[opendtv] The numerology doesn't go away...
- From: Olivier Houot <olho_avatar_i@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 04 Jun 2007 21:55:53 +0200
Some news back from NAB 2007 about a Thomson H.264 encoder that
compresses 1080i down to 6 or even 4 Mbps. Hype has it that this is done
without sacrificing quality, but rather by making full use of all the
tricks in the AVC toolbox with an optimized chipset :
http://www.screenplaysmag.com/Editor/Article/tabid/96/articleType/ArticleView/articleId/442/Default.aspx
Some even older news about a Thomson oversampling 1080p camera :
http://www.broadcastbuyer.tv/publish/Grass_Valley_149/KPN_Selects_Thomson_Latest_Range_Of_Transmitters_For_Dutch_DVB-T_Network_Extension_11554.shtml
I can't help telling to myself that if it is acceptable to broadcast
720p in 14 Mbps today, and considering that 1080p compresses as well or
perhaps better than 1080i, which apparently could tolerate 6Mbps, surely
there must be a way to transmit 1080p in that same 6Mhz channel without
suffering too adverse economic effects (at least from the broadcasting
point of view).
Or are we saying that there is an irreductible information core in a
1080p signal, and that better encoders can only get closer to that core,
and not reduce it?
Are we saying that those brand new encoders will break down more often
and more drastically than good old MPEG2?
Are we saying that even if we achieve a nice picture at those bitrates,
we will finally discover that it does not contain more usable, real
information for the human vision than the current 720p signal? (do we
have some funny equations to support that ?)
But if we transmit in 1080p for slow movements, where resolution
matters, and at 720p for high motion, switching on the fly, then we
should be able to transmit the 1080p in its full glory when it matters.
The receiver would of course automatically upscale 720p to 1080p so that
no resolution pumping is obvious (and also because existing displays are
not specified for resolution switching speed, better feed them with a
constant one). Even better, change the resolution only for the parts of
the picture that are moving, so that the background remains at a
constant high resolution and there is really no pumping at all where it
can be seen easily.
Er...wait, wasn't HD-MAC doing exactly that some 15 years ago ? We
should be able to achieve the feat at mass market prices by now.
I am just wondering how far the current standard would need to be
tweaked to allow for on the fly resolution switching, at least for the
whole picture, if we choose to pick one of 576p (480p), 720p or 1080p at
a given moment. Could it be from GOP to GOP? I seem to remember this
question has already been asked...
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