You might not have noticed that not everyone on TV is fat. Yes, this month's rant is about image shapes.
Here's what I mean. There are some things that are pretty obvious and some that are hard to discern. Take whether it's day or night out.
Now then, a civilian might think that's pretty obvious, but those of us who live in control rooms, studios and transmitter shacks might not have such an easy time guessing whether 12 o'clock means noon or midnight. On the other hand, I ain't yet met anyone in this biz who can't tell a circle from an oval.
For a case in point, take my old nemesis, Professor Nitpick. The way I hear it told, a manufacturer that shall remain nameless (but its name rhymes with glass alley) was holding a pre-NAB press conference when the evil professor, who shall also remain nameless (but whose initials are Mark Schubin), asked a nasty question or three about why people looked too fat on the screen, and suddenly things got very quiet.
Personally, whatever else I might think about manufacturers, I've got to admit that their ads make my boss rich, and, unfortunately, I have a medical condition called starvation that requires periodic ingestion of sustenance.
So fat, normal, or skinny in a press conference are all OK in my book, especially if there's food. Professor Nitpick seems to have thought otherwise, and, from what I've heard, his analysis of the anonymous manufacturer's disquisition on the subject wasn't the most appreciated commentary of the day.
Methinks I've ranted here already about the silliness of switching from 4:3 to 16:9, but that horse has already sailed (and so has the even sillier switch from Rec. 601's luma equation to Rec. 709's). So the shape of TV screens of the future is going to be 16:9, and we need to get used to it.
Too bad the future ain't here yet. Back in 1950 or so, the BBC switched from 5:4 to 4:3 pictures, and I figured we were done with the former--but, no, Sony's still selling HDTVs with a 5:4 aspect ratio in 2006. I am not making this up.
The Consumer Electronics Association says a little less than 17 percent of American homes had HDTVs at the beginning of this year, and about two-thirds of those were widescreen (8:5, 5:3, 16:9, and maybe even a few 3:2).
That means (if Nellie the Neuron remembered how to work the calculator) at least seven-eighths of folks watching TV around New Year's Day were looking at 4:3 screens. But we TV technologists are nothing if not forward looking (after all, who wants to stare at her mistakes?), so we help some producers make widescreen programming.
Too bad most programming is still 4:3. If you insert a 4:3 shot in a 16:9 show, there are black bars on the sides. If you then run the show letterboxed for the analog audience, you get bars across the top and bottom, too, something called the "postage stamp" on account of that's the size the picture is shrinking to. The result is folks with 4:3 TVs watching 4:3 programs surrounded by a thick black border, as if someone died.
If you think that's bad, you should see what happens in an American home with a widescreen TV. Do you remember the part about how most U.S. TV programming is still 4:3? Good.
So, if some of that 4:3 programming is shown on that widescreen TV, the choices are: stretch it out so everyone looks too fat, chop off characters' foreheads and chins, shrink it so there are black bars at either side, or do some combination (or even a nonlinear stretch, so folks gain weight as they move to the edges of the screen). Near as I can figure, most folks set their widescreen TVs to "FAT" and leave them that way.
WIDESCREEN ABROAD
"But, Mario, why did you say 'American home?' Aren't there widescreen TVs in Europe and Japan?"
Rest assured that there are--a lot more than there are here. Methinks it's actually against the law to air a non-widescreen commercial these days in Britain. But no one looks fat on those widescreen TVs, and it ain't on account of our eating more. It's just that they've got a signal that tells TVs what shape the pix are.
Guess what! We've now got it, too. It's called "active format description," and it's changeable on a frame-by-frame basis, so 4:3 material can always fill a 4:3 screen, even if it's buried in a widescreen, letterbox show. But, wait! There's more!
AFD works to tell TVs whether pictures are 4:3 or 16:9. But what if they're the 14:9 that that they sometimes use overseas? Or, better yet, what if it's a 16:9 show that the producer has protected for 4:3, so it's maybe okay if some of the sides get chopped off on a 4:3 set?
That's what bar_data() is for. Like the federally required dialnorm, with which I'm sure you're all familiar, bar_data() is metadata carried in ATSC digital TV signals. It specifies precisely how many lines high or how many pixels wide letterbox or pillarbox bars are supposed to be, and it, too, can vary on a frame-by-frame basis.
Are you confused yet? If you're reading this in time, rush over to hear Bill Miller's presentation on the subject on the last day of the NAB Engineering Conference. It's the session called "Interoperability in the DTV Facility," which ain't what the subject's about. He'll even tell you about another chunk of metadata that describes image positioning.
If you're reading this too late, don't worry. ATSC's A/54A will get you started on figuring out AFD and the other metadata.
It's only a little more than 20 years since the 16:9 aspect ratio was standardized, so maybe it's about time to get it right on home TVs. Then next month we can work on lip-sync.
