[opendtv] Re: Finally anamorphically compressed 480i

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
  • Date: Sun, 23 Jan 2011 18:54:03 -0600

John Shutt wrote:

> Since PBS doesn't send SD to their member stations, legacy full
> screen SD material is sent as pillarboxed 4:3 within a 1080i30
> frame, with the appropriate AFD code "center cut safe."  If
> that content is broadcast on an HD channel to the viewer, the
> AFD code is also transmitted.  If it is downconverted to SD by
> the station for a subchannel, it should be center cut by the
> station for a full frame 4:3 program.

Okay, good dope. Thanks. Now, my suggestion here would be, if the legacy 4:3 
material is transmitted on an HD subchannel, continue doing what you're doing. 
This seems to be the norm in the TV industry. Transmit the pillars as data, and 
the actual 4:3 image resolution becomes something like 1440 X 1080 or 960 X 720.

If instead the 4:3 material is transmitted on one of the SD multicast channels, 
do *exactly* the same thing! Isn't that easier to do the same thing than to do 
things differently? It seems like the stations do have control of how the SD 
streams are transmitted, from what you describe, so this should be a doable do.

Over 704 X 480, the resolution of the 4:3 image becomes 526 X 480.

For 16:9 display users, the resolution of the central 4:3 image is the same, 
per unit area, as the resolution of a SD anamorphically compressed 16:9 image. 
So, no surprising loss in sharpness occurs when viewing SD of different aspect 
ratios. And, for these same 16:9 users, any SD wide screen material would look 
far better than the zoomed in postage stamp stuff they commonly see now. Just 
seems wrong to make SD 16:9 SD material almost always worse than legacy 4:3 
material, on the SD subchannels, when viewed over wide screen monitors.

For legacy analog TV users, *especially* those who connect their TVs via the RF 
antenna feed from the STB, 526 horizontal is more than lavish enough anyway. 
They won't see any loss of image quality, even compared to the HD content they 
watch. I think typical NTSC TV resolution is an effective 330 X 330 anyway, 
right? And even over a baseband composite interface, the best of these analog 
sets might perhaps see something like an effective horizontal 533 pixels? So 
526 horizontal should be adequate under most circumstances.

My two old ATSC STBs, Accurian and Digital Stream, seemed to have no problem at 
all filling a legacy 4:3 analog TV with DTV images, whether they were showing 
HD or SD subchannels. And I'm sure they didn't have no stinkin' AFD. And 
certainly, the analog TV set didn't have any image post-processing capability.

> By contrast, legacy letterboxed SD material is upconverted by PBS
> to a full screen 1080i30 frame, and AFD coded to letterbox upon
> downconversion to SD 4:3.

Right. But wow, this is simply wrong! If PBS goes to the trouble of making this 
great upconverted full screen 16:9 image stream, why on earth would stations 
degrade it so much right at the transmission end? When you could be sending it 
out anamorphic squeeze 16:9 SD.

> The second source of the postage stamp effect, and I believe the
> one you are referring to, results when SD source material consists
> of letterboxed 16:9 within a 4:3 frame, is not AFD coded, and gets
> upconverted to HD. In the absence of AFD codes, the default up
> conversion is to pillarbox the 4:3 frame, which results in postage
> stamping at the receiver when viewed in HD.

Can't manual intervention save the day here? I mean, upon transmission? Because 
again, I would send that stuff out to fill a 16:9 704 X 480 SD container. Don't 
stations have the ability to do the 16:9 zoom-in function before transmission, 
say at the beginning of that broadcast? 

Sorry if I'm not understanding something here. It seems like AFD is doing as 
much harm as good!

Oh, and here's another bit of trivia for you. Universal Sports, transmitted as 
a subchannel from NBC O&Os, has this really nasty habit of NOT centering their 
postage stamp images, when they transmit 16:9. How annoying is that? Zooming in 
doesn't work right. And many or most of the foreign postage stamp shows, which 
come with subtitles, have a nasty habit of putting some or all of the subtitles 
in the bottom black bar. How annoying is that? Zoom in and the subtitles 
disappear.

Bert
 
 
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