[opendtv] Re: 1080i vrs 720P
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 29 Sep 2005 13:13:23 -0400
At 11:57 AM -0400 9/29/05, John Golitsis wrote:
>Surely you know better than to post such claptrap.
>
>I'll ask you two stupidly obvious questions: What affect did the
>conversion to 720p have on the 1080i image? What was the bitrate of
>the HD program stream delivered by your local CBS affiliate, versus
>the bitrate of the ESPN broadcast?
This is not clap trap...just reality.
There is no question that inter-format conversions can impact image
quality. There is ALSO no question that de-interlacing is an
imprecise art at best. I have the SA box set-up to pass through the
actual broadcast format, as my Samsung HD display seems to do a
slightly better job with the inter-format conversions.
Some of the interlace artifacts I was seeing are no doubt the result
of these inter-format conversions; the same was true for my first HD
capable display which I only used to de-interlace analog STDV
sources. This is the unfortunate reality of having an DTV standard
that includes interlaced formats. But many interlace artifacts are
inevitable, irregardless of the display format. Interlace is a crude
compression scheme with many drawbacks, INCLUDING a significant
reduction in compression efficiency, which i believe to be the
problem at the heart of my earlier posting.
I do not have any way to determine the bit rates of the respective
sources. I DO know - from conversations with the local technical
staff - that Cox cable is no longer doing interformat conversions
and recompressing HD sources to deal with the limitations of the
first generation SA boxes, which only supported 1080i. To the best of
my knowledge, Cox now passes through the bits they get; and to the
best of my knowledge the local CBS affiliate is using the entire
transport stream for CBS HD broadcasts.
The fact that the quality of 1080i sports broadcasts is compromised
relative to 720P is not some new revelation. I have observed this in
many demonstrations, at many facilities, in recent years. I have
observed nasty 1080i interlace and compression artifacts in major
demonstrations at NAB and in other forums over the years. The only
thing that is "new" here is that I can now observe these same
problems on the TV in my family room.
The compression artifact i observed were very real. They were NOT
caused by local image processing. They MAY have been caused by
mishandling and/or processing of the compressed video during
distribution. I have not observed similar problems with other 1080i
programming from CBS, NBC, or Discovery networks - This is simply the
reality of pushing 1080i beyond what is desirable given the
application and the available bandwidth.
Regards
Craig
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