[opendtv] Re: Why Europe should choose 720P for HDTV
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 14 Dec 2004 10:42:42 -0500
At 7:17 AM -0500 12/14/04, Tom Barry wrote:
>In practical terms that is probably what happens when anyone watches a
>DVD these days on a 720p or 1080i display. The image is first captured
>on film, telecined quite often to higher resolutions, telecined and
>compressed to 480p (except still with interlace filtering) and then for
>customers that have progressive DVD players scaled to the larger size of
>the display.
>
>There is a fairly large consensus on AVS that upscaling of DVD's does
>indeed look better and I've seem some convincing screen shots.
>
>But it is still not HD, just better than 480p.
>
>Due to limitations of my own HTPC setup I've been mostly limited to 540p
>myself. And this on a slower machine where I can't take advantage of
>the better software scaling available in the common ffdshow filter.
Several interesting issues here:
First, upscaling does work quite well with one caveat - you need high
quality samples to scale. If your samples are compromised, the result
of the scaling will also be compromised.
In the case of DVD movies, there are several things working in favor
of the production of high quality samples.
First, the spatial resolution is limited to 720 x 480/576, and more
important, the source frame rate is 24P. Also of importance is the
benefit of the source having been oversampled, typically on film, but
sometimes by an HD camera.
This source must be compressed to an AVERAGE bit rate of about 5-6
Mbps, but data rates can spike up to about 11 Mbps for short bursts.
Even with this headroom, however, many scenes still fall apart and
require the attention of a compressionist. By tweaking the MPEG
encoder settings, and or low pass filtering the source, objectionable
artefacts can be minimized.
As a result, the quality of the samples on a DVD are about as good as
you will find, when comparing various sources of MPEG-2 compressed
material. In addition, progressive DVD players can use flags in the
transport stream to help with de-interlacing.
There are perceptible benefits in bumping the resolution. But the
biggest advantage to an HD DVD, comes from the removal of the
interlaced footprint. It is indeed unfortunate, but as Tom points
out, the current generation of DVDs is limited by the need to filter
for interlace. This WAS NOT NECESSARY, but it happened. IF all DVD
players had included a simple low pass filter, then the source could
be optimized for progressive display, adding more vertical detail -
the filters would remove this detail on the interlaced outputs of the
player.
One must assume that the same mistake will not happen again with
HD-DVD. One would expect that the movie would be encoded with the
highest levels of detail possible, and that the player would create a
filtered interlaced output after downconversion from the HD format.
What I would like to see is 1024 x 576 @24P with full vertical detail
and full color detail (4:4:4). I am virtually certain that this would
compare very well with 720@24P using 4:2:0 encoding when upconverted
to 720P.
Regards
Craig
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