[opendtv] Re: Finally anamorphically compressed 480i

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
  • Date: Wed, 2 Feb 2011 14:24:07 -0600

Craig Birkmaier wrote:

>> Is it not true that progressive compresses more efficiently than
>> interlace? Why are the SD subchannels universally using 480i? I
>> haven't ever seen any that use 480p. How come? Even without a
>> 360p option, can't prefiltering of the image result in a bit
>> rate constrained SD stream, say 480/24p?
>
> The major limitation is ATSC Table 3. As you note, there is no
> 360P option. And since the ATSC does not support any line length
> other than 704 for interlaced SD (640 for progressive 4:3 480P),
> a broadcaster cannot save bits with a lower number of samples per
> line.

It should not matter.

If it is true that progressive is more efficient than interlaced, then you 
should be able to demonstrate that 480/30p is at least as good as 480/60i, as 
far as bit rate for a given image quality. All I'm asking is, has this ever 
been demonstrated, and are we likely to start seeing 480p as the normal mode 
for SD subchannels anything soon? Are ~2.5 Mb/s 480/30p streams decent to look 
at?

Bert
 
 
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