[opendtv] Re: Case for 720p60
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 21 Apr 2010 10:35:51 -0400
At 10:32 AM -0400 4/20/10, Hunold, Ken wrote:
While ATSC may "support" only certain sampling structures, I'm sure you
know that the FCC specifically left out the ATSC format tables when they
adopted the ATSC standard. From what I read at the time, certain groups
within the industry thought that having (only) 18 formats would stifle
development and advancement of new formats. Program
producers/providers/distributors could use any sampling structure they
wish. It was always known that any new format might not be receivable
on all receivers, but it was assumed that the almighty marketplace would
ensure that popular sampling formats would be supported. Even so, just
to be safe, many TV manufacturers made sure that they supported at least
the ATSC's 18 formats. Some closed-system providers provided "non-ATSC"
formats, but always provided the receivers to go with them.
There are two ways to look at why the FCC eliminated Table 3.
The computer industry was promoting the idea that the FCC should only
standardize the modulation system and the transport stream standard;
they wanted the ability to send ANY kind of bits via the new
broadcast standard, and they knew that the higher layers of the ATSC
standard would quickly grow obsolete, as the technology for digital
content creation and delivery evolved.
They computer industry was also adamantly against the continued use
of interlace, which in their view was just the concatenation of an
analog compression algorithm with a digital compression algorithm -
they knew that MPEG compression would work far better with only
progressive formats and that all displays would migrate to
progressive as we moved from CRTs to lithographed displays.
The other way to look at the removal of Table 3, although I don't
think the folks at the FCC were thinking along these lines, is that
it was inappropriate to impose format restrictions on a video
compression standard that was specifically designed to be format
agnostic. It is the levels and profiles in MPEG-2 that determine what
can be delivered, and these levels are performance based. A standard
compliant MPEG-2 decoder can handle ANY video format as long as it
does not exceed the parameters of the level and profile. Thus, for
example, it is possible to offer 854 x 480@24P within MP@ML. Indeed,
this is the way things work on the web - formats are irrelevant, as
are aspect ratios and frame rates - the decoder and local image
processing system simply does the best job accommodating the source
to the display.
Unfortunately, whether intentional or not, MANY early MPEG2 decoder
implementations - including ALL decoders that used only the ATSC
formats - did not conform to the MPEG-2 standard. To make things even
worse, many decoders did not follow the "rules" for reserved
extensions, hard coding around them. This made it virtually
impossible to use these extensions, as their use would break existing
decoders in the field. As a result the MPEG-2 standard has remained
virtually frozen because many vendors with non-conformant products
blocked any attempt to update the standard. I was involved in two
such failed attempts.
Maybe "everything we predicted has come to pass," but other things have
come to pass that were *not* predicted. The broadcast proponents of 720p
correctly "predicted" that future displays would be natively
progressive, but I don't think they thought that these displays would be
capable of 1920x1080 resolution. "Too many pixels," they said. Now we
have 1920x1080 display panels, so why not 60 (progressive) frames per
second on those? Limits of MPEG2 compression, we are told.
I tend to disagree. While displays do not follow the same Moore's Law
progression as chips, there is significant overlap, and the cost of
LCD computer displays was already coming down by 1994 while
resolutions were going up. It all came down to one thing:
DEMAND
The computer industry knew it would move to panel displays before the
end of the decade, and rightly assumed that the technology would
replace CRT TVs after that. And there were other developments like
the TI DLP chips that were expected to grow to meet the demand for
large progressive displays.
The larger issue in the early '90s was the cost/performance of
decoders. There were many in the broadcast/consumer electronics
business who were concerned bout the memory requirements for an MP@ML
decoder; this influenced the limits placed on MP@HL, along with the
very strong push by the Japanese to salvage 1125/60i.
But all of this misses the real point.
We all understand the benefits of oversampling as it relates to image
acquisition. But few understand the relationship between source
formats and display oversampling.
Simply stated, 720P provides a good balance of performance versus
bandwidth, and it can easily be scaled for presentation on large
1080p displays. Even more important, the video folks did not
understand the limitations of entropy coding and the reality that
less is often more when you are trying to cram HD through a bandwidth
constrained channel. It s now obvious that 1080i typically requires
more bits to deliver an inferior picture to ANY display.
With the focus now shifting to mobile DTV, interest in 1080P is
likely to erode, as 720P becomes the format of choice for HD and 480P
(or less) for mobile.
Interest has been low for 1080/60p, but now 3-D HDTV is all the rage.
Side-by-side distribution is the most predominant method of
distribution, but is 720p60 the best choice for it? Side-by-side cuts
the horizontal resolution in half, so is 640x720 really HD? Remember,
720x576 is commonly considered SD.
I'll avoid the temptation to further decimate the SD line count because
it is interlaced, because that's not the point. 3-D sports is a big
motivator here, and even 60 Hz is too slow for sports programs. A
blurry replay of a 60 Hz field or frame is *still* blurry, regardless of
how it is scanned. 90-100 Hz is more like it.
Me thinks its a bit premature to conclude that 3-D is going to be a
driver for what is left of Broadcast TV. I agree that 3-D for movies
and sports may find a niche market like the one that has developed
for Blu Ray. But sports is already migrating to cable and DBS because
the cost for rights requires two revenue streams. I envision 3-D
being a premium service for cable and DBS, and perhaps for live
theater viewing of major events.
Regards
Craig
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
Other related posts: