mei Optoelectronics, one of the world’s largest LCD manufacturers, first showed a 56-inch 3840 x 2160 display in 2005. This year, they were joined by Sharp with a 64-inch 4096 x 2160 display.
It takes some time for such demonstrations to become actual products. Speaking at the DisplaySearch HDTV Conference in August, Sony Electronics president Stan Glasgow said resolutions five-to-ten times better than 1080-line were a reasonable target for the consumer electronics industry and that the next big leap in screen detail could occur in three to five years.
Resolutions that high are beyond the realm of MPEG-2 compression. Digital cinema will use JPEG2000 compression to distribute as many as 4096 picture elements per line, and there are other possibilities.
There’s just one problem. In the U.S., digital broadcasters are constrained to use MPEG-2 compression only for their primary video service. Digital-television receivers are further constrained if they follow a table of video formats the FCC removed from the ATSC standard when it was codified.
For years after the first U.S. HDTV stations went on the air, only a small number of receivers had been sold. Then the FCC’s digital-reception mandate kicked in. As of March of this year, all tuner-equipped TVs 25-inch and up, imported or shipped interstate, have had to have digital-reception capability. By March of next year, it will be anything with a TV tuner: A 3-inch LCD TV, a TiVo recorder, a tuner-equipped computer, etc.
None of those devices will be equipped for 2160-active-line HDTV or for any compression system that can carry it to homes. Meanwhile, Panasonic is selling 103-inch plasmas.
Mark Schubin is an engineering consultant with a diverse range of clients, from the Metropolitan Opera to Sesame Workshop.
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