[opendtv] Re: News: CEA FORECASTS CONSUMER ELECTRONICS REVENUE
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 16 Jan 2007 10:51:20 -0500
At 2:45 PM -0500 1/14/07, Albert Manfredi wrote:
So Craig, is 20 MHz better or worse than 3.8 MHz?
That depends on the overall quality of the delivered HDTV images. If
the encoder is starved for bits, it may pass real information at 20
MHz when the entropy in the image is very low, but when the entropy
increases, the image may have highly visible compression artifacts.
That being said, I would still suggest looking at a decoded ATSV HDTV
transmission to determine what the actual frequency response of
delivered source. My educated guess is that you wil not see much
image detail in the 15-20 MHz range, but you will see plenty of
quantization noise.
And in the UK PAL system, the equivalent "typical" max bandwidth is
probably what? Less than 5 MHz? Same question.
This is getting ridiculous. Obviously HDTV has more image detail than
NTSC or PAL. There are different trade-offs in analog versus digital
transmissions. The whole point of this thread was to try to convince
you that just because the source may have a specification that says
you can go out to 30 MHz does not mean that the source actually does
that. Ditto for displays. But more important, the NATURE of digital
compression and channel loss errors for ATSC HDTV assures that you
will not get anything close to the image detail in the original
"uncompressed" source.
I say uncompressed source with reservations as well. Most of the
commercial HDTV acquisition systems use compression, which removes
most of the detail above 20MHz. AND THEN the finished program must go
through MPEG-2 compression that further reduced the level of detail.
Regards
Craig
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