[opendtv] Re: MPs back Ofcom stance on spectrum sale
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 25 May 2007 12:28:46 -0400
At 3:55 PM -0400 5/24/07, Manfredi, Albert E wrote:
Craig Birkmaier wrote:
You are talking about the number of samples that are transferred
to the display over some unit of time. This has NOTHING to do
with the information content of those samples.
What I am talking about is 960 cycles/line, 1080 lines/frame, 60
frames/sec for 1080 at 60p, compared with 640 cycles/line, 720
lines/frame, 60 frames/sec for 720p, and half again as much info in each
case for the chrominance. So this is as much image info as each format
can carry, including any spurious noise or anything else, and any amount
of entropy or lack thereof.
Still not getting it. This has nothing to do with the information
content or the entropy in the respective images. All you are
conveying is the limits on the frequencies that each format can
deliver. We could also go a step further and talk about the potential
MTF of each, recognizing that the samples are not accurate as soon as
we attempt to deliver any information that is above the MTF curve -
that is, we have now filtered the samples to reduce their contrast.
This is both intentional - to conform with sampling theory - and
unavoidable, due to the concatenation of MTF limitations introduced
by lenses, etc.
Now that can be compressed by any algorithm you like. Just use the same
algorithm for each format, when making the comparison of channel
capacity requirement.
Fine. No argument that both can be compressed. But all of the
arguments I have outlined in the previous posts will impact the
channel requirements to deliver these formats without visible
distortions. THERE IS NO RATIO that can be applied, because the
compression efficiency eiwill be impacted by the actual information
content and entropy (the inaccuracy of the sampling and noise).
What we can say is that by resampling to the lower resolution we will
reduce any entropy in the higher resolution source and provide more
overhead to deal with the encoding requirements at any channel
bitrate.
I gave you the maximum theoretical. Max content, including noise, in
each format. The ratio is 2.25:1.
This ratio is irrelevant.
Now certainly, you can posit any number of situations that are less than
that max. For example, a 720p example of flat gray, compared with a very
detailed color scene in 1080p. Or a nice clean signal used for the 720p
stream, and a noisy static-filled signal for the 1080p source. But give
me a scene loaded with detail and color, then capture that in both 720p
and 1080p, with both cameras equally noise free, and the difference in
bit rate should not exceed 2.25:1.
Not true.
Allowing for a 1080p transmission mode in no way precludes 720, 480p,
etc. It is simply an additional mode that was not practical back in
1994, so it wasn't considered in the original HDTV transmission formats.
I understand this. I also understand that 1080@60P is not necessary
for a mass market DTV system where the average display size will
remain under 40 inch diagonal.
The "legacy thinking" part is to consider what might apply today as what
must apply in the future. You know, just like a couple or three years
ago, when it seemed to some people unlikely that LCDs would replace CRTs
in short order. They cited production costs, production volumes, and
whatever else. But LCDs took over regardless. I'm saying that 1080p
displays are becoming commonplace now, and if new codecs are added to
ATSC and DVB-T, I would not rule out that a 1080/60p transmission mode
could also be added. If the new codec is truly capable of 2:1
improvement, the 1080/60p mode *IS* feasible.
Nobody is questioning the feasibility, OTHER THAN the issue that
there is not sufficient bandwidth to deal with the peak bit rate
requirements of the 1080@60P format. What Iam questioning is the NEED
to deliver this format in a mass market DTV system.
Again, I am not going to reiterate the arguments, the record speaks for itself.
And flat panels DO make larger screen sizes practical, compared to
hulking CRTs. With larger screen sizes, people CAN appreciate the need
for good HD modes. And old movies or old TV shows archived in 35mm film
CAN be retransmitted as HDTV in the future.
Absolutely. So it comes down to how much resolution is needed to
deliver a sharp picture on a given screen size at the designed
viewing distance. When you look at these requirement, it becomes
obvious that we never needed 1080 line formats. Even NHK determined -
in the late '70s - that 800 lines is adequate.
I'm really growing tired of the numerology arguments. What I want is
good HDTV, delivered without excessive distortions, and it does not
take 1080 lines to do this.
Regards
Craig
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