[opendtv] Re: Redefining anamorphic
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 7 Mar 2008 17:33:47 -0500
At 1:00 PM -0800 3/7/08, Ron Economos wrote:
DVD is not a good example. DVD only allows 720x480, 704x480 and 352x480 for
NTSC and 720x576, 704x576 and 352x576 for PAL. It's more limited than ATSC.
Actually, I was alluding to the way Hollywwod is using DVD to deliver
movies in their original aspect ratio. For content that is 16:9 or
wider, they always fill the width of the screen with letterbox throw
away areas. I'm not certain what they are doing with 1.66:1 probably
just cropping a bit.
A better example would be cable, satellite or the now defunct HD DVD where
all the "standard" sub-sampled horizontal resolutions are allowed
and at least for
cable and satellite, in use.
Yes, this is what happened in the rest of the world - not complete
variability, but widespread use of sub line lengths with integer
relationships to the full line length.
Vertical resolutions that don't match the uncompressed input/output format are
a non-starter. Too difficult to scale in a commodity decoder
(especially for interlace).
Same is true for oddball horizontal resolutions, since the polyphase
up/sub-sampling
filters are not that extravagant.
This certainly has been the case in TV land, but the use of interlace
in both SDTV and the "highest resolution format," play a major role
in that. No doubt some decoder manufacturers take shortcut on their
filters when they know the chip is going into a TV.
What is happening on the web is a different story. This is
progressive scan territory - you take the hit when you try to bring
interlaced source into this world - just look at you-tube. If you are
trying to deliver high quality video you choose a progressive format
container that is optimized for your target display and average
sustained bit rate. Moderan graphics cards have good scaling filters
and can deal with virtually any source.
Perhaps a better example is that we can all look at digital photos at
virtually any resolution. We can display samples 1:1 with the display
and scale to fit.
The point I am trying to make, is that when you have progressive
formats the numbers are less critical. This is the reason that you
can do real 4:2:2 sampling of progressive frames - when I say real, I
mean scaling the color difference samples by half in both the H and V
axis. They call this 4:2:0, but it is interlaced 4:2:2 that is
improperly labeled. The need to use 4:2:0 sampling for MPEG-2 based
SDTV is very problematic because of interlace.
So just specifying MP@ML and MP@HL doesn't get you unlimited resolutions
in the real world of hardware encoders and decoders.
This has more to do with market optimization that necessity. MPEG 2/4
doesn't care.
That being said, the world is filled with MPEG-2 decoders that are
not conformant to the standard.
Regards
Craig
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