olympic motion artifacts

Archived from groups: alt.tv.tech.hdtv (More info?)

I am receiving olympic coverage OTA. Picture quality is pretty
spectacular on stationary and slow moving scenes. However, there are
blocky artifacts surrounding moving objects. IE, during the diving,
the static background remains perfectly displayed, while the divers
blur and pixellate as they fall through the scene. On replays, the
exact same artifact patterns appear even in super slow-mo, leading me
to believe that the problem is with the original HD mpeg, as opposed
to my local station, my reception, or my TV. What do you think?

Archived from groups: alt.tv.tech.hdtv (More info?)

On Sun, 15 Aug 2004 09:54:17 -0700, LS wrote:

> I am receiving olympic coverage OTA. Picture quality is pretty
> spectacular on stationary and slow moving scenes. However, there are
> blocky artifacts surrounding moving objects. IE, during the diving,
> the static background remains perfectly displayed, while the divers
> blur and pixellate as they fall through the scene. On replays, the
> exact same artifact patterns appear even in super slow-mo, leading me
> to believe that the problem is with the original HD mpeg, as opposed
> to my local station, my reception, or my TV. What do you think?

Looks good to me, I'm on Comcast.

Archived from groups: alt.tv.tech.hdtv (More info?)

"RV" <race1000k_nospam_@yahoo.com> wrote in message
news:NsTTc.23234$nx2.6110@newsread2.news.atl.earthlink.net...
>
> You can see the same thing every week night if you watch "The Tonight Show
> with Jay Leno" in Hi-Def. The opening shot of the studio includes a very
> fast, wide pan of the studio audience, and the image is momentarily very
> blotchy until the camera stops panning. I just always assumed that this
was
> a current weakness or limitation of the hi-def cameras (and if I'm wrong,
I'
> m sure someone here will set me straight.)
>
Most of the MPEG2 encode/decode artifacts that you appear to see are due
to the limited amount of bps (bits per second) or payload that are allocated
(or available) for the show that you are seeing. This 'blotchiness' can be
very
significant depending upon the complexity of the scene, the amount of
movement,
and the quality of the encoder.

Even if a show is allocated ALL of the channel payload capability for a
1080i at
30 frames per second (60 fields per second) on ATSC, then it is still
possible to
get the compression artifacts. When I have seen full payload allocated to
1080i,
it seems to seldom have the artifacts (and occur less obnoxioiusly.) At
16Mbps,
the artifacts can happen on normal high motion, moderate detail scenes. At
about
14-15Mbps (almost the minimum useful) that I have seen on WB, then the
picture
can get so bad as to break up (well, it doesn't loose sync, but it can do a
well
ordered/controllled blocky effect.)

On most normal film originated materal (less bandwidth demand than video
original material because of more repeats on film), I have seldom seen
artifacts
from our local station that (AFAIR) seems to do about 16-17Mbps. However,
given live, high detail, sports video, the image quality suffers very
significantly.

John

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <41201130.9080407@optonline.net>,
Dave Hines <n2lak@optonline.net> writes:
> When DISH announced the NBC-HD Olympic feed last Monday night (Tech-Chat
> CH-101 at 9PM EDT) they said it was a 20mbps feed. FYI
>
My question is whether or not the full 20mbps is available to the
end user, or if the 'feed' is the 'bps' allocation before the final mpeg2
encoder?

For example, some network feeds might be mpeg2 encoded with a slightly
wider bandwidth, and then decoded/re-encoded before broadcast. This
is likely done to make the pre-existing bandwidths useful for HDTV
distribution. It appears (just from outside observation) that CBS
network feed seems much wider than the MPEG2 ATSC signal. This supports
easy addition of crawls, bugs and other nuisance video thingies without
a full (atsc level) set of encoded/decode artifacts. If the network
only distributes 20mpbs, then an additional encode/decode cycle where
the video image is moved around a ltitle will cause a loss of detail.

A full detail, 1080i, 30fps could easily cause artifacts at 16Mbps, but a
properly pre-processed MPEG2 encoded video signal shouldn't have lots of
artifacts at 20mbps (except in fairly severe cases.) The tradeoff is to
throw away some detail in a domain other than truncating the DCT coefficients.

That 'blocky' or 'stairsteppy' (or sometimes weird confused choppiness)
results from truncating DCT coefficients. The extreme 'softening' results
from filtering in the fourier domain (other effects might be ringing
effects or somesuch.) There are other domains that detail can be
removed, with other 'side effects' (where the pattern of detail loss is
of varying visibility.)

My guess is that if you are being provided a full 20mbps feed, and you
are seeing significant artifacts on scenes with reasonable (not excess)
detail (e.g. the image doesn't contain lots of moving detail in the
background like in a bleacher scene with lots of detailed cheering and
fan activity), then perhaps the encoder isnt' perfectly set-up, perhaps
there are multiple encode/decode cycles, or there is a feed somewhere
with a significantly more restricted payload capability than 20mbps.

One SERIOUS possibility: perhaps they are using 20mpbs with a 1080p60
signal? That would certainly be problematical, but that would probably
be extreme??!?!?

In order to fully understand the 'problem', it would be important to
understand all of the various transports, bandwidths, compression schemes.

John

Archived from groups: alt.tv.tech.hdtv (More info?)

"John Dyson" <dyson@iquest.net> wrote in message
news:cfp208$206e$1@news.iquest.net...
>
> Most of the MPEG2 encode/decode artifacts that you appear to see are due
> to the limited amount of bps (bits per second) or payload that are
allocated
> (or available) for the show that you are seeing.


If this blotchiness is a function of compression and bandwidth limitations,
then we should expect that this will only become worse for cable customers
as more and more stations are available in hi-def, right? Bandwidth
limitations will mean an even more radical use of compression or something?





RV