In the whole, NBC's high-definition coverage of the Athens Olympics made for pretty dismal TV. The same segments repeated ad nauseam only served to show how few sports bear up to repeated viewing. Who needs to see a failed baton pass, a gymnast falling on his or her butt, or a disappointing basketball game again and again . . . and again. Even the swimming events where Michael Phelps won his medals became tedious once you knew who won them. One of the few highlights of the HDTV programming was Steve Foley's astoundingly knowledge-able, polite, constructive, and instructive commentary on diving — with every dive you learned enough to believe that eventually you, too, could score diving like a real Olympic judge.

Despite the dramatic deficiencies of the coverage, fans of high-def technology still had reason to rejoice. For those lucky enough to receive it, NBC's HDTV feed provided an education in high-definition fully as eye-opening as Foley's diving commentary. Much of the imagery the network aired was superb. And some of it provided acid tests for the whole HDTV system, from camera to the home screen. Some segments could even be used to test an HDTV broadcaster's performance — or that of the home equipment used to watch it.

Any test pattern, static or moving, must be repeatable. The continuously looping NBC feed fulfilled that criterion with a vengeance worthy of a Greek tragedy. If you were using an HDTV hard-disk recorder, like the LG LST-3410A that I had (see review on our Web site), the coverage was even infinitely repeatable. Recorded footage could be viewed in a variety of situations — for example, on different types of monitors — or even used to test other devices (click to read my review of Panasonic's DMR-E95H DVD recorder).

With a test segment, any image degradation should be readily visible, which is not always the case with a casually chosen movie passage. The Olympics provided many situations almost ideally suited for seeing encoding “artifacts,” or image distortions caused by errors in MPEG video encoding or decoding. They all involved relatively simple visual situations, where it's obvious what is moving and where, and familiar objects and backgrounds whose distortion would be immediately apparent.

A space-opera battle scene with lots of intergalactic cruisers flying around is likely to present an easier challenge for HDTV than a gymnastics or swimming competition. Backgrounds in space are usually black, for one thing, which can hide distortions around the edges of objects like the notorious “mosquito noise,” which is a roughness or “busyness” along any sharply defined edge. The moderately lit, single-color backgrounds of many of the Olympic events — such as the blue floor-exercise mats in the gymnastics competition and the back wall of the diving pool — made them ideal for detecting this problem.

The considerable splashing in the Olympics racing pool also provided a tough test for the other main type of encoding artifact — “blocking,” in which the image breaks up into areas of mosaic-like squares. Blocking is easy to see in pool and fountain footage because its very squarishness is extremely unwaterlike. And even though, from an encoder standpoint, the movement of splashing water is pretty much as random as the static from an empty TV channel, we know how the water is supposed to look.

The NBC high-def feed seemed to have some residual blocking in the swimming coverage. And rapid movements by gymnasts and divers often displayed both mosquito noise and blocking simultaneously. But it's not clear whether I noticed these artifacts because of poor encoding by NBC, poor reception with the indoor antenna in our offices (buried deep within a skyscraper), poor decoding by the HDTV recorder, or the peculiarities of the LCD monitor I used for most of my viewing — or simply because the characteristics of the segments made them easily visible. Quite possibly all of these factors contributed.

 

Gymnastics and swimming contests at the 2004 Olympics turned out to be tough tests for the HDTV system (screen grabs from NBC's HDTV coverage).

Some Sound & Vision editors re ceiving the NBC high-def feed via cable reported seeing pristine images, and the visibility of both mosquito noise and blocking decreased markedly when I watched the high-def recordings I'd made on a plasma TV. (There should be a Greek chorus calling for research on whether and how different types of screen interact with encoding artifacts, making them more or less visible.)

I also noticed some very peculiar effects, when reception was very poor, stemming from the way MPEG encoding operates — by transmitting “reference” frames and generating the frames in between by interpolation. Once a gymnast standing under the high bar dematerialized, à la Star Trek, and then rematerialized up on the apparatus! I don't think any country would protest if

I gave that a score of 11.