[opendtv] Re: 1080i vrs 720P
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 1 Oct 2005 08:45:58 -0400
At 1:35 PM -0400 9/29/05, John Golitsis wrote:
>On 29-Sep-05, at 1:13 PM, Craig Birkmaier wrote:
>
>> This is the unfortunate reality of having an DTV standard
>> that includes interlaced formats.
>
>Funny how you wanted a DTV standard that offered many different
>emission signal configurations, but not one that offers many
>different image configurations.
It's not funny, because it is not true.
The truth is that a properly designed digital image architecture can
support true scalability for any compliant display. There is no need
for formats, because ANY raster can be presented properly using the
required scaling capabilities, needed when there is more than ONE
possible raster size and/or aspect ratio.
The problem comes when you add the additional complexity required to
deal with interlaced formats. This requires not on image scaling
capabilities, but sophisticated de-interlacing capabilities. Even
standards converters that cost more than six figures cannot do a good
job with de-interlacing, as it is impossible to properly predict the
information that was not sampled in the first place. It's even worse
when you have to rely on a $10-20 chip in the decoder/display to do
the de-interlacing.
The truth is that I and many others pushed very hard during the
Advanced Television process to eliminate interlace from the digital
televisions standard - both for SD and HD formats. This would have
required that any interlaced source be de-interlaced, using the best
professional equipment - before encoding for emission. It would have
made it much easier to build display systems that use only
progressive rasters, and with a cheap convolution filter, it would
still have been possible to re-interlace the decoded source for
presentation on legacy interlaced displays.
But this did not happen. What happened is that interlace was
entrenched in both SD and HD for many decades, and the MPEG-2
standard was corrupted to deal with interlace...and sadly the same
has happened with H.264. This was done to control the IP in MPEG-2
and H.264, by updating old IP that was about to move into the public
domain. Without interlace there would be little need for MPEG-LA, as
all of the necessary IP is now in the public domain.
>
>SA never had a box that only supported 1080i. The earlier models had
>1080i output only, but had no trouble internally converting 720p.
>Believe me 'cause I've had just about every single one of them, plus
>a friend who was the VP of Technology at my cable company.
Wrong. SA builds what the MSOs ask for. The first boxes that Cox
ordered 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.
>
>"To the best of your knowledge" is a guess.
I'll try to check into this. But I am virtually certain that I am correct.
>
>> This is simply the
>> reality of pushing 1080i beyond what is desirable given the
>> application and the available bandwidth.
>
>Yet 1080i football looks better to my eye (primarily sharper), and
>I'm hardly a sole voice in the wilderness here, either. Hockey too
>has looked better to me in 1080i versus 720p.
Probably because you have a 1080i display. Internal processing can
have a major impact on image quality. And interlacing progressive
source will cause a loss in quality.
>
>But don't assume I'm pro-1080i or anti-720p as everything I do at
>work is 720p, which was my choice.
>
We could easily have allowed only progressive formats. This would not
have precluded 1920 x 1080 at 24P and 30P.
Regards
Craig
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