[opendtv] Re: 20040921 Twang's Tuesday Tribune (Mark's Monday Memo)
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 26 Sep 2004 09:50:09 -0400
At 12:35 PM -0400 9/25/04, Tom Barry wrote:
>I'd agree that, when properly done, 1024x576p could probably match
>almost all of what is currently sent in HDTV today, especially if it was
>really in 4:2:2 format. But, as you said, it mostly does not exist
>here. And 720p is only 25% greater in each direction so it's probably
>close enough to have similar economics.
One important note here. For a progressive raster, 4:2:2 buys you
NOTHING. 4:2:0 is absolutely appropriate for a progressive raster,
since it is easy to subsample the color difference signals in both
the H & V axis. Having full color resolution in the vertical and half
in the horizontal does little if anything to enhance the image
quality. If, however, you were to use 4:4:4 encoding, then there
would be a significant improvement in color detail. This is quite
feasible, especially for an improved DVD presentation. It probably is
not that important for a terrestrial DTV broadcast system.
There is a growing consensus that 720P is an attainable goal, so
there is little reason to bother with EDTV. This may well be true,
but it ignores the reality that MPEG has been designed to deliver
almost ANY raster efficiently - it is the job of the local image
processor to scale the raster to the local display resolution. So, as
we already have seen with streaming video, formats are just a
marketing tool for the companies that produce production gear. In the
world of distribution, formats simply do not matter.
>
>The intermediate resolution I miss would probably have been something
>like 1280x1080i or even 1440x1080i since I think this would be closer to
>"effectively square" pixels in a 16x9 format. But I suppose I have a
>bias towards interlaced resolutions since most HD RPTV's like mine still
>use them. This of course may change with new technology.
You are not missing 1440 x 1080i. The reality is that this is all you
are getting, even if the encoder is set to 1920 x 1080i. There is no
useful information to fill the spectra above that which can be
reproduced with 1440 encoded samples. Few if any HD camera/recording
systems even try to record 1920 samples per line; And then the MPEG-2
encoder quantizes any high frequency details that might exist away.
The only way to get 1920 samples with "filled spectra" is to
oversample - the only source available today that can do this is film
that is then scanned at 19920 x 1080.
The Digital Cinema projectors using TI's 1280 x 1024 DLP chips with
an anamorphic lens to stretch out the raster to proper width come
very close to the 1280 x 1080 raster you mentioned, except that this
is progressive, not interlaced.
Regards
Craig
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