[opendtv] Re: Popular screen aspect ratios

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 28 Dec 2010 09:26:35 -0500

At 6:50 PM -0600 12/27/10, Manfredi, Albert E wrote:
Even more reason to disagree with your initial comment, that multiple aspect ratios were added to Table 3. The aspect ratios continue to be, from what you said here, 4:3 or 16:9 ONLY.
This is true ONLY for ATSC. It is not true for the underlying MPEG-2 standard or h.264. 




 And remember, the ATSC table is just a subset of what is actually being
 used in the real world. Cable and DBS use a variety of line lengths, and
 for Over the Top almost anything goes.


But, you keep confusing two different subjects.

Line lengths is one thing, and anamorphic squeeze into that frame is another.
NO. They are exactly the same thing from the perspective of compression. IF you are talking about anamorphic lenses this is true, although the result from a compression perspective is the same; the samples on the line must be expanded or increase in number to achieve the proper pixel geometry and aspect ratio. And by the way, hardly anyone is using anamorphic lenses these days except for some lenses used for film acquisition. Virtuall all video cameras have standard 16:9 lenses and when you shoot 4:3 SD a subset of the total sensor pixels are used.
I doubt very seriously that the "real world" of TV, i.e. DBS and cable according to you, supports any more anamorphic squeezing than 16:9 into a 4:3 frame. I'll bet you a lot of money that if you managed to find a square TV monitor, say 480 X 480, and plugged it into your cable's STB, you'd get image distortion. I'll bet you a load of cash that the very vast majority of cable STBs do not support square monitors, or monitors that are taller than they are wide. This has NOTHING to do with pixels along the horizontal axis.
Cable and DBS have been using 544 x 480 and 352 x 480 for years for both 4:3 and 16:9 sources. It is the responsibility of the MPEG decoder to present the system with decoded pixels AND the aspect ratio to which they may need to be scaled for presentation; some decoder have the scaler built in, but this is typically the responsibility of the display processor.
1440 x 1080, 1080 x 1080 and even 960 x 1080 are also used by DBS and cable for bandwidth conservation reasons - all of these are expanded to 16:9 (1920).
It is the responsibility of the display processor (part of an ATSC TV that is duplicated in cable and DBS STBs), to scale the decoded image properly. This is a requirement for ANY product that deal with multiple compressed formats.
If someone wanted to build a 480 x 480 monitor, they would need to include a display processor to present other formats properly on this display. It's NO BIG DEAL, just as the Phillips 21:9 monitor can easily present any of the DVB or ATSC formats properly. 




 You just need to take off your ATSC blinders.
It has nothing to do with ATSC. And what's more, if people start watching streaming media the way I can do nowadays, they will complain about black bars just as much as they do on broadcast or cable TV material. It's not the distribution media that make any difference, Craig. It is how the content is consumed.
It is called aspect ratio accommodation. In a world with multiple formats there will be formats that have different aspect ratios then your display. The display is required to do the best job possible accommodating the source, and it may give you some zoom/crop options.
Seems like you are the one who continues to complain about black bars, while "most" of the rest of the world has gotten past this issue. 

Regards
Craig


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